Modeling Photosynthetically Available Radiation from satellite and Field Data and Its Impact on Ocean Primary Production

Abstract

v newlineOcean colour remote sensing is a useful tool and it provides quantitative information of newlineseawater constituents. OCEANSAT-1 OCM and OCEANSAT-2 OCM are two Indian Ocean newlineobservation satellites which have been extensively used for various societal and scientific newlineapplications like Potential Fishing Zone identification, ocean primary productivity estimation, newlinealgal bloom detection and studying the coastal processes etc. Photosynthetically available newlineradiation (PAR) with spatially invariant and uniform aerosol optical depth under clear sky newlinecondition has been used in current primary production models using OCM data. Thus, newlinemodeling PAR from OCM under variable aerosol loading and cloud coverage is a desirable newlineinput parameter to estimate ocean primary production from OCM more accurately. newlinePAR has been estimated from OCM using two different methods for spatially variable newlineaerosols and cloudy condition. In method I, the atmosphere is treated as a single layer in clear newlinesky condition or as double layer in cloudy conditions i.e., a layer above the cloud top and a newlinelayer from the cloud top downwards. The two main input parameters to estimate PAR i.e., newlineaerosol optical depth (AOD) and cloud optical depth (COD) have been estimated from OCM newlinedata. Surface reflectance has been neglected in the first method. In method II, the effects of newlineclouds and clear atmosphere can be decoupled with cloud system and surface albedo. In the newlinesecond method, surface and cloud albedo have been estimated from OCM. newlinePAR estimated from OCM has been compared with PAR measured from surface newlinedownwelling flux measurement instrument during different seasons in the Arabian Sea. Other newlinethan in-situ data obtained from ship cruise, OCEANSAT-2 OCM estimated PAR have been newlinevalidated with in-situ measured PAR obtained from surface irradiance data of a buoy located newlineat the CAL-VAL site situated between Kavaratti and Agatti island in the Arabian Sea. The newlineroot mean square (r.m.s) difference between OCEANSAT-1 OCM PAR estimated using both newlinethe methods compared to in-sit