Abstract
The radiometric calibration coefficients that are required to enhance the preflight calibration coefficients to improve the performance of the Ocean Colour Monitor (OCM-2) onboard the Indian Remote Sensing Satellite (IRS) are determined using in-situ measurements in coastal waters around southern India. These coefficients were applied to OCM-2 data acquired over coastal waters off Point Calimere (Palk Strait) and Gulf of Mannar of the Bay of Bengal, and are compared with similar coefficients included in the SeaDAS software and those provided by the Space Application Centre (SAC). Two atmospheric correction algorithms were used in conjunction with these coefficients to obtain the water-leaving radiances (Lw) from OCM-2 data, namely the CAAS algorithm and SeaDAS algorithm. An evaluation of the results of these coefficients and atmospheric correction algorithms showed large deviations in Lw values derived with the SAC (positive deviation) coefficients and SeaDAS (negative deviation) coefficients when applied to OCM-2 data along with the SeaDAS atmospheric correction algorithm. The deviations were less remarkable with new coefficients when the same (SeaDAS) atmospheric correction algorithm was used. However, application all three coefficients to OCM-2 using the CAAS algorithm showed a similar trend but with less deviations with respect to in-situ Lw data. The results obtained with the new coefficients showed good agreement with the in-situ water-leaving radiances (except channels 412-443nm). These results suggest that the new calibration coefficients can be used along with the CAAS atmospheric correction algorithm to improve the performance of OCM-2 sensor for quantitative assessments of the various water constituents in coastal waters (including bloom) around India.
Highlights
OCEANSAT-2 spacecraft launched on September 23, 2009 by the Indian Space Research Organization (ISRO) carries the Ocean Colour Monitor (OCM-2) sensor, which was designed to provide continuity to the OCEANSAT-1 OCM-1 instrument, and to obtain quantitative information of ocean colour variables such as Chlorophyll-a concentration, suspended sediment (SS) concentration, coloured dissolved organic matter (CDOM), diffuse attenuation coefficient and remote sensing reflectance (Rrs)
According to the criteria of horizontal water homogeneity, distance to land, horizontal homogeneity aerosols, and temporal difference between satellite over-flight and in situ measurements, the calibration coefficients were determined and listed in table 3 along with those provided in the SeaDAS software and those provided with OCM-2 data (SC)
Radiometric and laboratory data collected for a wide range of such waters are necessary in the calibration and validation exercise so that the calibration coefficients determined from using these data can be extended to similar coastal waters in other regions
Summary
OCEANSAT-2 spacecraft launched on September 23, 2009 by the Indian Space Research Organization (ISRO) carries the Ocean Colour Monitor (OCM-2) sensor, which was designed to provide continuity to the OCEANSAT-1 OCM-1 instrument (launched on 26 May 1999), and to obtain quantitative information of ocean colour variables such as Chlorophyll-a concentration, suspended sediment (SS) concentration, coloured dissolved organic matter (CDOM), diffuse attenuation coefficient and remote sensing reflectance (Rrs). The process of removing the atmospherically scattered signal in order to retrieve the desired ocean colour signal (i.e. water-leaving radiance) is referred to as atmospheric correction [3] It has been demonstrated in the previous studies that SeaDAS atmospheric correction algorithm provides satisfactory results for clear oceanic waters with uncertainties
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