subject: sentinel convoy for land applications workshop report … · 2012-02-20 · ref:...

ref: SCL-ULE-TN-01_V3.1

Issue: 2

Date: 19/01/2012

Sentinel Convoy for Land Applications: Workshop Report Page : i

- i -

SUBJECT: Sentinel Convoy for Land Applications Workshop

Report

PREPARED BY: JJ Remedios, N Humpage

CHECKED BY: …D. Ghent Date: ……..…

APPROVED BY: . . . . . . . . . Date: ………..

Distribution List:


Issue: 2

Date: 19/01/2012

Sentinel Convoy for Land Applications: Workshop Report Page : ii

- ii -

CHANGE RECORD:

ISSUE SECTION REASON FOR CHANGE

1 All First Issue

REFERENCE DOCUMENTS:

[RD1] Sentinel Convoy: Synergetic Observations with Satellites Flying in Formation with European

Operational Missions, A. Regan et al (URL: http://due.esrin.esa.int/stse/files/project/131-176-149-

30_2010924133848.pdf)

[RD2] The Changing Earth: New Scientific Challenges for ESA‟s Living Planet Programme (URL:

http://esamultimedia.esa.int/docs/SP-1304.pdf)

[RD3] Systematic Observation Requirements for Satellite-Based Products for Climate, 2011 Update (URL:

http://www.wmo.int/pages/prog/gcos/documents/SatelliteSupplement2011Update.pdf)

[RD4] Retrieval of growing stock volume in boreal forest using hyper-temporal series of Envisat ASAR

ScanSAR backscatter measurements, M. Santoro et al, Remote Sensing of Environment 115 (2011) 490-

507, DOI: 10.1016/j.rse.2010.09.018

[RD5] Spectral invariants and scattering across multiple scales from within-leaf to canopy, P. Lewis and M.

Disney, Remote Sensing of Environment 109 (2007) 196-206, DOI: 10.1016/j.rse.2006.12.015

[RD6] Canopy spectral invariants. Part 1: A new concept in remote sensing of vegetation, Y. Knyazikhin et

al, Journal of Quantitative Spectroscopy and Radiative Transfer 112 (2011) 727-735, DOI:

10.1016/j.jqsrt.2010.06.014

[RD7] Global patterns of land-atmosphere fluxes of carbon dioxide, latent heat, and sensible heat derived

from eddy covariance, satellite and meteorological observations, M. Jung et al, Journal of Geophysical

Research 116 (2011) G00J07, DOI: 10.1029/2010JG001566

[RD8] Extended Kalman Filter soil-moisture analysis in the IFS, P. de Rosnay et al, ECMWF Newsletter

No. 127 - Spring 2011 12-16 (URL: http://www.ecmwf.int/publications/newsletters/pdf/127.pdf)

[RD9] Use of SMOS data at ECMWF, J. Munoz Sabater et al, ECMWF Newsletter No. 127 - Spring 2011

23-27 (URL: http://www.ecmwf.int/publications/newsletters/pdf/127.pdf)

[RD10] Development of a virtual active fire product for Africa through a synthesis of geostationary and

polar orbiting satellite data, P.H. Freeborn et al, Remote Sensing of Environment 113 (2009) 1700-1711,

DOI: 10.1016/j.rse.2009.03.013

http://due.esrin.esa.int/stse/files/project/131-176-149-30_2010924133848.pdf

http://due.esrin.esa.int/stse/files/project/131-176-149-30_2010924133848.pdf

http://esamultimedia.esa.int/docs/SP-1304.pdf

http://www.wmo.int/pages/prog/gcos/documents/SatelliteSupplement2011Update.pdf

http://www.ecmwf.int/publications/newsletters/pdf/127.pdf

http://www.ecmwf.int/publications/newsletters/pdf/127.pdf


Issue: 2

Date: 19/01/2012

Sentinel Convoy for Land Applications: Workshop Report Page : iii

- iii -

[RD11] Biomass burning emissions estimated with a global fire assimilation system based on observed fire

radiative power, J.W. Kaiser et al, Biogeosciences Discussions 8 (2011) 7339-7398, DOI: 10.5194/bgd-8-

7339-2011

[RD12] Parameterization of Surface Heat Fluxes above Forest with Satellite Thermal Sensing and

Boundary-Layer Soundings, W. Brutsaert et al, Journal of Applied Meteorology 32 (1993) 909-917

[RD13] Assessing the Spatial Distribution of Evapotranspiration Using Remotely Sensed Inputs, M.S.

Moran and R.D. Jackson, Journal of Environmental Quality 20 (1991) 725-737

[RD14] Assimilation of land surface temperature into the land surface model JULES with an ensemble

Kalman filter, D. Ghent et al, Journal of Geophysical Research 115 (2010) D19112, DOI:

10.1029/2010JD014392

[RD15] Data assimilation into land surface models: the implications for climate feedbacks, D. Ghent et al,

International Journal of Remote Sensing 32 (2011) 617-632, DOI: 10.1080/01431161.2010.517794

[RD16] Thermal remote sensing of urban climates, J.A. Voogt and T.R. Oke, Remote Sensing of

Environment 86 (2003) 370-384, DOI: 10.1016/S0034-4257(03)00079-8

[RD17] Effects of remote sensing pixel resolution on modeled energy flux variability of croplands in Iowa,

W.P. Kustas et al, Remote Sensing of Environment 92 (2004) 535-547, DOI: 10.1016/j.rse.2004.02.020

[RD18] GrapeLook: space based services to improve water use efficiency of vineyards in South Africa.

Klaasse, A., Jarmain, C., Roux, A., Becu, O., and Ginati A., 2011. 62nd International Astronautical

Congress, Cape Town, South Africa.

URL: http://iap.esa.int/sites/default/files/IAC%20Manuscript%20GrapeLook%20final.pdf

[RD19] GrapeLook: Improving agricultural water management using satellite earth observation. Klaasse,

Annemarie, and Caren Jarmain, 2011. Earthzine Water Availability Theme Sept. 23 – Dec. 21, 2011.

URL: http://www.earthzine.org/2011/12/23/grapelook-improving-agricultural-water-management-using-

satellite-earth-observation/

[RD20] Forests and Climate Change: Forcings, Feedbacks, and the Climate Benefits of Forests, G.B.

Bonan, Science 320, 1444 (2008), DOI: 10.1126/science.1155121

http://iap.esa.int/sites/default/files/IAC%20Manuscript%20GrapeLook%20final.pdf

http://www.earthzine.org/2011/12/23/grapelook-improving-agricultural-water-management-using-satellite-earth-observation/

http://www.earthzine.org/2011/12/23/grapelook-improving-agricultural-water-management-using-satellite-earth-observation/


Issue: 2

Date: 19/01/2012

Sentinel Convoy for Land Applications: Workshop Report Page : iv

- iv -

TABLE OF CONTENTS:

Executive summary

List of participants

List of acronyms

1. Introduction

2. Workshop structure and agenda

3. ESA science strategy

4. The Sentinel missions and scientific capabilities

4.1 Sentinel-1

4.2 Sentinel-2

4.3 Sentinel-3

4.4 Formation flying of satellites

5. Examining the science areas

5.1 Carbon/water cycles and vegetation

5.2 Land surface information: operational systems and biodiversity

5.3 Fire and thermal sensing

5.4 Drawing the science together

6. Identification of science gaps

6.1 Carbon cycle

6.2 Surface energy balance

6.3 Water cycle

6.4 Land use and land cover

6.5 Biodiversity

6.6 Human population dynamics


Issue: 2

Date: 19/01/2012

Sentinel Convoy for Land Applications: Workshop Report Page : v

- v -

6.7 Volcanoes

7. Potential convoy concepts

7.1 Sentinel-1

7.2 Sentinel-2

7.3 Sentinel-3

7.4 Other possibilities/issues

8. Summary

Appendix 1: Workshop agenda

Appendix 2: Formation flying of satellites: mission considerations

Appendix 3: The Sentinel missions and scientific capabilities


Issue: 2

Date: 19/01/2012

Sentinel Convoy for Land Applications: Workshop Report Page : 1

EXECUTIVE SUMMARY: A two day workshop on Sentinel Convoy for Land Application was held at ESA ESTEC on October 31

st

and November 1st 2011, as a science gap analysis and mission concept workshop engaging a wider

scientific community in the formulation of Sentinel Convoy science. The intention was for participants to

articulate and discuss challenges in land surface science, to identify gaps in remote sensing capability, and

to suggest possible new research mission concepts to fly in convoy with operational satellites. The

specific objectives of the workshop were:

1) To identify science gaps in current/planned measurements to address the land surface domain, particularly those that might be addressed by convoy missions

2) To identify candidate mission concepts that may address these gaps.

The workshop was led by the University of Leicester and supported by the other Sentinel Convoy Land

study partners, SSTL and Astrium, by the study consultants from the Universities of Leicester, University

College London and King‟s College London, and by ESA who hosted the workshop. The workshop was

attended by 30 science and instrumentation experts.

The workshop provided an excellent insight into many of the aspects of land surface process observations

and modelling, and to observation of the critical parameters. The workshop focused on the following

areas, based on the expertise available: carbon cycle, surface energy balance, water cycle, biodiversity,

human population dynamics and volcanoes. Terrestrial ecosystems and ECVs were not explicitly

discussed or presented as dedicated topics due to lack of expert availability for this workshop.

A number of critical science challenges were addressed including carbon stocks and fluxes; vegetation

stocks and productivity; upscaling of point observations of carbon fluxes; water cycle fluxes particularly

evapotranspiration; carbon losses due to fires; surface radiative balance (albedo/emissivity); urban energy

balance; volcanic thermal anomalies; data assimilation of land parameters. Biodiversity is still at an early

stage in terms of identifying generic needs, although clear synergies were identified with the other areas

particularly in terms of land cover identification and vegetation structure.

The following concepts were identified in the workshop for possible Convoy implementation:

SAR interferometry and/or canopy lidar for vegetation height and biomass inference (using S-1)

Multi-angle visible/SWIR optical measurements for BRDF and vegetation structure (in

combination with S-2 or S-3)

Medium-high spatial resolution mid infra-red for fire (in combination with S-2 or S-3; or loose

constellation using same ground-track but different time of day)

High spatial resolution thermal infra-red radiometers (multi-channel) for land surface temperature

and emissivity (in combination with S-2 or S-3)

Vegetation fluorescence (Flex in combination with S-3)

High spatial resolution, thermal and mid-infrared radiometers (in combination with S-2 f, and S-3

for high temperature and low temperature phenomena accessing eruptive and pre-eruptive

conditions (potential to include gas emissions))


Issue: 2

Date: 19/01/2012


In addition, it is suggested that multi-wavelength SAR, high spectral resolution red-edge imaging, and

very high spatial resolution optical imaging are worthy of future investigation.


Issue: 2

Date: 19/01/2012


LIST OF WORKSHOP PARTICIPANTS:

Forename Surname Affiliation Area of Interest

Clement Albergel ECMWF Data assimilation

Stefania Amici INGV Volcanoes/thermal sensing

Heiko Balzter Gaia Remote Sensing/Leicester Carbon cycle

Fabrizia Buongiorno INGV Volcanoes/thermal sensing

Mike Cutter SSTL Satellite technology

Mark Danson Salford Land cover change

Matthias Drusch ESA Water cycle

Stuart Eves SSTL Mission concept development

Richard Fernandes Canada Centre for Remote

Sensing

Carbon cycle

Diego Fernandez ESA Mission concept development

Darren Ghent Leicester Land surface temperature

David Hall EADS-Astrium Radar technology

Simon Hook JPL Thermal sensing

Neil Humpage Leicester Infrared spectroscopy

Joshua Johnston Natural Resources Canada Fire monitoring

Rob Jongman Alterra, Wageningen UR Biodiversity

Annemarie Klaasse WaterWatch Land resource management

Alexander Kokhanovsky IUP Bremen Snow cover

Mathias Leidig Portsmouth Geo-informatics

Philip Lewis UCL Carbon cycle

Tim Lynham Natural Resources Canada Fire monitoring

Miguel Mahecha MPI for Biogeochemistry, Jena Carbon cycle

Bino Maiheu VITO Urban heat islands

Sander Mucher Alterra, Wageningen UR Land cover/surface energy balance

Andreas Mueller DLR Volcanoes/thermal sensing

Amanda Regan ESA Mission concept development

John Remedios Leicester Land surface temperature

Klaus Scipal ESA Synthetic aperture radar

Tony Sephton ESA Mission concept development

Martin Wooster KCL Fire monitoring and urban heat

islands


Issue: 2

Date: 19/01/2012


LIST OF ACRONYMS: Acronym Definition

ALOS Advanced Land Observing Satellite

ASAR Advanced Synthetic Aperture Radar

BRDF Bidirectional Reflectance Distribution Function

CC Carbon Cycle

ECO Environmental Change Observatory

EO Earth Observation

EOS Earth Observation Science

EPS EUMETSAT Polar System

ESA European Space Agency

ET Evapotranspiration

ETM Enhanced Thematic Mapper

FLEX Fluorescence Explorer

FRP Fire Radiative Power

GCOS Global Climate Observing System

GEO Geostationary Orbit

GLAS Geoscience Laser Altimeter System

GMES Global Monitoring for Environment and Security

GNC Guidance Navigation and Control

GPP Gross Primary Production

GPS Global Positioning System

HD Human Population Dynamics

HRS High Resolution Sensor

IFS Integrated Forecasting System

IR Infrared

JPSS Joint Polar Satellite System

LAI Leaf Area Index

LC Land Cover

LDCM Landsat Data Continuity Mission

LP Living Planet

LRM Low Rate Mode

LRR Laser Retro-Reflector

LST Land Surface Temperature

LTDN Local Time of Descending Node

MIR Mid-Infrared

MISR Multi-angle Imaging Spectro-Radiometer

MSG Meteosat Second Generation

MSI Multi-Spectral Imager

MTG Meteosat Third Generation

MWR Microwave Radiometer

NASA National Aeronautics and Space Administration


Issue: 2

Date: 19/01/2012


Acronym Definition

NBP Net Biome Productivity

NDRE Normalised Difference in Red Edge

NDVI Normalised Difference Vegetation Index

NEDT Noise Equivalent Delta Temperature

NEE Net Ecosystem Exchange

NEP Net Ecosystem Productivity

NIR Near Infrared

NOAA National Oceanic and Atmospheric Administration

NPOESS National Polar Orbiting Operational Environmental Satellite System

NPP NPOESS Preparatory Project

NRT Near Real Time

OLCI Ocean and Land Colour Instrument

OLI Operational Land Imager

OP Operational Monitoring

PAR Photosynthetically Active Radiation

POD Precise Orbit Determination

RA Radar Altimetry

REIP Red Edge Inflection Point

SAR Synthetic Aperture Radar

SCE Snow Cover Extent

SE Surface Energy Balance

SEKF Simplified Extended Kalman Filter

SLSTR Sea and Land Surface Temperature Radiometer

SMAP Soil Moisture Active Passive

SMOS Soil Moisture and Ocean Salinity

SPOT Satellite Pour l‟Observation de la Terre

SRAL Synthetic Aperture Radar Altimeter

SSP Sub Satellite Point

STSE Support To Science Element

SWE Snow Water Equivalent

SWIR Shortwave Infrared

SWOT Surface Water and Ocean Topography

TER Terrestrial Ecosystem Respiration

TES-GAP Temperature Emissivity Signatures for Geosphere and Pedosphere

TH Thermal

TIR Thermal Infrared

TIRS Thermal Infrared Sensor

UHI Urban Heat Island

VDEO Vegetation Dynamics from Earth Observation

VO Volcanic

WC Water Cycle


Issue: 2

Date: 19/01/2012


1. INTRODUCTION

A two day workshop on Sentinel Convoy for Land Application was held at ESA ESTEC on October 31st

and November 1st 2011, as a science gap analysis and mission concept workshop engaging a wider

scientific community in the formulation of Sentinel Convoy science. The workshop was organised by the

University of Leicester, in co-operation with ESA, as part of the Sentinel Convoy for Land Study, with

organisational support from SSTL (project co-ordinator; technical lead) and Astrium UK (technical

support).

The concept of satellite constellations and formations has gained more attention in the Earth observation

sector as an alternative way to accomplish complex scientific objectives exploiting the synergies among

different types of missions [RD1], following the recent successes of the A-Train set of missions

(comprising EOS-Aqua, Cloudsat, CALIPSO, PARASOL and EOS-Aura) and the formation consisting of

EOS-Terra, Landsat-7, EO-1 and SAC-C. The next decade will see the development, launch and

continued operation of several European operational missions (including the GMES-Sentinels, MetOp

and Post-EPS), which shall provide long-term streams of EO data in a reliable way. These missions will

provide a capacity for systematic, continuous and long-term Earth observation and monitoring. And a

stable baseline from which dedicated complementary satellite missions can be designed. The possibility

of flying additional satellite missions in formation with this baseline opens new opportunities to address

novel areas of Earth science which would not have been possible previously. In particular, focussed

missions might take advantage of the synergetic EO opportunities offered to achieve new EO science

objectives which might be unachievable with single satellite measurements.

In this context, ESA defined three thematic activities (focusing on Ocean and Ice, Land and Atmosphere

respectively) aiming to explore potential concepts for satellite formation configurations which could

exploit the European EO capabilities already available/planned. The Ocean and Ice activity is already

underway (see [RD1] for initial concepts identified), whilst this workshop contributes directly towards the

Land Convoy activity.

These activities are based on an assessment of the science gaps in each Earth domain matched to the

capabilities of the planned Sentinel missions and other European operational missions such as Metop (2nd

generation). This allows the identification of synergetic convoy mission concepts that could meet the

challenges for EO in each domain which would enable new science to be done. A critical part of each

study is therefore to understand the science for each domain and the future needs of the science

community. These needs will often also be connected with operational applications which are therefore of

relevance.

The Sentinel Convoy for Land Applications study is led by Surrey Satellite Technology Ltd with partners

from the University of Leicester and Astrium Ltd. The study is planned to proceed in five steps:

identification of science gaps that might be addressed by a “convoy” mission flying with the Sentinel

satellites; identification of candidate mission concepts that may address the identified gaps; down-

selection of most promising concepts from list of candidates; detailed technical study of selected

concepts; cost and schedule analysis of selected concepts


Issue: 2

Date: 19/01/2012


Uniquely amongst the Convoy studies, this land study identified the relevance of a workshop involving a

wider scientific community in the formulation of the science challenges and in the identification of

possible convoy mission concepts. Within the study team, the University of Leicester is responsible for

the science gap analysis and therefore was the main organiser of the workshop.

The specific objectives of the workshop were:

1) To identify science gaps in current/planned measurements to address the land surface domain, particularly those that might be addressed by convoy missions

2) To identify candidate mission concepts that may address these gaps.

The intention was for participants to articulate and discuss challenges in land surface science, to identify

gaps in remote sensing capability, and to suggest possible new research mission concepts to fly in convoy

with operational satellites; concepts were expected to be derived from the gap analysis. As well as the

study partners and ESA, the workshop was supported by the study consultants from GAIA remote sensing

(Balzter), University College London and King‟s College London. The workshop was attended by 30

science and instrumentation experts from across Europe, Canada and the United States.

The workshop was structured in three parts: an introduction to the study and workshop; presentations on

the science needs for land surface; a plenary session identifying the major science gaps and possible

convoy options.

All the details of the workshop, including the presentations and the final version of this report, can be

found at the workshop web-site: www.le.ac.uk/sentinel-convoy-land

2. WORKSHOP STRUCTURE AND AGENDA

In the first part of the workshop, presentations by Amanda Regan (ESA), Stuart Eves (SSTL) and John

Remedios (Leicester) described the concept of Sentinel Convoys and the aspects particular relevant to

land surface process and applications. The presentations covered the essentials of ESA‟s science strategy,

their forthcoming operational satellite programmes (particularly Sentinels), and formation flying concepts

(Sections 3 and 4 of this report).

The first day of the workshop also provided a platform for experts in the remote sensing of land surface

properties from space to outline the current state of knowledge and science challenges to be addressed in

the near future. These presentations were grouped into four sessions, which are described in detail in

Sections 5.1 to 5.4 inclusive.

The second day of the workshop was much more discussion based. The morning session focused on

identification of the science and operational gaps which needed addressing, with discussions directed in

turn towards a list of eight science challenge areas (see Section 6 of this workshop report for details). The

final session looked at gathering and discussing suggestions for potential convoy concepts that could

operate in conjunction with one of the three Sentinel spacecraft (see Section 7).

http://www.le.ac.uk/sentinel-convoy-land


Issue: 2

Date: 19/01/2012


All the details of the workshop, including the presentations and the final version of this report (when

available), can be found at the workshop web-site: www.le.ac.uk/sentinel-convoy-land. A copy of the

workshop agenda is included in Appendix 1 of this report for reference.

3. ESA SCIENCE STRATEGY

A major context for the workshop was ESA‟s “The Changing Earth: New Scientific Challenges for ESA‟s

Living Planet Programme” (http://esamultimedia.esa.int/docs/SP-1304.pdf) [RD2] which lays out a

general overview of the challenges of land surface science for EO observations. Four challenges are

specifically laid out.

Challenge 1: Understand how terrestrial ecosystems interact with water, carbon and energy exchange.

Challenge 2: Understand the interactions between biological diversity, climate and ecosystem

properties.

Challenge 3: Understand how human dynamics affect the functioning of terrestrial ecosystems.

Challenge 4: Understand the terrestrial carbon cycle and its control and feedback mechanisms.

From these challenges, the ESA report identifies the following science areas to which has been added

Essential Climate Variables based on the the Global Climate Observing System (GCOS:

http://www.wmo.int/pages/prog/gcos/documents/SatelliteSupplement2011Update.pdf) [RD3]. Surface

energy balance and volcanoes (indicated by “workshop” in the list) were also added as a result of the

discussions at the workshop. Hence these are not reflected explicitly in the workshop agenda or in the

original guidance to participants, but were an integral part of the discussions that took place.

• The carbon cycle

• The surface energy balance (workshop)

• The water cycle

• Terrestrial ecosystems

• Biodiversity

• Land use and land use cover

• Human population dynamics

• ECVs (Essential Climate Variables)

• Volcanoes (workshop)

These areas were used as a basis for the presentations and the plenary discussions at the workshop.

http://www.le.ac.uk/sentinel-convoy-land

http://esamultimedia.esa.int/docs/SP-1304.pdf


Issue: 2

Date: 19/01/2012


4. THE SENTINEL MISSIONS AND SCIENTIFIC CAPABILITIES

During the workshop, it was important to understand the capabilities of the Sentinels, as presented by

Amanda Regan (ESA)

These capabilities are briefly laid out here since they provide a major context for discussions on both the

science gaps and the possible convoy mission concepts. Details can be found in Appendix 3.

The Sentinel missions have been commissioned by the Global Monitoring for Environment and Security

(GMES) programme, which aims to develop a European capability to acquire, to process and to distribute

Earth observation data which meets the demands of governmental, public, scientific, meteorological and

security services. Specifically, the programme addresses issues within the following categories:

1. Monitoring and forecasting the changes in the Earth‟s land, marine and atmospheric environments

over both regional and global scales

2. Monitoring and assessing the effects of climate change, its causes and effectiveness of mitigation

strategies.

3. Provision of situational awareness information over rapid time periods in the cases of emergency

(natural or man-made disasters) or security (e.g. border control)

The Sentinels have been designed to deliver the space segment of the GMES programme. ESA will

deliver five unique Sentinel missions during the next decade, which will provide global systematic

coverage to meet the requirements of GMES for Earth observation data.

The most relevant to this study workshop on land surface processes are the first three Sentinels:

Sentinel 1, a C-band SAR, flying in a dawn-dusk orbit, swath of 80 km to 400 km, resolutions of

5 to 40 m. When both satellites are operational a revisit time of 1-3 days will be achievable,

regardless of weather conditions.

Sentinel 2, a visible and shortwave infra-red (SWIR) spectrometer, 10.30 Equator crossing time,

swath of 290 km, resolutions of 10-60 m and typical repeat coverage of around 5 days (reduced

by cloud).

Sentinel 3, which will carry three instruments for land: an Ocean and Land Colour Instrument

(OLCI), a Sea and Land Surface Temperature Radiometer (SLSTR) and a radar altimeter. OLCI

and SLSTR offer medium spatial resolution at 300 m to 1 km in visible, SWIR and thermal infra-

red bands, with a repeat cycle of 27 days. SLSTR offers dual-view capability (nadir and

backwards). The radar altimeter offers lake altimetry data.

These Sentinels are due for launch in 2013 (the “A” units) with B units scheduled for launch in

forthcoming years so that sampling of the Earth is obtained with two satellites. The satellites are expected

to have standard operating modes so that consistent and regular coverage is obtained.


Issue: 2

Date: 19/01/2012


4.1 FORMATION FLYING

Eves provided an overview of formation flying of satellites and mission considerations, a summary of

which can be found in Appendix 2. It is clear that a number of European missions at an advanced level of

development are pursuing formation flying concepts (such as PREMIER, Sentinel-5 Precursor, FLEX and

CarbonSat), hence the relevance of this workshop to future mission proposals.

5. EXAMINING THE SCIENCE AREAS

5.1 SESSION 1: CARBON/WATER CYCLES AND VEGETATION

Balzter highlighted uncertainties in quantitative knowledge and spatial distributions of carbon stocks and

fluxes, noting that land use change, deforestation and forest degradation were releasing carbon into the

atmosphere and increasing drought stress. Total biomass uncertainties are large. SAR backscatter allows

forest biomass estimation (but due to saturation, longer wavelengths are preferred: P better than L better

than C-band). SAR interferometry (forest edges or underlying terrain model required), polarimetric SAR

interferometry, SAR tomography (multi-angle imaging), and LiDAR (e.g. ICESAT-GLAS) give forest

height and biomass by allometry. Allometry is a very useful empirical technique, requiring measurements

of forest height. However, new multi-temporal C-band SAR gives reasonable accuracy of biomass at 10

km scale [RD4]. Global measurements, continuity and simultaneous measures of biomass and height are

important e.g. SAR and LiDAR in formation. The use of high resolution SAR data for early stage

deforestation was also presented e.g. the monitoring of logging tracks etc.

The theme of vegetation (and carbon) was continued by Lewis. The importance of vegetation

measurements lies in land use/cover change (as a result of anthropogenic activities), estimation of

vegetation stocks and productivity, the interaction with energy/water/momentum/gas fluxes, vegetation

stocks. Leaf area index (LAI) has a major role in evapotranspiration (ET), carbon fluxes, nutrients, and in

exponential transform is proportional to radiation intercepted for photosynthesis. Vegetation structure is a

key factor, starting with height (which can be related to biomass) but also spatial arrangement aids

classification and clumping knowledge can be tied to radiation interception and improved estimates of

LAI. Vertical and horizontal structure has ecological importance (biodiversity, habitat quality), and

through canopy cover is related to rainfall interception (homogeneous situations). Without consideration

of structural arrangement, only effective LAI can be inferred. Optical Earth observation can be used to

infer some scales of structural arrangement both by passive, multi-angle measurements of BRDF and by

active LiDAR. (e.g. BRDF, LiDAR),

Improvements expected from Sentinel missions include, for Sentinel-3, some improved sampling for LAI,

and better atmospheric correction and cloud clearing. For Sentinel-2, there is good repeat coverage for

vegetation dynamics (cloud issues will always be a problem however). Spectral sampling is sufficient for

LAI and estimation of most parameters in 1D radiative transfer models (e.g. chlorophyll, water content).


Issue: 2

Date: 19/01/2012


However, observational gaps clearly are present and point to the following: a lack of BRDF sampling

means that we can usually only retrieve „effective‟ LAI; LiDAR would aid interpretation by providing

canopy heights and cover; and improved BRDF sampling would also benefit observations of surface

albedo. For LAI, however, there is saturation at higher levels. Some scales of structural arrangements are

accessible to optical EO, and hence good angular sampling is important. Various results were presented

by Lewis showing that the accuracy of effective LAI depends on viewing angles. Hence, at least 3 and

possibly 5 viewing angles are desirable.

Fernandes focused on LAI itself rather than the vegetation structure, expressing the potential for deriving

multi-scale LAI from Sentinels. Requirements from GCOS are for 1km spatial resolution, less than 1

month sampling interval (currently ~2 months with LandSat), < 20% (or 1 unit) at biome scale (a biome is

a land surface class categorized by the same dominant vegetation ecosystem and sharing similar surface

climatic conditions). Regional requirements are less than 100m spatial resolution, bi-weekly sampling

interval, and less than 20% (or 1 unit) on a local (100km2) basis. Sentinel 2A alone will not meet the

regional requirement, but the 2 unit solution (A and B) will.

Improvements needed in LAI knowledge at local scale require knowledge/use of p, where p is the

probability of photon re-collision [RD5, RD6], and can be solved using Normalized Difference in Red

Edge (NDRE) or Red Edge Inflection Point (REIP). From Sentinel-2, one might be able to map p at high

spatial resolution, which can then be averaged to provide p for lower spatial resolution sensors such as

MERIS. However, p may still need calibration at in situ sites. In general, high spectral resolution of the

“red edge” between 700 and 735 nm is desirable to reduce land use bias in LAI.

Mahecha approached the carbon problem with reference to fluxes. One can think about fluxes in terms of

NEE (net ecosystem exchange); GPP (gross primary production) and TER (terrestrial ecosystem

respiration). There are a wide range of processes releasing carbon dioxide into the atmosphere, which

remain highly uncertain. A particular challenge is upscaling of point in-situ observations to global scales,

which needs the relation of co-varying variables (e.g. phenology, vegetation type) to observed fluxes

(surface-atmosphere exchange of greenhouse gases) [RD7].

Future integration of carbon and other science areas will benefit from:

1) Forcing / assimilation into carbon models of more physically relevant variables than simply

vegetation indices, e.g. water cycle properties:

i. soil moisture

ii. interception

iii. LST

1) Incorporation into carbon models of changes in land use/cover, carbon losses via fire, changes in

stand structure (wind throw); insect outbreaks;

2) Extension of carbon models to other greenhouse gases e.g. methane (would need to include soil

moisture, wetland extent, LST…).


Issue: 2

Date: 19/01/2012


EO already contributes to carbon cycle studies by supporting lines of evidence with better interpretable

remote sensing indicators, for example, the recent observations of chlorophyll fluorescence agree globally

reasonably well with upscaled GPP estimates. Much more is possible and needed. The carbon cycle

operates from seconds up to centennial time scales so there is a need for consistency with previous

missions and maximal mission extension. Full transparency of data uncertainty is needed for model-data

fusion. Sentinel and in situ monitoring networks need to be linked very well. The workshop user needs for

investigating the carbon cycle are summarised in Table 5.1.

Science ref

no.

Science need Variable ref

no.

Relevant EO

variables

Workshop

presenter

Comments

W-S-CC-01 Quantitative

knowledge and

spatial distribution

of carbon stocks

and fluxes

W-V-CC-01

W-V-CC-02

- Biomass

- Vegetation

height

Balzter Requires sensitivity

to a range of

biomass.

Vegetation height

also can give

estimates of

biomass

(allometry)

W-S-CC-02 Estimation of

vegetation stocks

and productivity

W-V-CC-03

W-V-CC-04

W-V-CC-05

W-V-SE-01

W-V-CC-06

- LAI

- NDVI

- fAPAR

- BRDF

- Vegetation

type

Lewis,

Fernandes

Vegetation

structure is required

to support these

parameters (vertical

and horizontal)

Assumes canopy

cover can be related

to LAI.

Red edge spectral

resolution may be

important for

improved

vegetation indices

and information on

plant health


Issue: 2

Date: 19/01/2012


Science ref

no.


no.

Relevant EO

variables

Workshop

presenter

Comments

W-S-CC-03 Upscaling of point

observations of

carbon fluxes

(NEE, GPP, TER)

to global scales

W-V-LC-01

W-V-WC-01

W-V-CC-07

W-V-CC-08

W-V-CC-06

- Land cover

- Soil moisture

- Fluorescence

- Fire

emissions

- Vegetation

type

Mahecha,

Lewis

Needs relation of

co-varying

variables to

observed fluxes,

i.e., observations of

similar spatial and

temporal coverage

(gridded).

Insect outbreaks

were also noted as

a potentially

important variable

but is related to

plant/vegetation

indices

W-S-CC-04 Interaction of

vegetation with

water cycle

variables

W-V-WC-01

W-V-SE-02

W-V-CC-09

- Soil moisture

- LST

- Wetland

extent

Mahecha,

Lewis

Wetland extent is

identified for

methane studies.

TABLE 5.1: SUMMARY OF WORKSHOP USER NEEDS FOR THE CARBON CYCLE

5.2 SESSION 2: LAND SURFACE INFORMATION: OPERATIONAL SYSTEMS AND BIODIVERSITY

Albergel provided insight into the use of EO land surface observations for assimilation into numerical

models. Initialisation of soil variables has a significant impact on numerical weather forecast on both short

and medium ranges. Success in assimilating EO data for a particular parameter also relies on both the

quality of the land surface model, and the quality of the observations available. Currently the European

Centre for Medium range Weather Forecasts (ECMWF) is investigating the assimilation into their models

of soil moisture, snow cover, snow extent, to some extent LAI, and fires (see next section). Kokhanovsky

provided information on current capabilities for snow parameters, particularly snow grain size using

MERIS and AATSR on Envisat with application to Sentinel-3 and Sentinel-2 data.

For soil moisture, SEKF (Simplified Extended Kalman Filter) method will be used by ECMWF to

investigate use of new generation of satellite data with the following characteristics [RD8]: Active

microwave: ASCAT, L-band SMAP; Passive microwave: L-band SMOS, SMAP [RD9]; L-band (1.4

GHz) is sensitive to ~5 cm depth; C band (5 GHz) is sensitive to ~2 cm depth. There are near real-time


Issue: 2

Date: 19/01/2012


requirements for ECMWF assimilation: Latency < 3h; Revisit < 3 days. There are also spatial resolution

requirements for better than 10 km resolution in future.; Synergy between active and passive observations

may well provide solutions in the future to the spatial resolution problem and in fact there is probably a

greater need for accurate measurement of variability, rather than absolute magnitude.

For snow, future plans at ECMWF (Albergel) are to include SWE (Snow Water Equivalent) and SCE

(Snow Cover Extent) in an Extended Kalman Filter analysis. Requirements for assimilation of snow data

into ECMWF models include: Short latency (NRT within 3 hours); accurate location and variation of

SWE effects and snow line (related to albedo); global coverage with frequent revisit time, ideally within 1

day; spatial resolution: < 10 km by 2015, < 5 km by 2020.

In the long-term, land surface modelling will increase in spatial resolution leading to possible synergies

between soil moisture, other hydrological variables and vegetation parameters. This will increase the

importance, in water cycle modelling, of horizontal transport processes (river routing) and the use of

integrated hydrological variables such as river discharges (e.g. Surface Water Ocean Topography (SWOT)

mission)

For biodiversity, the remote sensing role is in monitoring of habitat types, ecosystems, land/coastal use.

General requirements are for pixels down to 20 m in dimension (exact requirement dependent on habitat

type, location); narrow linear elements such as streams and hedges resolved; weekly to seasonal revisit

time; high precision (EU directives ask member states to report on 25% change over 25 years, so able to

identify trends < 1% per year); and data continuity for long term assessment. However, in detail the

biodiversity community will be working through GEO BON (Group on Earth Observations Biodiversity

Observation Network, an international collaboration aiming to provide comprehensive global monitoring

of trends in individual species, populations and ecosystems) in the coming years to identify which

variables are primary measurements, and which variables are derived from primary measurements; to

identify links to essential climate variables in other disciplines (Jongman). The process will be

comparable with the ECV development. The first meeting on this will be held on 28-29 February at ESA

in Frascati.

Danson and Boyd illustrated these points with potential improvements to land cover and forestry

estimation using DMC data at 22 m spatial resolution.

The workshop user needs identified for operational monitoring (including biodiversity) are summarised in

Table 5.2.


Issue: 2

Date: 19/01/2012


Science ref

no.


no.

Relevant EO

variables

Workshop

presenter

Comments

W-S-OP-01 Assimilation of

land surface

parameters into

numerical weather

prediction models

W-V-WC-01

W-V-WC-02

W-V-WC-03

W-V-CC-03

W-V-CC-09

- Soil moisture

- Snow cover

- Snow water

equivalent

- LAI

- Fire radiative

power

Albergel Higher spatial

resolution required

for soil moisture;

Snow line

definition and

change with time is

important

W-S-OP-02 Modelling of

horizontal water

transport

W-V-WC-03

W-V-WC-04

- River routing

- River

discharge

Albergel

Likely future need

W-S-OP-03 Monitoring of

habitat types,

ecosystems, land

use/management

for biodiversity

W-V-LC-01

W-V-CC-04

W-V-WC-01

W-V-CC-03

- Land cover

- NDVI

- Soil moisture

- LAI

Jongman Vegetation

structure also

important here

(LiDAR)

TABLE 5.2: SUMMARY OF WORKSHOP USER NEEDS FOR OPERATIONAL MONITORING

INCLUDING BIODIVERISTY

5.3 SESSION 3: FIRE AND THERMAL SENSING

This session was composed of two related but scientifically distinct themes: fires (hot, location defined

but disruptively variable) and passive temperature scenes (ambient, defined everywhere but with strong

heterogeneity and abrupt changes).

Wooster provided an overview of satellite-derived measurements of fires. Fires are important indicators

for monitoring the carbon cycle and atmospheric composition. Global biomass burning is the second

largest source of trace gases and the largest source of fine carbon particles in the troposphere; a key

parameter for models is the emission rates from fires. Biomass burning shows very high variability on all

spatio-temporal scales, hence the need for satellite observations. However, there are currently large biases,

uncertainties and differences between current Earth observation products looking at biomass burning

[RD10]. Wooster concentrated on Fire Radiative Power (FRP [RD11]). Requirements are higher spatial

resolution (~250 m) than SLSTR to improve sensitivity to smaller fires (as things stand, emissions would

be underestimated without taking these into account); channel saturation linked to spatial resolution (>

500 K saturation temperature); alternative overpass time to sample daily peak in fire activity. Typically,

future instruments such as SLSTR sample in the morning, which is far from ideal with respect to the peak

of the fire cycle (close to 14.00 or even later).


Issue: 2

Date: 19/01/2012


Lynham provided an operational perspective on these aspects, but one which was largely in accord with

Wooster. Wildfire activity determines whether Canada is a net source or sink of atmospheric carbon.

Hence the desire to use EO data – this needs to be internationally consistent and defensible, and which is

sufficiently timely for annual operational reporting. It was emphasized that one should never

underestimate the value of hotspots as these show: the location of current fires; the estimate of fire rate of

spread; that a disturbance or land use change is a fire; and identifies burning pixels with a unique date and

time stamp which are required for completing emissions calculations. FRP for instance enables the

estimation of fuel consumption without knowing the fuel type.

Moving to ambient thermal measurements, Ghent, Wooster and Maiheu presented the benefits of land

surface temperature (LST) for evapotranspiration (ET), urban energy balance and urban heat islands.

Ghent noted that ET is the transfer of moisture from the Earth‟s land surface to the atmosphere, via a

combination of evaporation and transpiration. ET may be constrained by land surface energy balance

models, via observations of land surface temperature (which can be used as a proxy for ET as water loss

to the atmosphere cools the surface, thus affecting the diurnal cycle of surface temperature). Since varying

soil moisture conditions yield distinctive soil and canopy thermal signatures, LST is a valuable

characteristic for constraining ET. An estimation of ET and soil moisture via land surface temperature

alone would be very useful for hydrological applications in water resource management and agriculture.

However both high temporal and spatial resolution land surface temperature data are strictly necessary. A

0.5K LST error can result in a 10% error in sensible heat flux [RD12] and a 1.0K LST error can lead to a

10% error in ET [RD13]. Finally it is important to note that assimilation of LST into land surface models

can constrain soil moisture and evapotranspiration [RD14, RD15]. LST and soil moisture therefore play

coupled roles in the characterisation of the water cycle.

Wooster focused on the urban energy balance. Understanding surface climate, surface cover and

anthropogenic impacts requires knowledge of urban energy fluxes. The partitioning between sensible and

latent heat flux is crucial for human thermal comfort and energy consumption. Growing urban areas need

better representation in modelling to support decision making for greater than 50% of World Population.

Large spatial heterogeneity in urban areas is a challenge. Using EO to study the urban area is very useful

if both thermal temperature and emissivity are available in conjunction with spectral reflectance,

broadband albedo, vegetation fraction and land cover classification. Requirements are for resolution of

surface emissivity of different urban land types which requires multispectral (5 bands minimum) thermal

infrared at high spatial resolution (90 m or better). Synergy with the hyperspectral optical information of

Sentinel 2 is important but a potential thermal infra-red instrument does not need to image at the same

time. Formation flying with Sentinel-3: would allow high spatial resolution interpretation of moderate

spatial resolution SLSTR (TIR) and OLCI (optical) products.

Maiheu noted that there is a clear benefit to urban heat island studies from inclusion of land surface

temperature retrievals [RD16]. Thermal infrared requirements from some urban heat islands studies are as

follows: 2-3 images a day; spatial resolution < 500 m; daily revisit time; at least two spectral bands

(ideally four); and near real time data availability. Urban emissivity assignment is important as emissivity

varies greatly between different surface types (hence need for multiple wavelength bands).

Buongiorno (on behalf also of Mueller and Amici) discussed the science which led to the TES-GAP

proposal (proposed as an ESA Earth Explorer 8 candidate) which is more cross-cutting across areas


Issue: 2

Date: 19/01/2012


accessible to thermal infra-red measurements. The key drivers were observation of volcano thermal

anomalies including gas emissions from continuous degassing sources, the potential for soil

characterisation with infra-red spectroscopy, and applications of thermal imagery to other areas such as

urban heat islands and fires. For volcanic observations, three main aspects can be distinguished: active

lava flows; volcanic plumes, and pre-eruptive thermal anomalies and gas emissions. Active lava flows

need observations of temperatures in two main ranges: 300-420 K (crust temperature) at spatial scales of

<30m, and 800-1500 K (lava) at medium to low spatial resolution (<100 m). These applications are best

suited to a combinations of SWIR, MIR and TIR channels avoiding channel saturation.. Eruptive plumes

which contain ash and SO2 could be observed and loading parameters could be retrieved, for example

using sentinel-3 SLSTR capabilities in formation with a system with better spectral capabilities in the TIR

range to cover SO2 bands. The observation of pre-eruptive precursors requires data at high spatial

resolution (< 60m) using a multispectral TIR instrument with good radiometric characteristics (<0.5-1 K,

absolute accuracy) and ideally spectral capabilities to retrieve SO2 emissions for degassing plumes

Finally, two additional presentations from Sobrino (represented by Remedios) and Klaasse were given.

Sobrino discussed the combination of high spatial resolution and revisit capabilities in the thermal infra-

red and the science behind this which had led to the MISTIGRI (a French/Spanish mission scheduled for

launch in 2015) and TIREX (another Earth Explorer 8 candidate) concepts. High spatial resolution: gives

access to full range of land types in areas where spatial variability is high, e.g. urban environments, fields

[RD17]. Frequent revisit capabilities to specific pre-determined target sites: provides rapid response to

surface forcing, e.g. meteorological conditions, water status. The two main areas of scientific focus are

therefore: a) monitoring energy and water status of continental biosphere and b) urban environments. In

spatial resolution terms, the concept should address mean size of fields: < ~100 m required, turbulence

impacts: > ~40 m required. Therefore, the MISTIGRI and TIREX concepts aim for 50 m (TIR) spatial

resolution.

Klaasse provided an insight into applications of LST for surface energy balance modelling. Modelling the

surface energy balance requires knowledge of the following parameters: surface albedo, NDVI,

meteorological fields and LST. The surface energy balance is important in understanding the water

balance and water availability. Water availability is expected to be one of the greater challenges for

mankind in the years to come, as it is closely related to food security. Projections show that feeding a

world population of 9.1 billion people in 2050 would require an increase in overall food production by

~70% between 2005/7 and 2050. Optimising the use of land and water in agriculture is essential to

increasing food production to the required level. An example of how the surface energy balance is used to

improve water use efficiency in agriculture is the GrapeLook pre-operational service [RD18, RD19].

Services such as GrapeLook are highly dependent on the availability of LST. The need is for continuous

high spatial resolution land surface temperature data to use as input to surface energy balance models (50

– 100 m), as currently provided by LandSat. Weekly or better temporal resolution is also needed with

sensitivity to small changes in ambient land temperatures (not just fires).

The workshop user needs identified for fire, thermal sensing and urban heat islands are summarised in

Table 5.3.


Issue: 2

Date: 19/01/2012


Science ref

no.


no.

Relevant EO

variables

Workshop

presenter

Comments

W-S-TH-01 Monitoring the

impact of fires on

the carbon cycle

and atmospheric

composition

W-V-CC-08

W-V-CC-09

- Burnt area

- Fire radiative

power

Wooster,

Lynham

Need to know

emission rates of

fires and their

spatial extent,

particularly at high

spatial resolution.

Active fire

information is

important at all

times but

particularly in the

afternoon.

W-S-TH-02 Flux of moisture

between the Earth‟s

surface and

atmosphere by

evapotranspiration

W-V-SE-02

W-V-WC-01

- LST

- Soil moisture

Ghent Contributes to

understanding of

surface energy

balance

W-S-TH-03 Urban energy

balance and

characterisation

W-V-HD-01

W-V-HD-02

W-V-SE-03

W-V-HD-03

- Urban

emissivity

- Urban

surface

temperature

- Albedo

- Urban land

cover

Wooster,

Maiheu

Need to know

urban topography

and urban spread in

addition to urban

surface temperature

and albedo


Issue: 2

Date: 19/01/2012


Science ref

no.


no.

Relevant EO

variables

Workshop

presenter

Comments

W-S-TH-04 Observation of

volcano thermal

anomalies

W-V-SE-02 - Crust

temperature

- Lava

temperature

Pre-eruptive

thermal

anomalies and

gas emissions

Buongiorno Temperatures

needed in the

ranges 300-420K

for crust

temperature and

800-1500K for

active lava (<100

m)

Temperature ranges

283-360 K; ideally

emissivity and SO2

retrievals (<60 m)

W-S-TH-05 Monitoring of

surface energy

balance and water

status of

continental

biosphere

W-V-WC-01

W-V-HD-04

W-V-SE-03

W-V-SE-02

W-V-CC-04

W-V-SE-04

- Soil moisture

- Land use

- Albedo

- LST

- NDVI

- Thermal

emissivity

Sobrino

Hook

Ghent

Klaasse

High spatial

resolution and

frequent revisit

needed

Emissivity required

in addition to LST

TABLE 5.3: SUMMARY OF WORKSHOP USER NEEDS FOR FIRE, THERMAL SENSING, URBAN

DEVELOPMENT AND VOLCANOES

5.4 SESSION 4: DRAWING THE SCIENCE TOGETHER

Hook (HyspIRI) and Fernandes (SEN4SCI) provided presentations which provided top level illustrations

of the science requirements and how these can be drawn together to inform and prioritise science

requirements. The HyspIRI mission has 5 science challenges: Volcanic/seismic activity; Wildfires; Water

use and availability; Urbanisation/human health; Earth surface composition and change. Within each area,

there are many individual challenges which should be targeted. HyspIRI arrived at instrument

requirements through a science traceability matrix: a) Science questions (as listed in Decadal Survey); b)

Measurement requirements; c) Instrument requirements; d) Mission requirements; e) Not possible to

satisfy every requirement; f) prioritise requirements based on the science; Also need to understand

engineering trade-offs (e.g. between different scanning mechanisms, detector types…). The concept

eventually resulted in at a Multispectral TIR Scanner with 7 spectral channels between 7.5 and 12 microns


Issue: 2

Date: 19/01/2012


and 1 spectral channel at 4 microns for hot targets (up to 1200 K); absolute accuracy is better than 0.5K.

NEdT is 0.2K. Swath width is 600 km; 60 m spatial resolution, 5 days revisit.

SEN4SCI (Fernandes) is a study being funded by the ESA STSE programme addressing where Sentinel

data can contribute in the context of the scientific challenges of the ESA‟s Living Planet (LP) Programme

and other research questions. The SEN4SCI study emphasis is on the following: a) Identification of ESA

science challenges towards which Sentinel data can contribute; b) Identification of required data products,

with particular emphasis on those not planned for baseline Sentinel (or other ESA) missions but could

enhance the scientific yield from these missions; c) To gather inputs from the broader scientific

community with respect to these requirements; describe characteristics of the missing products and

provide recommendations for further implementation and validation; d) To determine characteristics of

the missing products and recommendations for further implementation and validation.

A SEN4SCI workshop (March 2011) concluded that: Sentinel capabilities (long term spatial and temporal

coverage) provide potential for developing new scientific products; calibration/validation is essential for

science applications; Sentinel data archives should be reprocessed in a timely fashion; open data policy

boosts scientific use. The SEN4SCI workshop recommendations for constellation data products were: a)

Global 30 m land cover with annual land cover change; b) Global monthly 30 m LAI with consistent

300m NDVI, fAPAR and (possibly) albedo at 10 day to weekly intervals; c) Synoptic terrain deformation

monitoring over sensitive regions; d) Synthesis microwave soil moisture analysis; e) LST driven

evapotranspiration estimation. An example was given of the LAI synthesis product which uses red-edge

derivative (OLCI, MSI) to retrieve photon re-collision probability p in the canopy, allow physically

consistent scaling; and then derive LAI, faPAR using off-line calibrations to p (as explained previously).

Limits arise from clumping, from sensitivity to large variations in chlorophyll and dry matter, and woody

material may bias retrievals. For leaf optical properties, need hyperspectral sensor. For vegetation

clumping, need multi-angle sensor. For mapping of LAI over dense evergreen forests, need lidar sensor.

The user needs relevant to this example are listed in Table 5.4.

Science ref

no.


no.

Relevant EO

variables

Workshop

presenter

Comments

W-S-CC-05 Improved

estimation of LAI

using red-edge

information

W-V-CC-03

W-V-CC-05

W-V-CC-06

- LAI

- fAPAR

- Vegetation

type

Fernandes Hyperspectral

sensor needed for

leaf optical

properties, multi-

angle sensor for

vegetation

clumping, LiDAR

sensor for canopy

in dense evergreen

forests

TABLE 5.4: SUMMARY OF WORKSHOP USER NEEDS FOR LAI

The SEN4SCI study was able to identify some gaps across the Sentinels. The Sentinels are unable to

monitor soil moisture over vegetation, for which a SMAP or SMOS-like mission is necessary. Data gaps


Issue: 2

Date: 19/01/2012


also exist due to cloudy conditions over forested areas, for which the solution is L-band or P-band SAR.

The Sentinels are also unable to map species and biochemistry, and cannot relate physical changes to

human activities. For all of these gaps, the solution is very high resolution imaging or hyperspectral

imaging. The vertical stratification of vegetation, for which the solution is LiDAR, is also unavailable

through Sentinel observations alone. The Sentinels are unable to meet all the requirements for biomass,

for which the solution is LiDAR or P-band SAR. Finally, there is a need to map vegetation water and

photosynthetic status, for which hyperspectral and fluorescence imaging is necessary. The gaps listed here

are included in the tables presented in Section 6.


Issue: 2

Date: 19/01/2012


6. IDENTIFICATION OF SCIENCE/OPERATIONAL GAPS

In order to examine the science gaps in more detail, some key plots were used as a basis for discussion.

Figure 6.1 shows how the different science challenge areas considered interact with one another [RD20]).

FIGURE 6.1: ILLUSTRATION OF INTERACTIONS BETWEEN SOME OF THE DIFFERENT SCIENCE

CHALLENGE AREAS CONSIDERED DURING THE WORKSHOP [RD20]

A key conclusion was to include the surface energy balance as a separate area although this had not been

explicitly organised into the agenda. In addition, volcanoes were considered to be an important aspect of

the land surface (although often considered to be in the solid Earth domain).


Issue: 2

Date: 19/01/2012


Based on the presentations and the discussion, it was possible to categorize parameters into key groupings

each identified with a science challenge. In each of these domains, a * indicates those parameters for

which there are particular gaps in current and planned capability and then comments are made in the text

as to which parameters are covered by proposed missions.

Terrestrial ecosystems and ECVs were not explicitly discussed or presented as a dedicated topic in the

meeting and are therefore not reported here. The conclusions reflect the fact that experts in these domains

did not participate in the workshop.

6.1 CARBON CYCLE

List of parameters identified in the presentations as important for the carbon cycle:

Carbon stocks and fluxes, disturbances and abrupt changes, and their spatial distributions*

Above-ground biomass*

Vegetation height (for biomass)*

Vegetation structure*

Leaf Area Index

Drought or water stress.

Burned area

Fire (at resolutions < 250 m)*

Fluorescence (for GPP)* (at resolutions less than 4 km)

Above-ground biomass is a particular problem which the proposed P-band Biomass and the current

ALOS/anticipated L-band ALOS-2 would address. However C-band tomography could provide an

operational/monitoring approach. Global monitoring is a clear requirement. A 10 day revisit period is

likely to be sufficient to monitor biomass.

To assess vegetation height a LiDAR is needed and Icesat-GLAS has provided some measurements. The

Icesat-2 mission concept should be considered in this context. Vegetation structure information is lacking

and can also be obtained from LiDAR measurements or can be partially inferred from BRDF angular

measurements.

Leaf area index data is available from the MODIS instrument (Aqua/Terra) at medium spatial resolution.

LAI will be derived from Sentinel-2 data. LAI requires systematic measurement. Carbon fluxes are also

determined by vegetation health, of which drought/water stress is a key controlling factor (see also the

Sobrino presentation). Fluorescence was shown to be a very good additional piece of information, even

from the relatively low spatial resolution GOSAT, and is proposed in the FLEX mission. An implication

is that any mission with high spectral resolution in its O2 A-band could provide fluorescence information.

For vegetation measures which vary diurnally, time of day of measurements is an important consideration.


Issue: 2

Date: 19/01/2012


Carbon fluxes, such as gross primary productivity (GPP), terrestrial ecosystem respiration (TER) and net

uptake fluxes – net ecosystem productivity (NEP), and net biome productivity (NBP) cannot be measured

directly from satellites, but directly derivable EO parameters can be used in algorithms to derive carbon

fluxes. For example, the MODIS GPP product uses an algorithm based on photosynthetically active

radiation (PAR) and meteorological variables such as air temperature and water pressure deficit –

improved spatial resolution, and overpass times coinciding with maximum absorption rates of PAR would

help reduce uncertainties here. TER is particularly difficult to observe since it is a function of many

different variables, such as soil moisture and soil temperature.

In general, biogeochemical models are the principle tools for estimating carbon fluxes globally. However,

the large uncertainties in these model estimates could be reduced by constraining the processes with

observations of key variables from Earth Observation. For example, soil moisture and LST measurements

from satellite at appropriate spatial and temporal resolutions could constrain estimates of TER and GPP,

while fire activity could constrain NBP.

A gap in fire observations was identified at medium to high resolution (< 250 m) in the medium and

thermal red; active tasking of measurements was identified as a possible approach to maximise

observations. It is important to design instruments which do not saturate for the temperatures of interest.

Of particular importance is a strategy for monitoring fire during the local afternoon peak biomass burning

periods.

The science and operational gaps in carbon cycle observations identified during the workshop are listed in

Table 6.1.


Issue: 2

Date: 19/01/2012


Gap ref

no.

Variable Existing

satellite

observations

Planned

satellite

observations

Status Gap

W-G-CC-

01

Biomass C-band SAR

(ASAR)

L-band SAR

(ALOS-

PALSAR)

C-band SAR

(S-1)

L-band SAR

(ALOS-2)

Icesat-2

Multi-temporal C-

band SAR can give

reasonable accuracy

of biomass at 10km

scale

Backscatter-stem

volume relation much

more consistent

(independent of

vegetation type) for

P-band than L-band.

L-band more limited

than P-band for

higher biomass

amounts

Biomass can be

inferred from height

from lidar, but spatial

extrapolants needed

to deal with sampling

issues. Icesat lidar not

ideal for vegetation.

Sensitivity to

higher biomass

amounts at

spatial

resolutions of

much less than

10 km is

missing.

Gap in L-band

SAR data

continuity

between ALOS

missions.

ALOS-2 status

No confirmed

P-band SAR

missions

(BIOMASS

proposed)

No planned

vegetation lidar.


Issue: 2

Date: 19/01/2012


Gap ref

no.

Variable Existing

satellite

observations

Planned

satellite

observations

Status Gap

W-G-CC-

02

Vegetation

height

LIDAR

(Icesat-

GLAS) (no

longer

operational)

SAR

interferometry

LIDAR (Icesat-

2)

Lidar measurements

provide precise forest

height measurements

under narrow

footprint if dedicated

design

Icesat no longer

working – Icesat-2

may give improved

slope estimates but

needs to use off-nadir

to see larger scales (1

km scale planned).

SAR interferometry

requires correct

baseline repeat period

for one satellite or

more than one

satellite

Dedicated

vegetation

LiDAR is

missing

(Desdyni on

hold)

Consistent SAR

interferometry

needs both

Sentinel-1 units

to be launched.

Combined SAR

and LIDAR

sensor for

simultaneous

retrieval of

vegetation

height and

biomass

W-G-CC-

03

LAI Terra/Aqua

MODIS

S-2 MSI

S-3 OLCI

MODIS provides

moderate spatial

resolution (250m)

LAI

Similarly MERIS on

Envisat/OLCI on S-3

S-2 MSI expected to

provide spatial

resolution of 10s of m

with 5 day coverage

Lack of BRDF

sampling limits

retrievals to

effective LAI

only

Height/cover

data from

LIDAR would

aid

interpretation


Issue: 2

Date: 19/01/2012


Gap ref

no.

Variable Existing

satellite

observations

Planned

satellite

observations

Status Gap

W-G-CC-

04

Fire sensing Terra/Aqua

MODIS

NOAA/Metop

AVHRR

MSG SEVIRI

S-3 SLSTR

MTG Imager

MODIS provides 4

observations a day in

many areas at 1 km

spatial resolution (2

instruments). Two S-

3 units (SLSTR)

needed to maintain

this.

SEVIRI in GEO orbit

provides much better

temporal sampling

(15min) but only 3km

spatial resolution –

small fires missed

Better spatial

resolution

(~250m) is

needed to

sample smaller

fires

S-3 diurnal

revisit time

(10.00) is not

optimal (13.30

ideal)

W-G-CC-

05

Vegetation

fluorescence

GOSAT None planned

Proposed FLEX

mission

Medium / high

spatial

resolution

(<500m) is

needed

TABLE 6.1 SCIENCE AND OPERATIONAL GAPS IN CARBON CYCLE OBSERVATIONS

6.2 SURFACE ENERGY BALANCE

List of parameters identified in the presentations as important for the surface energy balance:

Surface albedo and BRDF (* at high spatial resolution < 100m)

Thermal infra-red emissivity*

Land surface temperature (* at high spatial resolution < 100m)

Soil temperature*

Note that land cover biome and fractional vegetation may be required as an auxiliary datasets, although

these variables are really implicit in surface albedo and emissivity which are more fundamental.

Imaging of surface albedo will be available at a range of wavelengths through the visible, and in fact

through the near infra-red and shortwave infra-red wavelengths. One clearly identifiable gap is in


Issue: 2

Date: 19/01/2012


measurements of BRDF at relatively high spatial scales (10s of metres) which enable both better

determination of surface albedo and information on vegetation structure.

Thermal infrared emissivity remains one of the challenges, despite progress in recent years from ground-

based and low spatial resolution satellite spectrometers combined with MODIS. The need from the

surface energy balance and water cycle community is for such data at medium-high spatial resolutions (<

100 m); such a mission would require multiple channels in the 3-14μm range. Land surface temperature is

similarly required globally (over land) at similar spatial resolutions. The proposed HyspIRI mission does

target these quantities as a stand-alone mission; ASTER data (90 m TIR) are not available globally. Soil

temperature is another gap in our current ability to observe. However, soil temperature could be derived

using algorithms based on measurable variables such as LST which then constrains both the heat flux

into/out of the ground, and the soil moisture.

The science and operational gaps in surface energy balance observations identified during the workshop

are listed in Table 6.2.

Gap ref

no.

Variable Existing satellite

observations

Planned

satellite

observations

Status Gap

W-G-

SE-01

Surface

albedo

and

BRDF

Terra

ASTER/MODIS/MISR

Envisat/MERIS

S-2 MSI ASTER horizontal

resolution ranges

from 15m (NIR) to

90m (TIR) with

swath width 60km

Best resolution for

bidirectional data

(MISR) is 275m

S-2 MSI will

achieve 10s of m.

No multi-angle

information

Higher spatial

resolution

BRDF, multi-

angle data

(10s of m)

would provide

more

information

on vegetation

structure


Issue: 2

Date: 19/01/2012


Gap ref

no.

Variable Existing satellite

observations

Planned

satellite

observations

Status Gap

W-G-

SE-02

LST Envisat AATSR

Terra ASTER

S-3 SLSTR

LDCM TIRS

AATSR provides 1

km spatial resolution

but requires detailed

knowledge of

surface

emissivity(SLSTR

to have similar

resolution)

TIRS will have 100

m spatial resolution

but over a narrower

swath with (185 km

compared with 1685

km)

ASTER has

achieved fine

resolution but data

are difficult to get

hold of.

Emissivity has been

derived from

MODIS but quality

is uncertain.

Accurate LST

needs good

emissivity.

No instrument

does this well

at spatial

resolution

<100m

More spectral

channels

required to

take into

account

spectral

variations in

emissivity

(e.g. HyspIRI)

TABLE 6.2 SCIENCE AND OPERATIONAL GAPS IN SURFACE ENERGY BALANCE OBSERVATIONS

6.3 WATER CYCLE

List of parameters identified in the presentations as important for the water cycle:

Soil moisture (* at medium and high spatial resolutions ~ 1km)

Land surface temperature (* at high spatial resolution < 100m)

Snow water equivalent*

Snow line*


Issue: 2

Date: 19/01/2012


Soil moisture information is available at global model grid scales, for example down to 25 km from

ASCAT, or 35-50 km for SMOS, but not at medium or high spatial resolutions. For this reason and for

evapotranspiration calculations, land surface temperature is required at medium and high spatial

resolutions; LST anomalies can be used as a proxy for soil moisture anomalies, and LST controls the

partitioning of surface energy into sensible and latent heat fluxes – the latter of which is directly

proportional to ET. Applications such as crop monitoring require high spatial resolution.

It should be noted that issues such as run-off and river discharge were not in detail discussed at this

workshop and so are not presented in the tables in this section.

Snow is an important characteristic of the land surface and was shown to be a parameter that global

analysis models are beginning to use in assimilation schemes. As well as snow water equivalent, which is

targeted by the proposed EE7 CoreH2O mission, it was also desirable to target the determination of the

snow line marking the transition from clear surface to snowy surfaces. Snow extent/cover at spatial

resolutions with modelling of less than 10 km is possible in 2010 and better than 5 km in 2020.

The science and operational gaps in water cycle observations identified during the workshop are listed in

Table 6.3.

Gap ref no. Variable Existing

satellite

observations

Planned

satellite

observations

Status Gap

W-G-WC-01 Soil

moisture

SMOS (L-

band imaging

radiometer)

Metop

ASCAT (C-

band

scatterometer)

S-1 C-band

SAR

ALOS-2 L-band

SAR

SMOS data at 35-

50km resolution, 3

day revisit at equator

ASCAT achieves

25km resolution in hi-

res mode

Much better spatial

resolution (10s of m

as needed for

evapotranspiration

calculations) will be

achieved using SAR

Crop

monitoring

demands high

spatial

resolution and

frequent revisit

(better than

weekly)


Issue: 2

Date: 19/01/2012



satellite

observations

Planned

satellite

observations

Status Gap

W-G-WC-02 LST Envisat

AATSR

Terra ASTER

S-3 SLSTR

LDCM TIRS

AATSR provides 1

km spatial resolution

but requires detailed

knowledge of surface

albedo (SLSTR to

have similar

resolution)

TIRS will have 100m

spatial resolution but

over a narrower swath

with (185km

compared with

1685km)

Spatial

resolution

<100m

More spectral

channels to take

into account

spectral

variations in

albedo (e.g.

HyspIRI)

Anomalies in

LST as proxy

for soil moisture

anomalies

TABLE 6.3 SCIENCE AND OPERATIONAL GAPS IN WATER CYCLE OBSERVATIONS

6.4 LAND USE AND LAND USE COVER

List of parameters identified in the presentations as important for land use/land cover measurements

Small scale vegetation disturbances

Biome identification

Land cover change

Land surface topography (* at high spatial resolution < 100m)

The science and operational gaps in land use and land cover observations identified during the workshop

are listed in Table 6.4.


Issue: 2

Date: 19/01/2012



satellite

observations

Planned

satellite

observations

Status Gap

W-G-LC-01 Land cover

change

Terra/Aqua

MODIS

Landsat-7

ETM+

S-2 MSI

S-3 OLCI

LDCM

OLI+TIRS

Currently achieve

moderate spatial

resolution (1 km) with

good coverage

(MODIS, swath width

2330km), and high

spatial resolution (15-

60m) with less

frequent coverage

(ETM+, swath width

185km)

S-2 MSI to provide

similar performance

to ETM+ but with

more spectral bands

and wider swath

(290km)

Regular global

coverage at high

spatial

resolution needs

continuously

measuring all-

weather

imagery (e.g.

SAR)

W-G-LC-02 Land

surface

topography

Terra ASTER

SPOT-5 HRS

TerraSAR-

X/TanDEM-

X

S-1 C-band

SAR

S-3 SRAL

ALOS-2 L-band

SAR

Achieve topography

observations through

stereo imaging –

either through data

from single orbit (e.g.

ASTER), multiple

orbits (e.g. SPOT) or

two instruments in

formation (e.g.

TanDEM-X)

High spatial

resolution

achievable with

all current

instrumentation

(10s of m), but

all have narrow

swath widths

(≤100km)

TABLE 6.4 SCIENCE AND OPERATIONAL GAPS IN LAND USE AND LAND COVER OBSERVATIONS

6.5 BIODIVERSITY

Global biodiversity area is a highly significant area whose requirements which become much clearer as

the GeoBon project gathers key requirements from stakeholder agencies. Therefore, no key variables were

absolutely identified as requirements.


Issue: 2

Date: 19/01/2012


However, it was recognised that the key areas for biodiversity are likely to include improved land cover

classification with recognition of species, spatial resolutions appropriate to varying spatial resolution

requirements (depending on terrain), types or biomes (but much greater differentiation than in land cover

maps), vertical structure, spatial structure, habitat extent, fragmentation. Some of these requirements, such

as vertical and spatial structure, and habitat extent, will be addressed in part by meeting requirements for

carbon cycle data.

6.6 HUMAN POPULATION DYNAMICS

List of parameters identified in the presentations as important for human population dynamics

Urban spread (night lights)

Urban heat islands

Urban topography

Managed landscapes – monitoring of land type via spectroscopy

There are many aspects of human activities which impact on the terrestrial environment, the atmosphere

and beyond. In the workshop, discussion mainly centred around settlements, health and urban impact, and

secondly on landscapes and how they change. The characteristics of the urban environment require,

ideally, high spatial resolution since they are highly heterogeneous. As such, for urban heat islands high

spatial resolution thermal emissivity is critical for accurate temperature measurements. However, much

can still be done with Landsat-type resolutions in the thermal infra-red, and empirical methods are being

used to estimate sub-pixel LST using high resolution land cover classification.

The science and operational gaps in human population dynamics observations identified during the

workshop are listed in Table 6.5.


Issue: 2

Date: 19/01/2012


Gap ref

no.

Variable Existing

satellite

observations

Planned

satellite

observations

Status Gap

W-G-HD-

01

Urban

LST

Urban

emissivity

Urban

albedo

Urban

land

cover

MSG

SEVIRI

NOAA

AVHRR

Terra/Aqua

MODIS

ENVISAT

AATSR

Landsat

ETM+

Terra

ASTER

S-3 SLSTR

LDCM TIRS

NPP/NPOESS

VIIRS

Currently achieve

either moderate

spatial resolution

(~1 km) with

frequent revisit

(~1 day) using

SEVIRI,

AVHRR,

MODIS,

AATSR, or high

spatial resolution

(~100m) with

less frequent

revisit (~16 days)

using ETM+,

ASTER. ASTER

data difficult to

obtain.

Very high resolution

visible (~25m)

observations for urban

planning and energy

efficiency applications

(would only need

~monthly revisit)

High resolution

(~100m) observations

with more frequent

revisit (~1 week or

better) needed to

monitor environmental

quality and urban scale

meteorology

Multispectral TIR

would enable highly

variable surface

emissivity to be

accounted for and more

accurate LST to be

obtained.

TABLE 6.5 SCIENCE AND OPERATIONAL GAPS IN HUMAN POPULATION DYNAMICS

OBSERVATIONS

6.7 VOLCANOES

Thermal anomalies on fumarole fields within a crater.

Lava flows thermal characteristics

Pre-eruptive thermal anomaly

Thermal sensing in the shortwave/medium infra-red could provide good monitoring of volcanoes but a

good knowledge of clouds and aerosols may be required.

The VIIRS instrument is now launched on NPP but suffers from saturated thresholds, and averaging errors

may also cause problems.


Issue: 2

Date: 19/01/2012


The science and operational gaps in volcano observations identified during the workshop are listed in

Table 6.6.

Gap ref

no.

Variable Existing

satellite

observations

Planned

satellite

observations

Status Gap

W-G-

VO-01

Thermal

anomalies

Landsat

ETM+

Terra

ASTER

LDCM TIRS Few instruments

have the

required spatial

resolution

(<100m) at TIR

wavelengths

needed to

identify thermal

anomalies on

fumaroles fields

Need for thermal IR

observations at

spatial resolutions

better than ~60m

Accuracy better than

1 K needed over

temperature range

283-360K

W-G-

VO-02

Lava thermal

characteristics

and mapping

Terra

ASTER

NPP/NPOESS

VIIRS

Thermal and

mid-infrared

imagers at mid-

high resolution

provide useful

data, though

current

observations

suffer from

saturated

thresholds at

high brightness

temperatures

Need for

medium/high spatial

resolution ( 30 m) IR

mapping sensitive to

temperatures up to

1500 K (implies

SWIR-MIR-TIR)


Issue: 2

Date: 19/01/2012


Gap ref

no.

Variable Existing

satellite

observations

Planned

satellite

observations

Status Gap

W-G-

VO-03

Pre-eruptive

precursors and

SO2 degassing

plumes

Terra

ASTER

MODIS

Multispectral

TIR imagers are

able to detect

SO2 emissions

from summit

craters during

quiescent

periods but in

general they

have not enough

spatial

resolution

combined with a

good

radiometric

accuracy

Need for mid/high

spatial resolution (<

60 m) multispectral

TIR imager

Radiometric absolute

accuracy 0.5 to 1 K.

TABLE 6.6 SCIENCE AND OPERATIONAL GAPS IN VOLCANO OBSERVATIONS

7. SESSION 5: POTENTIAL CONVOY CONCEPTS

A number of potential convoy concepts exist. These are now discussed in terms of the appropriate

Sentinel satellites. The potential concepts discussed during the workshop are listed in Table 7.1.

7.1 SENTINEL-1

The primary instrument is a C-band SAR. Part of the discussion emphasized the desirability of a re-visit

time of at least 10 days to be able to use a new temporal C-band technique to obtain better biomass

information. The flight of two C-band SARs as in Units A and B should enable a 6 day revisit and

therefore a strong priority is given to configurations which enable this.

Two convoy options were discussed. There is a gain to flying another C-band SAR receiver (bistatic

SAR) in close proximity to enable the InSAR technique to be used. Tandem-X has shown that close

formation flying is possible for such a mission. This is likely to give an enhanced capability for mid-to-

high latitude biomass, and would need to be studied for the tropics. The option for flying another SAR

operating at a different wavelength, e.g. S band or L band, to C-band SAR was discussed, but no


Issue: 2

Date: 19/01/2012


conclusions were reached as to the utility of this approach. In addition such an approach would not need

proximity of flight.

There would be a possibility of flying a lidar instrument in convoy with Sentinel-1 for vertical vegetation

structure (such as canopy) and for height. However these systems require spatial extrapolants and

therefore the benefits of convoy operations are not yet fully understood.

7.2 SENTINEL-2

The primary instrument on Sentinel-2 is a multi-spectral imager (MSI) operating at visible, near-infrared

and shortwave infra-red wavelengths

One possible convoy concept which was discussed included a BRDF instrument measuring at a range

of angles but with spatial resolutions related to those of Sentinel-2. Two important considerations are: 1)

the type of image acquisition, i.e. whether by separate spectrometers or by agile platforms; The agile

platform approach results in gaps in the measurement time of order 5 minute; 2) cross-calibration scheme

against Sentinel-2.

Another possible concept included flying a medium – high resolution thermal infrared, multi-band

radiometer satellite with Sentinel-2. Channel selection would include typically 7 bands; spatial

resolution should be < 100 m. Such an instrument would aim to achieve both emissivity and LST

measurements across the Sentinel-2 swath.

A fire mission is a possibility to fly in convoy with Sentinel-2. This would require specific bands in the

medium to short wave infra-red with spatial resolution of less than 250 m, and avoiding saturation of

channels.

Sentinel-2 has a LTDN of 10:30 which is not optimal for measuring processes such as evapotranspiration

(a later time of ~12.00 would be preferable).

A volcano mission with appropriate thermal channels and high spatial resolution would most likely target

active lava flows and potentially detect SO2 in eruptive plumes, the resolution of <100m will permit the

analysis of pre-eruptive anomalies and degassing plumes in the crater area the analysis of fumarole field

activity will need better spatial resolution < 60m

A convoy system would need to take into account high data rate from Sentinel-2 would need to fly a

convoy satellite a certain distance ahead of or behind Sentinel-2 to ensure that sufficient downlink

bandwidth is available

There would be a possibility of flying a lidar instrument in convoy with Sentinel-2 for vertical vegetation

structure (such as canopy) and for height. However these systems require spatial extrapolants and

therefore the benefits of convoy operations are not yet fully understood.


Issue: 2

Date: 19/01/2012


7.3 SENTINEL-3

The main instruments are SLSTR (Sea and Land Surface Temperature Radiometer), which is an infrared

dual-view radiometer with visible and shortwave infra-red bands, and OLCI (Ocean and Land Colour

Instrument), which is a visible wavelength imaging spectrometer.

The EE8 FLuorescence EXplorer (FLEX) optical mission is presently being designed to fly with Sentinel-

3 which will investigate vegetation fluorescence. Combined with Sentinel-3, this allows a comprehensive

investigation of vegetation parameters. A BRDF payload in convoy with Sentinel-3 could also allow for

a more complete description of vegetation and possibly also some synergy with the dual-view SLSTR

instrument.

Flying a higher spatial resolution thermal imager with Sentinel-3 would provide a test of upscaling of

SLSTR thermal LST measurements to the hundreds of metres scales. Such a system would still benefit

from Sentinel-2 visible channel measurements although better correlations between thermal and visible

channels might be obtained from co-flight with Sentinel-3.

Similarly for fire a high resolution thermal infrared satellites flying with Sentinel-3 would test

upscaling of fire information. Concern was expressed with the apparent lack of operational fire products

for SLSTR on Sentinel-3 although specified. Such data could be made operational in future or produced

by another agency and so should be available for Sentinel Convoy activities. The key issue in terms of

observational capability is to address the fact that there may be significantly more fires observed at high

spatial resolution leading to a much larger carbon flux.

A volcano mission with appropriate thermal channels and high spatial resolution would most likely target

pre-eruptive volcanoes if the spatial resolution is high, and possibly also eruptive volcanoes, noting that

there are varying mission requirements depending on objectives and capabilities of the mission concept.

7.4 OTHER POSSIBILITIES/ISSUES

Two broader issues were identified for the Sentinel-2 and Sentinel-3 optical and thermal payload optional.

The optimal time of day to observe for fire and for LST related to evapotranspiration would be later in the

day, so ~10.00 local time is not optimal for, e.g. fire monitoring (fire activity peaks at ~14.00 local time).

A second issue concerns the trade-off between agile pointed and standard-mode observations. In

particular, a higher spatial resolution, narrow swath convoy instrument could fly behind the wide-swath

moderate resolution Sentinel-3. The convoy instrument could then be intelligently pointed at interesting

targets identified by the Sentinel-3.

For the fire case in particular, an option for investigation would be to fly the convoy satellite at a later

time in day but with the same ground track as the Sentinel-3. Intelligent pointing might then be more of an

option.


Issue: 2

Date: 19/01/2012


Gap ref no. Variables Focus Option 1 Option 2

W-G-CC-01

W-G-CC-02

Biomass

Vegetation height

Improvement in

observations of

vegetation 3D

structure

Fly a second C-

band SAR in close

proximity with S-1

to enable use of

InSAR techniques

with fine baseline

Fly another SAR

which operates at a

different frequency

(L-band or S-band)

– less need to fly

closely in

formation with S-

1. Gives multi-

wavelength scatter.

W-G-CC-03

W-G-SE-01

LAI (veg,

structure)

Surface albedo

True retrieval of

LAI requires

multi-directional

observations

Albedo

observations

dependent on

viewing angle –

need for bi-

directional data

BRDF instrument

to fly in

conjunction with

S-2 to add

observations over

a range of angles

to those of the MSI

BRDF instrument

to fly in

conjunction with

S-3 to add fine

scale observations

and take advantage

of S3 cloud

clearing and

vegetation

information (dual-

view on SLSTR)

W-G-SE-02 LST

Thermal

emissivity

High spatial

resolution LST

observations

needed to model

surface energy

balance and water

cycle

Both LST and

emissivity are

req‟d both to

provide complete

variables and also

to obtain accuracy

of LST

Multi-channel

thermal imager

(spatial resolution

< 100m)

Option 1(a) with

S-2 – effectively

extend MSI

spectral range into

thermal

wavelengths

Option 1(b) with

S-3 – provide fine

scale LST

alongside medium

resolution LST,

and inter-calibrate

Similar instrument

to MSI flown ~90

minutes behind S-

2 (12.00 overpass

instead of 10.30)

but with same

ground track to

better sample daily

peak in

evapotranspiration

activity


Issue: 2

Date: 19/01/2012


Gap ref no. Variables Focus Option 1 Option 2

W-G-CC-04

W-G-VO-01

W-G-VO-02

Fire sensing

Volcanic

fumaroles and lava

temperatures

Higher spatial

resolution (<

250m) to ensure

that small fires are

correctly sampled

MIR/SWIR imager

with dedicated fire

channels at fine

spatial resolution

to fly alongside S-

3 (exploits synergy

with SLSTR

thermal IR

channels) to

determine

upscaling of fire

MIR/SWIR imager

with dedicated fire

channels at fine

spatial resolution

behind S-2 (12.00

overpass instead of

10.30) but with

same ground track

to better sample

daily peak in fires

TABLE 7.1 POTENTIAL SENTINEL CONVOY MISSION CONCEPTS FOR LAND APPLICATIONS

8. SUMMARY

The workshop provided an excellent insight into many of the aspects of land surface process observations

and modeling, and to observation of the critical parameters.

A list of the science challenge domains was derived based on a priori expectations and discussions at the

workshop: the carbon cycle, surface energy balance, water cycle, terrestrial ecosystems, biodiversity, land

use and land cover changes, human population dynamics, essential climate variables (ECVs), and

volcanoes.

The workshop addressed a number of areas within the Land domain including the carbon cycle, surface

energy, water cycle, human population dynamics and volcanoes. In addition biodiversity is still at an early

stage in terms of identifying generic needs, although clear synergies were identified with the other areas.

For each area considered in detail, it was possible to identify critical functions and variables, which future

missions need to address.

For carbon cycle, the critical functions are carbon stocks, fluxes and productivity (release of carbon

dioxide into the atmosphere). Parameters which particularly need addressing are above-ground biomass,

vegetation height (for allometry), vegetation descriptions particularly structure and LAI, vegetation

fluorescence, fires, and moisture/heat fluxes. For surface energy balance, soil moisture, surface albedo and

BRDF (* at high spatial resolution), thermal infra-red emissivity*, land surface temperature (* at high

spatial resolution) and soil temperature are important. For water cycle, soil moisture (at medium and high

spatial resolutions), land surface temperature (at high spatial resolution), snow water equivalent and snow

line are needed. The workshop identified human population issues as being associated with urban areas:

urban spread (night lights), urban heat islands, urban topography, managed landscapes – monitoring of

land type via spectroscopy. For surfaces volcanoes, the issues noted were thermal anomalies on fumarole

fields within a crater, lava flows thermal characteristics, pre-eruptive thermal anomalies.


Issue: 2

Date: 19/01/2012


From the workshop discussions, progress was made on Sentinel Convoy concepts in broad outline which

could address many of these gaps:

SAR interferometry for vegetation height (using S-1)

Multi-angle visible/SWIR optical measurements for BRDF and vegetation structure (in

combination with S-2 or S-3)

Medium-high spatial resolution mid infra-red for fire (in combination with S-2 or S-3; or loose

constellation using same ground-track but different time of day)

High spatial resolution thermal infra-red radiometers (multi-channel) for land surface temperature

and emissivity (in combination with S-2 or S-3)

Vegetation fluorescence (Flex in combination with S-3)

High spatial resolution, thermal and mid-infrared radiometers (S-2 for active volcanoes, S-3 for

pre-eruptive)

Further studies are required to address:

Multi-wavelength SAR coincidences and their utility

The spatial scales and operability of vegetation lidar and spatial extrapolants to scales of other

vegetation-sensitive instruments.

Spatial scale and angular sampling configuration requirements for a BRDF supplement to S-2 or

S-3.

Adequacy of red-edge wavelength resolution

Time of day for fire and LST measurements (constellation approach also)

Use of very high spatial resolution optical imaging for biodiversity (and also SWIR).

No of channels required for LST-emissivity radiometers

Measurements of snow line

Urban night lights; urban topography


Issue: 2

Date: 19/01/2012


APPENDIX 1: WORKSHOP AGENDA

SESSION 1: INTRODUCING SENTINEL CONVOY LAND

10.30 Welcome and objectives of the workshop (John Remedios) 10.35 Introduction to the Sentinel Convoy studies (Amanda Regan) 10.50 Introduction to the Sentinel Convoy Land project (Stuart Eves) 11.05 Science analysis for the Sentinel Convoy Land project (John Remedios and Neil Humpage)

SESSION 2: CARBON/WATER CYCLES AND VEGETATION

11.15 Investigations of the carbon cycle (Heiko Balzter) 11.30 Optical sensing of vegetation and carbon (Philip Lewis) 11.45 A multi-scale LAI product from Sentinel data (Richard Fernandes) 12.00 Ecosystem-atmosphere interactions and states of the (terrestrial) biosphere (Miguel Mahecha) 12.15 Discussion

12.30 LUNCH

SESSION 3: LAND SURFACE INFORMATION: OPERATIONAL SYSTEMS AND BIODIVERSITY

13.30 Land surface data assimilation at ECMWF (Clement Albergel) 13.45 Defining essential biodiversity variables (Rob Jongman) 14.00 Discussion

SESSION 4: FIRE AND THERMAL SENSING

14.15 Fire sensing: current status and future needs (Martin Wooster) 14.30 The Fire Monitoring, Accounting and Reporting System (FireMARS) in support of National Forest Carbon Accounting (Tim Lynham) 14.45 Thermal sensing of evapotranspiration and urban heat (Darren Ghent) 15.00 Urban energy balance (Martin Wooster) 15.15 Urban heat island: results of the ESA-DUE UHI project (Bino Maiheu) 15.30 TES-GAP: Temperature Emissivity Signatures for Geosphere And Pedosphere (Fabrizia Buongiorno)

15.45 COFFEE

SESSION 5: DRAWING THE SCIENCE TOGETHER

16:15 HyspIRI experiences (Simon Hook) 16.30 SEN4SCI: Assessing Land Product Requirements for the Scientific Exploitation of the SENTINEL Missions (Richard Fernandes) 16.45 Energy balance modelling (Annemarie Klaasse) 17.00 Combining high spatial resolution and revisit capabilities in the thermal infrared (Jose Sobrino)

17.15: Discussion: assessing the science/operational gaps and future needs


Issue: 2

Date: 19/01/2012


POSTER SESSION (ALL DAY):

Vegetation Dynamics from Earth Observation (VDEO): developing and testing a UK high

resolution environmental change observatory (UK-CEO) (Mark Danson)

Remote sensing of snow properties using Sentinel-2 and Sentinel-3 (Alexander Kokhanovsky)

WORKSHOP DINNER

DAY 2: TUESDAY NOVEMBER 1ST

SESSION 5 (CONT.): SUMMARY AND DISCUSSION OF SCIENCE GAPS (PLENARY)

08.30 Presentation of science gaps (John Remedios)

SESSION 6: LAND SURFACE MISSION CONCEPTS FOR SENTINEL CONVOY

09.30 Sentinel Convoy candidates 1-3 slides on candidate mission concepts

10.30 COFFEE

11.00 Working groups/plenary session

12.30 LUNCH

SESSION 7: CONSOLIDATION OF SCIENCE GAPS AND CONVOY MISSION CONCEPTS (PLENARY)

13.30 Presentation of science summary (Leicester team) 14.00 Refinement of concepts and evidence

15.00 Future activities, road mapping, publications 15.30 Workshop close


Issue: 2

Date: 19/01/2012


APPENDIX 2: FORMATION FLYING OF SATELLITES: MISSION

CONSIDERATIONS

The principle of convoy flying has already been demonstrated by the NASA A-train, which arguably

provides a very good set of co-located observations for studying climate. Examples of planned

Sentinel/ESA convoy missions already exist such as the Earth Explorer-7 candidate mission, PREMIER

(atmospheric chemistry limb sounding mission) which will fly ahead of the nadir viewing MetOp satellite.

This delivers synergy of atmospheric observations down to the Earth‟s surface. Sentinel-5 Precursor

(S5p) which sounds the atmosphere in nadir will fly with NPP/JPSS taking advantage of the available

cloud information. Finally, of relevance to the land study, the Earth Explorer 8 candidates FLuorescence

Explorer (FLEX) and CarbonSat are being studied for flight with Sentinel-3, in the case of the former to

take advantage of surface temperature and vegetation information, and for the latter to use cloud

information.

When considering the flight of more than one satellite in „convoy‟, the manner in which they fly with

respect to one another may be defined in terms of one of two broad categories, namely „formation flying‟

and „flying in constellation‟. The differences between these two modes of flying in convoy are

summarised in the table below:

ATTRIBUTE CONSTELLATION FORMATION FLYING

Number of spacecraft 2 or more 2 or more

Relative positions and velocities Not controlled Controlled

Distribution Typically in the same orbit (e.g. in

tandem flights) but may also

operate on different orbits

Quasi-coplanar orbits, or possibly

occupying Lagrange points

Proximity No close proximity in terms of

manoeuvring and state vector

coordination

Close proximity (less than a few

km separation where the relative

motion is in a linear domain)

Common plane for inter-

spacecraft positions

None defined (other than orbital

plane)

Yes (with arbitrary orientation in

space and with respect to a possible

local orbital frame)

GNC requirements Typically low to medium Typically high to very high

Other - Spacecraft states are directly

coupled such that changing the state

of one spacecraft changes the states

of all of the others

TABLE A2.1: COMPARISON OF TWO DIFFERENT CONVOY FLIGHT MODES


Issue: 2

Date: 19/01/2012


APPENDIX 3: THE SENTINEL MISSIONS AND SCIENTIFIC CAPABILITIES

Here, in this Appendix, the specifications of first three Sentinels are outlined, since they are most relevant

to the observation of land surface processes.

A3.1 SENTINEL-1

Sentinel-1 is a C-band SAR (synthetic aperture radar) mission, planned for launch in 2013. It will fly in a

sun synchronous dawn-dusk orbit at an altitude of 693km, and will provide SAR interferometric imagery

during day and night for all weather conditions (since the radar frequency used is not attenuated by cloud

or precipitation). The applications for such an instrument include:

• Monitoring sea ice zones & the arctic environment

• Surveillance of marine environment

• Monitoring land surface motion risks

• Monitoring of land surfaces: forest, water, soil and agriculture

• Mapping in support of humanitarian aid in crisis situations

The SAR will be able to operate in one of four nominal operation modes, depending on the desired target

and application:

• Strip map (80 km swath, 5 m x 5 m res. (range x azimuth))

• Interferometric wide swath (250 km swath, 5 m x 20 m res.) with burst synchronisation for

interferometry

• Extra wide swath (400 km swath, 20x40 m res.)

• Wave (5x5 m res, leap-frog sampled images of 20x20 km at 100 km along the orbit)

A3.2 SENTINEL-2

The primary instrument on board Sentinel-2 (scheduled for launch in 2013) is a pushbroom filter based

multi-spectral imager, which will sample 13 spectral bands across the visible and short-wave infrared

regions of the electromagnetic spectrum. The aim is to provide continuity of observations currently

provided by the Landsat and SPOT platforms, which address the following applications:


Issue: 2

Date: 19/01/2012


• Generic land coverage maps

• Risk mapping and fast images for disaster relief

• Generation of leaf coverage, leaf chlorophyll content and leaf water content

Sentinel-2 will fly in a sun synchronous orbit at 786 km, with a local overpass time of 10.30 am. The

observations will cover a 290 km wide swath at spatial resolutions of 10, 20 and 60 m. A five day cloud-

free repeat cycle is expected to be achievable once the second Sentinel-2 platform is in orbit (estimated

launch in 2016).

A3.3 SENTINEL-3

Sentinel-3 is a multi-instrument platform designed for ocean and global land monitoring. The three

instruments will provide wide-swath measurements of ocean colour and vegetation, sea surface and land

surface temperature, and radar altimetry respectively as outlined here:

• Ocean and Land Colour Instrument (OLCI):

- 5 cameras, total swath of 1270 km

- 8 bands (at visible wavelengths) for open ocean (low resolution)

- 15 bands (at visible wavelengths) for coastal zones (high resolution)

- In total 21 bands ranging from 400 to 1020 nm in wavelength

- Spatial sampling: 300 m @ SSP

- Radiometric accuracy: absolute: 2 %, relative: 0.1%

• Sea and Land Surface Temperature Radiometer (SLSTR):

- 9 spectral bands ranging from 0.55 to 12 μm;

- 0.5 km resolution (visible, shortwave infrared), 1 km resolution (mid-infrared, thermal

infrared)

- Thermal infrared NEDT: 0.05 K

- Swath: 180-rpm dual-view scan, nadir (1420 km) & backwards (750 km)

• Radar altimetry (RA) package:

- 3-cm accuracy SRAL Ku-C altimeter with LRM and SAR measurement modes, supported by

MWR and POD (with LRR, GPS, DORIS)

subject: sentinel convoy for land applications workshop report … · 2012-02-20 · ref:...

Documents