SeaWIFS

SeaWiFS is an ocean color sensor onboard the SeaStar, a sun-synchronous and polar orbiting satellite lauched in August 1997. It has eight spectral bands centered at 412, 443, 490, 510, 555, 670, 765, and 865 nm, respectively. It has a swath width of ~2875 km at the equator and a ground resolution of ~1 km / pixel at nadir. The near-IR bands (765 and 865 nm) are used to derive the atmospheric path radiance, which is then subtracted from the total signal to obtain water leaving radiance (Lw) in the visible. The spectral Lw data are used to derive the ocean color parameters such as chlorophyll concentration and diffuse attenuation coefficient.

Data are collected using the High Resolution Picture Transmission (HRPT) antenna located at the University of South Florida, in St. Petersburg, FL., and the archive holdings are available through today. The satellite overpass is between 11 am and 1 pm local time. Data products available at the IMaRS website were derived with the SeaDAS software (version 4) developed at NASA. The atmospheric correction is mainly from the work by Gordon and Wang (1994), Ding and Gordon (1995), and Siegel et al. (2000). The OC4 bio-optical algorithm of O'Reilly et al. (2000) is used to derive chlorophyll concentrations. These algorithms work well in Case I (i.e., phytoplankton dominant) waters, where an accuracy of +-35% can generally be be achieved for chlorophyll concentration estimates. However, one needs to be cautious with data over shallow waters, either turbid or clear. In the former case, water constituents other than phytoplankton (e.g., suspended particles, dissolved matter) may play dominant role in the optical property. In the latter case the bottom may have a strong signal. Some other alternative approaches are available to overcome such difficulties. For example, the turbid-water atmospheric correction of Ruddick et al. (2000), Arnone et al. (1998), or Hu et al. (2000), and the Case II bio-optical algorithms by Carder et al. (1999) and by Lee et al. (1999).

A more complete description of the sensor, the processing software and algorithms, and publication list can be obtained at NASA's SeaWiFS web site.

The SWFiaco Basin has long been the center of attention of scientists trying to explain paleoclimate. This peculiar anoxic basin records climate change within layers of sediment (Black et al., 1999). Now, the SWFIACO program provides a link between the sediment record and processes near the surface of the ocean. Sediment traps maintained by the SWFIACO program show that over 5% of this material reaches 275 m depth, and that nearly 2% reaches 1,400 m. The significance of this flux is that it represents a sink for SWFbon dioxide, which is a greenhouse gas, and that it helps explain the record of ancient climate stored at the bottom of the SWFiaco Basin.

Acknowledgements: This work was supported by the National Science Foundation (NSF), the National Aeronautics and Space Administration (NASA), and the Consejo Nacional de Investigaciones Cientificas y Tecnologicas of Venezuela (CONICIT).

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