Objectives Fengyun-4 （FY-4）, the second generation geostationary meteorological satellite of China, is the first series of three-axis stabilized geostationary meteorological satellites, which can continuously and stably observe the full disk of the Earth with high temporal resolution. To ensure imaging accuracy and stability, orbit motion compensation (OMC), attitude motion compensation and thermal deformation motion compensation must be implemented for payload pointing in real time, which can compensate for the influence of satellite orbit drift, attitude motion and thermal deformation on payload pointing deviation. The orbit drift makes the pixels deviate from the nominal position periodically. So the navigation and registration system needs to compensate the mechanical scanning angle misalignments of the payloads determined from OMC to guide the line-of-sight（LOS）to the expected target.

Methods First, the principle of orbit motion compensation algorithm is introduced, and the geometric pointing model and nominal fixed grid are generated for the advanced geosynchronous radiation imager of FY-4. Second, the OMC conversion models of FY-4 are deduced according to the three attitude reference frames, including orbit coordinate system, instantaneous southeast coordinate system and southeast coordinate system. Two conversion methods of orbit coordinate system and Earth fixed coordinate system are proposed, namely, definition method and rotation method. Third, based on the above OMC algorithm, the LOS compensation error of the long-line detector is analyzed for FY-4B geosynchronous high-speed imager.

Results The experimental results show that： (1) Characteristic analysis of swath-to-swath OMC shows the average root mean square error of the fourth-order Fourier series fitting is less than 1 μrad, which is better than the polynomial fitting and Gaussian fitting. (2) Ground simulation calculation depending on on-orbit data shows the difference between the two coordinate system conversion methods on OMC accuracy is about －1.1 μrad on average. (3)The compensation error of FY-4B long-array detector shows that when the satellite deviates 0.1° from the nominal position, the maximum north-south high latitude OMC error and low latitude error of 2 048×1 dimension detector can reach 8.2 pixels and 8.3 pixels at 250 m resolution, and the maximum registration error of two neighbouring swaths can reach 11.6 pixels.

Conclusions In order to improve NRS efficiency, the definition method should be adopted when the orbit and the southeast coordinate system are selected as the OMC compensation referen‑ce frame, and the rotation method should be adopted when the instantaneous southeast is selected.