Key result
For nadir imaging cameras WFV2 and WFV3, the image-based method yielded higher precision, whereas for non-nadir cameras WFV1 and WFV4, the RTM-BRDF method provided higher precision calibration.
The optimal cross-calibration method for GF-1 satellite instruments depends on the camera's imaging angle, with a combined approach yielding the best calibration coefficients.
Four wide-field-of-view (WFV) instruments are on board the Gaofen-1 (or GF-1) satellite, providing a combined swath of ~800 km. Before appling to quantitative remote sensing, precision radiometric calibration is needed. Currently, there are two cross-calibration methods. One is the traditional cross-calibration method (image-based), the other is based on radiative transfer model and bidirectional reflectance distribution function(RTM-BRDF). In this study, the two methods were used to cross-calibrate the WFVs of GF-1, and the comparisons were made at the same time. The verification based on satellite data and in situ measurements have shown that, for the two approximately nadir imaging camera WFV2 and WFV3, Image-based method could get higher precision radiometric calibration coefficients, while for two non-nadir imaging cameras WFV1 and WFV4, high precision calibration coefficients would be obtained by the RTM-BRDF method. Finally, the calibration coefficients of GF-1 was derived by the combination of the two methods.
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Li et al. (2017) studied this question. RTM-BRDF method vs. Image-based method was evaluated on Radiometric calibration precision. For nadir imaging cameras WFV2 and WFV3, the image-based method yielded higher precision, whereas for non-nadir cameras WFV1 and WFV4, the RTM-BRDF method provided higher precision calibration.
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