Abstract
Abstract. The GaoFen-7 (GF-7) satellite is successfully launched on November 3, 2019, and its laser altimeter system is officially and firstly employed as the main payload for earth observations in China, which includes two sets of laser altimeters and laser footprint cameras. The Laser Footprint Image (LFI) is used to capture laser spots on the ground. In order to make up for the shortcomings of high cost field work for the traditional laser altimeter ground detector-based calibration method, this paper proposes a novel laser altimeter calibration method based on LFI. Firstly, the spaceborne laser calibration model and the Laser Footprint Camera (LFC) geolocation model are established. Secondly, the image coordinates of laser spot centroid are extracted from LFI, and the ground location of is obtained by ray intersecting with the reference Digital Surface Model (DSM). Finally, the centroid of laser spot is considered as Ground Control Point (GCP), and the pointing bias of GF-7 laser altimeter is calibrated by the Least Squares Estimation (LSE). The ALOS Global Digital Surface Model “ALOS World 3D-30m” (AW3D30) is used to evaluate the elevation accuracy of GF-7 laser altimeter before and after the calibration. The results indicate that elevation accuracy of the GF-7 laser altimeter is improved significantly after calibration. The proposed method can be effectively applied for high-frequency geometric calibration of GF-7 laser altimeter.
Highlights
GF-7 Satellite was successfully launched on November 3, 2019, which is equipped with the Chinese first official spaceborne laser altimeter system for Earth observation
We propose an in-orbit pointing bias calibration method for GF-7 laser altimeter based on single footprint image
The elevation accuracy of the GF7 laser has improved significantly after calibration, the GF-7 laser maximum elevation error after calibration is still close to 5 m from table 5 and 6. It is related with the elevation accuracy of reference Digital Surface Model (DSM)
Summary
GF-7 Satellite was successfully launched on November 3, 2019, which is equipped with the Chinese first official spaceborne laser altimeter system for Earth observation. The two linear array optical cameras and two laser altimeters mounted on the satellite can respectively acquire high spatial resolution stereo mapping remote sensing data and high precision laser data. According to the different types of reference data, the in-orbit geometric calibration method for spaceborne laser altimeter mainly includes the ground-based infrared detector calibration, airborne infrared camera imaging calibration, Corner Cube Retroreflectors (CCR) calibration, attitude-maneuver calibration and surface matching calibration. The laser spot is geolocated by the ray resection with single LFI and the reference DSM data This location of the laser spot centroid on the ground is employed as GCPs. the pointing bias of GF-7 laser can be calibrated. ALOS Global DSM-AW3D30 (Takaku et al, 2016a; Takaku et al, 2016b)
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