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Applications of Remote Sensing: SeaWiFS and MODIS Ocean ColorApplications of Remote Sensing:

SeaWiFS and MODIS Ocean Color

Outline Physical principles behind the remote sensing of

ocean color parameters Satellite sensors enabling remote sensing of

ocean color–SeaWiFS, OCTS, MODIS, GLI

Instrument characteristics–Spacecraft, spatial resolution, swath width, sensor characteristics, and unique characteristics

Ocean color monitoring from existing satellite systems

Future capabilities Opportunities for the future

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“Course” spatial resolution (i.e., >1 km) but frequent temporal resolution (i.e., every other day)–Low marine biomass/high primary production–Marine primary production poorly understood–Single satellite with wide field of view (i.e.,CZCS and SeaWiFS)»Highly variable atmospheric effects»Variable directional reflectance effects»Forming composite images is the key

–Coastal Zone Color Scanner (1979-1986)–SeaWiFS (August 1997 › …)–MODIS (February 2000 › …)

Ocean Color Time Series Remote Sensing

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Applications Ocean Color Studies — all channels Atmospheric Studies (clouds, aerosols) — all channels Land Vegetation Index — all channels Cryosphere Studies — all channels

Objectives To determine the spatial and temporal distributions of

phytoplankton blooms, along with the magnitude and variability of primary production by marine phytoplankton on a global scale

To quantify the ocean’s role in the global carbon cycle and other biogeochemical cycles

To identify and quantify the relationships between ocean physics and large-scale patterns of productivity

Sea-viewing Wide Field of View Sensor

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Radiative Accuracy: <5% absolute each band Relative Precision: <1% linearity Between Band <5% relative band-to-band

Precision: (over 0.5 - 0.9 full scale) Polarization: <2% sensitivity (all angles) Nadir Resolution: 1.1 km LAC, 4.5 km GAC

Orbit Type: Sun synchronous at 750 km Equator Crossing: Noon ± 20 minutes descending Saturation Recovery: <10 samples Swath Width 2,801 km LAC

(at equator) 1,502 km GAC Scan Plane Tilt +20°, 0°, -20° Digitization: 10 bits

SeaWiFS Mission Characteristics and Sensor Accuracy

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OrbView-2 Satellite and SeaWiFS Scanning

GeometryLaunched August 1, 1997

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Sea-viewing Wide Field-of-view Sensor (SeaWiFS)

NASA, OrbView-2– launched August 1997– descending polar orbit of

705 km, noon crossing time Sensor Characteristics

– eight spectral bands, from 412 to 865 nm

– daily global coverage– scan angle of ±58.3°; scan

swath of 2800 km– ±20° tilt to avoid sun glint– resolution of 1.13 km (with

optional 4.5 km) at nadir– solar and lunar maneuvers

for calibration– polarization sensitivity ≤

1%

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SeaWiFS Instrument Schematic

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Rayleigh Scattering Coefficients for the Eight SeaWiFS Channels

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OrbView-2 Launch Sequence and Satellite with Solar Panels

Deployed

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Simulated Pigment Absorption and Chlorophyll-a versus Total

Pigments Ca

– chlorophyll-a Cb

– chlorophyll-b Cc

– chlorophyll-c Cps

– photosynthetic carotenoids

Cpp

– photoprotectant carotenoids

Ctp – total pigment

concentration, a sum of all the other parameters

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Simulated Pigment Absorption and Chlorophyll-a versus Total

Pigments

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July 1998

Correlation of AVHRR Sea Surface Temperature and Chlorophyll-a

Concentration

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Galapagos Islands El Niño/La Niña Transitions

14Ocean: Chlorophyll-a ConcentrationLand: Normalized Difference Vegetation Index

SeaWiFS Captures El Niño/La Niña Transitions in the

Equatorial Pacific

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April 25, 1998

Coccolithophore Bloom in the Bering

Sea

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Chlorophyll and SeaWiFS-derived NDVI September-November 1997

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Chlorophyll and SeaWiFS-derived NDVI December 1997 - February 1998

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Chlorophyll and SeaWiFS-derived NDVI March-May 1998

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Chlorophyll and SeaWiFS-derived NDVI May-August 1998

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Moderate Resolution Imaging Spectroradiometer (MODIS) on

Terra

MODIS

Terra

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MODIS Ocean Color/Phytoplankton Bands

BandBandwidthSpectral RadianceRequired SNR

8 405 - 420 44.9 8809 438 - 448 41.9 83810 483 - 493 32.1 80211 526 - 536 27.9 75412 546 - 556 21.0 75013 662 - 672 9.5 91014 673 - 683 8.7 108715 743 - 753 10.2 58616 862 - 877 6.2 516

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6 years of Seawifs data 6 years of Seawifs data seawifs.gsfc.nasa.govseawifs.gsfc.nasa.gov