Calibration Accuracy Evaluation Of Visible And Near-Infrared Bands Of Fy-3b Meris

FY-3B medium resolution imaging spectrometer (MERIS) cannot achieve the absolute calibration for the visible and near-infrared bands. To improve the MERIS absolute calibration accuracy, the six widely used north African desert pseudo-invariant targets arc adopted herein, taking the advantage of the high-quality SeaWiFS data to construct the bidirectional reflectance distribution function(BRDF) model and then using the MODTRAN radiative transfer model and ERA-Interim absorption gas reanalysis data to construct the spectral band adjustment factor (SHAF). Lastly, five years of FY-3B MERIS data arc used for the cross-calibration. The constructed BRDF model in this study can accurately express the top of atmosphere (TOA) reflectance (rho(TOA)) over the pseudo-invariant targets, and the prediction error is basically within 3%. The TOA reflectance of MERIS can be effectively predicted through the parameterized SHAF which considers the observation geometry and absorbed gas content. Cross-calibration results show that the time series arc extremely stable and have no obvious trends, which arc consistent with the characters of TOA reflectance over pseudo-invariant targets. Compared with the operational calibration results of MERIS L1, the cross-calibration results of bands 8-12 arc lower and the bias is less than zero, whereas for bands 13-16, the results arc higher and the bias is greater than zero. Except for band 8, the biases of the other eight bands arc within -5%-5%. The monthly mean deviation of bands with a wavelength less than 600 nm arc larger, particularly the three blue bands (bands 8-10). The monthly mean relative deviations of bands 13-16 arc relatively stable, and they arc basically within -5%-5%.