Geometric Accuracy Verification of GF-7 Satellite Stereo Imagery Without GCPs

The GaoFen-7 (GF-7) satellite is the China's first civil optical stereo-mapping satellite with submeter resolution. GF-7 is also equipped with a laser altimeter, which can obtain sparse laser altimetry points (LAPs) to improve the vertical accuracy of stereo images. Verifying the geometric accuracy of GF-7 imagery without ground-control points (GCPs) is of great significance for evaluating the mapping capability of GF-7. In this study, 147 stereo images and 804 LAPs of the GF-7 satellite covering Jiangsu Province, Hebei Province, and Sichuan Province in China were selected as experimental data. Subsequently, 455 high-precision independent check points were used to verify the geometric accuracy of the GF-7 images. The results show that, without GCPs, the root-mean-square errors (RMSEs) in the horizontal direction of the experimental images in flat, hilly, mountainous, and high-mountainous terrains, and over the entire area were 4.91, 3.81, 4.38, 6.39, and 4.91 m, respectively. The RMSEs in the vertical direction were 3.42, 4.68, 3.00, 4.41, and 3.52 m, respectively. After performing combined block adjustments of the LAPs and stereo images, the RMSEs of the experimental images in the vertical direction decreased to 0.43, 0.66, 0.76, 1.14, and 0.68 m, respectively, whereas those in the horizontal direction saw only minor changes. Therefore, in the absence of GCPs, the geometric accuracy of GF-7 imagery can fully meet the accuracy requirements of China's 1:10 000 scale stereo mapping by using the GF-7 LAPs as control points.