Vertical Accuracy Evaluation Model for Laser Altimetry Points and Stereo Images of the Gaofen-7 Satellite Without Ground Control Points

Gaofen-7 (GF-7) is the world's first Earth observation satellite to integrate optical stereo cameras and laser altimeters, mainly serving global 1:10000 scale stereo mapping. GF-7 can synchronously acquire laser altimetry points (LAPs) and stereo images with submeter resolution, aiming to effectively improve the vertical positioning accuracy of stereo images through joint geopositioning of LAPs and stereo images. This study proposed a quantitative evaluation model for theoretical vertical accuracy of GF-7 stereo images, LAPs, and the joint geopositioning of LAPs and stereo images. Without using ground control points (GCPs), the estimated theoretical vertical root mean square errors (RMSEs) of GF-7 stereo images, LAPs, and joint geopositioning of LAPs and stereo images were 2.02-8.49, 0.09, and 0.59-0.75 m, respectively. Subsequently, accuracy verification experiments were conducted using GF-7 data covering Hubei Province, China. The actual vertical RMSE of stereo images and joint geopositioning of LAPs and stereo images were 3.19 and 0.68 m, respectively, and the actual vertical RMSE of LAPs was consistent with the theoretical value. The experimental results confirm that the method proposed in this study is effective. The results of theoretical estimation and experimental verification both indicate that with the assistance of LAPs, the vertical accuracy of GF-7 stereo images without GCPs can meet the requirements of 1:10000 scale mapping. The results of this study have important reference value for improving GF-7 data processing methods and guiding the design of future satellites that integrate optical stereo cameras and laser altimeters.