This paper mainly studies the influence of skylight background on the single-step cumulative duration in the SLR automatic tracking process. During the satellite laser ranging (SLR) experiment, when the skylight background is strong, the signal photons reflected by the satellite will be drowned by the noise photons. It is necessary to clarify the influence of different noise intensities on the single-step cumulative duration. First, the relationship between the number of noise photons and signal photons responses is analyzed through background noise simulation and Monte Carlo simulation. Then, the single-step duration is determined based on the Poisson filter algorithm, the relative error of parameter estimation, and the number of echo signals at different distances. Finally, the automatic tracking technology based on the SLR echo signal is verified at the Tianqin station, and the experimental results show that when the target capture is completed, the number of signal photons responding approaches the theoretical limit threshold for signal extraction. The single-step duration is determined through daytime experiments.

The thresholds for signal extraction under different noise conditions are different, and the echo signal strength varies greatly for targets at different orbital altitudes. It is necessary to consider the number of signal responses at different cumulative durations under different noise conditions and at different orbital altitudes to provide theoretical support for the single-step cumulative duration setting in automatic tracking of ranging targets. Based on combined atmospheric radiative transfer (CART), the number of the skylight background noise photons at the Tianqin station is simulated and calculated. Based on the simulation results, Monte Carlo simulation is used to solve the probability P_nnof a noise-free photon response in the previous recovery time period at the signal photon response under the gated superconducting nanowire single photon detector (SNSPD) scenario of the Tianqin station, and then the signal extraction thresholds under different noise conditions are simulated. Considering the signal estimation error of 10%, the signal extraction thresholds under different noise conditions and the single-step cumulative durations at different distances are given.

In order to verify the correctness of the signal extraction threshold simulation results under different noise intensities, automatic tracking experiments are carried out on targets under different noise conditions and different orbital heights. The noise intensity statistics and single-step cumulative duration statistics are conducted for targets at different times and different orbital heights. According to the statistical results, it can be found that the number of signal photon responses for target capture under different noise conditions and different single-step durations is above the signal extraction-threshold surface. The minimum difference between the number of signal photon responses and the threshold is 0.13 s^-1, which can be approximately considered to be close to the limit value of the signal extraction threshold.

This paper conducts theoretical simulation analysis on the situation that strong noise will cause SLR signal photons to be drowned and then unable to respond. The simulation results show that when the number of noise photons is less than 8×10⁷, at least 0.6 s are needed to effectively extract the SLR signal. Based on the Tianqin Project laser ranging station, an automatic tracking experiment based on SLR echo signals is carried out, verifying the feasibility of 2 s single-step accumulation time for automatic tracking of geosynchronous orbit satellites based on SLR echo signals during the day, and a single-step time of 1 s can be used when the number of noise photons is less than 2×10⁶. The correctness of the simulation results of signal extraction thresholds under different noise conditions is verified by experiments, providing theoretical guidance for the subsequent optimization of automatic tracking. However, the experimental verification under strong noise conditions in this paper is not sufficient. In the future, reasonable measures should be taken to protect SNSPD, explore the signal extraction thresholds under strong noise conditions, and provide theoretical and experimental support for all-weather SLR automatic tracking.