Objective Laser return number is an important parameter to perform the detection ability of a satellite laser ranging (SLR) system, which is proven to be closely related to the atmospheric transmission characteristics of laser. Accurate evaluation of the laser return number in the SLR system not only provides a theoretical basis for system design and optimization but also is a key issue and primary link in the future development of SLR automation systems. In SLR system operation, the atmospheric scattering effect, atmospheric absorption effect, and atmospheric turbulence effect continuously reduce the laser energy during atmospheric channel transmission, directly affecting the size of the average laser return number in the SLR system. The influence of the atmospheric environment on photon detection becomes increasingly evident as the detection distance further increases. To effectively evaluate the average laser return number in the SLR system and explore the relationship between laser atmospheric transmission characteristics and the detection performance of the SLR system, we should analyze the atmospheric transmission characteristics of lasers. Methods Lidar atmospheric correction (LAC) model based on Mie scattering theory and actual meteorological conditions is built in our study. First, based on the tilted propagation theory of laser, the entire atmosphere transmittance at different wavelengths (450, 500, 550 nm) is calculated. Then, the average laser return number per unit time of the SLR system in different meteorological conditions is calculated, and the model is validated by the actual observation results of the 60 cm SLR system at Changchun Observatory. Finally, the effects of visibility and relative humidity on the average laser return number are analyzed. Results and Discussions Compared with the empirical formula adopted in conventional lidar equations, the mean average relative error of atmospheric transmittance calculated using the laser slanting revise theory decreases from 14. 201% to 5. 992%, which is about an order of magnitude smaller (Fig. 2 and Table 1). The calculated average laser return number per unit time of SLR system based on the LAC model exhibits good consistency with the measured data, with an average relative error of less than 15% (Fig. 4 and Table 2). The average laser return number received by the SLR system is proportional to visibility and inversely proportional to relative humidity (Figs. 5 and 6). When the elevation angle of the telescope is less than 15 degrees, the influence of visibility and relative humidity on the average laser return number is not significantly different. When the elevation angle of the telescope is greater than 15 degrees, the influence of visibility is slightly greater than that of relative humidity, and reaches its peak around 60 degrees (Fig. 7). Additionally, we also find that due to the temperate continental climate of Changchun Observatory, there are significant seasonal variations in the average laser return number per unit time received by the SLR system (Fig. 8). Conclusions Average laser return number in SLR system is an important parameter characterizing the detection ability of the system, which is closely related to the atmospheric transmission characteristics of lasers. Based on Mie scattering theory and the actual distribution of aerosol particles, the LAC model is proposed and employed to calculate the average laser return number in the SLR system. By taking the 60 cm SLR system at Changchun Observatory as an example, the effect of climate conditions on the average laser return number in the SLR system is analyzed. The results indicate that the average laser return number in SLR system increases with the rising visibility near the surface and decreases with the increasing relative humidity. When the elevation angle of the telescope is greater than 15 degrees, the influence of visibility is greater than that of relative humidity, and their influence reaches its peak around 60 degrees. Our study not only elucidates the inherent mechanism by which climate conditions affect the detection performance of SLR system but also provides new theoretical solutions and technical support for SLR system site selection and performance evaluation.
