Preliminary validation of Himawari-8/AHI navigation and calibration

Abstract

The next-generation geostationary meteorological satellite of the Japan Meteorological Agency (JMA), Himawari-8, entered operation on 7 July 2015. Himawari-8 features the new 16-band Advanced Himawari Imager (AHI), whose spatial resolution and observation frequency are improved over those of its predecessor MTSAT-series satellites. These improvements will bring unprecedented levels of performance in nowcasting services and short-range weather forecasting systems. In view of the essential nature of navigation and radiometric calibration in fully leveraging the imager's potential, this study reports on the current status of navigation and calibration for the AHI. Image navigation is accurate to within 1 km, and band-to-band co-registration has also been validated. Infrared-band calibration is accurate to within 0.2 K with no significant diurnal variation, and is being validated using an approach developed under the GSICS project. Validation approaches are currently being tested for the visible and near-infrared bands. In this study, two of such approaches were compared and found to produce largely consistent results.

Comparison of the Calibration Algorithms and SI Traceability of MODIS, VIIRS, GOES, and GOES-R ABI Sensors

“…L obc_r f l pT sh , T cav , T tele , λq "´1´ε obc pλq¯¨´F sh¨L pT sh , λq`F cav¨L pT cav , λq`F tele¨L pT tele , λ q¯ (38) where the factors F sh , F cav , F tele represent the fraction of the reflectance off the OBC blackbody originating from the blackbody shield, cavity and telescope. Assuming the emissivity of these three sources to be 1, it follows F sh + F cav + F tele = 1.…”

“…Therefore, m is updated on orbit at least viewing ICT every 15 min depending on the scan mode as is being done in AHI every 10 min [38]. The rest of the quantities are measured from the ICT view and the space view or deduced from measurements using the LUTs.…”

“…Assuming the emissivity of these three sources to be 1, it follows F sh + F cav + F tele = 1. The OBC blackbody reflected radiance is routinely updated knowing the temperatures of all relevant components in Equation (38). The scene radiance L ap pθ, Bq is obtained for Earth view angle θ using the Equations (34)- (37) and is given by the following calibration equation…”

“…The other way out is to have RVS for blackbody view same as for the space view by design and provide an accurate measurement of this RVS in LUT. This will eliminate background contribution and F can be determined from Equation (37) without getting coupled to RVS and Equation (38) [20].…”

“…However, the hardware configuration is similar to the Advanced Himawari Imager (AHI) in the geostationary meteorological satellite of the Japan Meteorological Agency (JMA), Himawari-8, that was launched in October 2014 and entered into operation in July 2015. The information for the review below is drawn from the JMA presentation [38] and presentations of ABI calibration scientists at technical meetings [39][40][41].…”