Semianalytic Moderate-Resolution Imaging Spectrometer algorithms for chlorophyll a and absorption with bio-optical domains based on nitrate-depletiontemperatures

This paper describes algorithms for retrieval of chlorophyll a concentratio n and phytoplankton and gelbstoff absorption coefficients for the Moderate- Resolution Imaging Spectrometer (MODIS) or sensors with similar spectral ch annels. The algorithms are based on a semianalytical, bio-optical model of remote sensing reflectance, R-rs(lambda). The R-rs(lambda) model has two fr ee variables, the absorption coefficient due to phytoplankton at 675 nn, a( phi)(675), and the absorption coefficient due to gelbstoff at 400 nm, a(g)( 400). The R-rs model has several parameters that are fixed or can be specif ied based on the region and season of the MODIS scene. These control the sp ectral shapes of the optical constituents of the model. R-rs(lambda(i)) val ues from the MODIS data processing system are placed into the model, the mo del is inverted, and a(phi)(675), a(g)(400), and chlorophyll a are computed . The algorithm also derives the total absorption coefficients a(lambda(i)) and the phytoplankton absorption coefficients a(phi)(lambda(i)) at the vis ible MODIS wavelengths. MODIS algorithms are parameterized for three differ ent bio-optical domains: (1) high photoprotective pigment to chlorophyll ra tio and low self-shading, which for brevity, we designate as "unpackaged"; (2) low photoprotective pigment to chlorophyll ratio and high self shading, which we designate as "packaged"; and (3) a transitional or global-average type. These domains can be identified from space by comparing sea-surface temperature to nitrogen-depletion temperatures for each domain. Algorithm e rrors of more than 45% are reduced to errors of less than 30% with this app roach, with the greatest effect occurring at the eastern and polar boundari es of the basins.