This data set consists of global satellite measurements by the Sea-viewing Wide
Field-of-view Sensor (SeaWiFS), in orbit on the OrbView-2 (formerly SeaStar)
platform. SeaWiFS acquires approximately 15 pole-to-pole orbital swaths of
data per day, and approximately 90% of the ocean surface is scanned every two
days. SeaWiFS products are processed and distributed by the Ocean Biology
Processing ... Group (OBPG). Processing details can be found at
The OBPG first processes SeaWiFS Level 0 to Level 1A using l1a_gen, by
appending calibration data, navigation data, instrument telemetry information,
and selected spacecraft telemetry information to form a Level 1A HDF file
that contains raw radiance values for each of the eight SeaWiFS bands.
The input Level 0 data used to produce the Level 1A can be of two spatial
resolutions - either LAC (Local Area Coverage), which is 1.1 km at nadir, or
GAC (Global Area Coverage), which is 1.1 km resolution but with pixels spaced
at 4.4km intervals.
Four types of Level 1 SeaWiFS data are processed by OBPG: GAC, LAC, HRPT, and
MLAC. Of the Level 1 SeaWiFS data, only GAC and MLAC data are distributed via
the Ocean Color Web.
The Level 1A Global Area Coverage (GAC) product consists of radiance data for
all 8 SeaWiFS bands, subsampled at 4.5 km resolution. A single file consists of
all the scans in a north-to-south swath (Arctic to Antarctic). The average file
size for a single level 1A GAC file is 19.1 MB, with approximately 14 swaths
obtained per day.
The Level 1A Local Area Coverage (LAC) product consists of radiance data at
1.1 km resolution and is intended for calibration and validation of the sensor
and to obtain high resolution data for areas of special interest.
The Level 1A High Resolution Picture Transmission (HRPT) product consists of
all the data collected at a given High Resolution Picture Transmission (HRPT)
ground station during a single overpass. SeaWiFS broadcasts direct downlink
data at 1 kilometer resolution. The approximate size of each file is 35 MB,
with most stations obtaining two overpasses per day.
The Level 1A Merged LAC (MLAC) product contains all available SeaWiFS HRPT and
LAC data for a given orbit. This is done by consolidating all SeaWiFS
1-km-resolution data which have been collected by various HRPT stations, as
well as the LAC data recorded onboard the spacecraft into Level 1A files on a
per orbit basis. Level-1A or Level-2 MLAC data is identical in format to
SeaWiFS LAC and HRPT, except that the scan times may be discontinuous due to
gaps in the HRPT/LAC geographic coverage. For MLAC data, each product contains
the best available full-resolution data for a single orbit, without
Browse Level 1 (GAC, LAC and MLAC) data at