【作者】 王飞；

【导师】 孙秀冬；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2010， 博士

【摘要】 无扫描激光主动三维成像技术解决了扫描激光三维成像技术成像速度慢的缺陷,具有成像速度快,重量轻,体积小等优势,因此成为激光主动成像技术的主要发展方向。然而在采用面阵探测器时,不可避免的会减小单个探测器单元所获得的能量,使得系统的作用距离大大降低。Geiger模式的雪崩光电二极管具有单光子级的探测灵敏度,同时输出信号为数字信息,利于大规模集成。以Geiger模式探测器为基础的脉冲飞行时间测距成像系统具有灵敏度高、成像速度快、测距精度高、探测器集成度高、对激光器能量要求低、系统体积小、功耗低等多方面的优势,近年来受到极大关注。目前针对Geiger模式无扫描成像的研究多集中在探测器的制造以及探测器性能改进上,而对整个系统的性能研究开展较少。在分析了基于Geiger模式探测器阵列的激光三维成像系统目前存在的问题后,对基于Geiger模式探测器的激光成像性能及测距精度进行了深入研究。首先根据Geiger模式探测器测距与传统的阈值测距方法的差异,利用传统激光雷达方程和光子统计学理论,研究激光目标回波信号以及系统中存在的各种噪声的统计规律,研究获得了系统的探测性能与系统器件间的量化关系;包括系统的探测概率,虚警概率,最大作用距离,以及探测景深等参数与系统器件参数的关系,为系统设计以及系统性能分析及测距精度分析提供理论基础。在此基础上,进一步研究获得了系统测距精度与激光脉冲宽度,距离门信号以及探测噪声等参数的关系的计算方法。分别对无噪声方波信号以及含噪声的一般脉冲激光信号进行理论分析,得到系统的测距精度与误差随系统器件的变化规律,包括激光回波强度,激光脉冲宽度,目标位置,探测噪声等。分析结果表明目标回波强度和激光脉冲宽度对系统的测距精度具有极大的影响,目标回波强度越强,激光脉冲宽度越窄,所能获得的测距精度越高。利用MonteCarlo方法对误差模型进行了验证,结果与理论分析结果一致。针对Geiger模式探测器的脉冲飞行时间测距方法无法直接获取目标强度信息的缺陷,提出一种利用多脉冲统计获取目标强度信息的方法。理论分析得到了其探测精度以及探测动态范围随统计的探测次数间的关系,结果表明统计探测次数越多,测量精度越高,测量动态范围越大。利用MonteCarlo方法进行了实验验证,获得了与理论相一致的实验结果。针对Geiger模式探测器高灵敏度条件下易受噪声影响的缺点,提出了一种通过多脉冲统计方法提高系统探测概率以及降低系统虚警概率的算法,分析了多脉冲探测时的探测概率以及虚警概率随多脉冲统计的脉冲次数间的联系,结果表明随着统计的脉冲次数的增加,此算法的探测概率与虚警概率均会提高。在统计次数为5次时,在同样的虚警概率条件下,探测概率可以提高一倍以上。利用MonteCarlo方法对理论进行了实验验证,获得了与理论相一致的实验结果。最后改进了PIN阵列探测系统的信号处理电路,建立了模拟Geiger模式激光无扫描三维成像的实验系统,对基于Geiger模式探测器阵列的脉冲三维成像系统的工作原理进行原理性验证,证明了采用Geiger模式探测器阵列的激光三维成像系统的可行性。采用5ns脉冲宽度的激光脉冲和5ns计时精度的计时电路,获得的测距误差小于1.5m。更多还原

【Abstract】 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.更多还原