Research On Detection Performance And Noise Suppression Method Of GM-APD Lidar

GM-APD(Geiger mode avalanche photodiode)is equipped with single-photon level detection ability,it greatly reduces the volume and power consumption of Li DAR(Light detection and ranging),the detector is very vulnerable to the influence of background noise,which limits the all-weather application of Li DAR.In order to solve this problem in this thesis,from the perspective of Li DAR system application level,it establishes the GM-APD Li DAR system detection performance model,investigates the background noise suppression method and speckle noise suppression method,verifies the effect of different methods on improving detection performance through the self-developed GM-APD Li DAR system,and it provides theoretical and experimental guidance for GM-APD Li DAR all-weather applications.This thesis will conduct researches from the following four aspects:Firstly,combining the traditional pulse-type Li DAR ranging equation and GM-APD triggering mechanism,the single-photon Li DAR ranging equation is derived,it analyses the effect of echo photon number and noise photon number on the triggering characteristics,and the constraints on the optimal triggering probability is obtained.Through the Monte Carlo simulation method,the restriction relationship between the number of statistics and the integrity of signal echo waveform is obtained.The average ranging walk-error and standard deviation models of the system are proposed,and the key parameters to improve the ranging performance are got.Besides,using the dual-wavelength(532nm and 1064nm)laser scattering properties’ data of typical target fit the existing three classical bidirectional reflection distribution function(BRDF),the results show that there is a large error between the fitting curve and the actual intensity distribution,and the scattering model needs to be improved.Secondly,target scattering properties is an important factor affecting single-photon echo detection probability.On the one hand,the directional scattering component of Gaussian function is introduced into the scattering model,and a modified Li-Liang BRDF model is proposed.By adjusting the intensity distribution of spatial light field,the parameters fitting error of scattering model is reduced,and the calculation accuracy of echo photon number is improved.On the other hand,the background light is introduced into the scattering model,and the modified single-photon Li DAR ranging equation is proposed,which realizes the accurate calculation of signal photon number and background photon number.A 64×64 GM-APD Li DAR is used for experimental verification of the ranging equation on the 1km target in the daytime,and the experimental results show that the average noise photon number error is 4.6%,and the average signal photon number error is 6.9%.Moreover,the modified equation is combined with Monte Carlo simulation method and maximum likelihood estimation method(MLE),the GM-APD Li DAR system all-weather detection model is developed,which can provide theoretical guidance for the analysis of detection performance under the condition of the strong background light,and the analysis shows that signal statistics amount and noise intensity are important factors affecting detection performance.Thirdly,in order to improve GM-APD Li DAR detection performace under the high background light intensity condition,on the one hand,a GM-APD Li DAR detection scheme based on the combination of spatial correlation method and adaptive adjustment of the aperture diameter method(AAAD)is proposed.AAAD can effectively reduce noise intensity and maximize the echo triggering probability by adjusting aperture to get an optimized aperture value,and improve signal detection probability under the constraint of limited statistical frame.The spatial correlation method uses neighborhood similarity to improve the single-pixel measurement amount and improves signal detection probability under the constraint of limited statistical frame.Under the condition that the background environmental illuminance is 19000 Lux,the outdoor experimental verification with area-array GM-APD Li DAR is accomplished,compared with the traditional detection scheme,the recovery ratio of the 500 m target can be increased by 6.59 times.On the other hand,considering suppressing noise by polarization detection method of optical transceiver,the theoretical model of polarization detection with GM-APD Li DAR is deduced,and a set of polarization single-photon imaging Li DAR experimental system is developed.The polarization detection is combined with the spatial correlation method and AAAD,the imaging experimental verifications are carried out on the target at 800 m under the condition that the background environmental illuminance is 21000 Lux,compared with the non-polarization direct detection sheme,the false alarm is reduced by 36.2%,the triggering probability is improved by 171.1%,the signal detection probability is increased by 80.8%,and achieving the target recovery ratio of 96.9%.Finally,in order to overcome the influence of light field speckle noise output by the coupling multi-mode fiber(MMF)on the detection performance of area-array GM-APD imaging Li DAR,a GM-APD laser imaging speckle noise suppression method with fiber vibration is adopted,and the theoretical model of suppressing the speckle noise based on the mode coupling theory is proposed,realizing the vibration parameters optimization.And the method of the spatial correlation method combined with AAAD is introduced into the speckle noise suppression method,under the condition that the background environmental illuminance is 20500 Lux,verification experiments are carried out on the target at 300 m,the experimental results show that the contrast of speckle intensity is reduced from 1.247 to 0.057,which is reduced by 95.4%,and the target recovery ratio is increased from 28.8% to 97.7%,which is improved by 68.9%,the daytime detection performance is further improved.