Forward diffuse reflectance laser heterodyne coherent underwater vehicle detection method and system

Abstract

The present disclosure provides a forward diffuse reflection laser heterodyne coherent underwater vehicle detection method and system, which comprises the following steps: S1, collecting first flow field phase information of an area without underwater vehicles; the first flow field phase information is obtained by signal demodulation output after the detection laser returns after being diffusely reflected by the area without underwater vehicles; S2, collecting second flow field phase information of a water area to be detected; the second flow field phase information is obtained by signal demodulation output after the detection laser returns after being diffusely reflected by the water area to be detected; S3, judging whether the wake flow field of the water area to be detected is caused by an underwater vehicle based on a preset threshold according to the first flow field phase information and the second flow field phase information, so as to determine whether the water area to be detected contains an underwater vehicle. The present disclosure takes the phase change of the detection light caused by the wake flow field of the underwater vehicle as the detection physical field, and realizes the detection of the underwater vehicle.

Description

Technical Field

[0001] This disclosure relates to the field of underwater vehicle detection technology, specifically to a forward diffuse reflection laser heterodyne coherent underwater vehicle detection method and system. Background Technology

[0002] In recent years, research on the detection and tracking of underwater vehicles has been a major focus of maritime powers. Currently, underwater vehicle detection methods mainly include acoustic and non-acoustic detection. Acoustic detection is currently a relatively effective method; however, when underwater vehicles navigate in the deep sea, the sound waves are refracted in various directions, causing a "sound blindness" phenomenon. Furthermore, with the development of vibration reduction and noise reduction technologies for underwater vehicles, their noise reduction performance has been significantly improved. Compared to the background noise of the ocean, the noise of underwater vehicles is no longer very noticeable, and the limitations of acoustic detection technology are becoming increasingly apparent. Therefore, non-acoustic detection has emerged, and common non-acoustic detection technologies include magnetic detection, electric field detection, biological detection, and optical detection.

[0003] Among the technologies used for wake detection, imaging technology and backward bubble detection technology are the main methods. However, as underwater vehicles travel at greater depths and their trajectories are optimized, the wake characteristics and bubble characteristics of their surface wakes dissipate quickly. Existing technologies cannot fully meet the detection needs of underwater vehicles. In response, the wake generated by underwater vehicles moving in seawater, especially when they frequently change speed and direction, can remain in the seawater for a long time. Its scale can reach several kilometers and its duration can be as long as tens of hours. Therefore, the position and movement of underwater vehicles can be determined based on the shape characteristics and speed changes of the wake, so as to track and detect them. Its characteristics are not affected by the travel depth, trajectories optimization, noise reduction processing, etc. Moreover, the existence of this wake is related to the physical scale and motion control of the underwater vehicle, which can be regarded as a new type of underwater vehicle detection technology. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the aforementioned issues, this disclosure provides a forward diffuse reflection laser heterodyne coherent underwater vehicle detection method and system, which at least partially solves the technical problems of traditional detection methods being difficult to accurately detect due to factors such as navigation depth, alignment optimization, and noise reduction processing.

[0006] (II) Technical Solution

[0007] This disclosure provides a forward diffuse reflection laser heterodyne coherent underwater vehicle detection method, comprising: S1, acquiring first flow field phase information of a region without underwater vehicles; the first flow field phase information is obtained by the detection laser passing through the region without underwater vehicles, returning after diffuse reflection, and then outputting the signal after demodulation; S2, acquiring second flow field phase information of the water area to be measured; the second flow field phase information is obtained by the detection laser passing through the water area to be measured, returning after diffuse reflection, and then outputting the signal after demodulation; S3, based on the first flow field phase information and the second flow field phase information, determining whether the wake flow field of the water area to be measured is caused by an underwater vehicle based on a preset threshold, thereby determining whether an underwater vehicle exists in the water area to be measured.

[0008] Furthermore, the signal demodulation output in S2 includes: photoelectric conversion of the coherent light of the probe laser, and obtaining the second flow field phase information i using a heterodyne intermediate frequency signal demodulation algorithm. IF :

[0009]

[0010] Where A is the DC signal caused by the intensity of the interference light, B is the magnitude of the interference light intensity, and C is the heterodyne modulation radian. The initial phase of the wakeless flow field region. The phase is caused by the wake flow field of the underwater vehicle, and t is time; the phase signal of the water area under test can be output through the intermediate frequency signal demodulation algorithm:

[0011]

[0012] Where λ is the wavelength of the probe laser, L is the inter-regional spacing of the water area to be measured, I0 is the reference light intensity, I1 is the probe light intensity, f is the phase change period of the wake flow field region, and t is time.

[0013] Further, S3 includes: obtaining the flow field amplitude and flow field frequency of the region without underwater vehicles based on the first flow field phase information; obtaining the flow field amplitude and flow field frequency of the water area to be measured based on the second flow field phase information; if the flow field amplitude of the water area to be measured is greater than the flow field amplitude of the region without underwater vehicles, and the flow field frequency range value of the water area to be measured is greater than the flow field frequency range value of the region without underwater vehicles, then the wake flow field of the water area to be measured is caused by an underwater vehicle, thereby determining that an underwater vehicle exists in the water area to be measured, wherein the flow field amplitude and flow field frequency range value of the region without underwater vehicles are preset threshold values.

[0014] Furthermore, the underwater vehicle detection method is non-acoustic detection.

[0015] Another aspect of this disclosure provides a forward diffuse reflection laser heterodyne coherent underwater vehicle detection system, comprising: a laser heterodyne coherent system including a laser for emitting a detection laser; a reflector for reflecting the detection laser to the water area to be measured and reflecting the diffusely reflected detection laser back to the laser heterodyne coherent system; a diffuse reflection object for diffusely reflecting the detection laser that has passed through the water area to be measured; and a signal demodulation and threshold determination system for receiving the reflected light from the detection laser, performing signal demodulation to output flow field phase information, and determining whether the wake flow field of the water area to be measured is caused by an underwater vehicle based on a preset threshold, thereby determining whether an underwater vehicle exists in the water area to be measured.

[0016] Furthermore, the laser is a narrow linewidth laser with a wavelength range of 400–700 nm.

[0017] Furthermore, diffuse reflective objects are Lambertian bodies whose surfaces can achieve diffuse reflection.

[0018] Furthermore, the laser heterodyne coherent system is a forward diffuse reflection type.

[0019] Furthermore, the signal demodulation and threshold determination system, used to receive the reflected light from the probe laser and perform signal demodulation to output flow field phase information, includes: photoelectric conversion of the coherent light of the probe laser, and using a heterodyne intermediate frequency signal demodulation algorithm to obtain the second flow field phase information i. IF :

[0020]

[0021] Where A is the DC signal caused by the intensity of the interference light, B is the magnitude of the interference light intensity, and C is the heterodyne modulation radian. The initial phase of the wakeless flow field region. The phase is caused by the wake flow field of the underwater vehicle, and t is time; the phase signal of the water area under test can be output through the intermediate frequency signal demodulation algorithm:

[0022]

[0023] Where λ is the wavelength of the probe laser, L is the inter-regional spacing of the water area to be measured, I0 is the reference light intensity, I1 is the probe light intensity, f is the phase change period of the wake flow field region, and t is time.

[0024] (III) Beneficial Effects

[0025] The forward diffuse reflection laser heterodyne coherent underwater vehicle detection method and system disclosed herein are designed for underwater vehicle wake characteristics in density-stratified seawater. Based on the principle of diffuse reflection laser heterodyne coherent detection, and addressing the changes in optical transmission phase caused by the underwater vehicle wake, a forward diffuse reflection laser heterodyne coherent underwater vehicle detection method is proposed. This method has advantages such as high sensitivity, long detection range, immunity to acoustic decoy interference, resistance to electromagnetic disturbances, and strong stealth, and solves the problem of high false alarm rate of acoustic detection caused by ocean stratification. Attached Figure Description

[0026] Figure 1 The schematic diagram illustrates a flow chart of a forward diffuse reflection laser heterodyne coherent underwater vehicle detection method according to an embodiment of the present disclosure;

[0027] Figure 2 The schematic diagram illustrates the principle of the forward diffuse reflection laser heterodyne coherent underwater vehicle detection method according to an embodiment of the present disclosure;

[0028] Figure 3 The schematic diagram illustrates a flowchart of the threshold determination method in the forward diffuse reflection laser heterodyne coherent underwater vehicle detection method according to an embodiment of the present disclosure;

[0029] Figure 4 The schematic diagram illustrates the structure of a forward diffuse laser heterodyne coherent underwater vehicle detection system according to an embodiment of the present disclosure. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0032] The use of ordinal numbers such as “first” and “second” in the specification and claims to modify components of the claims does not in itself imply or represent any prior ordinal number of the component, nor does it represent the order of one component with another component, or the order of manufacturing process. The use of these ordinal numbers is only to enable a component with a certain name to be clearly distinguished from another component with the same name.

[0033] This disclosure provides a forward diffuse reflection laser heterodyne coherent underwater vehicle detection method. Please refer to [link to relevant documentation]. Figure 1The process includes: S1, acquiring the first flow field phase information of the area without underwater vehicles; the first flow field phase information is obtained by the probe laser passing through the area without underwater vehicles, returning after diffuse reflection, and then outputting the signal after demodulation; S2, acquiring the second flow field phase information of the water area to be measured; the second flow field phase information is obtained by the probe laser passing through the water area to be measured, returning after diffuse reflection, and then outputting the signal after demodulation; S3, based on the first flow field phase information and the second flow field phase information, determining whether the wake flow field of the water area to be measured is caused by an underwater vehicle based on a preset threshold, thereby determining whether an underwater vehicle exists in the water area to be measured.

[0034] This disclosure provides a novel optical method for underwater vehicle detection. This method is a non-acoustic detection method that uses the phase change of the detection light caused by the wake flow field of the underwater vehicle as the detection physical field to achieve underwater vehicle detection. Specifically, as shown... Figure 2 As shown, the underwater vehicle travels through a density-stratified ocean, disrupting the seawater stratification and creating a wake. The flow field in this wake region differs from that in the non-wake region. For example, the probe laser propagates in the non-wake region as shown by the probe beam. When passing through the wake region, the probe beam is deflected multiple times. After being reflected by diffuse reflectors, the propagation phase of the laser changes compared to the non-wake region. The probe laser propagation in the non-wake region is shown by the dashed line, with an initial phase of... The laser incident in the wake region of the underwater vehicle is shown as a solid line. The phase caused by the wake flow field of the underwater vehicle is... The flow field in the wake region causes the deflected laser to be reflected by the diffuse reflector and then returned to the diffuse laser heterodyne coherent system. After coherence, the underwater vehicle can be detected by demodulating the phase change.

[0035] This method enables the detection of underwater vehicles with a large dynamic range, overcoming the shortcomings of existing transmission-type coherent heterodyne systems, which have a small dynamic range and cannot be compatible with the detection of underwater vehicles in gas and liquid two-phase wakes. Furthermore, this method also boasts advantages such as high sensitivity, long detection range, immunity to acoustic decoy interference, resistance to electromagnetic disturbances, and strong stealth, solving the problem of high false alarm rates in acoustic detection caused by ocean strata.

[0036] Based on the above embodiments, the signal demodulation output in S2 includes: photoelectric conversion of the coherent light of the probe laser, and obtaining the second flow field phase information i using a heterodyne intermediate frequency signal demodulation algorithm. IF :

[0037]

[0038] Where A is the DC signal caused by the intensity of the interference light, B is the magnitude of the interference light intensity, and C is the heterodyne modulation radian. The initial phase of the wakeless flow field region. The phase is caused by the wake flow field of the underwater vehicle, and t is time;

[0039] The phase signal of the water body under test can be output through the intermediate frequency signal demodulation algorithm:

[0040]

[0041] Where λ is the wavelength of the probe laser, L is the inter-regional spacing of the water area to be measured, I0 is the reference light intensity, I1 is the probe light intensity, f is the phase change period of the wake flow field region, and t is time.

[0042] The probe laser shines through the detection area onto the diffuse reflection object, causing diffuse reflection. The probe laser carrying the phase information of the flow field is received and demodulated by the diffuse reflection laser heterodyne coherent system, outputting the phase information of the probe laser caused by the underwater vehicle's flow field. The amplitude and frequency domain characteristics of this probe laser phase information are used as the standard for underwater vehicle wake detection.

[0043] Based on the above embodiments, S3 includes: obtaining the flow field amplitude and flow field frequency of the area without underwater vehicles according to the first flow field phase information; obtaining the flow field amplitude and flow field frequency of the water area to be measured according to the second flow field phase information; if the flow field amplitude of the water area to be measured is greater than the flow field amplitude of the area without underwater vehicles, and the flow field frequency range value of the water area to be measured is greater than the flow field frequency range value of the area without underwater vehicles, then the wake flow field of the water area to be measured is caused by an underwater vehicle, thereby determining that an underwater vehicle exists in the water area to be measured, wherein the flow field amplitude and flow field frequency range value of the area without underwater vehicles are preset threshold values.

[0044] Furthermore, based on the preset threshold judgment method, the judgment is made using the amplitude information (i.e., intensity information) in the flow field phase information and the frequency information in the phase information. As shown in formula (2), the demodulated phase signal encompasses the amplitude information. The frequency information sin(2πft) can be used to determine the amplitude threshold of the flow field signal by setting an amplitude threshold. Fourier transform can be used to output and determine the frequency domain information of the flow field. The amplitude intensity information and frequency domain information are compared with the ocean background (first flow field phase information) threshold, such as... Figure 3 As shown, this method determines whether an underwater vehicle exists in the tested water area. If the flow field amplitude in the tested water area is greater than that in the area without an underwater vehicle, and the flow field frequency range in the tested water area is greater than that in the area without an underwater vehicle, then the wake flow field in the tested water area is caused by an underwater vehicle, thus confirming the presence of an underwater vehicle in the tested water area; otherwise, no underwater vehicle exists in the tested water area.

[0045] The method disclosed herein can also provide a theoretical basis for underwater vehicle hull optimization design and structural optimization design by detecting and acquiring underwater vehicle wake data.

[0046] This disclosure also provides a forward diffuse reflection laser heterodyne coherent underwater vehicle detection system, such as Figure 4 As shown, it includes: a laser heterodyne coherent system, including a laser for emitting a probe laser; a reflector for reflecting the probe laser to the water body to be measured and reflecting the probe laser after diffuse reflection back to the laser heterodyne coherent system; a diffuse reflector for diffusely reflecting the probe laser that has passed through the water body to be measured; and a signal demodulation and threshold determination system for receiving the reflected light from the probe laser, demodulating the signal to output flow field phase information, and determining whether the wake flow field of the water body to be measured is caused by an underwater vehicle based on a preset threshold, thereby determining whether an underwater vehicle exists in the water body to be measured.

[0047] Specifically, the laser heterodyne coherent system emits a probe laser, which is reflected by a mirror, penetrates the flow field region, and reaches a diffusely reflecting object. The diffusely reflecting object is a Lambertian body with a surface capable of diffuse reflection, ensuring diffuse reflection of the probe beam in all directions without affecting the performance of the laser heterodyne coherent system. The probe light, carrying flow field phase change information, is received by the laser heterodyne coherent system after reflection from the diffusely reflecting object. After signal processing, the system outputs flow field phase information. Based on the amplitude and frequency information of the phase information, it determines whether the flow field is the wake of an underwater vehicle, thus enabling the detection of the underwater vehicle.

[0048] Based on the above embodiments, the laser is a narrow linewidth laser with a wavelength range of 400–700 nm, used to carry phase information of the wake flow field region of the underwater vehicle.

[0049] Based on the above embodiments, after the probe light passes through the flow field region, it reaches the diffuse reflection target, which is a rough metal surface that can achieve diffuse reflection of the probe light.

[0050] Based on the above embodiments, the laser heterodyne coherent system is a forward diffuse reflection type; the forward diffuse reflection type laser heterodyne coherent system can realize underwater vehicle detection within a large dynamic range, which can make up for the shortcomings of the existing transmission type coherent heterodyne system, which has a small dynamic range and cannot be compatible with the detection of underwater vehicles in gas and liquid two-phase wakes, and can also solve the problem of high false alarm rate of acoustic detection caused by ocean strata.

[0051] Based on the above embodiments, the length range of the detection area can be set according to the size of the system structure. It is a transmission type, generally emitting from the left and reflecting from the right.

[0052] Based on the above embodiments, the specific method of the signal demodulation and threshold judgment system for receiving the reflected light of the detection laser and demodulating the signal to obtain the flow field phase information has been described in detail in the section on forward diffuse reflection laser heterodyne coherent underwater vehicle detection system, and will not be repeated here.

[0053] The present disclosure will be further described below through specific embodiments. The following embodiments specifically illustrate the above-described forward diffuse reflection laser heterodyne coherent underwater vehicle detection method and system. However, the following embodiments are merely illustrative of the present disclosure, and the scope of the present disclosure is not limited thereto.

[0054] In this embodiment, the forward diffuse reflection laser heterodyne coherent underwater vehicle detection method includes the following steps:

[0055] Step 1: The diffuse reflection laser heterodyne coherent system emits a probe laser, which passes through the underwater flow field in the detection area and reaches the diffuse reflection target. The returned light is demodulated and output to generate the phase information of the probe laser caused by the underwater vehicle's flow field; this is equivalent to S1 and S2 above.

[0056] Step 2: Compare the detected laser phase information with a pre-set threshold of the marine background environment to perform a detected flow field analysis.

[0057] Step 3: Determine whether the flow field in the detection area is caused by an underwater vehicle by using the designed detection threshold judgment method.

[0058] Step 4: Achieve non-acoustic-optical detection of underwater vehicles based on the judgment results; equivalent to S3 above.

[0059] In this embodiment, the diffuse reflection laser heterodyne coherent system has a forward diffuse reflection detection area. The detection laser shines through the detection area onto the diffuse reflection object, causing diffuse reflection. The detection laser carrying the flow field phase information is received and demodulated by the diffuse reflection laser heterodyne coherent system.

[0060] Specifically, in this embodiment, the diffuse reflection laser heterodyne coherent system collects the flow field characteristics of the underwater vehicle in seawater, that is, the flow field characteristics against the background of the ocean.

[0061] In this embodiment, a diffuse reflection laser heterodyne coherent system collects the flow field characteristics of an underwater vehicle in seawater, namely the wake flow field characteristics.

[0062] In this embodiment, the diffuse reflection laser heterodyne coherent system is mounted on a moving carrier to perform real-time flow field detection and comparison.

[0063] In this embodiment, the threshold comparison mainly consists of the flow field amplitude characteristics and the flow field frequency characteristics, and the initial threshold is the ocean background threshold.

[0064] In this embodiment, when the detected flow field amplitude characteristics and flow field frequency characteristics are less than the initial threshold, it indicates that there is no underwater vehicle in the flow field; when the detected flow field amplitude characteristics and flow field frequency characteristics are greater than the initial threshold, it indicates that there is an underwater vehicle in the flow field, thereby achieving optical detection of underwater vehicles.

[0065] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A forward diffuse reflection laser heterodyne coherent underwater vehicle detection method, characterized in that, include: S1, Acquire the first flow field phase information of the area without underwater vehicles; the first flow field phase information is obtained by the probe laser passing through the area without underwater vehicles, returning after diffuse reflection, and then being output after signal demodulation; S2, Acquire the second flow field phase information of the water body to be measured; the second flow field phase information is obtained by the probe laser passing through the water body to be measured, returning after diffuse reflection, and then being output after signal demodulation; S3. Based on the first flow field phase information and the second flow field phase information, determine whether the wake flow field of the water area to be tested is caused by an underwater vehicle based on a preset threshold, thereby determining whether an underwater vehicle exists in the water area to be tested.

2. The forward diffuse reflection laser heterodyne coherent underwater vehicle detection method according to claim 1, characterized in that, The demodulated output in S2 includes: The coherent light of the probe laser is photoelectrically converted, and a heterodyne intermediate frequency signal demodulation algorithm is used to obtain the second flow field phase information i. IF : Where A is the DC signal caused by the intensity of the interference light, B is the magnitude of the interference light intensity, and C is the heterodyne modulation radian. The initial phase of the wakeless flow field region. The phase is caused by the wake flow field of the underwater vehicle, and t is time; The phase signal of the water body under test can be output through the intermediate frequency signal demodulation algorithm: Where λ is the wavelength of the probe laser, L is the inter-regional spacing of the water area to be measured, I0 is the reference light intensity, I1 is the probe light intensity, f is the phase change period of the wake flow field region, and t is time.

3. The forward diffuse reflection laser heterodyne coherent underwater vehicle detection method according to claim 1, characterized in that, S3 includes: Based on the first flow field phase information, the flow field amplitude and flow field frequency in the area without underwater vehicles are obtained; Based on the second flow field phase information, the flow field amplitude and flow field frequency of the water body to be measured are obtained; If the flow field amplitude of the water area to be tested is greater than the flow field amplitude of the area without underwater vehicles, and the flow field frequency range of the water area to be tested is greater than the flow field frequency range of the area without underwater vehicles, then the wake flow field of the water area to be tested is caused by an underwater vehicle, thereby determining that an underwater vehicle exists in the water area to be tested, wherein the flow field amplitude and flow field frequency range of the area without underwater vehicles are preset threshold values.

4. The forward diffuse reflection laser heterodyne coherent underwater vehicle detection method according to claim 1, characterized in that, The underwater vehicle detection method described above is a non-acoustic detection method.

5. A forward diffuse reflection laser heterodyne coherent underwater vehicle detection system, characterized in that, include: A laser heterodyne coherent system includes a laser for emitting a probe laser; A reflector is used to reflect the probe laser to the water body to be measured and to reflect the diffusely reflected probe laser to the laser heterodyne coherence system; A diffuse reflective object, used to diffusely reflect the probe laser light that has passed through the water area to be measured; The signal demodulation and threshold judgment system is used to receive the reflected light of the detection laser, demodulate the signal to output the flow field phase information, and determine whether the wake flow field of the water area to be measured is caused by an underwater vehicle based on a preset threshold, thereby determining whether an underwater vehicle exists in the water area to be measured.

6. The forward diffuse reflection laser heterodyne coherent underwater vehicle detection system according to claim 5, characterized in that, The laser is a narrow linewidth laser with a wavelength range of 400–700 nm.

7. The forward diffuse reflection laser heterodyne coherent underwater vehicle detection system according to claim 5, characterized in that, The diffuse reflective object is a Lambertian body whose surface can achieve diffuse reflection.

8. The forward diffuse reflection laser heterodyne coherent underwater vehicle detection system according to claim 5, characterized in that, The laser heterodyne coherent system is a forward diffuse reflection type.

9. The forward diffuse reflection laser heterodyne coherent underwater vehicle detection system according to claim 5, characterized in that, The signal demodulation and threshold determination system is used to receive the reflected light from the probe laser and perform signal demodulation to output flow field phase information, including: The coherent light of the probe laser is photoelectrically converted, and a heterodyne intermediate frequency signal demodulation algorithm is used to obtain the second flow field phase information i. IF : Where A is the DC signal caused by the intensity of the interference light, B is the magnitude of the interference light intensity, and C is the heterodyne modulation radian. The initial phase of the wakeless flow field region. The phase is caused by the wake flow field of the underwater vehicle, and t is time; The phase signal of the water body under test can be output through the intermediate frequency signal demodulation algorithm: Where λ is the wavelength of the probe laser, L is the inter-regional spacing of the water area to be measured, I0 is the reference light intensity, I1 is the probe light intensity, f is the phase change period of the wake flow field region, and t is time.

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