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GEO-LEO reflectance band inter- comparison with BRDF and atmospheric scattering corrections

TitleGEO-LEO reflectance band inter- comparison with BRDF and atmospheric scattering corrections
Publication TypePresentation
Year of Publication2017
AuthorsChang, T., X. Xiong, G. Keller, and X. Wu
ProceedingsProc. SPIE - Earth Observing Systems XXII
MCST ConferenceSPIE - Earth Observing Systems XXII
KeywordsBRDF; GOES-16; GOES-R; Himawari-8; Inter-comparison; MODIS; Radiometric calibration; VIIRS

The inter-comparison of the reflective solar bands between the instruments onboard a geostationary orbit satellite and
onboard a low Earth orbit satellite is very helpful to assess their calibration consistency. GOES-R was launched on
November 19, 2016 and Himawari 8 was launched October 7, 2014. Unlike the previous GOES instruments, the
Advanced Baseline Imager on GOES-16 (GOES-R became GOES-16 after November 29 when it reached orbit) and the
Advanced Himawari Imager (AHI) on Himawari 8 have onboard calibrators for the reflective solar bands. The
assessment of calibration is important for their product quality enhancement. MODIS and VIIRS, with their stringent
calibration requirements and excellent on-orbit calibration performance, provide good references. The simultaneous
nadir overpass (SNO) and ray-matching are widely used inter-comparison methods for reflective solar bands.
In this work, the inter-comparisons are performed over a pseudo-invariant target. The use of stable and uniform
calibration sites provides comparison with appropriate reflectance level, accurate adjustment for band spectral coverage
difference, reduction of impact from pixel mismatching, and consistency of BRDF and atmospheric correction. The site
in this work is a desert site in Australia (latitude -29.0 South; longitude 139.8 East). Due to the difference in solar and
view angles, two corrections are applied to have comparable measurements. The first is the atmospheric scattering
correction. The satellite sensor measurements are top of atmosphere reflectance. The scattering, especially Rayleigh
scattering, should be removed allowing the ground reflectance to be derived. Secondly, the angle differences magnify the
BRDF effect. The ground reflectance should be corrected to have comparable measurements. The atmospheric
correction is performed using a vector version of the Second Simulation of a Satellite Signal in the Solar Spectrum
modeling and BRDF correction is performed using a semi-empirical model. AHI band 1 (0.47μm) shows good matching
with VIIRS band M3 with difference of 0.15%. AHI band 5 (1.69μm) shows largest difference in comparison with