An approach to compute Photosynthetically Active Radiation using IRS P4 OCM

Abstract

An approach was developed using the IRS P4 Ocean Colour Monitor (OCM) for the estimation of Photosynthetically Active Radiation (PAR). Bird's clear sky model will be implemented using IRS P4 OCM data on an operational basis. IRS P4 OCM data (bands 6 and 8) were used in the present study to provide an instantaneous estimation of aerosol optical depth using the exponential approach. The transmittance coefficient required for aerosol optical depth was computed as a next step. This was further incorporated in Bird's clear sky model with other atmospheric transmittance coefficients due to absorption from water vapour, ozone, and uniformly mixed gases. Spectral irradiance was integrated over photosynthetically active wavelengths (400–700 nm), which provides instantaneous photosynthetically available radiation (IPAR) at the sea surface. Ship cruise data (SK 171 and SK 186) for PAR using Satalantic radiometer was compared with IRS P4 OCM derived IPAR within 5.2% accuracy on average for two different monsoon seasons in the Arabian sea. The root mean square error between the observed PAR (in situ) and estimated (model‐derived) PAR was found to be 21.28 W m⁻². This IPAR value is an important parameter for primary productivity estimation and will be used to compute primary productivity on an operational basis using IRS P4 OCM data.

Acknowledgements

The authors would like to thank the Ministry of Earth Sciences for facilitating the field work in the Northern Arabian Sea by making available their research verels ORV Sagar Kanya. The authors would also like to thank two anonymous reviewers for their critical comments and useful suggestions, which helped to improve the manuscript.