CoastWatch Ocean Color (OC) Overview
The CoastWatch mission is to provide and ensure timely access to near real-time satellite data to protect, restore, and manage United States coastal ocean resources, and understand climate variability and change to further enhance society's quality of life. The primary users include Federal, State, and local marine scientists, coastal resource managers, and the general public.
There are two components to CoastWatch: Central Operations and Regional Nodes. Central Operations, managed by NOAA's NESDIS, coordinates the processing, delivery, quality control and storage of data products. The regional nodes are made up of NOAA line offices that participate in the CoastWatch Program. They are located around the country, hosting equipment and personnel to provide near real-time data distribution and regional scientific expertise to the local user community. Together, central operations and the regional nodes provide for the distribution pathway for CoastWatch data products.
Biologists are using ocean color and chlorophyll-a products to predict harmful algal blooms, manage living marine resources, and assess ocean climate effects. CoastWatch provides near real-time ocean color products, e.g., chlorophyll-a, with data from NASA's EOS Terra and Aqua satellites, as well as the GeoEye's Orbview-2 satellite (via contractual purchase). Each satellite specific product has unique characteristics dependent on the sensor and the algorithm applied.
Ocean Color Spatial Characteristics
Spatial Coverage is global with an emphasis on coastal regions. Spatial coverage varied widely and was very irregular. The first plot below shows a composite of the spatial coverage for the entire CZCS mission while the following 9 plots show the geographic distribution of CZCS data for each of the nine years from 1978-1986. Each dot on these plots represents the center point of one CZCS Level 1 scene. These images show the irregular spatial distribution of the CZCS data set graphically.
Level 1 CZCS scenes had a spatial resolution at nadir of 800 meters in each of the 6 co-registered channels.
Ocean Color Temporal Characteristics
The archive of CZCS data products began on November 2, 1978 and continued until June 22, l986. However, there are several periods of intermittent coverage. When operating full time, approximately 400 images were collected each month. The following figure shows a graphical display of the temporal distribution of the CZCS Level 1 data set.
Each CZCS scan viewed the Earth for approximately 27.5 microseconds. During this period, each channel of the analog data output was digitized to obtain a total of about 2000 samples. Successive scans occured at the rate of 8 per second. Subsequent coverage of the same geographic area varied greatly from place to place and over the lifetime of the instrument.
Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Data Description
The SeaWiFS instrument aboard the OrbView-2 spacecraft provides multi-spectral imagery data in eight channels, six in the visible and two in the infrared spectrum, with a spatial resolution of 1.1 km. SeaWiFS L1A data, provided to CLASS by the CoastWatch Ocean Color Program, is processed from SeaWiFS Level 0 data (raw radiance counts from all channels as well as spacecraft and instrument telemetry) that is collected by selected High Resolution Picture Transmission (HRPT) ground stations.
SeaWiFS L1A data contains all the Level 0 data, appended calibration and navigation data, and instrument and selected spacecraft telemetry that are reformatted and appended. SeaWiFS L1A data from a single pass is packaged as one physical Hierarchical Data Format (HDF) file. Details regarding the file contents are provided in the Okeanos System ICD (Reference Document 2.3. item 1).
Summary of Level 1 Parameters:
Level 1 data consists of at-spacecraft raw radiance counts with calibration and navigation information available separately in the data file. The following table lists the center wavelength for each of the eight SeaWiFS bands, along with the primary use of each wavelength. SeaWiFS bands 1-6 are 20nm wide, and bands 7 and 8 are 40 nm wide.
Band Center
nmWavelength
("color")Primary Use 1 412 (violet) Disolved organic matter (incl. Gelbstoffe 2 443 (blue) Chlorophyll absorption 3 490 (blue-green) Pigment absorption (Case 2), K (490) 4 510 (blue-green) Chlorophyll absorption 5 555 (green) Pigments, optical properties, sediments 6 670 (red) Atmospheric correction and sediments (CZCS heritage) 7 765 (near IR) Atmospheric correction, areosol radiance 8 865 (near IR) Atmospheric correction, areosol radiance
Summary of Level 2 Geophysical Products
Level 2 data consists of five normalized water-leaving radiances (radiance data corrected for atmospheric light scattering and sun angles differing from nadir), and seven geophysical parameters derived from the radinace data. The following table lists the 11 SeaWiFS geophysical products.
Normalized water-leaving radiances at:
412 nm
443 nm
490 nm
510 nm
555 nm
670 nm
Chlorophyll a concentration
K(490)
Angstrom coefficient, 510-865 nm
Epsilon of aerosol correction at 765 and 865 nm
Aerosol optical thickness at 865 nm
SeaWiFS Spatial Characteristics
Coverage:
Spatial coverage is global, with full GAC coverage every two days. (Cloud cover limits actual imaging of the entire ocean surface to approximately every eight days, meaning that at least one view of any area on the ocean surface can be obtained in an eight-day period.) Coverage along the equator is slightly degraded due to instrument tilt to avoid sun glint effects.
Resolution:
L1A and Level 2 GAC has a spatial resolution at nadir of 4.5 km. Level 1A LAC data has a spatial resolution of 1.13 km, also at nadir.
Projection:
Level 1A HRPT, Level 1A GAC, and Level 2 GAC data have satellite swath projection.
SeaWiFS Temporal Characteristics
Coverage:
The archive of SeaWiFS data products began on September 18, 1997. Partial orbit data was first obtained on September 4, 1997. Full-time operation of SeaWiFS obtains approximately 14.5 swaths of Level 1A and Level 2 GAC data per day, with each swath representing approximately 40 minutes of data (~20 MB).
Resolution:
The SeaWiFS rotating mirror rotates at a rate of 6 resolutions per second, or 0.167 seconds per revolution. GAC scans represent an Earth view of 21 milliseconds.