NOS/NOAA routinely generates HAB bulletins for the Southeast US coastal waters over the Gulf of Mexico and Florida basin using ocean color products from SeaWiFS and lately MODIS sensor on Aqua. From the consideration of life and safety, availability of products that can provide continuity in case the current sensors retire or fail before VIIRS becomes operational is very important. NOAA CoastWatch program is exploring the suitability of products from non-US satellite platforms as a possible option. We need to investigate inter-sensor product variation. We present results from such an evaluation study done with data from MERIS for the US coastal waters. A time series of the variability of color products available from the three sensors is presented. Comparisons are analyzed for different geographical areas and different optical ranges with a view to investigate systematic effects. We plan to extend this analysis to other sensors in future.
To enable the production of the best chlorophyll products from SeaWiFS data NOAA (Coastwatch and NOS) evaluated the various atmospheric correction algorithms by comparing the satellite derived water reflectance derived for each algorithm with in situ data. Gordon and Wang (1994) introduced a method to correct for Rayleigh and aerosol scattering in the atmosphere so that water reflectance may be derived from the radiance measured at the top of the atmosphere. However, since the correction assumed near infrared scattering to be negligible in coastal waters an invalid assumption, the method over estimates the atmospheric contribution and consequently under estimates water reflectance for the lower wavelength bands on extrapolation. Several improved methods to estimate near infrared correction exist: Siegel et al. (2000); Ruddick et al. (2000); Stumpf et al. (2002) and Stumpf et al. (2003), where an absorbing aerosol correction is also applied along with an additional 1.01% calibration adjustment for the 412 nm band. The evaluation show that the near infrared correction developed by Stumpf et al. (2003) result in an overall minimum error for U.S. waters. As of July 2004, NASA (SEADAS) has selected this as the default method for the atmospheric correction used to produce chlorophyll products.