The remote-sensing reflectance (Rrs) is directly related to the inherent optical properties of the water and its dissolved and particulate constituents. Rrs is calculated by the ratio of the normalized-water leaving radiance divided by the downwelling irradiance. Normalized water-leaving radiances from ocean color sensors can be converted to remote-sensing reflectance values, if the spectral responses of the sensor are known.

The remote sensing reflectance in the red wavelengths (667 or 670 nm) has been used as a surrogate for sediment concentration in the water column (Stumpf and Pennock, 1989; T. Wynne et al. 2005). As the sediment load in the water column increases, the reflectance in the 667 or 670 nm wavelength will increase. Wynne (2005) used a SeaWiFS Rrs670 value to estimate resuspended benthic chlorophyll a concentrations, with the assumption that benthic chlorophyll is resuspended at about the same rate as sediment.

CoastWatch provides MODIS Rrs667 products in near-real time from global data collected by the NASA Goddard Space Flight Center (GSFC). NOAA obtains Level-0 data from NASA GSFC in 5-minute granules. These Level- 0 datasets are processed to geolocated, calibrated radiances (Level 1b) and to derived MODIS data products (Level 2) using NASA SeaDAS 'msl12' software. The products are then mapped (Level 3) to the CoastWatch geographic regions.

References:
Stumpf, R.P., Pennock, J.R., 1989. Calibration of a general optical equation for remote sensing of suspended sediments in a moderately turbid estuary. J. Geophys. Res. 94 (C10), 14363-14371.

Wynne, Timothy T. et al., 2005. Detecting Karenia brevis blooms and algal resuspension in the western Gulf of Mexico with satellite ocean color imagery. Harmful Algae 4, 992-1003.

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