EVALUATION OF BIOOPTICAL ALGORITHMS TO REMOTELY SENSE MARINE PRIMARY PRODUCTION FROM SPACE

In situ bio-optical measurements from several oceanographic campaigns have been analyzed to derive a direct relationship between water colum n primary production P(t) ocean color as expressed by the ratio of ref lectances R1 at 440 nm and R3 at 550 nm and photosynthetically availab le radiation (PAR). The study is restricted to the Morel case I waters for which the following algorithm is proposed: log (P(t)) = -4.286 - 1.390 log (R1/R3) + 0.621 log (PAR), with P(t) in g C m-2 d-1 and PAR in J m-2 d-1. Using this algorithm the rms accuracy of primary product ion estimate is 0.17 on a logarithmic scale, i.e., a factor of 1.5. Us ing spectral reflectance measurements in the entire visible spectral r ange, the central wavelength, spectral bandwidth, and radiometric nois e level requirements are investigated for the channels to be used by a n ocean color space mission dedicated to estimating global marine prim ary production and the associated carbon fluxes. Nearly all the useful information is provided by two channels centered at 440 nm and 550 nm , but the accuracy of primary production estimate appears weakly sensi tive to spectral bandwidth, which, consequently, may be enlarged by se veral tens of nanometers. The sensitivity to radiometric noise, on the contrary, is strong, and a noise equivalent reflectance of 0.005 degr aded the accuracy on the primary production estimate by a factor 2 (0. 14-0.25 on a logarithmic scale). The results should be applicable to e valuating the primary production of oligotrophic and mesotrophic water s, which constitute most of the open ocean.