MODIS Remote Sensing Reflectance at 667 nm (Rrs667)
The remote-sensing reflectance (Rrs) is 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 to the downwelling solar irradiance.
The remote sensing reflectance in the red wavelengths (667 nm on MODIS or 670 nm on SeaWiFS) 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 red wavelengths 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.
As a sediment index, Rrs for red wavelenths indicates relative amounts of sediment only (high vs. low sediment amounts) and is not an estimation of sediment concentration or suspended matter concentration.
CoastWatch provides Rrs667 products in near-real time from the Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the NASA Earth Observing System (EOS) Terra and Aqua satellites. NOAA obtains Rate Buffered Data (RBD) from NASA GSFC. These RBD datasets are processed to Level 0 datasets, then to Level 1A radiances, and then to Level 1B calibrated, geolocated radiances. CoastWatch produces derived geophysical products (Level 2) from the calibrated Level 1B radiances using the NASA SeaDAS software. These products are then mapped (Level 3) to the CoastWatch geographic regions.
Products generated by NOAA are of operational quality and will likely differ from the same product generated by NASA. Effort is made by NOAA to keep Level 1B code version ("collection") and calibration coefficients updated to NASA's processing. However, the collection run by NOAA is that of the MODIS program overall which may differ from that of the collection used by NASA's Ocean Biology Processing Group. Also, lags in implementation of the NASA Level 1B calibration coefficients may occur. Science quality MODIS ocean color products are available from NASA's Ocean Biology Processing Group.