The GF-7 satellite is China’s first civil sub-meter resolution stereo mapping satellite, aiming at 1:10,000-scale mapping. To achieve this goal, apart from the stereo optical cameras that reach sub-meter resolution, the GF-7 satellite is equipped with a laser altimetry system capable of obtaining three-dimensional laser points (LPs) with high elevation accuracy. However, the combination of laser altimetry data and optical stereo images has not been thoroughly studied. In this paper, we exploit the images recorded by the highly integrated laser footprint cameras and propose a hierarchical phase correlation method based on a geographic pyramid for the registration of laser altimetry data and high-resolution optical stereo images, which lays a solid foundation for the following combined adjustment. Experiments show that the proposed registration method can automatically locate the LPs on high-resolution stereo images and meet the requirements of bundle adjustment. A series of bundle adjustment experiments were carried out, showing that laser altimetry data can significantly enhance the vertical accuracy of optical image stereo mapping and that elevation accuracy can reach roughly 1.0 m (RSME) without ground control points. Therefore, this study could be a good guide for global high-precision DSM acquisition with the GF-7 satellite.

Satellite laser altimetry can obtain sub-meter or even centimeter-scale surface elevation data over large areas, but it is inevitably affected by scattering caused by clouds, aerosols, and other atmospheric particles. This laser ranging error caused by scattering cannot be ignored. In this study, we systematically combined existing atmospheric scattering identification technology used in satellite laser altimetry and observed that the traditional algorithm cannot effectively estimate the laser multiple scattering of the GaoFen-7 (GF-7) satellite. To solve this problem, we used data from the GF-7 satellite to analyze the importance of atmospheric scattering and propose an identification scheme for atmospheric scattering data over land and water areas. We also used a look-up table and a multi-layer perceptron (MLP) model to identify and correct atmospheric scattering, for which the availability of land and water data reached 16.67% and 26.09%, respectively. After correction using the MLP model, the availability of land and water data increased to 21% and 30%, respectively. These corrections mitigated the low identification accuracy due to atmospheric scattering, which is significant for facilitating satellite laser altimetry data processing.

In cold mountain environments, rock glaciers and talus represent common periglacial landforms. Accurate monitoring of their activity is crucial for understanding alpine kinematics. Presently, spaceborne SAR satellites monitor periglacial landform deformations mainly utilizing medium-resolution data. However, capturing surface structure deformations accurately and comprehending the movement mechanisms remain challenging. This study employs high-resolution GF-7 optical stereo images and Radarsat-2 SAR data, introducing a multi-baseline persistent scatterer and distributed scatterer combined MT-InSAR method to identify rock glaciers and talus landforms, as well as to analyze their deformations. Initially, rock glaciers and talus are outlined using GF-7 optical images, and Digital Surface Models (DSM) are extracted. The developed MT-InSAR method then detects the line of sight (LOS) and slope-parallel deformations of these landforms. Radarsat-2 monitoring reveals that 47.5% of identified rock glaciers are classified as active, while talus deformations are less active compared to rock glaciers. By utilizing high-resolution optical and SAR satellite data, we first documented the intricate deformation features within standard rock glaciers, such as the front, lateral margins, and optionally ridge-and-furrow deformations, as well as their interaction with the surrounding terrain topography. This discovery offers evidence of gravity-driven forces impacting rock glacier movement. We have also conducted a deformation analysis of the talus, obtaining spatial deformation characteristics of typical talus. It was observed that the deformation of the talus is jointly influenced by the conditions of surface debris cover and the slope of the terrain. This study highlights the value of high-resolution optical and SAR satellites in studying periglacial geomorphology dynamics.

The Gaofen-7 (GF-7) satellite uses a two-beam laser altimetry system in which each beam is equipped with a laser footprint camera (LFC) to provide geometric processing of the laser footprint images that assist in optical image stereo mapping. Because of the violent vibrations during launch and the difference in the environment before and after entering orbit, the key parameters for geometric processing of the laser footprint images may change, which will cause large geolocation errors. Therefore, it is essential to carry out on-orbit calibration and validation for the laser footprint cameras. This study first constructs a rigorous geometric positioning model for the LFC of the GF-7 satellite and analyses various error sources that affect the geometric positioning accuracy of laser footprint images. Then, a comprehensive calibration method, which effectively eliminates the distortion of the LFC optical system, and the positioning error caused by the long-period jitter of the satellite platform, is proposed based on the multi-scene images combined with image simulation. The proposed method can effectively eliminate various errors that affect the geometric positioning accuracy of the GF-7 laser footprint image. The internal geometric positioning accuracy of the calibrated LFC is better than 0.7 pixels, and the absolute geometric positioning accuracy is within 6.0 m after using precise post-processing orbital and attitude data. Our study will contribute to the processing and application of laser altimetry data from the GF-7 satellite.

The Gaofen-7 (GF-7) satellite represents China's first civil satellite equipped with a full waveform laser altimeter. This study aims to evaluate its on-orbit performance by analyzing the transmitting and receiving systems through the examination of waveform parameter and laser energy. The results indicate that the transmitting waveform of Beam 1 exhibits a little instability compared to that of Beam 2. It is supposed that the extreme solar activity on March 31st, 2022, affected the stability of the receiving waveform of Beam 1 in April 2022, while simultaneously impacting the stability of transmitting waveform and the receiving waveform of Beam 2’s transmitting and receiving. As a result, the pulse width of the receiving waveform for both Beams has been extended by approximately 1.5 ns and 2.4 ns, respectively after April 2022. Both beams have experienced a decline in ability to emit laser energy, with Beam 1 decreasing by 0.4 mJ per month and Beam 2 by 0.08 mJ per month. Notably, following the extreme solar activity, the rate of decline became more pronounced, escalating to 0.5 mJ per month for Beam 2. Overall, Beam 1 demonstrated superior transmitting and receiving radiation capacity compared with Beam 2, while the receiving radiation performance of both beams remained relatively stable. Nevertheless, there were some changes in the full waveform data transmitted and received by the altimetry system during the four years on-orbit peroid of the GF-7 satellite, the changes were very small, highlighting the overall stability of the laser altimetry system.