Ocean OverviewScience, Applications, & Observation

RequirementsChuck McClain

GeoCAPE Workshop

August 18-20, 2008

Potomac

Rappahannock

Patuxent

Nan

ticok

e

Wicomico

Pocomoke

York

JamesChl-a (mg/m3)

SeaWiFS 1.1 km

MODIS 250 mFalse Color

Chesapeake Bay

“Mesoscale” Biological Variability: U.S. West Coast

California

Oregon

• SeaWiFS– Rotating telescope– 412, 443, 490, 510, 555, 670, 765, 865 nm bands– 12 bit digitization truncated to 10 bits on spacecraft– 4 focal planes, 4 detectors/band, 4 gain settings,

bilinear gain configuration– Polarization scrambler: sensitivity at 0.25% level– Solar diffuser (daily observations)– Monthly lunar views at 7° phase angle via pitch

maneuvers

• NPP/VIIRS (Ocean Color)– SeaWiFS-like rotating telescope– MODIS-like focal plane arrays (16 detectors/band)– 12 bit digitization– No polarization scrambler– Solar diffuser with stability monitor– 7 OC bands (412, 445, 488, 555, 672, 746, 865 nm)

• Dual gains except 746 nm (single gain)– Monthly lunar views at 55° phase angle via space

view port with roll maneuvers (feasible, but not approved)

SeaWiFS, MODIS, & VIIRS• MODIS (Ocean Color)

– Rotating mirror– 413, 443, 488, 531, 551, 667, 678, 748, 870

nm bands• Single gain (NIR saturation)

– 12 bit digitization– 4 focal planes (7-11 bands each)

• OC Visible: 412-547 nm (5 bands-10 detectors each)

• OC NIR: 667-869 (4 bands-10 detectors each)

– No polarization scrambler: sensitivity at ~3% level

– Spectral Radiometric Calibration Assembly (SRCA)

– Solar diffuser (observations every orbit), Solar Diffuser Stability Monitor (SDSM)

– Monthly lunar views at 55° phase angle via space view port

Sensor designs & performance are never identical.

MODIS Bands

1240

1640

300 500400 600 800700 900

412

443

490

532

547

667

678

748

869

NIR/SWIR: Atmospheric correction/ Coastal/Turbid Water

VISIBLE: Taxonomy Pigment biomass

Diffuse Attenuation

ULTRAVIOLET: Colored Dissolved Organic Matter Particulate scattering Atmospheric correction

+ Solar calibration (spectral & temporal) + Lunar calibration (temporal)+ Comprehensive Cal/Val (inc. vicarious cal sites)

2135

Quantifying Phytoplankton Processes from Space

CH3

Chlorophyll-a

Marine Spectral Reflectance

Chlorophyll Algorithm

SeaWiFS

From chlorophyll absorption to chlorophyll concentration

via optics

• Sensor radiometric calibration ±5% absolute ±1% band-to-band relative

• Water-leaving radiances ±5% absolute

• Chlorophyll-a ±35% over range of 0.05-50.0 mg/m3

Historical Ocean Color Accuracy Goals:Open Ocean

These accuracy specifications need to be redefined to reflect future ocean science product accuracy requirements

Current Ocean Biogeochemistry CDRs.

Revised requirements should be ~ 0.5% and 0.1% respectively.

2007 Advanced Plan for NASA’s Ocean Biology and Biogeochemistry Program

Four key science questions requiring new observations:

• “How are ocean ecosystems and the biodiversity they support influenced by climate and environmental variability and change, and how will these changes occur over time?”

• “How do carbon and other elements transition between ocean pools and pass through the Earth System, and how do biogeochemical fluxes impact the ocean and Earth's climate over time?”

• “How (and why) is the diversity and geographical distribution of coastal marine habitats changing, and what are the implications for the well-being of human society?”

• “How do hazards and pollutants impact the hydrography and biology of the coastal zone? How do they affect us, and can we mitigate their effects?”

Ocean phytoplankton have a profound influence on the global carbon cycle. Important groups, such these calcifying phytoplankton in the Bering Sea, are seriously threatened by climate change.

Harmful algae that cause ‘red tides’ are a serious health hazard for humans. They are now more frequent and widely dispersed.

Ocean Biology/Biogeochemistry Science Overview Ocean Biology/Biogeochemistry Science Overview (cont’d)(cont’d)

Ocean Biology/Biogeochemistry Research Goals to Ocean Biology/Biogeochemistry Research Goals to ObservationsObservations

SW

IRACE Ocean Radiometer ObservationsACE Ocean Radiometer Observations

trace directly to trace directly to Science GoalsScience Goals

NASAStrategic Plan

● Understand Earth system● New observations to detect and predict change

Ocean Biology &Biogeochemistry Plan

● Ecosystems & biodiversity● Carbon/elemental cycles● Habitats● Hazards

Key Biochemistry & Biology Properties

* Short UV for advanced atmospheric correction

98 ban

ds fro

m 335 – 865 n

m, 19 ag

greg

ate ban

ds to

talACE OceanACE OceanRadiometerRadiometer

NIR

Vis

ible

UV*

Research objectives for Earth Science

Ocean biology and biogeochemistry

questions

Key environmental

parameters

Measurement requirements

leadto

leadto

leadto

● Dissolved carbon● Phytoplankton pigments● Functional groups● Physiology● Particle size● Calcite● Fluorescence● Coastal biology● Atmospheric corrections*

Ocean Products• Current Global Products

– Normalized water-leaving radiances (visible bands)– Chlorophyll-a concentration– Colored dissolved organic matter– Primary productivity– Diffuse attenuation @ 490 nm– Photosynthetically available radiation– Calcite concentration– Fluorescence line height (MODIS only)– Particulate organic carbon (next reprocessing)– Inherent optical properties (absorption and scattering coefficients)

• Regionally-specific Products– Dissolved organic carbon concentration– Harmful algal bloom detection/spatial extent– …and others

• Additional Future Products (Decadal Survey ocean sensors)– Phytoplankton functional groups– Particle size distributions– Habitat classifications– …others

SeaWiFS & MODIS spectral bands limit the accuracy and variety of marine data products, particularly in coastal regions.

Calibration/Validation ParadigmProgram Elements:

• Laboratory - prelaunch sensor calibration & characterization

• On-orbit - solar and lunar observations are used to track changes in sensor response

• Field - comparison of satellite data retrievals to in-water, above-water and atmospheric observations

– Vicarious calibration - adjust instrument gains to match water-leaving radiances

– Product validation (water-leaving radiances, chl-a, etc.)

SeaWiFS Band

SeaWiFS (nm)

1 412 2 443 3 490 4 510 5 555 6 670 7 765 8 865

SeaWiFS Temporal Degradation

Once a month, the SeaWiFS satellite (Orbview-2) is pitched to observe the Moon at a phase angle ~ 7° to tracksensor sensitivity loss.

Marine Optical Buoy (MOBY) is used to adjust prelaunch calibration for visible bands using satellite-buoy comparisons.

Only a small % of samples result in a MOBY-satellite “match-up” for the “vicarious calibration”.

Vicarious Calibration

MOBY Water-leaving Radiance Time Series (1997-2000)

Issues in Coastal Regions

• Variety of aerosol types & atmospheric corrections• High reflectance in NIR (induces errors in aerosol radiance

estimation)• NO2 absorption at UV and blue wavelengths• High SNR requirements (low ocean radiances in UV, visible,

& NIR)• Dissolved organic materials & suspended sediments• Bottom influences on water-leaving radiances• Adjacency effects (scattered light from nearby bright land

features)• Collection of high quality field data in turbid water• Quantification of spatial and temporal variability of marine

properties and processes

Synergisms: Ocean & Atmospheric Sciences in Coastal Regions• Aerosol loading and properties

– Ocean atmospheric corrections

• Ozone & NO2 concentrations– Ocean atmospheric corrections

• Surface reflectances– Ocean & atmosphere derived products

• Air-sea gas exchanges– CO2

– Atmospheric nitrogen sources (nutrients)• UV bands

– Ocean pigment discrimination– Atmospheric corrections

• Cross-calibration with LEO sensors

BACK-UP

Green wavelength551 nm

Total top-of-the-atmosphere radiance

0 – 4 mW cm2 sr m

U.S. East CoastApril 28, 2003

Green wavelength551 nm

Total top-of-the-atmosphere radiance corrected for ozone absorption and Rayleigh (gas molecule) scattering

mW

cm2 sr m0 – 4

Green wavelength551 nm

Total top-of-the-atmosphere radiance corrected for ozone absorption, Rayleigh & aerosol scattering

0 – 4 mW

cm2 sr m

Green wavelength551 nm

Normalized water-leaving radiance

0 – 2 mW cm2 sr m

Chlorophyll-a concentration

0 – 64 mg / m3

Chesapeake Bay Chlorophyll-a RetrievalsChesapeake Bay Chlorophyll-a Retrievals

MODIS SWIR-based vs. NIR-based aerosol correctionsMODIS SWIR-based vs. NIR-based aerosol corrections

middle

upper

lower

Chesapeake Bay

Chlorophyll (mode)

Field: 10 mg/m3

w/o SWIR: 22 mg/m3

w/ SWIR: 8 mg/m3

Field: 8 mg/m3

w/o SWIR: 16 mg/m3

w/ SWIR: 6 mg/m3

Field: 6 mg/m3

w/o SWIR: 8 mg/m3

w/ SWIR: 6 mg/m3