AbstractNavigation of images from lightning mapping instruments in geostationary orbits is very important for data applications. However, few scientific peer-reviewed papers have been reported, except a few works in the pre-launch tests. On December 11, 2016, China launched the three-axis stabilized geostationary meteorological satellite Fengyun-4A(FY-4A), which carries a lightning mapping imager (LMI) onboard. LMI is now providing lightning observations above the equator at 104.7E and covers a large portion of the eastern Asian continent. In this study, a new method has been set up to perform the image navigation for FY-4A/LMI. Firstly, landmarks were used to calculate thermal deformation parameters and edge-binding technique was proposed to solve the inconsistency between the two tubes pointing directions. Secondly, temperatures of the mounting plate were used to be correlated with the daytime thermal deformation parameters to deduce the nighttime pointing directions when the landmarks were not available. Furthermore, the operational timetable for LMI was determined by analyzing the variations of navigation accuracy caused by the landmark observation interval and the sensors integration time for landmarks. Analysis of about 9200 background images of 153 consecutive days from the housekeeping data were investigated to validate the proposed methods accuracy for LMI image navigation. Compared to the baseline algorithm, navigation accuracy has been improved on average from 2-10 pixels to 1 pixel. The FY-4A/LMI navigation system has been put into operation since May 1, 2018, which has been in normal service ever since.

The visible-IR scanning radiometer (VIRR) of FY1-C/D meteorological satellites consists of 10 bands with 4 different focal plane assemblies (FPAs). However, there are significant band-to-band registration (BBR) errors between different bands, which cannot be compensated for by a simple shift in the along-scan direction. A rigorous BBR frame was proposed to analyze the sources of misregistration in the whisk-broom camera. According to theory, the 45° scanning mirror introduces tangent function style misregistration in the along-track direction and secant function style misregistration in the across-track direction between different bands if the bands are not in the same optical axis. As proven by the experiments of both FY-1C and FY-1D, the image rotation caused by the 45° scanning mirrors plays a major role in the misregistration. However, misregistration between different FPAs does not strictly adhere to this theory. Therefore, a polynomial-based co-registration method was proposed to model the BBR errors for the VIRR. To achieve 0.1 pixel accuracy, a fourth-degree polynomial was used for BBR in the along-scan direction, and a fifth-degree polynomial was used for the along-track direction. For the reflective bands, the root-mean-square errors (RMSEs) of misregistration could be improved from 3 pixels to 0.11 pixels. Limited by matching accuracy, the RMSEs of misregistration between thermal bands and reflective bands were approximately 0.2 to 0.4 pixels, depending on the signal-to-noise ratio.