Vehicle-mounted ranging device and method

Abstract

A kind of vehicle-mounted ranging device and method, belong to distance detection technical field, device is by short coherence broadband light source, fiber coupler, wavelength division multiplexer, beam expander, optical splitter, lens, filter, area array camera and vehicle-mounted computer etc.; by vehicle-mounted computer real-time comparison two cameras image difference and the size of set threshold value, when vehicle-mounted computer determines that image difference is greater than threshold value, then it is explained that there is obstacle at the distance L in front of vehicle, vehicle-mounted computer issues alarm signal at this time.The present application adopts two light sources and two cameras, imaging twice in the same time, by the two images obtained are subtracted, eliminate interference fluctuation;The present application uses short coherence light interference technology, improves signal-to-noise ratio, can detect weak reflection signal;The present application selects broadband light source, longitudinal resolution is high, guarantees measurement accuracy while saves extra timing circuit;The present application uses area array camera to collect image, speed is fast, the number of imaging dot matrix is large, and lateral resolution is high.

Description

Technical Field

[0001] This invention belongs to the field of distance detection technology, and in particular relates to a vehicle-mounted ranging device and method. Background Technology

[0002] To support autonomous driving capabilities, vehicles typically require onboard LiDAR (Light Detection and Ranging) systems. As a crucial sensor, onboard LiDAR plays a vital role in determining vehicle detection range and collision avoidance warning functions. Currently, commonly used ranging methods for onboard LiDAR include Time-of-Flight (TOF) and Amplitude Modulated Continuous Wave (FMCW) methods.

[0003] For the Time-of-Flight (TOF) method, the distance to the target is obtained by measuring the time interval between the emitted pulse and the target echo pulse, i.e., the round-trip time T of the laser pulse from the laser to the target. Multiplying T / 2 by the speed of light c yields the target distance. However, TOF requires a highly sophisticated clock circuit and a laser emission circuit with extremely narrow pulse widths, leading to significant development challenges. When used for short-distance measurements, the extremely high speed of light and the very short pulse flight time limit its measurement accuracy.

[0004] For amplitude-modulated continuous wave (FMCW) light modulation, a phase difference is created in the light intensity waveform as it travels from the object back to the detector. By measuring this phase difference, the time of flight of the light can be obtained, and thus the flight distance can be deduced. However, FMCW places more stringent requirements on the optical modulation and receiving systems, has a longer measurement time, is more difficult to implement using circuitry, is susceptible to noise interference, and suffers from inherent limitations such as distance ambiguity.

[0005] In addition, existing vehicle-mounted LiDAR systems are generally based on point-by-point scanning imaging, which results in drawbacks such as slow speed and low resolution. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a vehicle-mounted ranging device and method. It employs two light sources and two cameras to image twice simultaneously. By subtracting the two images, interference fluctuations can be further eliminated. This invention uses short-coherence optical interferometry, effectively improving the signal-to-noise ratio and enabling the detection of weak reflected signals. This invention selects a broadband light source to achieve high-precision longitudinal resolution, eliminating the need for additional timing circuitry while ensuring measurement accuracy. This invention uses an area array camera to acquire images, featuring high speed, a large number of imaging points, and high lateral resolution.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a vehicle-mounted ranging device, comprising a first short-coherence broadband light source, a first fiber coupler, a second short-coherence broadband light source, a second fiber coupler, a first wavelength division multiplexer (WDM), a second WDM, a first beam expander, a second beam expander, a first beam splitter, a second beam splitter, a first lens, a first filter, a first area array camera, a second lens, a second filter, a second area array camera, and a vehicle-mounted computer; the first short-coherence broadband light source is optically connected to the first fiber coupler via an optical fiber, the first fiber coupler has two outputs, the first output is optically connected to the first WDM multiplexer via an optical fiber, and the second output is optically connected to the second WDM multiplexer via an optical fiber; the second short-coherence broadband light source is optically connected to the second fiber coupler via an optical fiber, the second fiber coupler has two outputs, the first output is optically connected to the first WDM multiplexer via an optical fiber, and the second output is optically connected to the second WDM multiplexer via an optical fiber. The multiplexer establishes an optical connection; the first wavelength division multiplexer emits a probe beam, which is sequentially directed to the surface of the object under test via a first beam expander and a first beam splitter. The probe beam reflected from the surface of the object under test is then directed to a second beam splitter via the first beam splitter. The second wavelength division multiplexer emits a reference beam, which is directed to a second beam splitter via a second beam expander. The probe beam reflected from the surface of the object under test and the reference beam emitted from the second wavelength division multiplexer are combined by the second beam splitter and then split into two beams. The first beam is directed to a first area array camera via a first lens and a first filter, and the second beam is directed to a second area array camera via a second lens and a second filter. Both the first and second area array cameras are electrically connected to an onboard computer. The first area array camera acquires a first interferometric image, and the second area array camera acquires a second interferometric image. The onboard computer demodulates the first and second interferometric images.

[0008] A vehicle-mounted ranging method, employing the aforementioned vehicle-mounted ranging device, includes the following steps:

[0009] Step 1: Activate the first and second short-coherence broadband light sources. The probe light is emitted from the first wavelength division multiplexer, and the reference light is emitted from the second wavelength division multiplexer. The probe light is directed toward the surface of the object under test through the first beam expander and the first beam splitter in sequence. The probe light reflected from the surface of the object under test is directed toward the second beam splitter through the first beam splitter. The reference light is directed toward the second beam splitter through the second beam expander. The probe light and the reference light are combined by the second beam splitter and then emitted as two beams. The first beam is directed toward the first area array camera through the first lens and the first filter in sequence. The second beam is directed toward the second area array camera through the second lens and the second filter in sequence.

[0010] Assuming the linewidth of low-coherence light is Δλ and the wavelength is λ, then L C =λ 2 / Δλ, where L CThe coherence length is L; therefore, the coherence length L between the probe and reference beams is only near the equipathic plane. C Interference occurs within the range;

[0011] Let L be the distance between the equioptic surface and the vehicle-mounted ranging device. When the measured object appears near the equioptic surface, the coherence length L is... C Within the range, the probe light and the reference light interfere; when the object being measured appears near the equioptic path surface, the coherence length L... C When outside the range, the probe light and the reference light do not interfere;

[0012] Step 2: Camera gain calibration; for coherence length L C When the measured object outside the range is imaged by the first array camera and the second array camera, the relative gain of the camera is defined as k(x,y)=MEAN(I2(x,y)) / MEAN(I1(x,y)), where MEAN represents the average of the images at each point, I1(x,y) represents the image acquired by the first array camera, and I2(x,y) represents the image acquired by the second array camera.

[0013] Step 3: During vehicle movement, images are rapidly and continuously acquired by the first and second array cameras. Assuming an object is detected in front of the vehicle, when the surface of the object enters the coherence length L... C Within the range, the first array camera acquires the interference image I1(x,y;i), and the second array camera acquires the interference image I2(x,y;i). The expressions for the interference images I1(x,y;i) and I2(x,y;i) are as follows:

[0014] ①、

[0015] ②、

[0016] In the formula, I1(x,y;i) represents the coherence length L of the surface of the measured object. C The first probe beam image is within the range, where I2(x,y;i) represents the coherence length L of the surface of the measured object. C The first reference beam image is within the range, and I′1(x,y;i) ​​represents the coherence length L of the surface of the measured object. C The image of the second probe beam is within the range, where I′2(x,y;i) ​​represents the coherence length L of the surface of the measured object. C The second reference beam image within the range, where L(x,y;i) ​​represents the optical path, λ c1 λ represents the center wavelength of the first short-coherent broadband light source. c2 Let i represent the center wavelength of the second short-coherent broadband light source; where i represents t i Images captured in real time;

[0017] When the surface of the object being measured does not enter the coherence length L C Within the range, the reference light and the probe light do not interfere with each other. Image I3(x,y;i) is acquired by the first array camera, and image I4(x,y;i) is acquired by the second array camera. The expressions for images I3(x,y;i) and I4(x,y;i) are as follows:

[0018] ①、I3(x,y;i)=I 11 (x,y;i)+I 21 (x, y; i)

[0019] ②、I4(x,y;i)=I' 12 (x,y;i)+I' 22 (x, y; i)

[0020] In the formula, I 11 (x, y; i) indicates that the surface of the measured object has not entered the coherence length L. C The first probe light image within range, I 21 (x, y; i) indicates that the surface of the measured object has not entered the coherence length L. C The first reference light image within the range, I′ 12 (x, y; i) indicates that the surface of the measured object has not entered the coherence length L. C The image of the second probe beam within the range, I′ 22 (x, y; i) indicates that the surface of the measured object has not entered the coherence length L. C The second reference beam image within the range; where i represents t i Images captured in real time;

[0021] When the surface of the measured object 18 enters the coherence length L C When within the specified range, the following calculation formula applies:

[0022] S(x,y;i)=k(x,y)·I1(x,y;i)-I2(x,y;i)

[0023] In the formula, k(x,y) represents the relative gain of the camera. Substituting the expressions for the interferometric images I1(x,y;i) ​​and I2(x,y;i) ​​into the formula, we can obtain the following expression:

[0024]

[0025] In the formula, S(x,y;i) ​​represents the image difference between the interference image I1(x,y;i) ​​and the interference image I2(x,y;i), and λ c1 ≠λ c2 Therefore, S(x,y;i)≠0;

[0026] When the surface of the object being measured does not enter the coherence length L C When within the specified range, the following calculation formula applies:

[0027] S'(x,y;i)=k(x,y)·I3(x,y;i)-I4(x,y;i)

[0028] In the formula, k(x,y) represents the relative gain of the camera. After substituting the expressions of image I3(x,y;i) ​​and image I4(x,y;i), we can get S′(x,y;i)≈0; where S′(x,y;i) ​​represents the image difference between image I3(x,y;i) ​​and image I4(x,y;i).

[0029] A threshold is set based on the system signal-to-noise ratio. The onboard computer compares S(x,y;i) with the threshold in real time. When the onboard computer determines that S(x,y;i) is greater than the threshold, it indicates that there is an obstacle at a distance L in front of the vehicle. At this time, the onboard computer issues an alarm signal.

[0030] The beneficial effects of this invention are:

[0031] The vehicle-mounted ranging device and method of the present invention employs two light sources and two cameras to image twice within the same time. By subtracting the two images, interference fluctuations can be further eliminated. The present invention uses short coherence optical interferometry, which effectively improves the signal-to-noise ratio and can detect weak reflection signals. The present invention selects a broadband light source to achieve high-precision longitudinal resolution, which eliminates the need for additional timing circuits while ensuring measurement accuracy. The present invention uses an area array camera to acquire images, which has the characteristics of fast speed, large number of imaging points, and high lateral resolution. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of a vehicle-mounted ranging device according to the present invention;

[0033] In the figure, 1—first short-coherence broadband light source, 2—first fiber coupler, 3—second short-coherence broadband light source, 4—second fiber coupler, 5—first wavelength division multiplexer, 6—second wavelength division multiplexer, 7—first beam expander, 8—second beam expander, 9—first beam splitter, 10—second beam splitter, 11—first lens, 12—first filter, 13—first area array camera, 14—second lens, 15—second filter, 16—second area array camera, 17—vehicle-mounted computer, 18—object under test, 19—equal optical path surface. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0035] like Figure 1 As shown, a vehicle-mounted ranging device includes a first short-coherence broadband light source 1, a first fiber coupler 2, a second short-coherence broadband light source 3, a second fiber coupler 4, a first wavelength division multiplexer 5, a second wavelength division multiplexer 6, a first beam expander 7, a second beam expander 8, a first beam splitter 9, a second beam splitter 10, a first lens 11, a first filter 12, a first area array camera 13, a second lens 14, a second filter 15, a second area array camera 16, and a vehicle-mounted computer 17; the first short-coherence broadband light source 1... The first fiber coupler 2 is optically connected to the second short-coherence broadband light source 3 via an optical fiber. The first fiber coupler 2 outputs two paths: the first path is optically connected to the first wavelength division multiplexer 5 via an optical fiber, and the second path is optically connected to the second wavelength division multiplexer 6 via an optical fiber. The second short-coherence broadband light source 3 is optically connected to the second fiber coupler 4 via an optical fiber. The second fiber coupler 4 outputs two paths: the first path is optically connected to the first wavelength division multiplexer 5 via an optical fiber, and the second path is optically connected to the second wavelength division multiplexer 6 via an optical fiber. Wavelength division multiplexer 5 emits probe light. The probe light emitted from the first wavelength division multiplexer 5 is sequentially directed to the surface of the object under test 18 via the first beam expander 7 and the first beam splitter 9. The probe light reflected from the surface of the object under test 18 is directed to the second beam splitter 10 via the first beam splitter 9. The second wavelength division multiplexer 6 emits reference light. The reference light emitted from the second wavelength division multiplexer 6 is directed to the second beam splitter 10 via the second beam expander 8. The probe light reflected from the surface of the object under test 18 and the reference light emitted from the second wavelength division multiplexer 6 are directed to the second beam splitter 10. After the light source 10 converges, it is split into two beams. The first beam passes through the first lens 11 and the first filter 12 in sequence and is directed to the first area array camera 13. The second beam passes through the second lens 14 and the second filter 15 in sequence and is directed to the second area array camera 16. Both the first area array camera 13 and the second area array camera 16 are electrically connected to the vehicle-mounted computer 17. The first area array camera 13 acquires the first interference image, and the second area array camera 16 acquires the second interference image. The vehicle-mounted computer 17 demodulates the first interference image and the second interference image.

[0036] A vehicle-mounted ranging method, employing the aforementioned vehicle-mounted ranging device, includes the following steps:

[0037] Step 1: Activate the first short coherence broadband light source 1 and the second short coherence broadband light source 3. The probe light is emitted from the first wavelength division multiplexer 5, and the reference light is emitted from the second wavelength division multiplexer 6. The probe light is directed toward the surface of the object under test 18 through the first beam expander 7 and the first beam splitter 9. The probe light reflected from the surface of the object under test 18 is directed toward the second beam splitter 10 through the first beam splitter 9. The reference light is directed toward the second beam splitter 10 through the second beam expander 8. The probe light and the reference light are combined by the second beam splitter 10 and then split into two beams. The first beam is directed toward the first area array camera 13 through the first lens 11 and the first filter 12, and the second beam is directed toward the second area array camera 16 through the second lens 14 and the second filter 15.

[0038] Assuming the linewidth of low-coherence light is Δλ and the wavelength is λ, then L C =λ 2 / Δλ, where L C The coherence length is L; therefore, the probe and reference beams are only coherent by a length L near the equipathic surface 19. C Interference occurs within the range, such as Figure 1 As shown in the figure, the z-axis represents the direction of vehicle movement;

[0039] The distance between the equal optical path surface 19 and the vehicle-mounted ranging device is set to L. When the measured object 18 appears near the equal optical path surface 19, the coherence length L is... C Within the range, the probe light and the reference light interfere; when the measured object 18 appears near the equioptic path surface 19, the coherence length L... C When outside the range, the probe light and the reference light do not interfere;

[0040] Step 2: Camera gain calibration; for coherence length L C When the measured object 18 outside the range is imaged by the first array camera 13 and the second array camera 16, the relative gain of the camera is defined as k(x,y)=MEAN(I2(x,y)) / MEAN(I1(x,y)), where MEAN represents the average of the images at each point, I1(x,y) represents the image acquired by the first array camera 13, and I2(x,y) represents the image acquired by the second array camera 16.

[0041] Step 3: During vehicle operation, images are rapidly and continuously acquired by the first array camera 13 and the second array camera 16. Assuming that the object to be measured 18 appears in front of the vehicle, when the surface of the object to be measured 18 enters the coherence length L... C When the interference is within range, the first array camera 13 acquires the interference image I1(x,y;i), and the second array camera 16 acquires the interference image I2(x,y;i). The expressions for the interference images I1(x,y;i) and I2(x,y;i) are as follows:

[0042] ①、

[0043] ②、

[0044] In the formula, I1(x,y;i) represents the coherence length L of the surface of the measured object 18. C The first probe beam image is within the range, where I2(x,y;i) represents the coherence length L of the surface of the measured object 18. C Within the range, the first reference light image is shown, and I′1(x,y;i) ​​represents the coherence length L of the surface of the measured object 18. CThe image of the second probe beam is within the range, where I′2(x,y;i) ​​represents the coherence length L of the surface of the measured object 18. C The second reference beam image within the range, where L(x,y;i) ​​represents the optical path, λ c1 λ represents the center wavelength of the first short-coherent broadband light source 1. c2 The center wavelength of the second short-coherent broadband light source 3 is represented by i; where i represents t i Images captured in real time;

[0045] When the surface of the measured object 18 does not enter the coherence length L C Within the range, the reference light and the probe light do not interfere with each other. Image I3(x,y;i) is acquired by the first array camera 13, and image I4(x,y;i) is acquired by the second array camera 16. The expressions for images I3(x,y;i) and I4(x,y;i) are as follows:

[0046] ①、I3(x,y;i)=I 11 (x,y;i)+I 21 (x, y; i)

[0047] ②、I4(x,y;i)=I' 12 (x,y;i)+I' 22 (x, y; i)

[0048] In the formula, I 11 (x, y; i) indicates that the surface of the measured object 18 has not entered the coherence length L. C The first probe light image within range, I 21 (x, y; i) indicates that the surface of the measured object 18 has not entered the coherence length L. C The first reference light image within the range, I′ 12 (x, y; i) indicates that the surface of the measured object 18 has not entered the coherence length L. C The image of the second probe beam within the range, I′ 22 (x, y; i) indicates that the surface of the measured object 18 has not entered the coherence length L. C The second reference beam image within the range; where i represents t i Images captured in real time;

[0049] When the surface of the measured object 18 enters the coherence length L C When within the specified range, the following calculation formula applies:

[0050] S(x,y;i)=k(x,y)·I1(x,y;i)-I2(x,y;i)

[0051] In the formula, k(x,y) represents the relative gain of the camera. Substituting the expressions for the interferometric images I1(x,y;i) ​​and I2(x,y;i) ​​into the formula, we can obtain the following expression:

[0052]

[0053] In the formula, S(x,y;i) ​​represents the image difference between the interference image I1(x,y;i) ​​and the interference image I2(x,y;i), and λ c1 ≠λ c2 Therefore, S(x,y;i)≠0;

[0054] When the surface of the measured object 18 does not enter the coherence length L C When within the specified range, the following calculation formula applies:

[0055] S'(x,y;i)=k(x,y)·I3(x,y;i)-I4(x,y;i)

[0056] In the formula, k(x,y) represents the relative gain of the camera. After substituting the expressions of image I3(x,y;i) ​​and image I4(x,y;i), we can get S′(x,y;i)≈0; where S′(x,y;i) ​​represents the image difference between image I3(x,y;i) ​​and image I4(x,y;i).

[0057] The threshold is set according to the system signal-to-noise ratio. The vehicle computer 17 compares the threshold with S(x,y;i) in real time. When the vehicle computer 17 determines that S(x,y;i) is greater than the threshold, it means that there is an obstacle at a distance L in front of the vehicle. At this time, the vehicle computer 17 issues an alarm signal.

[0058] The solutions described in the embodiments are not intended to limit the scope of patent protection of this invention. All equivalent implementations or modifications that do not depart from the scope of this invention are included in the patent scope of this case.

Claims

1. A vehicle-mounted ranging device, characterized in that: The system includes a first short-coherence broadband light source, a first fiber coupler, a second short-coherence broadband light source, a second fiber coupler, a first wavelength division multiplexer (WDM), a second WDM, a first beam expander, a second beam expander, a first beam splitter, a second beam splitter, a first lens, a first filter, a first area array camera, a second lens, a second filter, a second area array camera, and an onboard computer. The first short-coherence broadband light source is optically connected to the first fiber coupler via an optical fiber. The first fiber coupler has two outputs: one output is optically connected to the first WDM multiplexer via an optical fiber, and the other output is optically connected to the second WDM multiplexer via an optical fiber. The second short-coherence broadband light source is optically connected to the second fiber coupler via an optical fiber. The second fiber coupler has two outputs: one output is optically connected to the first WDM multiplexer via an optical fiber, and the other output is optically connected to the second WDM multiplexer via an optical fiber. The first WDM... The multiplexer emits a probe beam. The probe beam emitted by the first wavelength division multiplexer is sequentially directed to the surface of the object under test via a first beam expander and a first beam splitter. The probe beam reflected from the surface of the object under test is directed to a second beam splitter via the first beam splitter. The second wavelength division multiplexer emits a reference beam. The reference beam emitted by the second wavelength division multiplexer is directed to a second beam splitter via a second beam expander. The probe beam reflected from the surface of the object under test and the reference beam emitted by the second wavelength division multiplexer are combined by the second beam splitter and then emitted as two beams. The first beam is directed to a first area array camera via a first lens and a first filter. The second beam is directed to a second area array camera via a second lens and a second filter. Both the first and second area array cameras are electrically connected to an onboard computer. The first area array camera acquires a first interferometric image, and the second area array camera acquires a second interferometric image. The onboard computer demodulates the first and second interferometric images.

2. A vehicle-mounted ranging method, employing the vehicle-mounted ranging device as described in claim 1, characterized in that... Includes the following steps: Step 1: Activate the first and second short-coherence broadband light sources. The probe light is emitted from the first wavelength division multiplexer, and the reference light is emitted from the second wavelength division multiplexer. The probe light is directed toward the surface of the object under test through the first beam expander and the first beam splitter in sequence. The probe light reflected from the surface of the object under test is directed toward the second beam splitter through the first beam splitter. The reference light is directed toward the second beam splitter through the second beam expander. The probe light and the reference light are combined by the second beam splitter and then emitted as two beams. The first beam is directed toward the first area array camera through the first lens and the first filter in sequence. The second beam is directed toward the second area array camera through the second lens and the second filter in sequence. Assuming the linewidth of low-coherence light is Δλ and the wavelength is λ, then L C =λ 2 / Δλ, where L C The coherence length is L; therefore, the coherence length L between the probe and reference beams is only near the equipathic plane. C Interference occurs within the range; Let L be the distance between the equioptic surface and the vehicle-mounted ranging device. When the measured object appears near the equioptic surface, the coherence length L is... C Within the range, the probe light and the reference light interfere; when the object being measured appears near the equioptic path surface, the coherence length L... C When outside the range, the probe light and the reference light do not interfere; Step 2: Camera gain calibration; for coherence length L C When the measured object outside the range is imaged by the first array camera and the second array camera, the relative gain of the camera is defined as k(x,y)=MEAN(I2(x,y)) / MEAN(I1(x,y)), where MEAN represents the average of the images at each point, I1(x,y) represents the image acquired by the first array camera, and I2(x,y) represents the image acquired by the second array camera. Step 3: During vehicle movement, images are rapidly and continuously acquired by the first and second array cameras. Assuming an object is detected in front of the vehicle, when the surface of the object enters the coherence length L... C Within the range, the first array camera acquires the interference image I1(x,y;i), and the second array camera acquires the interference image I2(x,y;i). The expressions for the interference images I1(x,y;i) and I2(x,y;i) are as follows: ①、 ②、 In the formula, I1(x,y;i) represents the coherence length L of the surface of the measured object. C The first probe beam image is within the range, where I2(x,y;i) represents the coherence length L of the surface of the measured object. C The first reference beam image is within the range, and I′1(x,y;i) ​​represents the coherence length L of the surface of the measured object. C The image of the second probe beam is within the range, where I′2(x,y;i) ​​represents the coherence length L of the surface of the measured object. C The second reference beam image within the range, where L(x,y;i) ​​represents the optical path, λ c1 λ represents the center wavelength of the first short-coherent broadband light source. c2 Let i represent the center wavelength of the second short-coherent broadband light source; where i represents t i Images captured in real time; When the surface of the object being measured does not enter the coherence length L C Within the range, the reference light and the probe light do not interfere with each other. Image I3(x,y;i) ​​is acquired by the first array camera, and image I4(x,y;i) ​​is acquired by the second array camera. The expressions for images I3(x,y;i) ​​and I4(x,y;i) ​​are as follows: ①、I3(x,y;i)=I 11 (x,y;i)+I 21 (x,y;i) ②、I4(x,y;i)=I' 12 (x,y;i)+I' 22 (x,y;i) In the formula, I 11 (x, y; i) indicates that the surface of the measured object has not entered the coherence length L. C The first probe light image within range, I 21 (x, y; i) indicates that the surface of the measured object has not entered the coherence length L. C The first reference light image within the range, I′ 12 (x, y; i) indicates that the surface of the measured object has not entered the coherence length L. C The image of the second probe beam within range, I′ 22 (x, y; i) indicates that the surface of the measured object has not entered the coherence length L. C The second reference beam image within the range; where i represents t i Images captured in real time; When the surface of the measured object 18 enters the coherence length L C When within the specified range, the following calculation formula applies: S(x,y;i)=k(x,y)·I1(x,y;i)-I2(x,y;i) In the formula, k(x,y) represents the relative gain of the camera. Substituting the expressions for the interferometric images I1(x,y;i) ​​and I2(x,y;i) ​​into the formula, we can obtain the following expression: In the formula, S(x,y;i) ​​represents the image difference between the interference image I1(x,y;i) ​​and the interference image I2(x,y;i), and λ c1 ≠λ c2 Therefore, S(x,y;i)≠0; When the surface of the object being measured does not enter the coherence length L C When within the specified range, the following calculation formula applies: S'(x,y;i)=k(x,y)·I3(x,y;i)-I4(x,y;i) In the formula, k(x,y) represents the relative gain of the camera. After substituting the expressions of image I3(x,y;i) ​​and image I4(x,y;i), we can get S′(x,y;i)≈0; where S′(x,y;i) ​​represents the image difference between image I3(x,y;i) ​​and image I4(x,y;i). A threshold is set based on the system signal-to-noise ratio. The onboard computer compares S(x,y;i) with the threshold in real time. When the onboard computer determines that S(x,y;i) is greater than the threshold, it indicates that there is an obstacle at a distance L in front of the vehicle. At this time, the onboard computer issues an alarm signal.

Images