Research On The Extraction Of Ranging Value Of The Terrains For Spaceborne Single-photon Lidar

Spaceborne single-photon lidar is a new type of earth observation system,which uses multi-beam,micro-pulse and high repetition frequency laser beam to measure the distance to the target.Different from the linear-mode spaceborne lidar,single-photon lidar can only record random single-photon point cloud data.The distribution of point cloud data is related to the spatial distribution of the target and the system parameters of the lidar.The laser ranging value extracted based on the single-photon point cloud data will be affected by the randomness of photon events,resulting in different degrees of laser ranging error.Accurately extracting the laser ranging value from the discrete single-photon point cloud data is an important prerequisite for ensuring the accuracy of spaceborne single-photon lidar observation results.According to the working principle and the detection probability model of the spaceborne single-photon lidar,the ranging error model of the spaceborne singlephoton lidar is constructed.Based on the observation data of the airborne lidar and the spaceborne single-photon lidar as initial inputs,a combination method of numerical simulation and actual data processing is proposed to systematically investigate the influencing factors and calculation methods on the laser ranging value for the terrain.The distribution regularities of laser ranging error for the different targets are analyzed.The research results obtained include the following aspects:(1)Through theoretical model of laser ranging error and Monte Carlo's photon events simulation method,the effects of echo energy,dead time,noise level,target topography on the laser ranging error are explored in the case of limited detection.The result shows that the ranging error can be effectively reduced for the shorter dead time,the smaller target slope,the smaller average noise rate,and the less echo photons number of 0.2?1.(2)Using high-precision airborne lidar point cloud data to simulate single-photon point cloud data of different terrain reliefs,we provide the calculation method of laser ranging value based on the cumulative photon histogram and the inverse calculation of the echo photoelectrons number distribution for the long and short dead times.The quantitative relationship between the accumulative spots number and terrain slope is given.The results demonstrate that the ranging error can be minimized when the accumulative spot number is set to 17 for the unknown topography,and the ranging error can be corrected by the inversed echo photoelectron distribution for the long dead time.(3)Based on the result of the optimal number of accumulative spots,the distribution of the laser ranging error is analyzed for the observation data of the ATLAS spaceborne single-photon lidar at different slopes of the terrain.By comparing the resolved results with the laser ranging data published by ATLAS products,we perform the accuracy evaluation of the proposed laser ranging extraction method.The result shows that the ranging performance can be improved by accumulative spots without sacrificing spatial resolution.The analysis of the above results reveals that the ranging accuracy of the singlephoton lidar can be effectively improved based on the photon histogram obtained by optimal accumulative spots number and the inversed echo photoelectron distribution.The conclusions might provide a reference for the hardware design and data processing of spaceborne single-photon lidar in the future.