Diurnal variation of solar-blind ultraviolet upwelling radiance led by observation geometry factors on geostationary attitude sensor limb viewing

For feasibility study of satellite autonomous navigation on geostationary orbit using the ultraviolet (UV) attitude sensor, the spatial distributions of solar-blind ultraviolet (SBUV) upwelling radiance from the earth surface points or the limb viewing path is simulated every two hours at all seasons based on the MODTRAN4 model. The target points are arranged from where the sensor can receive the earth radiance including eight limb viewing points in the altitude range of 0 to 90 km with an interval of 5 km and nine surface points. A hypothetical ultraviolet attitude sensor with 9.6° field of view is set at the geostationary orbit, 3.6×107 m away from the sea level of equator, and the nadir point of which is considered to be located at 102° E and Equator. The results show that Solar-blind ultraviolet (SBUV, 200-280 nm) upwelling radiance from the limb viewing points can increase to a maximum and then decreases with the raise of altitude of the limb points. The average SBUV radiance on the observation plane can presents a regular bright crescent or ring, which has the maximum about 0.433 W•m-2•sr- 1•μm-1 at the altitude from 50 to 60 km. The maximum of the upwelling radiance in the 242-267 nm spectra has the optimal characteristic considering the contrast and the altitude continuity of maximum of radiance at the limb points.