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Compared with optical remote sensing satellites, the geometric positioning accuracy of synthetic aperture radar (SAR) satellite is not affected by satellite attitude or weather conditions. SAR satellites can achieve relatively high positioning accuracy without ground control points, which is particularly important in global surveying and mapping. However, the stereo positioning accuracy of SAR satellites is mainly affected by the SAR systematic delay and the atmospheric propagation delay of radar signals. An iterative compensation method for the SAR systematic time delay is proposed based on digital elevation model to improve the stereo positioning accuracy of SAR satellites without control points. In addition, to address the non‐real‐time updates of external reference atmospheric param, an iterative compensation method to estimate the atmospheric propagation delay of radar signals is proposed based on standard atmospheric models. In this study, SAR images from the Gaofen‐3 (GF‐3) satellite with 5 m resolutions were used as experimental data to verify the effectiveness of our proposed method. Simultaneously, the 2D positioning accuracy was better than 3 m and increased by 42.9%, and the elevation positioning accuracy was better than 3 m and increased by 90.2%. [ABSTRACT FROM AUTHOR]

After mastering the key technologies of manufacturing spaceborne Synthetic Aperture Radar (SAR), China's SAR satellites have been successfully launched into space. As the only civil microwave satellite listed in the "National High-resolution Earth Observation System Major Project," the Gaofen-3 (GF-3) 01 satellite is the first C-band multi-polarization SAR satellite with a resolution of 1 m. GF-3 series satellites stand out among civil SAR satellites worldwide because of their high resolution, wide swath, high geometric radiation quality, multiple imaging modes, and long operation time. Taking GF-3 series satellites as an example, this study introduces the development of China's civil SAR satellites, as well as their processing strategies and applications. The success of the GF-3 series satellites shows that China's SAR remote sensing technology has stepped into a new era of high-quality and high-precision Earth observations. [ABSTRACT FROM AUTHOR]

To address blur and noise issues caused by airlight and atmospheric scattering in nighttime imaging environment, we proposed a multi-frame image restoration method. First, the Luojia 1–01 night-light image degradation model was derived. Thereafter, the APSF (Atmospheric Point Spread Function) for night-light images was estimated. Improved dark channel prior and sparse constraint models were used to eliminate effects ofairlight and atmospheric scattering. Finally, a multi-frame sparse constraint model was established to eliminate image noise. The results show the proposed method is effective as it can reduce the image blur phenomenon, suppress image noise, and improve image quality. [ABSTRACT FROM AUTHOR]

The YG-13A mission, launched in late 2015, is the first Chinese synthetic aperture radar (SAR) satellite to achieve sub-meter resolution. In this paper, we briefly introduce this milestone satellite and describe a method for improving YG-13A’s absolute positioning accuracy. We evaluated the plane and three-dimensional absolute positioning accuracy over five test sites. The results indicate that high-accuracy absolute positioning can now be achieved with a horizontal accuracy of 3 m or better for strip-map data and 2 m or better for sliding spot data, without regard to the elevation error. In addition, the three-dimensional absolute positioning accuracy in plane and elevation is within 3 m and 2 m, respectively, which satisfies the requirements for high-precision three-dimensional control points. [ABSTRACT FROM PUBLISHER]

Yaogan-5(YG-5), launched in December 2008, is a Chinese high-resolution spaceborne synthetic aperture radar (SAR) satellite, with a ground resolution of 3 m. However, the direct geometric positioning accuracy of YG-5 slant range images is low and so is the mosaic accuracy of the orthoimages. To improve the geometric accuracy of YG-5 orthoimages, this article proposes a strategy to calculate the rational polynomial coefficients for each SAR image and then uses a planar block adjustment method to solve for the orientation research parameters of the SAR images to achieve the orthorectification while a auxiliary digital elevation model is necessary for height constraint. Compared with the traditional orthorectification method using a single image, this strategy can ensure both uniformity in positioning accuracy of orthorectified images and high mosaic accuracy of adjacent orthoimages based on a small number of ground control points (GCPs). Tests using Chinese YG-5 satellite data over Xi’an and Xianning, China show that, using four GCPs positioned in the four corners of the test area, we can achieve independent check point plane accuracies better than ±4 m after the planar block adjustment. Finally, this article demonstrated that seamless mosaic geometry levels can be attained after the block orthorectification. [ABSTRACT FROM PUBLISHER]

In recent years, China has launched YaoGan-13 and GaoFen-3, high-resolution synthetic aperture radar (SAR) satellites that can acquire global high-resolution images. The absolute positioning accuracy of such satellites is important for mapping areas without ground reference points and for automated processing. However, satellites without geometric calibration have poor absolute positioning accuracy, greatly restricting their application (e.g., land resource surveys). Therefore, they cannot meet national demands for high-resolution SAR images with good geometric accuracy. Here, we propose a series of methods to improve the absolute positioning accuracy of YaoGan-13 and GaoFen-3, such as the multiple-image combined calibration strategy and geometric calibration model for a real continuously moving configuration, including consideration of atmospheric propagation delay. Using high-accuracy ground control data collected from different areas, the 2-D and 3-D absolute positioning accuracies of YaoGan-13 and GaoFen-3 were assessed after implementation of the improvement measures. Experimental results showed that, after calibration, the 2-D absolute positioning accuracy of YaoGan-13 and GaoFen-3 are improved from 43.86 m to 2.57 m and from 30.34 m to 4.29 m, respectively. In addition, the 3-D absolute positioning accuracies of YaoGan-13 in plane and elevation are 3.21 m and 2.22 m, respectively. Improving the absolute positioning accuracy of these satellites could broaden the scope of their potential applications in the future. [ABSTRACT FROM AUTHOR]