MTF analysis using lunar observations for Himawari-8/AHI

The modulation transfer function, or MTF, is a common measure of image fidelity, which has been historically characterized on-orbit using high contrast images of the lunar limb obtained by remote sensing instruments onboard both low-orbit and geostationary satellites. Himawari-8, launched in 2014, is a Japanese geostationary satellite that carries the Advanced Himawari Imager (AHI), a near-identical copy of the Advanced Baseline Imager (ABI) instrument onboard the GOES-16 satellite. In this paper, we apply a variation of the slantededge method for deriving the MTF from lunar images, first verified by us on simulated test images, to the Himawari-8/AHI L1A and L1B data. The MTF is derived along the North/South and East/West directions separately. The AHI L1A images used in the characterization of the MTF are obtained from lunar observations routinely acquired for validating the radiometric calibration. The L1B data, which is spatially re-sampled, come from serendipitous lunar observations where the Moon appears close to the Earth's disk. We developed and implemented an algorithm to identify such occurrences using the SPICE/Icy package to predict the times where the Moon is visible in the L1B imagery and demonstrate their use for MTF derivation.