Research On Photon Counting Lidar Technology Based On Coding

Photon counting Lidar maintains the advantages of linear detection Lidar(high angle resolution,high range resolution,high velocity resolution,high confidentiality,all-time operation).The Geiger mode avalanche photodiode(Gm-APD)detector replaces the photodiode detector working in linear mode,which greatly improves the detection sensitivity.Therefore,the photon counting Lidar has obvious advantages in the field of weak signal detection.More and more researchers are interested in it,and it is widely used in the field of space-borne topographic mapping,underwater target detection,biological detection,astronomical observation,etc.Gm-APD detector has extremely high detection sensitivity at the expense of not being able to obtain the echo intensity directly.In other words,Gm-APD detector is a binary output detector and cannot distinguish the number of echo photons.In the application scenarios of Lidar,there are noises caused by ambient light,so it is difficult to distinguish the target signal and ambient noise by single pulse detection.To solve this problem,multi-period accumulation technology is widely used to build statistical histograms by accumulating enough photon events.The target location is extracted by the histogram.However,the multi-period accumulation slows down the measuring speed and it is not suitable for scenarios that require quick measurements.In order to solve this problem,researchers propose to use high pulse repetition frequency(MHz)laser source to reduce the acquisition time,but high pulse repetition frequency will significantly reduce the maximum unambiguous range.Therefore,for the traditional pulse accumulation photon counting Lidar,there is an irreconcilable contradiction between the long unambiguous range and the short acquisition time.In other words,it is difficult to realize the fast detection of long-distance targets by using traditional pulse accumulation photon counting Lidar.In order to realize the rapid detection of weak signals,the coding method is introduced into the photon counting Lidar,and the photon counting Lidar based on coding is studied.The main innovations and features of this thesis are as follows:This thesis focuses on the fast detection of weak signals.The evaluation model is established for pseudo-random coding photon counting Lidar.At the same time,based on the pseudo-random coding method,the true random coding method for the short and middle distance,and the macro pulse coding method for the long distance are proposed.A true random coding photon counting Lidar is proposed in this thesis,in which a single photon detector acts as the true random sequence signal generator instead of the traditional function generator.Compared with the pseudo-random coding Lidar,the true random coded method not only improves the anti-crosstalk capability of the system,but also greatly reduces the ‘1' bit missed detection caused by the limited Gm-APD count rate.The theoretical model of true random coding photon counting Lidar is established,and a high precision range extraction method based on orthogonal demodulation is proposed.It is an effective weak signal,high precision and fast detection method.Finally,the performance of the true random coding photon counting Lidar is verified by experiments.The proposed macro-pulse coding photon counting Lidar greatly reduces the pulse accumulation time by transmitting pulse train,and effectively avoids the impact of the fast movement of targets on the detection performance.Meanwhile,according to the macro-pulse coding method,a time-shift accumulation method to extract the target distance is proposed,which can obtain the target distance easily and effectively and improve the practicability of the macro-pulse coding photon counting Lidar.In this thesis,the photon counting Lidar system based on coding is studied.The complete theoretical model is established.The numerical simulation and experimental analysis results prove the correctness and validity of the proposed method.The complete theoretical support is provided for the rapid detection of weak signals.