Researches On Performance And Range Accuracy Of Laser Imaging System Based On Geiger Mode Detectors

Scannerless active laser three dimensional imaging systems overcome the slowimaging speed of scanning imaging technique, and have the advantages of fast imag-ing speed, low weight, small volume. When using area detectors, it is inevitable to getless energy for a single pixel comparing to single detector, which results in shorter detec-tion range. Geiger mode detectors have single photon sensitivity, and use digital outputwhich can be easily integrated to form larger detector arrays. Geiger array detector basedimaging system has drawn many attentions from the researchers due to the advantagesof fast imaging speed, high ranging precision, easy integration, less laser energy require-ment, small system volume and less energy consumption. At present much attention ispaid to the development of detector arrays and the performance improvement of detectorperformance, but little to the performance of the whole system. The problems existed incurrent imaging system based on Geiger mode detectors are discussed, then researches onperformance and range accuracy are carried out.Based on the difference between Geiger mode ranging and threshold ranging, thestatistical properties of laser echo and noise signal are analyzed using lidar equation andphoton statistical theory. The relations between system performance and system param-eters are acquired, including the detection probability, the false alarm probability, themaximum detectable range, and depth of field are discussed, which are used as basis forsystem performance and range accuracy analysis.Based on the above analysis, a precision theory is proposed for Geiger mode laserrange systems. The range accuracy and precision are calculated for the system. Thenthe accuracy and precision of rect shape laser pulse without noise and general shape laserpulse with noise are calculated and discussed. The in?uence on range accuracy and pre-cision of pulse echo strength, pulse width, target position, detection noise are discussed.Results show that the pulse echo strength and pulse width have dominant in?uence onrange accuracy and precision, higher echo strength and narrower pulse width result inbetter accuracy. The theory is testified with Monte Carlo simulation which produces sameresults as theoretical analysis.Geiger detectors can not get the signal intensity directly. Therefore an algorithm to get the signal intensity using multi-pulse statistics is introduced. The detection accuracyand detection range of this method are discussed which shows that the accuracy and de-tection range increase with the number of detections. This method is testified with MonteCarlo simulation which produces same results as theoretical analysis.Geiger mode detector suffers from the noise photons due to high sensitivity. A falsealarm reduction method based on multi-pulse statistic is introduced and discussed. Therelations between the detection probability, false alarm probability and number of detec-tions are discussed, which shows that the detection probability and false alarm probabilityincrease with the number of detections. With a detection number of 5, detection proba-bility can double the detection probability of single detection with the same false alarmprobability. Monte Carlo simulation is carried out to testify the method, which producessame results as theoretical analysis.To testify the availability of 3D imaging system based on Geiger mode detectors, apulse ?ight-of-time 3D imaging system based on modified PIN array detectors is intro-duced. Experiment result shows that 3D imaging systems based on Geiger mode detec-tors are practical and with a 5n pulse width laser and 5ns time accuracy counting circuit,a range precision of about 1.5m is obtained.