Evaluation of CMODIS-measured radiance by a hyperspectral model

A Chinese Moderate Resolution Imaging Spectrometer (CMODIS), an ocean colour sensor onboard the ‘Shenzhou-3’ spaceship, was launched on 25 March 2002. Because CMODIS was not equipped with any onboard calibration systems, there were major concerns about the accuracy of the CMODIS radiance measurements as well as the reliability of the data processing and oceanographic applications. To clarify these concerns, a hyperspectral satellite remote sensing radiance evaluation model (HRSREM) was developed, based on a radiative transfer model with consideration of multiple-scattering effects and atmospheric absorption. The model was used to compute the total radiance at the top of the atmosphere (TOA) to evaluate the CMODIS-derived radiance. The accuracy of the model was validated by Gordon's algorithms [Wang, M. and Gordon, H.R., 1994, A simple, moderately accurate, atmospheric correction algorithm for SeaWiFS. Remote Sensing of Environment, 50, pp. 231–239] and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data. The results show that the average relative error in the atmospheric scattering radiance computed by the HRSREM is less than 1.5% and the average error in the HRSREM TOA radiance is about 3.0%. Therefore, the HRSREM can be used to evaluate the accuracy of CMODIS-measured radiance. The results show that CMODIS has relatively small errors at the visible bands but large errors at the near-infrared (NIR) bands with an average error of more than 100%. The laboratory calibration coefficients are not reliable and the CMODIS data were recalibrated by the HRSREM to recover the archive of CMODIS data.