Accuracy Assessment of GF-7 Geolocation Without GCPs Considering Atmospheric Refraction and Aberration of Light

Considering that the atmospheric refraction and aberration of light (AOL) bend the path of light and thus affect the geolocation accuracy, a rigorous imaging geometric model with corrections of atmospheric refraction and AOL is proposed to improve the accuracy of geolocation for GaoFen-7 (GF-7) images without ground control points (GCPs). The correction of atmospheric refraction is calculated using a simplified two-layer atmospheric refraction model, while the correction of AOL is calculated using the satellite altitude and velocity. Then, the rigorous imaging geometric model is refined with both corrections. A total of 68 scenes of GF-7 satellite backward images in ten regions with different roll-off-nadir angles are selected to compare and detect the variation of accuracy with and without the corrections. The results show that the average geolocation accuracy is improved by 0.14 m in object space, and about 0.20 pixels in image space if the corrections of atmospheric refraction and AOL are taken into the geometric model. The average improvement of RMSEs is about 1.00 pixels and the ratio of improved scenes reaches 88.89% when the roll-off-nadir angle is larger than 15(degrees), whereas there is no need to consider atmospheric refraction and AOL if the off-nadir angle is smaller than 5(degrees). The methodology and results can provide support for the need for corrections for high-precision positioning and the promotion of GF-7 imagery.