Coarse-to-Fine Image Matching-Based Footprint Camera Calibration of the GF-7 Satellite.

Lirong Liu,Jiyi Chen,Ren Liu,Chaofeng Ren,Junfeng Xie,Xinming Tang

doi:10.3390/s21072297

Lirong Liu, Jiyi Chen + Show 4 more

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https://doi.org/10.3390/s21072297

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Abstract

The GF-7 satellite is China’s first high-resolution stereo mapping satellite that reaches sub-meter resolution, equipped with new-type payloads, such as an area array footprint camera that can achieve synchronization acquisition of laser spots. When the satellite is in space, the variation of camera parameters may occur due to launch vibration and environmental changes, and on-orbit geometric calibration thereby must be made. Coupled with the data from the GF-7 satellite, this paper constructs a geometric imaging model of the area array footprint camera based on the two-dimensional direction angle, and proposes a coarse-to-fine “LPM-SIFT + Phase correlation” matching strategy for the automatic extraction of calibration control points. The single-image calibration experiment shows that the on-orbit geometric calibration model of the footprint camera constructed in this paper is correct and effective. The matching method proposed is used to register the footprint images with the DOM (Digital Orthophoto Map) reference data to obtain dense control points. Compared with the calibration result using a small number of manually collected control points, the root mean square error (RMSE) of the residual of the control points is improved from half a pixel to 1/3, and the RMSE of the same orbit checkpoints in the image space is improved from 1 pixel to 0.7. It can be concluded that using the coarse-to-fine image matching method proposed in this paper to extract control points can significantly improve the on-orbit calibration accuracy of the footprint camera on the GF-7 satellite.

Highlights

The GF-7 satellite, successfully launched on 3 November 2019, has been equipped with such payloads as bi-linear array stereo cameras, two-beam laser altimeters, as well as two area-array footprint cameras that capture laser spots synchronously
The footprint camera of GF-7 satellite images the ground at the time of laser altimeter emission; the position of laser spot center can be determined via the footprint image, and the footprint image can be matched with the high-resolution images of the same area taken by the bi-linear array camera
On-orbit geometric calibration is important to ensure the follow-up application of footprint images of GF-7

Summary

Introduction

The GF-7 satellite, successfully launched on 3 November 2019, has been equipped with such payloads as bi-linear array stereo cameras, two-beam laser altimeters, as well as two area-array footprint cameras that capture laser spots synchronously. Camera calibration serves to establish the corresponding relationship between the image coordinates and the object space coordinates by using the geometric imaging model, and restores each detector beam to norm. There are two main types of models: the rigorous geometric imaging model and the generalized model The former is a conformation model to establish the remote sensing image based on the orbit, attitude of the satellite, imaging geometry and other aspects, and the rigorous models of sensors of various types are different. The latter describes the geometric relationship between the object point and the image point by directly resorting to mathematical functions such as the widely used

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