Spectral band unification and inter-calibration of Himawari AHI with MODIS and VIIRS: Constructing virtual dual-view remote sensors from geostationary and low-Earth-orbiting sensors

Through band unification and inter-calibration this paper develops and presents a method to construct virtual dual-view sensors from compatible geostationary and low-Earth-orbiting (LEO) sensors such that spectrally unified and radiometrically consistent observations from two different angles can be acquired using these virtual sensors. Results for three virtual dual-view sensors constructed from Himawari-8/AHI (one of the next generation of geostationary sensors) paired with MODIS (Aqua and Terra) and VIIRS are reported. Over 1270 representative Hyperion passes were used to reproduce, by spectral band integration, simultaneous observations by the three pairs of sensors, and linear relationships between AHI-MODIS and AHI-VIIRS were established, allowing the conversion of MODIS bands and VIIRS bands to AHI bands. For 95% of the sample pixels, a maximum reflectance conversion error < 0.004 was achieved. Following band conversion, inter-calibration was conducted using a ray-matching technique, involving up to 2100 matchup areas from 20 months of imagery. Overall the final calibration accuracy is high as indicated by high correlation r(2) (similar to 0.98), small estimated parameter errors, small regression errors and negligible regression biases. The temporal drifting of the paired sensors over a 20 month period was also analysed. It shows that all the involved sensors are very stable. Accurate inter-calibration not only provides an economical solution for the calibration an Fd validation of remote sensors, it is also essential for synergetic multi-sensor applications. Lack of sufficient information from single-view sensors has been a common bottleneck in many remote sensing applications. Constructing virtual dual-view sensors using the presented method provides an effective way to overcome the limitations of single-view sensors, without incurring extra costs. The method can be applied to other next generation geostationary sensors leading to near global coverage and enhanced products. Inter-calibration between geostationary sensors, such as Himawari AHI - and GOES-R ABI, may be conducted using the LEO sensors as bridges.