In‐orbit geometric calibration approach and positioning accuracy analysis for the Gaofen‐7 laser footprint camera

Abstract The Gaofen‐7 (GF‐7) satellite is China's first submeter high‐resolution optical stereo‐mapping satellite. The satellite is equipped with two area‐array laser footprint cameras to capture the laser spots emitted by laser altimeters. To accurately identify and locate the geographical positions of laser spots, a stepwise geometric calibration method with ground laboratory information for high‐resolution area‐array camera is proposed in this paper. It includes the internal and external calibration. First, the initial values of the camera's internal parameters are determined based on the laboratory calibration results. Then, based on a high‐precision reference ortho‐image and a digital elevation model, the ground control points (GCPs) for multi‐scene footprint images are obtained by image matching. Finally, the external and internal calibration methods for the laser footprint camera are implemented successively. The experimental results indicate that this method can restore geometric imaging relationships with high precision. After the internal and external calibration, the systematic residual error of the image point is eliminated, the remaining residual achieves 0.38 pixel, and the accuracy of direct positioning on the ground is better than 5.0 m, and the elevation accuracy is within 1.5 m