Joint experiments programme in remote sensing of marine fish resources

A joint experiments programme was undertaken between three government agencies to pool their resources and expertise to develop techniques for ocean-colour sensing. During October, November and December 1981 a remote-sensing experiment was carried out using vessel-based observations and aircraft underflights synchronous to NIMBUS-7 overpasses in coastal waters off Cochin. The area is well known for the abundance of surface schools of oil sardine (Sardinella hngiceps Val) and mackerel (Rastrelliger kanagurta). An aircraft sensor (Ocean Colour Radiometer) with spectral channels similar to that of the Coastal Zone Colour Scanner (CZCS) on board the NIMBUS-7 satellite was flown to collect data at different altitudes to examine the aspects of atmospheric correction and developing a pigment algorithm. From the analysis of the data it was found that (i) vessel-based measurement of upwelling/downwelling irradiance and the derivation of the spectral diffuse attenuation coefficient and reflectance factor is useful in understanding the optical properties of ocean water, (ii) upwelled radiance data derived from the aircraft sensor could be suitably used in the understanding of atmospheric effects and in developing a pigment algorithm and (iii) a non-linear relationship is observed between fish catch and pigment concentration.