Research On High Range Accuracy Hybrid Three Dimensional Laser Imaging Based On Streak Array Detecting And Single-photon Counting

Lidar has been widely used in target three dimensional(3D)reconstruction,topographic mapping,underwater detection,and so on in recent years.However,there is a commom problem in the practical applications,because of the variation of targets' reflection and the atmospheric transmission characteristics,the intensity of echo signals has a large dynamic range with 2-3 orders of magnitud.The traditional lidar cannot give the consideration to both the saturation when detecting strong signals and the nonresponse when detecting weak signals,which will lead to the decrease of the range accuracy in large dynamic range measurement.To solve this problem,a hybrid three dimensional laser imaging technique is present in this paper based on the theoretical and experimental studies of signal intensity,measuring system and range accuracy.Processing of the echo signals is the key to achieve high-accuracy imaging result in large dynamic range mesasurement,which is related to the detection system of lidar.Currently,waveforem sampling lidar and time-correlated single-photon counting(TCSPC)lidar are two kinds of most watched lidar detection systems.In this paper,the influence of echo signal intensity on the range accuracy of the two kinds of lidars is studied.The waveform sampling system uses array detectors,which has the advantages of high equivalent integration.When the echo signal is strong,the measurement results with high range accuracy can be obtained.However,when the echo signal is strong,because the waveform sampling technology needs the echo signal with high signal-to-noise ratio to ensure the range accuracy,the low signal-to-noise ratio will lead to low range accuracy,even the range result cannot be obtained.TCSPC technique has the advantage of high sensitivity,we can use milliwatt laser to detect the target at a distance of 10 km.When the detection probability is less than 0.1,the distance accuracy can reach the centimeter level.However,when the echo signal is strong(e.g.the echo is more than 10 photons),there will appear a pile up phenomenon in TCSPC lidar detection process,which will lead to range walk error.According to the advantages and disadvantages of the two kinds of lidars,a new three-dimensional imaging technology based on streak array detection technology and TCSPC technology is proposed in this paper.Based on the working principle and composition structure of STIL system,and adopting lidar equation,the theoretical expression of intensity of echo signal on one pixel of CCD(charge coupled device)is derived.And also,the expression is corrected on the basis of analysis on the working system,target reflection characteristics and some other factors.Then the research on sensitivity of STIL system is carried out in two aspects,the maximum working distance and the dynamic range of response to the intensity of echo signals.The result shows that STIL system has the potential for long range detection,however,when the echo signal is weak,the range accuracy will be reduced.The dynamic range of STIL system is not great enough to meet the measurement requirement under the condition of large dynamic range.Based on the working principle and composition structure of TCSPC lidar system,and adopting lidar equation,the theoretical expression of intensity of echo signals reaching the detector is derived,and the research on sensitivity of TCSPC lidar is carried out.Besides,the cause of range walk error when detecting strong echo signal is analyzed in principle.A Gaussian curve is utilized to fit the rising edge of signal obtained by a PMT(photomultiplier tube),and the probability of photon event is calculated on every time interval in one signal period,the width of time interval is determined by the time bin size.An expression of target distance is presented,which can be used to calculate the range walk error.A correction method is proposed on the basis of the computational equation of the range error.At last,a series of optical range experiments are carried out in order to validate the feasibility of the correction method.In this paper,the experimental study of the hybrid laser three-dimensional imaging technology based on streak array detecting technology and TCSPC technology is carried out.An indoor three-dimensional imaging experiment was carried out for a target with different reflection characteristics.The experimental results show that the high range accuracy three-dimensional image of echo signal can be obtained by using the hybrid three-dimensional imaging technology under the condition of large dynamic range.Range accuracy is one of the most critical issues to evaluate the quality of a lidar.This paper presents a three-laser-beam scheme to improve the range accuracy of the hybrid lidar system.Besides the main measuring laser beam(Beam A),the first aid beam(Beam B)is used to decrease the error caused by the system time jitter.The second aid beam(Beam C)has an n+0.5 time bins' difference with the main measuring laser beam,and it is used to decrease the range error caused by discrete sampling process.At first,three-laser-beam STIL system is researched,the time jitter and the effect of Beam B on decreasing range error are analyzed.The generation process of discrete sampling error is described,and the effect of Beam C on decreasing the discrete sampling error is analyzed in theory.A 3D imaging experiment validates that the improvement of the range accuracy is significant using three-laser-beam STIL system.Then,three-laser-beam TCSPC lidar system is researched,and the influence of laser pulse width and time bin size is analyzed.At last,three-laser-beam hybrid lidar system is studied in this paper,the effect of three-laser-beam scheme is discussed when the steak tube imaging system and TCSPC system have different time bin sizes.The optimum range of time bins difference between STIL system and TCSPC system is determined by simulation calculation.