from techniques to applications: noc's forefront role in coastal altimetry paolo cipollini with...
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From techniques to applications: NOC's forefront role in coastal altimetry
Paolo Cipolliniwith contributions from Val Byfield, Christine Gommenginger, Graham Quartly, Luke West
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Coastal altimetry• Satellite altimetry works well
for open ocean– measures sea surface height,
significant wave height, wind• Near coasts however…
– land contamination, calm water effects on waveform shape, poorer corrections, etc
– data normally flagged as ‘bad’ in the official products - but they can be recovered!
• Coastal region has enormous strategic importance
• 20 years of data over the coastal ocean are waiting to be processed
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We believe so, with dedicated reprocessing and corrections.
For instance - can we recover these?
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• WHY we want coastal altimetry– useful: we’ll see several applications (Sea Level,
currents, Storm Surges)– convenient: 20 years of data to dig in; and new missions
(Cryosat-2) even more promising for the coastal zone.
• But first HOW do we do it? (i.e. the techniques)• and WHAT have we done so far/are we doing now/
are planning to do in the future?
outline
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How we recover more valid data
A. Specialized retracking– Use better waveform models,
accounting for change of shape in coastal environment
– Use specialized (2-D or sequential) retracking techniques
B. Improved Corrections– Most crucial is the correction
of path delay due to water vapour (“wet tropospheric” correction)
– Some applications require correction of tidal and high-frequency signals, which are also difficult to model in the coastal zone
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0-10 km 0-50 km
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L.J. West, NOC
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Example of “wet tropospheric” problems
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Envisat track 343
South Africa
S Africa
J. Maina Mbui for ALTICORE-Africa
Effect of land
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• Wet Tropospheric correction:– DLM (Dynamically Linked Model) approach: Use
models to extend radiometer observations implemented in NOC COASTALT processor
– GPD (GNSS-derived Path Delay) - dry and wet tropo from GNSS (GPS/Galileo) measurements (Univ. Porto) computed and available in COASTALT pilot data
– GPD recommended by the ESA Sea Level CCI Consortium as Wet Tropospheric correction of choice in the coastal zone
– GPD included in V2.0r3 COASTALT products
• Tides– COASTALT Investigated local models
(UPorto/CIIMAR, WITM local tidal model for W Iberian shelf)
Corrections: the way forward
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The COASTALT Processor for Envisat
• Core deliverable and legacy of COASTALT– Flexible, user-configurable and modular software
• Baseline processor– Reads ENVISAT L2 SGDR files– Retracks all waveforms with different models
• Brown, Specular and Mixed, plus innovative retrackers (see later)
– Generates corrections at 18Hz– Generates Coastal Geophysical Data Records
(CGDRs) output files in NetCDF
• User-defined Geophysical Corrections module (“addcorr”)– Allows addition of any user-generated corrections– used to include GPD correction in CGDRs
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• Innovative retrackers: retrack each waveform not in isolation but using info from adjacent ones
• Two different approaches• The hyperbolic retracker to fit and remove
bright/dark targets is an example • Another example is the Bayes Linear retracker
– Based on the application of Bayesian methods– The idea is to treat the posterior from one waveform as the
prior for the next.
• Both these have been designed within COASTALT and prototyped
Innovative retrackers
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Hyperbolic retracker example
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• COASTALT just finished– very good incubator of technical ideas– final results, recommendations presented at 5th Coastal
Altimetry Workshop (San Diego 16-18 October)– processor is a lasting legacy
• ESA CCI Sea level– small contract (35 kEUR) to study effects of coastal
proximity on retracking – complements COASTALT work
• Main development now: ESA eSurge– started in June 2011, 370 K EUR– includes funding for NRT coastal altimetry
Where we are now
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eSurge
• ESA DUE (Data User Element) Project for 2011-2013– DUE runs user-driven projects to transfer research to
applications
• eSurge Objectives:• To contribute through Earth Observation to an
integrated approach to storm surge, wave, sea-level and flood forecasting as part of a wider optimal strategy for building an improved forecast and warning capability for coastal inundation.
• To increase the use of the advanced capabilities of ESA and other satellite data for Storm Surge applications
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The eSurge consortium
• Then there is “eSurge Venice”: a parallel project on surges in
Northern Adriatic – key area for this kind of application - led by Italian CNR
Coastal and Marine Resources Centre, I RL
Subcontractor
National Oceanography Centre, UK
Subcontractor
Danish Meteorological I nstitute, DK
Subcontractor
Logica, UK
Prime Contractor
Koninklijk NederlandsMeteo I nstituut, NL
Subcontractor
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The eSurge System
We aim to prove that by assimilating EO data our hindcasts improve!
SEARS: a database of surge events
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Example eSurge Input Data• Altimeter (ERS, Envisat, Geosat,
TOPEX, JASON, CryoSat)• Passive Microwave (SSM/I, AMSRE, TMI,
WindSat)• Scatterometer (ERS, QuickScat, ASCAT,
NSCAT, OceanSat-2 )• SAR (ERS, ENVISAT, RADARSAT,
COSMOSkyMed, TerraSAR-X, RISAT…)• Optical/IR data (MERIS, MODIS, AATSR,
AVHRR, geostationary satellites)• NWP and NOP model outputs• Storm Surge model output and forcing• Flood maps• In situ (Tide Gauges)
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• A very important component of eSurge will be the development, validation and provision of dedicated coastal altimetry products
• Coastal altimetry is important as it measures the Total Water Level Envelope (TWLE)– That’s the level you get – inclusive of tide, HF atmospheric effects,
wave setup, etc…– key quantity required by storm surge applications and services
• The wave field in the coastal strip is also relevant– helps development of more realistic wave models
• Of course there is a sampling issue – but altimetry is still useful, in combination with Tide Gauges, to ascertain the modes of variability of the coastal ocean
The role of coastal altimetry
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Scharroo et al 2005
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JASON ENVISAT CRYOSAT f(x)
RADS -based
Reader
E-Surge Processor: Abstract Input
Extensible design allows for future
missions andother types
of input
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E-Surge Processor: RADS-based Reader
• RADS (Radar Altimeter Database System) has already abstracted altimetry missions successfully
• E.g. string mission name standard– ‘tx’ – TOPEX– ‘e1’ – ERS-1
• Identified and codified numerous scalar quantities.
• Wet tropospheric correction• Different kinds of ‘height’• etc..
• We will allow for extending and adapting without reinventing RADS
• which was already used to define the COASTALT products
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E-Surge Processor : Input selection and filtering
Mission
LatLon
Time
Scalars &Waveforms f(x)
RADS -based
Reader
Landmask
Cycle/Passnumbers
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E-Surge Processor : preprocessing
Save internal
state
Interpolation
Low rate toHigh rate
Scalars &Waveforms
f(x)
Passthruto output without
processing
Averaging
High rate to Lo rate
Processing
Back to input module
output
other filtering
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E-surge Processor• Create new scalars from old ones
– Corrections• Create new scalars from waveforms
– Retracker parameters• Create new waveforms from scalars
– Synthetic data• Create new waveforms from old
– Retracking We want to design a system as simple as possible that does everything we want it to do without precluding everything we
might want it to do in the future!
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• In a later phase of the eSurge project (mid-2012 onwards) the eSurge coastal altimetry processor will be extended to be able to ingest NRT raw altimetric waveforms– like FDMAR streams from ESA
• (we need ESA, NASA and CNES to make sure we have access to the NRT waveforms)
• this is part of the ‘eSurge-Live’ effort for the provision of NRT data to users during storm surge events
• definitely uncharted waters for coastal altimetry!!!
…and we will venture in NRT territory!
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• For the science!– In particular, exploits synergy between NOC-S satellite
work and NOC-L surge research
• Capitalizes on COASTALT investments and allows further development of processor– NOC-S unique capability
• Encompasses whole spread of skills - from technical development through algorithms development to application
• Strengthens the links with BODC (ex Data Group)• Processor can them be redeployed over other areas
– more science!
Why eSurge is good for us
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Coastal Altimetry in the Agulhas
Collaboration NOC (K. Rizopoulou) / UMiami / UCT / HartRAO / UPorto
Aim: obtain 20 ys of Agulhas Current transport1) Calibrate Altimeter-derived transports with ACT array (UMiami cruises)2) Then use altimetry to go back to 1992
Needs multi-mission coastal altimetry!(one of the first climate applications)
New GNSS station in Hamburg, SA
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• ESA CP4O (Cryosat Plus for oceans), which has a coastal component– Cryosat-2 (Delay-Doppler altimeter) very good in coastal
zone, but needs specialized retracker– Builds heavily on the experience we gained in highly
successful SAMOSA project on Dealy-Doppler altimetry
• FP7 COSMOcean : integration of coastal altimetry with old and new in situ measurements (marine radars, ferrybox, fishing nets) in NW Mediterranean
• FP7 EORCEF, led by Val Byfield, see next slide
Some projects for the future
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FP7 Space Call: EORCEF* proposal*Earth Observation for Resilience to Coastal Erosion and Flooding
Mapping coastal hazard exposure: – Tsunamis, storm surges, waves
Partner countries: – UK, France, Norway, S-Africa,
Mozambique, MauritiusNOC contribution: – Extreme waves, sea level, storm surges– Observations and modelling
Part of NOC support for GOOS-Africa capacity development in coastal and marine RS
Started in 2003: – UNESCO-Bilko included in GOOS-Africa
first 5-year plan (ROOFS)– ESA support for NOC-led RS software
and lesson development
Past and ongoing projects: – AltiCoRe-Africa: coastal altimetry
group, 2008 - present – Agulhas Current coastal altimetry
(ongoing PhD project)– DevCoCast (FP7, 2008-2011)– EAMNet (FP7, 2010-2013): Data
dissemination, training, sharing analysis tools, MSc courses, fellowships.
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• With COASTALT we have acquired:– understanding of technical issues– analysis and prototyping capability– links to modellers and hydrographers– links to Tide Gauge community– international coordination role (Coastal Altimetry workshops)
• other ongoing studies complement that work (note Agulhas work has profound climate implications)
• eSurge important application (with significant extension to the processor + further links to modelling community)
• more funding requested (ESA/FP7) for R&D and applications• We are at the forefront of coastal altimetry – and we
should make sure we remain there.
Conclusions
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www.coastalaltimetry.org