## 1 Introduction
The selection conditions for distributed targets are stringent, and the radar cross-section (RCS) of natural point targets is different in different frequencies and incidence angles, which requires prior experimental measurements, so, in practice, artificial point targets are more feasible than other targets. In other words, radiometric calibration is more feasible through artificial point targets with known RCS. The in-orbit radiometric calibration campaigns of SAR systems, such as TerraSAR-X [3], Sentinel-1 [4,5], and RISAT-1 [6] have all used artificial point targets. The commonly used artificial point targets include active radar calibrator (ARC) and corner reflector (CR), among which CR has become the mainstream of ground reference in radiometric calibration due to its simple structure, stable performance, ease of installation, and low cost. The triangular trihedral corner reflector has a wide beam width in the azimuth and elevation direction [8], which is suitable for cross-frequency calibration [2] and is a typical instrument for SAR radiometric calibration in practice. [PERSON] et al. used three types of corner reflectors for radiometric and geometric calibration of RADARSAT-2 satellite data and verified the accuracy of the results [9]. [PERSON] et al. performed absolute radiometric calibration and verified the calibration accuracy of RISAT-1 satellite data of fine resolution scan (FRS) mode, by using trihedral CR via the peak method [10]. Both studies yielded satisfactory results. In the process of the radiometric calibration of SAR satellites employing the ground-based CRs, it is important to ensure that RCS presented by CR in the image conforms to the theoretical value [10], and this can be achieved by the following three aspects. First, by ensuring that the geometric structure and manufacturing accuracy of the corner reflector meet the requirements [11]; second, by ensuring a consistent direction between the ground CR and the incidence of radar beam during satellite transit; and third, by ensuring that the surrounding environment of CR deployment meets the requirements to minimize the influence of background clutter on the return signal of CR [12]. With the support of the Common Application Support Platform project for Land Observation Satellites of China's Civil Space Infrastructure (CASPLOS_CCSI), based on the Xilinhot Climate Observatory, a SAR satellite calibration and validation site, which is currently under construction, is built through the technical deployment of automatic triangular trihedral CRs and ARCs developed by CASPLOS_CCSI. Additionally, during the experiment, flexible automatic triangular trihedral CR are mainly deployed in the Xilinhot Climate Observatory in a mobile way to support the ground-synchronous measurement experiments. Based on the Xilinhot SAR satellite calibration and validation site, utilizing flexible automatic triangular trihedral CRs, the present study aims make a quick assessment of the image quality and radiometric calibration accuracy of C-SAR/01, which is now in the commissioning phase, by performing the radiometric calibration of C-SAR/01 and evaluating the calibration accuracy, using the peak and integral methods, to ensure the accuracy of backscatter intensity measurements so that C-SAR/01 images can accurately reflect characteristics of feature targets, as well as to meet the requirements of quantitative applications for C-SAR/01 image radiometric performance, which provides a basis for the C-SAR/01 data quality assessment and quantitative applications. This paper is organized as follows: Section 2 introduces the site and data in this experiment, Section 3 introduces the process and specific methods of radiometric calibration of this experiment, Section 4 assesses the quality of the experimental data, Section 5 describes the radiometric calibration results of the C-SAR/01 data, and Section 6 analyzes the radiometric calibration results of the C-SAR/01 data.