Direct sequence time correlation photon counting error compensation method

Abstract

The invention discloses a direct sequence time correlation photon counting error compensation method. The method comprises the following specific steps of correcting a photon counting value Rdetect (x, y) detected by corresponding pixels in an xth row and a yth column through area array scanning, calculating the corrected photon counting value according to a formula, and adjusting a fixed optical attenuator corresponding to an A Gerger mode avalanche diode so that a photon counting value Ractual (x, y) corrected by an A Gerger mode avalanche diode arrival time recorder is equal to the number of direct sequence codes 1 and is used as a reference path photon counting value recorded as Rbase;gradually reducing the light intensity of reflection echoes by adjusting a polaroid and a variable optical attenuator, and acquiring N groups of reflection echoes with different light intensities; and setting the number of photons, detected by a B Geiger mode avalanche diode, of the ith group of reflection echoes as Rdet (i). The direct sequence time correlation photon counting error compensation method can compensate depth errors and correct depth images with high precision in real time, and the measurement accuracy is further improved.

Description

technical field [0001] The invention relates to the technical field of laser ranging, in particular to a direct sequence time-correlated photon counting error compensation method. Background technique [0002] In recent years, research on direct-sequence time-correlated photon counting depth imaging systems has been extensively carried out. [0003] First, the existing systems mostly use one channel to transmit direct sequences and the other channel to generate synchronous high level for detection. The problem with this technology is that the high level pulses are often not completely synchronized with the time when the code starts to be sent, especially in When sending a high stream rate, this asynchrony will lead to the offset of the code pattern reconstruction, which will lead to problems such as the broadening of the time-related function waveform and the decrease of depth accuracy; and some use an external phase-locked loop to solve the synchronization problem. For sys...

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Problems solved by technology

[0003] First, the existing systems mostly use one channel to transmit direct sequences and the other channel to generate synchronous high level for detection. The problem with this technology is that the high level pulses are often not completely synchronized with the time when the code starts to be sent, especially in When sending a high stream rate, this asynchrony will lead to the offset of the code pattern reconstruction, which will lead to problems such as the broadening of the time-related function waveform and the decrease of depth accuracy; and some use an external phase-locked loop to solve the synchronization problem. system with sexual problems, the complexity of the hardware system increases

[0004] Second, the accuracy of the system is also one of the key performance parameters. Due to the existence of environmental factors, such as noise and uncertain factors such as target materials, there must be measurement errors in the direct sequence time-correlated photon counting depth imaging method. It has been reported that the The main reason for the error is that there is a "time walking error" or "time jitter" in the photon detector, that is, the more the number of photons detected per unit time, the greater the lead time of the resulting time arrival point, and the higher the system accuracy. Low, in this type of system, due to the "time-walking" effect of the Geiger mode avalanche diode, the time arrival point of multiple photons will shift, which will inevitably lead to the overall displacement of the time correlation function. It is necessary to give the Offset compensation method; while the offset compensation threshold comparison circuit for the Geiger mode avalanche diode itself is too complicated and has poor applicability; simple function fitting method, (such as: Weiji He, Bo yu Sima, Yun fei Chen, Hui dong Dai, Qian Chen, Guohua Gu. A correction method for range walk error in photon counting 3D imaging LIDAR[J]. Optics Communications, 2013, 308(1):211-217. Shanshan shen, Chen Qian, He Weiji, et al al.Boundary evaluation and error correction on Pseudo-randomspread spectrum photon counting system[J].Chinese Optics Letters, 2017, 15(9):090101-1-090101-6.)

Although the depth accuracy can be improved, the variance of the depth offset with low SNR and high SNR has obvious heterogeneity, and the variance of each component of the least square estimator of the parameter is large, resulting in a discrepancy between the estimated value and the real value. The fluctuation increases, that is, the heteroscedasticity in the model makes it no longer have the minimum variance, resulting in a decrease in the estimation accuracy, and the correction of the photon count rate is not considered, so the method is not effective in actual imaging

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