Gm-APD array lidar imaging method and system under strong background noise

Abstract

The disclosure discloses a Gm-APD array lidar imaging method under strong background noise, comprising following steps: respectively acquiring two sets of cumulative detection data of the Gm-APD array lidar at two different opening times of a range gate of the Gm-APD array lidar under strong background noise; respectively performing a statistic operation on the two sets of cumulative detection data of the Gm-APD array lidar with respect to all pixels, to obtain two cumulative detection result histograms of the Gm-APD array lidar; determining a range interval of the imaging target according to the two cumulative detection result histograms; and acquiring a lidar image by a peak discrimination method in the range interval of the imaging target. The Gm-APD array lidar imaging method according to the present disclosure is capable of improving the laser image quality by eliminating the interference of strong background noise in other range intervals.

Claims

1. A Gm-APD array lidar imaging method under strong background noise, the imaging method comprising following steps: (1) respectively acquiring, by the Gm-APD array lidar, first and second sets of cumulative detection data at two different opening times of a range gate of the Gm-APD array lidar under strong background noise, wherein the two different opening times are such that the first sets of cumulative detection data is acquired when an imaging target is located in the range gate, and the second sets of cumulative detection data is acquired when the imaging target is located out of the range gate; (2) respectively performing a statistic operation on the first and second sets of cumulative detection data with respect to all pixels, to obtain first and second cumulative detection result histograms of the Gm-APD array lidar; (3) determining a range interval of the imaging target according to the first and second cumulative detection result histograms; and (4) acquiring range and intensity information of the imaging target with respect to the respective pixels by using a peak discrimination method in the range interval of the imaging target, to obtain a lidar image.

2. The imaging method according to claim 1, wherein the lidar image includes a multi-pulse laser range image and a multi-pulse laser intensity image of the imaging target.

3. The imaging method according to claim 1, wherein in the first and second cumulative detection result histograms of the Gm-APD array lidar, the abscissa represents a range value, and the ordinate represents a detection result count value at a respective range value.

4. The imaging method according to claim 1, wherein the step (3) comprises: subtracting a detection result count value at a respective range value in the second cumulative detection result histogram from a detection result count value at a corresponding range value in the first cumulative detection result histogram to obtain a count difference histogram; acquiring a target interval result histogram according to the count difference histogram in such a way that if a result at a range value in the count difference histogram is larger than a preset threshold T.sub.1, the result at the range value is set to 1; otherwise, the result at the range value is set to 0; and traversing the target interval result histogram, if there are a plurality of consecutive range values where results are 1 and a number of the range values is larger than a preset threshold T.sub.2, retaining the results at the range values; otherwise, setting the results at the range values to be 0.

5. The imaging method according to claim 2, wherein in the peak discrimination method, a range value for a peak value in the first cumulative detection result histogram is used as a corresponding range value in the multi-pulse laser range image, and a sum of detection result count values within an envelope of the peak value is used as a corresponding gray value in the multi-pulse laser intensity image.

6. A Gm-APD array lidar imaging system under strong background noise, the imaging system comprising: a detection data acquisition module configured to acquire first and second sets of cumulative detection data of the Gm-APD array lidar at two different opening times of a range gate of the Gm-APD array lidar under strong background noise; a detection result histogram statistics module configured to respectively perform a statistic operation on the first and second sets of cumulative detection data of the Gm-APD array lidar with respect to all pixels, to obtain first and second cumulative detection result histograms of the Gm-APD array lidar; an imaging target range interval determination module configured to determine a range interval of the imaging target according to the first and second cumulative detection result histograms; and a lidar imaging module configured to acquire a lidar image by using a peak discrimination method within the range interval of the imaging target.

7. The imaging system according to claim 6, wherein the first and second sets of cumulative detection data are respectively acquired when the imaging target is located in and out of the range gate of the Gm-APD array lidar.

8. The imaging method according to claim 7, wherein the lidar image includes a multi-pulse laser range image and a multi-pulse laser intensity image of the imaging target.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a visible light image of a building to be imaged according to an embodiment of the present disclosure.

(2) FIG. 2 is a flowchart of a Gm-APD array lidar imaging method under strong background noise according to the embodiment of the present disclosure.

(3) FIG. 3 is a laser range image of the building shown in FIG. 1 obtained by the Gm-APD array lidar in one detection.

(4) FIG. 4 is a schematic diagram of acquiring two sets of cumulative detection data by the Gm-APD array lidar at two different opening times of a range gate according to the embodiment of the present disclosure.

(5) FIG. 5 is a cumulative detection result histogram of the two sets of cumulative detection data according to the embodiment of the present disclosure.

(6) FIG. 6 is a count difference histogram of the two sets of cumulative detection data according to the embodiment of the present disclosure.

(7) FIG. 7 is a target interval result histogram according to the embodiment of the present disclosure.

(8) FIG. 8 is a final target interval result histogram according to the embodiment of the present disclosure.

(9) FIG. 9(a) is a range image obtained by the GMD-APD array lidar under strong background noise according to the embodiment of the present disclosure.

(10) FIG. 9(b) is an intensity image obtained by the GMD-APD array lidar under strong background noise according to the embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(11) For clear understanding of the objectives, features and advantages of the present disclosure, detailed description of the present disclosure will be given below in conjunction with accompanying drawings and specific embodiments. It should be noted that the embodiments described herein are only meant to explain the present disclosure, and not to limit the scope of the present disclosure. Furthermore, the technical features related to the embodiments of the present disclosure described below can be mutually combined if they are not found to be mutually exclusive.

(12) The present disclosure provides a Gm-APD array lidar imaging method and system under strong background noise, the overall idea of which is as follows: in the detection result histograms of data obtained at different range gate positions in a certain time, the background noise and system internal noise have a similar distribution, but significantly different distribution is presented in a range interval of the target, so that the range interval of the target can be determined according to two sets of lidar data respectively obtained when the target is located in and out of the range gate, and when the laser range image and intensity image are generated, noise interference in other range intervals can be eliminated, thereby achieving noise suppression and improving the image quality.

(13) FIG. 1 is a visible light image of a scene where a building target is located according to the embodiment of the present disclosure. The Gm-APD array lidar imaging method under strong background noise according to the present disclosure will be described in detail below with reference to an example of the ground building shown in FIG. 1 (Laser data comes from the team of Jianfeng Sun in Harbin Institute of Technology).

(14) The present disclosure provides a Gm-APD array lidar imaging method under strong background noise, as shown in FIG. 2, and the imaging method comprises following steps:

(15) (1) Acquiring, by the Gm-APD array lidar, two sets of cumulative detection data at two different opening times of a range gate of the Gm-APD array lidar under strong background noise.

(16) Specifically, in this embodiment, two sets of laser image data were acquired by using a Gm-APD array lidar at a height of 46 meters and a distance of 2 km from the building target, and each set of laser image data includes 400 frames of laser images. As shown in FIG. 3, the collected laser images each have a size of 64×64 and a range resolution of 0.18 m. Cumulative detection data 1 and cumulative detection data 2 are respectively acquired when the target is located in and out of the range gate, and the range gate positions are shown in FIG. 4.

(17) (2) Respectively performing a statistic operation on the two set of cumulative detection data with respect to all pixels to obtain two cumulative detection result histograms of the Gm-APD array lidar.

(18) In the cumulative detection result histograms of the Gm-APD array lidar, the abscissa represents a range value, and the ordinate represents a detection result count value at a respective range value. A cumulative detection result histogram 1 is obtained from the cumulative detection data 1, as shown in data 1 in FIG. 5, and a cumulative detection result histogram 2 is obtained from the cumulative detection data 2, as shown in data 2 in FIG. 5.

(19) (3) Acquiring a range interval of a target according to the two cumulative detection result histograms.

(20) The method of acquiring the range interval of the target is specifically as follow.

(21) The cumulative detection result histogram 1 is obtained when the imaging target is located in the range gate, the cumulative detection result histogram 2 is obtained when the imaging target is located out of the range gate, and the detection result count value at a respective range value in the cumulative detection result histogram 2 is subtracted from the detection result count value at a corresponding range value in the cumulative detection result histogram 1 to obtain a count difference histogram, as shown in FIG. 6.

(22) A target interval result histogram is obtained according to the count difference histogram in such a way that if a result at a range value in the count difference histogram is larger than a preset threshold T.sub.1, the result at the range value is set to 1; otherwise, the result at the range value is set to 0, as shown in FIG. 7.

(23) The target interval result histogram is traversed, and if there are a plurality of consecutive range values where results are 1 and a number of the range values is larger than a preset threshold T.sub.2, the results at the range values are retained; otherwise, the results at the range values are set to 0, as shown in FIG. 8.

(24) T.sub.1 and T.sub.2 are preset thresholds, and can be determined according to actual requirements. In this embodiment, the preset threshold T.sub.1 is preferably 200, and the preset threshold T.sub.2 is preferably 1.

(25) (4) Acquiring range and intensity information of the imaging target with respect to the respective pixels by using a peak discrimination method in the range interval of the imaging target, to obtain a laser range image and a laser intensity image, in which a range value for a peak value in the cumulative detection result histogram is used as a corresponding range value in the multi-pulse laser range image, and a sum of detection result count values within an envelope of the peak value is used as a corresponding gray value in the multi-pulse laser intensity image, as shown in FIGS. 9(a) and 9(b).

(26) Two sets of laser data with the imaging target in and out of the range gate of the lidar are acquired, a range interval of the imaging target is determined according to the characteristic that detection result statistics histograms of the two sets of laser data have a large difference in the range interval of the target, and imaging is performed by a range restoration algorithm in the range interval, in which the interference of strong background noise in other range intervals is eliminated, thereby improving the laser image quality. In the laser range image, the range information of the target surface is more complete, and the range information restoration effect is significant. In the laser intensity image, the background noise is suppressed while ensuring the intensity of the target echo, and the contrast between the target area and the background area in the image is improved.

(27) Specifically, the imaging target is respectively located in and out of the range gate of the Gm-APD array lidar.

(28) Specifically, in the cumulative detection result histograms of the Gm-APD array lidar, the abscissa represents a range value, and the ordinate represents a detection result count value at a respective range value in the cumulative detection process.

(29) The present disclosure further provides a Gm-APD array lidar imaging system under strong background noise, and the imaging system includes a detection data acquisition module configured to acquire two sets of cumulative detection data of the Gm-APD array lidar at two different opening times of a range gate of the Gm-APD array lidar under strong background noise; a detection result histogram statistics module configured to respectively perform a statistic operation on the two sets of cumulative detection data of the Gm-APD array lidar with respect to all pixels, to obtain two cumulative detection result histograms of the Gm-APD array lidar; an imaging target range interval determination module configured to determine a range interval of the imaging target according to the two cumulative detection result histograms; and a lidar imaging module configured to acquire a lidar image by using a peak discrimination method within the range interval of the imaging target.

(30) Specifically, the two sets of cumulative detection data are respectively acquired when the imaging target is located in and out of the range gate of the Gm-APD array lidar.

(31) Specifically, the lidar image includes a multi-pulse laser range image and a multi-pulse laser intensity image of the imaging target.

(32) It should be readily understood to those skilled in the art that the above description is only preferred embodiments of the present disclosure, and does not limit the scope of the present disclosure. Any change, equivalent substitution and modification made without departing from the spirit and scope of the present disclosure should be included within the scope of the protection of the present disclosure.