Laboratory Calibration Scheme of In-Situ Spectroradiometers for the vicarious calibration of GOCI

Abstract

The retrieval of TOA(top-of-atmosphere) radiances from spaceborne instruments requires the sufficient level of radiometric accuracy to produce the quantitative ocean color products. Because vicarious calibration, one of the effective methods of radiometric calibration, relies on the collection of ground truth data, in-situ spectroradiometers need to be regularly calibrated in the laboratory. The optical laboratory in KOSC (Korea Ocean Satellite Center) has established for 1) the optical performance characterization of the in-situ ocean optical instruments such as ASD Fieldspec Spectroradiometer, 2) the quantification of the variation between before and after field work, and 3) the relative correction of them. The laboratory is equipped with a 20 inches integrating sphere (USS-2000S, LabSphere) for the standard light source, a reference spectrometer (MCPD9800, Photal) for the relative calibration, and an optical table (3600 × 1500 × 800 mm3) having a flatness of ± 0.1 mm. Furthermore, the numerical simulation systems composited with ZEMAX and ASAP assist to enhance a CAL/VAL accuracy. From March 2012, ASD instruments have been using more than 5 times at the in-situ observations and checked variations of optical characteristics at each time. The radiance discrepancy among each instruments shows average 2 ~ 3 percentage variations in the measurement results.Our study suggests that the cothods of radiometric calibration, relies on the collection of ground truth data, in-situ spectroradiometers need to be regularly calibrated in the laboratory. The optical laboratory in KOSC (Korea Ocean Satellite Center) has established for 1) the optical performance characterization of the in-situ ocean optical instruments such as ASD Fieldspec Spectroradiometer, 2) the quantification of the variation between before and after field work, and 3) the relative correction of them. The laboratory is equipped with a 20 inches integrating sphere (U