CN110988907B - Doppler compensation based three-dimensional coherent laser radar push-broom imaging method - Google Patents
Doppler compensation based three-dimensional coherent laser radar push-broom imaging method Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/88—Lidar systems specially adapted for specific applications
- G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/483—Details of pulse systems
- G01S7/486—Receivers
- G01S7/487—Extracting wanted echo signals, e.g. pulse detection
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/491—Details of non-pulse systems
- G01S7/493—Extracting wanted echo signals
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Abstract
A Doppler compensation based three-dimensional coherent laser radar push-broom imaging method utilizes the characteristics of simultaneous Doppler speed measurement and distance measurement of a coherent laser radar, uses speed and distance information carried by an echo signal to perform Doppler compensation on a three-dimensional coordinate of a target point cloud, and realizes Doppler compensation three-dimensional push-broom imaging in a push-broom state. And filtering and enhancing the point cloud, improving the imaging quality and finally dynamically displaying the obtained three-dimensional point cloud. The invention uses the laser radar coherent detection method, contains all advantages of coherent detection, and has higher signal conversion gain and higher detection sensitivity compared with the traditional direct detection method. Compared with the traditional side-view push-broom technology, the invention can utilize Doppler frequency shift to finish speed detection. The method saves an additional speed detector, is easy to realize, and has wide application prospect.
Description
Technical Field
The invention relates to the field of laser radar imaging and unmanned driving, in particular to a Doppler compensation-based three-dimensional coherent laser radar push-scanning imaging method.
Background
In the 60's of the 20 th century, a laser radar push-scan scanning mode was proposed for the first time and used in Airborne laser depth detection [ Gary C Guenther, Mark W Brooks, Paul E LaRocque. New Capabilities of the "SHOALS" air radar Bathmeter [ J ]. Remote Sensing of environmental, 2000,73(2) ], which has the characteristics of high resolution, wide field of view, and fast imaging, and the detection resolution and imaging rate of the laser radar can be greatly improved. In 1988, Japanese UCHU KAIHATSU JIGYO proposed the concept of push-scan scanning for satellite remote sensors [ Barry S, Mark G, Dale R, et al. push-zoom scanning sensor for aircraft or aircraft specific satellite [ C ]. Proc. of SPIE,1999,3707: 421-. The United states Lincoln Laboratory in 2003 proposed specific embodiments of airborne array arrangement Three-dimensional lidar push-broom [ Aull B F, Loomis A H, Young D J, et al. Geiger-mode Avalanche Photodiodes for Three-dimensional Imaging [ J ]. Lincoln Laboratory Journal,2002,13(2):335-350.], in the past 5 years, the push-broom scanning method has been widely used in aerospace missions such as ICESat-2 and LIDAR SURFACE TOPOGRAPHY (LIST) transmitted by NASA [ Dabney, P., Harding, D., Abshire, J., Huss, T., Jodor, G., Machan, R., Marzouk, J., Rush, K., Seas, A., Shuman, C., Xiioli Sun, Valett, S., Vasiliev, A., Yu, A., Yunhui Zheng, the Slope Imaging Multi-poling Photon-healing Lidar: development and performance stresses [ P ]. Geoscience and Remote Sensing Symposium (IGARSS),2010IEEE International,2010.
At present, the main application scene of the laser radar push-scan scanning mode is airborne satellite-borne ground scanning or satellite remote sensing detection. Their common feature is that the detection direction of the lidar is orthogonal to the direction of the pushing motion. When the scanning track and the target three-dimensional point cloud are imaged, the movement speed of the laser radar is indispensable, but the physical quantity can only be read from an additionally installed speed detector.
Disclosure of Invention
The invention provides a Doppler compensation based three-dimensional coherent laser radar push-scan imaging method, aiming at the defect that the conventional laser radar push-scan imaging method cannot automatically detect the movement speed of a laser radar. The method utilizes the characteristic that the coherent laser radar can simultaneously carry out Doppler velocity measurement and distance measurement to realize three-dimensional push-broom imaging based on Doppler compensation in a motion state. For the relative movement in the beam direction, the invention utilizes the Doppler frequency shift of the laser wavelength to carry out real-time detection on the movement speed of the laser wavelength, and carries out point-by-point movement compensation to remove the image stretching and distortion generated by the relative movement in the pushing scanning.
This approach is particularly well suited for axial motion push-broom imaging, as compared to other approaches. The three-dimensional coherent laser radar push-scanning imaging technology based on Doppler compensation has the advantages that: the method can directly utilize Doppler frequency shift without an additional speed detector, solves the pushing speed in the laser radar beam direction, and directly compensates the point cloud image stretching and distortion generated by pushing scanning. In addition, this approach uses coherent detection techniques, which include all the advantages of coherent detection.
The technical solution of the invention is as follows:
a Doppler compensation based three-dimensional coherent laser radar push-scanning imaging method comprises the following steps:
1) establishing a laser radar initial state coordinate system and a laser radar motion coordinate system: abstracting the laser radar to one point and taking the initial position of the laser radar as the origin of coordinates O l Establishing a stationary coordinate system x using the right-hand rule l y l z l O l After the time of delta t, the moving coordinate system where the laser radar is located takes the speed as
Straight line motion to x' l y′ l z′ l O′ l Wherein the speed
Direction of (a) and z l Positive direction of axis is same, origin of coordinates O' l Is the real-time position of the laser radar push state;
2) obtaining the distance L between the moving laser radar and the static target point in a real-time state, wherein the azimuth angle of an emergent beam is theta, and the pitch angle of the emergent beam is theta
3) And (3) solving a compensation quantity according to the corresponding relation between the laser radar moving speed and the Doppler frequency shift: the laser radar moving speed and the laser Doppler frequency shift are in the following relationship:
v＝f d λ/2
when the laser radar moving speed v is positive, the laser radar is close to a target object; when the laser radar moving speed v is negative, the laser radar is far away from the target object;
therefore, when the laser radar does variable speed movement, the laser radar speed value v obtained by each point is used i Multiplying the time interval Δ t of each point by a distance compensation amount corresponding to the time interval between each point and the previous point, where the distance compensation amount in the laser radar motion direction of the ith point of the laser radar scan × vdt is:
∫vdt＝v 1 Δt+v 2 Δt+···+v i Δt
4) writing out a point cloud space coordinate: scanning point spatial coordinates for time t
Comprises the following steps:
wherein,
and
respectively a rotation matrix and a translation matrix generated during the transformation of a coordinate system, delta is the angle of the laser radar rotating in the counterclockwise direction when viewed from the top, and is 0 here,
respectively, x between the lidar and the target object l 、y l 、z l Relative speed in direction, here
Is a non-volatile organic compound (I) with a value of 0,
the distance compensation quantity is obtained according to the Doppler frequency shift in the step 3);
the laser radar motion speed v obtained by using the laser doppler frequency shift of the receiving and transmitting laser can be represented as follows:
for a certain time period τ, the acquired set of spatial points may be written as:
and the point set sigma P forms the final point cloud image.
The invention has the following characteristics:
1. the echo signals carry signal frequency shift information, and are converted into motion speed information according to the Doppler effect, so that image correction motion compensation can be directly carried out, and independent detection is not needed.
2. This approach is particularly well suited for axial motion push-broom imaging, as compared to other approaches.
The invention has the technical effects that:
1. the invention can directly utilize Doppler frequency shift without an additional speed detector, solves the pushing speed in the laser radar beam direction to obtain, and directly compensates the point cloud image stretching and distortion generated by pushing scanning.
2. The present invention uses coherent detection techniques, which include all the advantages of coherent detection.
Drawings
FIG. 1 is a schematic diagram of a laser radar push-broom imaging coordinate system of the present invention;
FIG. 2 is a functional block diagram of the present invention;
fig. 3 is a block diagram of one embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following drawings and examples, but the scope of the present invention should not be limited thereto.
FIG. 1 is a schematic diagram of a laser radar push-broom imaging coordinate system according to the present invention.
FIG. 2 is a schematic block diagram of the present invention, and the Doppler compensation-based three-dimensional coherent lidar push-scanning imaging method of the present invention comprises the following steps:
1) establishing a laser radar initial state coordinate system and a laser radar motion coordinate system: abstracting the laser radar to one point and taking the initial position of the laser radar as the origin of coordinates O l Establishing a stationary coordinate system x using the right-hand rule l y l z l O l After the time of delta t, the moving coordinate system where the laser radar is located takes the speed as
Straight line motion to x' l y′ l z′ l O′ l Wherein the speed
Direction of (a) and z l Positive direction of axis is same, origin of coordinates O' l The real-time position of the laser radar push state. The change of the pitching attitude of the laser radar in the motion process is not considered;
2) obtaining the distance L between the moving laser radar and the static target point, the azimuth angle theta of the emergent beam and the pitch angle of the emergent beam in real time
3) And (3) solving a compensation quantity according to the corresponding relation between the laser radar moving speed and the Doppler frequency shift: the laser radar moving speed and the laser Doppler frequency shift are in the following relationship:
v＝f d λ/2
when the laser radar moving speed v is positive, the laser radar is close to a target object; and when the laser radar moving speed v is negative, the laser radar is far away from the target object.
Therefore, when the laser radar does variable speed movement, the laser radar speed value v obtained by each point is used i The time interval at each point is multiplied by the distance compensation amount corresponding to the time interval between each point and the previous point. The distance compensation amount ^ vdt of the ith point of laser radar scanning in the laser radar motion direction is:
∫vdt＝v 1 Δt+v 2 Δt+···+v i Δt
4) writing out a point cloud space coordinate: a laser radar motion coordinate system x 'of a certain position point P on a scanning target at the moment t' l y′ l z′ l O′ l In the above, there are:
the coordinates of the point in the initial stationary coordinate system of the laser radar at the time 0 are:
so for a certain scanning point P the coordinates in the laser radar initial coordinate system
Comprises the following steps:
wherein,
and
respectively a rotation matrix and a translation matrix generated when the coordinate system is transformed. Delta is the angle of the laser radar rotating in the counterclockwise direction when looking down,here, the number of the lines is 0,
respectively, x between the lidar and the target object l 、y l 、z l Relative speed in direction, here
Is a non-volatile organic compound (I) with a value of 0,
the distance compensation quantity is obtained according to the Doppler frequency shift in the step 3);
therefore, for the situation of the present invention, the laser radar motion velocity v obtained by using the doppler shift of the transmitted and received laser, the coordinates of any scanning point are expressed as:
for a certain time period τ, the acquired set of spatial points may be written as
And the point set sigma P forms the final point cloud image.
FIG. 3 is a scanning diagram of an embodiment of the present invention. As can be seen from the figure, the laser emitted by the laser radar is guided by the scanner to be scanned in a circular ring shape. When the laser radar scanning module moves linearly to the right, the radius of the scanning ring is gradually reduced, and then the target is scanned layer by layer from the outer edge to the center.
Another embodiment of the invention may be an intra-tunnel scan probe. And when the scanning system passes through the tunnel, the scanning rings pass through the inner wall of the tunnel layer by layer to finish detection.
The present specification has completed a detailed description of a three-dimensional coherent lidar push-scanning imaging method based on doppler compensation.
Those skilled in the art will appreciate that the invention may be practiced without such specific details.
Claims (1)
1. A Doppler compensation based three-dimensional coherent laser radar push-scanning imaging method is characterized in that: the method comprises the following steps:
1) establishing a laser radar initial state coordinate system and a laser radar motion coordinate system: abstracting the laser radar to one point and taking the initial position of the laser radar as the origin of coordinates O l Establishing a stationary coordinate system x with the right-hand rule l y l z l O l After the time of delta t, the moving coordinate system where the laser radar is located takes the speed as
Linear motion to x l 'y l 'z l 'O l ', speed therein
Direction of (a) and z l The positive direction of the axis is the same, and the origin of coordinates O l ' is the real-time position of the laser radar push state;
2) obtaining the distance L between the moving laser radar and a static target point in a real-time state, wherein the azimuth angle of an emergent beam is theta, and the pitch angle of the emergent beam is
3) And (3) solving a compensation quantity according to the corresponding relation between the laser radar moving speed and the Doppler frequency shift: laser radar moving speed
The Doppler frequency shift of the transmitting and receiving laser is in the following relation:
v＝f d λ/2
when the laser radar moving speed v is positive, the laser radar is close to the target object; when the movement speed v of the laser radar is negative, the laser radar is far away from the target object;
therefore, when the laser radar does variable speed movement, the laser radar speed value v obtained by each point is used i Multiplying the time interval Δ t of each point by a distance compensation amount corresponding to the time interval between each point and the previous point, where the distance compensation amount in the laser radar motion direction of the ith point of the laser radar scan × vdt is:
∫vdt＝v 1 Δt+v 2 Δt+…+v i Δt
4) writing out a point cloud space coordinate: scanning point spatial coordinates for time t
Comprises the following steps:
wherein,
and
respectively a rotation matrix and a translation matrix generated during the transformation of a coordinate system, wherein delta is the rotation angle of the laser radar in the overlooking and anticlockwise direction and is 0;
the laser radar motion speed v obtained by using the laser doppler frequency shift of the receiving and transmitting laser can be represented as follows:
for a certain time period τ, the acquired set of spatial points may be written as:
and the point set sigma P forms the final point cloud image.
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