The SeaWiFS instrument has been designed to provide the scientific community with quantitative data of bio-optical properties of the ocean.

Specifically, SeaWifs provides data of the sea surface’s colour, from which information about several pigment concentration, such as chlorophyll, can be derived. This information is directly related to the phytoplankton’s concentration. This is useful not only for activities like fishery, but also to study the global cycle of carbon.

Instruments Features

SeaWiFS is an instrument based on the Coastal Zone Color Scanner (CZCS) that was on board the Nimbus-7 satellite between 1978 and 1986.

Its bands selection was based on the spectral characteristics of some optical components of the water as well as in the spectral transmittance of oxygen and atmospherical water vapour.

Among the eight channels of the sensor, six operate in the visible band: 3 in the blue (B), 2 in green (G) and one in the red one (R). The two remaining channels operate in the near infrared. The scientific interest in the oceans' coloration is due to the fact that in most of them the colour (in the visible region of the spectrum) varies with the chlorophyll and other pigments’ concentration (e.g. the more phytoplankton the more intense the green colour will be).

The SeaWiFS transmits in two ways: LAC (Local Coverage Area) data and GAC (Global Coverage Area) data.

• LAC data is transmitted in a continuous way and present a resolution of 1.2 km in a strip 2800 km wide. GAC data is stored on board and sent every 12 hours to the ground station of Wallops Flight Facility in Virginia (USA).
• GAC data is obtained by sub-sampling LAC data, resulting in a resolution of 4 km in a 1,500 km strip.

The CREPAD program receives data in LAC mode.

Table 1. SeaWiFS Instrument.

Instrument	Spectral resolution	Spatial resolution	Radiometric resolution
SeaWiFS	8 bands 6 visible 2 Near IR	1100 m.	10 bits
Swath*	Field of view	IFOV	Spatial resolution
2800 Km.	58.3º around nadir	1.6 x 1.6 mrad	1.1 x 1.1 Km. nadir
*Maximum lenght of the pass is of approximately 3300 Km. N-S

1 SEAWIFS Instrument ....

2 SEAWIFS Archived ....

3 CREPAD Products ....