SeaWiFS (Sea-Viewing Wide Field-of-View Sensor) was a satellite-borne sensor designed to collect global ocean biological data. Active from September 1997 to December 2010, its primary mission was to quantify chlorophyll produced by marine phytoplankton (microscopic plants). Many of the objectives have been continued with other projects, such as the Terra MODIS, Aqua MODIS, Sentinel-3, and PACE mission.

SeaWiFS was the only scientific instrument on GeoEye's OrbView-2 (AKA SeaStar) satellite, and was a follow-on experiment to the Coastal Zone Color Scanner on Nimbus 7. Launched August 1, 1997 on an Orbital Sciences Pegasus small air-launched rocket, SeaWiFS began scientific operations on September 18, 1997 and stopped collecting data on December 11, 2010, far exceeding its designed operating period of 5 years. The sensor resolution is 1.1 km (LAC, "Local Area Coverage") and 4.5 km (GAC, "Global Area Coverage"). The sensor recorded information in the following optical bands:

The instrument was specifically designed to monitor ocean characteristics such as chlorophyll-a concentration and water clarity. It was able to tilt up to 20 degrees to avoid sunlight from the sea surface. This feature is important at equatorial latitudes where glint from sunlight often obscures water colour. SeaWiFS had used the Marine Optical Buoy for vicarious calibration.

The SeaWiFS Mission is an industry/government partnership, with NASA's Ocean Biology Processing Group at Goddard Space Flight Center having responsibility for the data collection, processing, calibration, validation, archive and distribution. The current SeaWiFS Project manager is Gene Carl Feldman.

Chlorophyll concentrations are derived from images of the ocean's color. Generally speaking, the greener the water, the more phytoplankton are present in the water, and the higher the chlorophyll concentrations. Chlorophyll a absorbs more blue and red light than green, with the resulting reflected light changing from blue to green as the amount of chlorophyll in the water increases. Using this knowledge, scientists were able to use ratios of different reflected colors to estimate chlorophyll concentrations.

Many formulas estimate chlorophyll by comparing the ratio of blue to green light and relating those ratios to known chlorophyll concentrations from the same times and locations as the satellite observations. The color of light is defined by its wavelength, and visible light has wavelengths from 400 to 700 nanometers, progressing from violet (400 nm) to red (700 nm). A typical formula used for SeaWiFS data (termed OC4v4) divides the reflectance of the maximum of several wavelengths (443, 490, or 510 nm) by the reflectance at 550 nm. This roughly equates to a ratio of blue light to green light for two of the numerator wavelengths, and a ratio of two different green wavelengths for the other possible combination.

The reflectance (R) returned by this formula is then plugged into a cubic polynomial that relates the band ratio to chlorophyll.

${\displaystyle Chl=antilog(0.366-3.067{\mathsf {R}}+1.93{\mathsf {R}}^{2}+0.64{\mathsf {R}}^{3}-1.53{\mathsf {R}}^{4})}$