Improvement On Detection Performances Of Pulses Accumulated Gm-APD Lidar

Lidar(light detection and ranging)has the advantages of high range precision,high anguler resolution,good direction and strong anti-interferences ability.It is widely used in the three-dimensional remote sensing,rendezvous and docking,missile guidance,automatic driving and other fields.Gm-APD(Geiger-mode Avanlanche Photodiode)has the advantages of single photon sensitivity and sub-picosecond time resolution,which has a strong application value in the long-range,weak signal detection with high precision.However,Gm-APD can only detects the presence and absence of the signal,which is a digital detection dechnology,it can not directly responds to the signal intensity information.An intensity information acquisition method with accumulated detection of Gm-APD lidar is proposed.Based on the Poissson probability detection model of Gm-APD and the time interval discrete method,the avalanche probability of Gm-APD in any time-bin is obtained.Then,the number of average signal photoelectrons is obtained,which represents the intensity information of the target.Finally,a Gm-APD lidar with accumulated detection is designed and to obtain the high precision intensity information in the experiment.The relative intensity precision is less than 3%.When the number of average signal photoeletrons is lager than 4,the signal and noise can be attenuated in the same proportion.The detection performances of Gm-APD lidar can be futher improved,while ensuring the saturation output of the avalanche probability of Gm-APD.The detection probabilty,false alarm probabilty and range accuracy of the Gm-APD lidar with narrow pulses less accumulated detection using semi-threshold method are obatined.The influence of the transmittance of the attenuator on the detection performacnes is studied.Then,the range imaging simulation is obtained.A Gm-APD lidar with wide pulses accumulated detection is designed in the laboratory.Under a strong backgroud noise condition,a 50 d B attenuator is used to perfectly extract the signal photon counting distribution histogram,which is completely submerged in the noise.There is a range walk error in the Gm-APD lidar,which depends on the signal intensity.With the increase of the signal intensity and the laser pulse width,the range walk error will become worsen.In order to restrain the range walk error,signal restoration & Gaussian functions fitting method and signal restoration & center-of-mass algorithm are proposed.Based on the Poisson avalanche probability detection model of Gm-APD,the signal photoelectrons distribution histogram is obtained from the signal photon counting distribution histogram.The first method used the Gaussian functions fitting method to find the peak position,which represents the target distance information.The second method uses the center-of-mass algorithm to find the center-of-mass of the signal waveform,which represents the target distance information.Both the two methods can obtain the high precison distance and intensity information of the target.The intensity precision of the first method is less than 0.015 photoelectrons,and range precision is 1.2 cm.The relative intensity precision of the second method is less than 3%,and range precision is less than 0.6 cm.Targets with different materials will exhibit different depolarization characteristics.By measuring the polarization of the refected light from the target,some additional information can be obtained compared with traditional intensity detection.We analyze the theory of polarized light transmission expressed by Muller matrix.Utilizing the different depolarization charateristics beteween the materials from the front and back surfaces of the water tank,the two reflected signals are separated to be detected by two Gm-APDs.A thickness of 10 cm of the water tank is obtained with high range precision of 1.1 cm.A polarization lidar with four Gm-APDs is designed to identify the targets with different materials.By comparing the differences between the intensity images obtained from the four Gm-APDs,the identification of different materials targets is achieved under a extreme weak signal condition by the polarization lidar.The depth image of the targets with high range precision of 0.8 cm is obtained.