Comparison of site calibration and cross calibration of Gao Fen (GF)-1 Wide Field of View (WFV)

Li Liu,Qiaoyan Fu,Wen Xu,Shuning Lu,Tingting Shi,Zhiqiang Pan

doi:10.1117/12.2199701

Li Liu, Qiaoyan Fu + Show 4 more

https://doi.org/10.1117/12.2199701

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The Wide Field of View (WFV) is one of the key instruments for China’s high resolution earth observing system, operating on the Gao Fen-1 (GF-1) satellite which was launched on April 26, 2013. WFV has 4 typical reflective solar bands from 0.45-0.89 μm with 16m nadir spatial resolution. Because of GF-1’s lacking in onboard calibrators, on-orbit radiometric calibration is mainly relies on site calibration. The reflectance-based method of site calibration has been used for the absolute radiometric calibration of the GF-1 WFV on June 26th, 2013 and August 3rd, 2014. The reflectance-based method relies on ground-based measurements of the surface reflectance and atmospheric conditions at Dunhuang test site nearly coincident with the imaging of the test site by the WFV. Site calibration is a time consuming and hard sledding method, which is also difficult to reveal or adequately correct for the deficiency of instrument calibration by its own calibration subsystem. Cross-calibration can be a powerful method to remedy the insufficient of the site calibration. Terra Moderate Resolution Imaging Spectroradiometer (MODIS) with its high accuracy onboard calibration system has been selected as reference sensor. Cross calibration between GF-1/WFV and Terra/MODIS are based on the near-simultaneous and cloud-free image pairs over Dunhuang test site on the same day with site calibration. Spectral band adjustment factors (SBAF) for the cross calibration are determined by SRF, solar zenith and azimuth angle, sensors’ zenith and azimuth angle and a typical reflectance spectrum over the Dunhuang test site obtained by in-situ measurements. The percentage difference between the site calibrations is within 5% which reflects that the GF-1/WFV is stable after the launch and the reflectance-based method itself is reliable. The comparison of site calibration and cross calibration shows that site calibration has higher accuracy than the cross calibration, the cross calibration is affected by the SBAF.

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