Comparison and validation of top of atmosphere (toa) radiance of oceansat-2 ocm sensor

This study involves comparison and validation of Top Of Atmosphere (TOA) radiance of OCEANSAT-2,OCM sensor derived from 6S radiative transfer model with insitu TOA. The 6S is to derive total radiance (Lt), by applying suitable atmospheric corrections, to remove the errors occurs due to gaseous absorption and molecular & aerosols scattering effects suggested by (T.Suresh, 2006). The in-situ measurements were taken coastal water off Goa, (15° 25 N and 73° 43 E). The in-situ instrument called hyperspectral Radiometer is used to measure the geophysical parameters which proves an significant improvement for comparison with derived OCM2 ocean color data products, (e.g., pigments, suspended sediments, CDOM, chlorophyll etc). The TOA radiances for all bands determined using 6S are found to be well correlated with the TOA radiances extracted from the L1B_GAC data of OCM2 are described in the following graphs. The total radiance (Lt) derived from OCM-2 is found to be under estimated and overestimated for particular spectral bands. Such small differences are in the first two wavelength bands, especially 412 nm and 443nm, occur quite often and are reasonable, are shown in the perspective graphs. Statistics analysis of Coefficient of Determination (R2) and Root Mean Square Error (RMSE) provides numerical analysis, perform a graphical criteria such as an indication on the non-linear behavior of the fit. The RMSE value obtained from the sampling points are 17.96, 11.10, and 9.20 respectively. Similarly a R2 value obtained from the sampling points are 0.883, 0.875, and 0.849 respectively. Thus TOA is made for comparison and validate for chlorophyll estimation. Due to the small number of data points the significance of the comparison with the in-situ data is limited. Nevertheless, the validation of OCM2 data is clearly positive. Thus the data analyses in this study provide an important baseline for optical information of the coastal waters off the Goa.