Visible Sensor Calibration of the Himawari-8 AHI Instrument Using MODIS and VIIRS

The Himawari-8 satellite, launched on 7 October 2014, is the first of the series of next generational weather satellites to enter geostationary orbit.  Operated by the Japan Meteorological Agency, it first entered operational status on 7 July 2015 with a subsatellite longitude at 140.7º E over the Japan domain.  The Advanced Himawari Imager (AHI) is the primary instrument aboard the spacecraft and provides a high resolution full-disk scan every 10 minutes across 16 different spectral channels.  This frequency of scheduled scans makes the AHI instrument a good candidate for inter-calibration with other low Earth orbit (LEO) satellite instruments. Two particular well-calibrated instruments that fit this category are MODIS, aboard the Aqua and Terra satellites, and VIIRS, aboard Suomi-NPP, as both of these instruments have several visible bands that correspond to the visible bands of AHI.

Two techniques for inter-calibration of the AHI bands in the Himawari-8 domain are utilized in this study.  The first is a gridded ray-matching technique, in which the AHI counts and the reference LEO instrument radiances are gridded to 0.5º inter-calibration foot prints (ICFs) and then matched into co-incident, spatially and angularly matched radiance pairs.  The second method relies on ray-matching 30-km averaged deep convective clouds (DCC), which has the advantage of utilizing data near the tropopause, where little water vapor absorption occurs.  A scene-specific spectral band adjustment factor (SBAF) is applied in both cases to alleviate any spectral response function (SRF) differences between the instrument bands.  The gain resulting from regressing the matched pairs in each technique monitors the temporal degradation of the AHI spectral bands and can be used to validate the calibration methods.