Abstract
To calibrate the low signal response of the ocean color (OC) bands and test the stability of the Fengyun-3D (FY-3D)/Medium Resolution Spectral Imager II (MERSI-II), an absolute radiometric calibration field test of FY-3D/MERSI-II at the Lake Qinghai Radiometric Calibration Site (RCS) was carried out in August 2018. The lake surface and atmospheric parameters were mainly measured by advanced observation instruments, and the MODerate spectral resolution atmospheric TRANsmittance algorithm and computer model (MODTRAN4.0) was used to simulate the multiple scattering radiance value at the altitude of the sensor. The results showed that the relative deviations between bands 9 and 12 are within 5.0%, while the relative deviations of bands 8, and 13 are 17.1%, and 12.0%, respectively. The precision of the calibration method was verified by calibrating the Aqua/Moderate-resolution Imaging Spectroradiometer (MODIS) and National Polar-orbiting Partnership (NPP)/Visible Infrared Imaging Radiometer (VIIRS), and the deviation of the calibration results was evaluated with the results of the Dunhuang RCS calibration and lunar calibration. The results showed that the relative deviations of NPP/VIIRS were within 7.0%, and the relative deviations of Aqua/MODIS were within 4.1% from 400 nm to 600 nm. The comparisons of three on-orbit calibration methods indicated that band 8 exhibited a large attenuation after launch and the calibration results had good consistency at the other bands except for band 13. The uncertainty value of the whole calibration system was approximately 6.3%, and the uncertainty brought by the field surface measurement reached 5.4%, which might be the main reason for the relatively large deviation of band 13. This study verifies the feasibility of the vicarious calibration method at the Lake Qinghai RCS and provides the basis and reference for the subsequent on-orbit calibration of FY-3D/MERSI-II.
Highlights
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Fengyun-3D (FY-3D) is a polar orbiting meteorological satellite launched on 15 November 2017
An attempt to calibrate of the ocean color (OC) bands for FY3D/MERSI-II based on the Lake Qinghai Radiometric Calibration Site (RCS) is proposed, which is different from the previous land calibration method at the Dunhuang RCS
We described the various instruments used in the field campaign, introduced the data processing in detail, and calculated the calibration coefficients via the radiative transfer model and satellite image extraction in reference to the calibration method described
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Sun et al proposed a new vicarious calibration method based on the surface bidirectional reflectance distribution function, the Second Simulation of a Satellite Signal in the Solar Spectrum (6SV) code and MODerate spectral resolution atmospheric TRANsmittance algorithm and computer model (MODTRAN4.0) for FY-3A/MERSI and FY-3B/MERSI [4]. Wu et al proposed an absolute radiometric calibration method based on FY-3D/MERSI-II lunar observation data Meteorological satellites such as FY-3D are equipped with ocean color (OC) sensors [7]. The field-measured data of the Lake Qinghai RCS were used to carry out vicarious calibration for the OC bands of FY-3D/MERSI-II to evaluate the decay condition of the satellite after launch and serve as a reference for other calibration methods. Since the detection element of the solar spectrophotometer is a linear element, there is a linear relationship between dn(λ) output by the instrument and the solar irradiance [32]; τa (λ)
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