A dual-frequency phase ratio underwater acoustic ranging method

Abstract

This disclosure provides a dual-frequency phase comparison underwater acoustic ranging method, comprising: Step 1: A sonar transmitter transmits dual-frequency continuous wave signals to a target, and a sonar receiver receives the target echo; Step 2: For a frame of data from the target echo, the peak values ​​of the two line spectra with the largest and second largest amplitudes in the power spectrum are found, and the frequency difference is obtained; based on the frequency difference range and amplitude threshold, the availability of the two line spectra peak values ​​is confirmed; Step 3: The phases corresponding to the peak points of the two line spectra peaks are compared, and the target distance in the current frame is determined by the phase difference. This invention utilizes a continuous wave sonar combined with multi-frequency phase comparison technology for target ranging. Since the accuracy of phase measurement is higher than that of time delay measurement, the phase difference of the dual-frequency signals is less sensitive to random noise, thus effectively reducing the influence of multipath effects and noise, and significantly improving the accuracy and reliability of ranging.

Description

Technical Field

[0001] This invention belongs to the fields of underwater acoustic detection technology and sonar technology, and specifically relates to a dual-frequency phase ratio underwater acoustic ranging method. Background Technology

[0002] Existing traditional underwater acoustic ranging methods include time delay measurement and Doppler effect ranging, which usually rely on the time difference of sound waves propagating in water to determine the distance to the target. These methods usually have problems such as resolution limitations, large measurement blind zones due to duty cycle, multipath effects, and signal distortion caused by environmental noise, which affect the accuracy of ranging. Summary of the Invention

[0003] In view of this, the present invention provides a dual-frequency phase ratio underwater acoustic ranging method, which can improve ranging accuracy.

[0004] To solve the above-mentioned technical problems, the present invention is implemented as follows.

[0005] A dual-frequency phase ratio underwater acoustic ranging method, the method comprising:

[0006] Step 1: The sonar transmitter transmits a dual-frequency continuous wave signal to the target, and the sonar receiver receives the target echo;

[0007] Step 2: For a frame of data from the target echo, find the peak values ​​of the two line spectra with the largest and second largest amplitudes in the power spectrum, and obtain the frequency difference; based on the frequency difference range and amplitude threshold, confirm the availability of the two line spectra peak values.

[0008] Step 3: Compare the phases corresponding to the peak points of the two line spectrum peaks, and determine the target distance in the current frame by the phase difference.

[0009] Preferably, in step 2, before finding the peak values ​​of the two line spectra, out-of-band interference is further filtered out: let P be the power spectrum of the target echo in the i-th frame. i (k), where k is the frequency, and the power spectrum P i The frequency corresponding to the maximum peak value (k) is denoted as k. max Zero power spectrum P i (k) P i (k max -TH,k max -TH+1,…,k max ,…,k max +TH-1,k max Values ​​other than +TH are used to eliminate out-of-band interference; TH represents half the length of the set out-of-band interference elimination range.

[0010] Preferably, in step 2, the frequency difference range is (f d -f th / 2,fd +f th / 2); where f th The length of the set frequency difference range; f d It is the quotient of the frequency difference of the transmitted dual-frequency continuous wave signal and the sampling frequency resolution of the sonar receiver system.

[0011] Preferably, f th Set to 2Hz.

[0012] Preferably, in step 3, determining the target distance of the current frame by phase difference is as follows: by substituting the phase difference corresponding to the current frame into the relationship between the dual-frequency phase difference of the target echo and the target distance, the target distance of the current frame is obtained.

[0013] Preferably, the relationship between the target echo dual-frequency difference and the distance is as follows:

[0014]

[0015] Among them, R i The target distance in the current frame i. Let f0 be the phase difference between the two frequencies of the target echo, c be the speed of sound in water, and f0 and f1 be the two frequencies at which the sonar transmitter transmits a dual-frequency continuous wave signal to the target.

[0016] Preferably, in step 2, if the number of line spectrum peaks extracted from the power spectrum is less than or equal to 2, it is considered that the current frame cannot obtain the correct dual-frequency echo, and the processing of the next frame begins.

[0017] Preferably, in step 2, if the current frame data does not meet the frequency difference and amplitude requirements based on the frequency difference range and amplitude threshold, it is considered that the current frame cannot obtain the correct dual-frequency echo, and the processing of the next frame begins.

[0018] Preferably, after step 3, the method further includes: performing fitting interpolation after multi-frame processing to obtain the target distance at each time point.

[0019] Beneficial effects:

[0020] (1) This invention utilizes a continuous wave sonar device in conjunction with multi-frequency phase comparison technology for target ranging. Since the accuracy of phase measurement is higher than that of time delay measurement, the influence of multipath effect is effectively reduced. The phase difference of dual-frequency signals has low sensitivity to random noise, effectively reducing the influence of noise. Therefore, this invention can significantly improve the accuracy and reliability of ranging, and is especially suitable for short-range ranging in water.

[0021] (2) The dual-frequency phase comparison ranging function is achieved using a single transmitter and receiver. The equipment is not complicated and is easy to implement.

[0022] (3) The present invention constructs a frequency difference range by using the quotient of the frequency difference of the dual-frequency continuous wave signal and the sampling frequency resolution of the sonar receiver system, ensuring that the line spectrum peaks on which the distance calculation is based are the echoes of the transmitted dual-frequency signals, rather than noise or other non-target spikes, thereby improving the accuracy of the distance measurement.

[0023] (4) In a preferred embodiment, the present invention obtains the target distance at each time point by performing fitting interpolation through multi-frame measurement, thereby realizing the tracking of the target trajectory.

[0024] (5) In a preferred embodiment, an operation to filter out out-of-band interference is added, thereby reducing the amount of data processing. Attached Figure Description

[0025] Figure 1 This is a flowchart of the dual-frequency phase ratio underwater acoustic ranging method of the present invention;

[0026] Figure 2 This is a schematic diagram of multi-frame echo FFT analysis;

[0027] Figure 3 This is a schematic diagram of the distance calculation results. Detailed Implementation

[0028] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0029] Continuous wave sonar devices are simple, lightweight, and offer high velocity resolution, leading to further research in recent years. However, simple continuous wave sonars are primarily used to measure the velocity and angle of moving targets. This invention utilizes a continuous wave sonar device in conjunction with multi-frequency phase comparison technology for target ranging. Because phase measurement is more accurate than time-delay measurement, and the phase difference between the two frequencies is less sensitive to random noise, it effectively reduces the impact of multipath effects and noise, significantly improving the accuracy and reliability of ranging and enhancing underwater acoustic ranging performance. It is particularly suitable for short-range ranging applications in water.

[0030] Figure 1 The flowchart of the dual-frequency phase ratio underwater acoustic ranging method provided by the present invention is as follows: Figure 1 As shown, the method includes the following steps:

[0031] Step 1: The sonar transmitter transmits a dual-frequency continuous wave signal to the target, and the sonar receiver receives the target echo and performs frame segmentation processing.

[0032] In this step, the sonar transmitter transmits a dual-frequency continuous wave signal x towards the target. T It consists of two single-frequency continuous sine wave signals with frequencies f0 and f1. and Composition, specifying f0 <f1, and The expression is

[0033]

[0034] Where f0 and f1 are the transmission frequencies of the dual-frequency continuous wave. and This is the initial phase of a dual-frequency continuous wave.

[0035] The sonar transmitter emits a dual-frequency continuous wave signal x towards the target. T for and The superposition of the two is expressed as:

[0036]

[0037] The sonar receiver receives the first frame of target echo as p1(n) (n = 1, ..., M-1, M); where M is the length of a data frame. Frames partially overlap, typically by 50%, so the value of n in the second frame of target echo p2(n) is... And so on, the target echo p in the i-th frame i The range of values ​​for n in (n) is:

[0038]

[0039] In the formula, the symbol This indicates rounding down to the nearest integer.

[0040] Step 2: For a frame of data from the target echo, find the peak values ​​of the two line spectra with the largest and second largest amplitudes in the power spectrum, and obtain the frequency difference; based on the frequency difference range and amplitude threshold, confirm the availability of the two line spectra peak values, and remove data that do not meet the requirements for frequency difference or amplitude.

[0041] Step 2 includes the following sub-steps:

[0042] Sub-step 21, FFT processing: Obtain the target echo p of the i-th frame. i After (n), calculate p. i The power spectrum P of (n) i (k).

[0043] Sub-step 22: Eliminate out-of-band interference: Calculate the power spectrum P i The position of the maximum value of (k) max To eliminate out-of-band interference, P is set to zero. i (k max -TH,…,k max Values ​​other than +TH, where TH represents the set range for eliminating out-of-band interference.

[0044] In this embodiment, TH = 9, so P is first set before searching for the peak value.i (1,…,k max -11,k max -10) and P i (k max +10,…,end-1,end) are set to zero, keeping only P. i (k max -9,…,k max The value of +9).

[0045] Sub-step 23: Locate the dual-frequency echo position. This involves the following steps:

[0046] 1) Finding the peak of the line spectrum: Traversing P i (k), find P i All peak values ​​P of (k) peaks and the x-coordinate k corresponding to the peak value locations , where P peaks and k locations Both are arrays.

[0047] 2) Determine if the number of peaks in the spectral line meets the requirements: Determine P peaks The length of the signal is ≥2, meaning there are two or more peaks. If not, it is considered that the correct dual-frequency echo cannot be obtained in this frame, and the process proceeds to the next frame. i+1 The processing of (n). If yes, then iterate through P. peaks and k locations Find P peaks The maximum value P peaks_max and the second largest value P peaks_secondMax and its corresponding x-coordinate value k locations_max and k locations_secondMax .

[0048] 3) Determine whether the frequency difference and amplitude of the peak values ​​of the largest and second largest line spectra meet the availability requirements. If they do, the echo dual-frequency location has been found. Specifically, this step determines whether the frequency difference and amplitude of the peak values ​​of the two line spectra are suitable for distance measurement based on the set frequency difference range and amplitude threshold.

[0049] Specifically, this invention provides two judgment conditions: frequency difference and amplitude.

[0050] The frequency difference judgment condition is based on the frequency difference threshold f. d Confirmed, f d The physical meaning is the digital frequency difference between the two frequencies, expressed as:

[0051]

[0052] Where f0 and f1 represent the frequencies at which the sonar transmitter transmits dual-frequency continuous wave signals, f sLet M be the system's sampling frequency, and M represent the length of each frame of data, i.e., the number of points in the Fourier transform. Then, equation (5) above represents the quotient of the frequency difference of the transmitted dual-frequency continuous wave signal and the sampling frequency resolution of the sonar receiver system. Then, using f... d The constructed frequency difference range is: (f d -f th / 2,f d +f th / 2); where f th The length of the set frequency difference range. In this embodiment, f th Set to 2Hz. Then the frequency difference constraint is: (f d -1)<|k locations_max -k locations_secondMax |<(f d +1).

[0053] The amplitude judgment condition is that the peak value of the line spectrum is greater than the set amplitude threshold A0. Physically, this means the amplitude of the dual-frequency echo should be greater than a certain threshold; if it is lower than this threshold, it is considered noise and interference. This should be understood as the peak values ​​of both line spectra being greater than the set amplitude threshold A0. For example, A0 can be selected between 3 and 6 dB.

[0054] Therefore, to determine whether the peak frequency difference and amplitude of the largest and second largest line spectra meet the requirements, we need to determine whether the following equation (6) holds true:

[0055]

[0056] If the result is negative, it is considered that the current frame cannot obtain the correct dual-frequency echo, and the process proceeds to the next frame. i+1 The processing of (n) is as follows: If the judgment result is yes, then compare the frequencies k of the two line spectrum peaks. locations_max and k locations_secondMax The smaller frequency is considered to be the echo signal frequency of the continuous wave with a transmission frequency of f0 after being reflected by the target, denoted as k0, and the larger frequency is considered to be the echo signal frequency of the continuous wave with a transmission frequency of f1 after being reflected by the target, denoted as k1.

[0057] Step 3: For the data retained in Step 2, compare the phases corresponding to the peak points of the two line spectrum peaks, and determine the target distance of the current frame by the phase difference.

[0058] In this step, the target echo p in the i-th frame is calculated. i The Fourier transform of (n) at frequencies k0 and k1 represents the phase. and That is, the phase difference is:

[0059]

[0060] Phase difference Substitute the target distance R in the current frame i Phase difference The relational expression is used to obtain R. i The value of . The relationship is derived from the Doppler principle and the target position, and is expressed as:

[0061]

[0062] Where c is the speed of sound in water.

[0063] Step 4: Save the target distance R in the current frame. i Calculate the target distance R in the next frame according to steps 2-3. i+1 Until the end. Figure 1 The power spectrum is for multi-frame echo FFT analysis.

[0064] Step 5: After processing multiple frames, the target distance at each time point is obtained by fitting and interpolating.

[0065] After calculating the target distance R for all frames i (i = 1, ..., N-1, N), assuming there are N frames of data, due to noise and interference, the correct values ​​cannot be estimated for some frames. In this case, interpolation and fitting are needed to obtain the target distance result R_interp at each time point. i (i = 1, ..., N-1, N), Figure 2 The distance calculation result R for each frame i and the interpolated result R_interp i .

[0066] The specific embodiments described above only illustrate the design principles of the present invention. The shapes and names of the components in this description may differ and are not limited. Therefore, those skilled in the art can modify or make equivalent substitutions to the technical solutions described in the foregoing embodiments; and these modifications and substitutions do not depart from the inventive spirit and technical solutions of the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A dual-frequency phase-ratio underwater acoustic ranging method, characterized in that, The method includes: Step 1: The sonar transmitter transmits a dual-frequency continuous wave signal to the target, and the sonar receiver receives the target echo; Step 2: For a frame of data from the target echo, find the peak values ​​of the two line spectra with the largest and second largest amplitudes in the power spectrum, and obtain the frequency difference; based on the frequency difference range and amplitude threshold, confirm the availability of the two line spectra peak values. Includes the following sub-steps: Sub-step 21, FFT processing: Obtain the target echo p of the i-th frame. i After (n), calculate p. i The power spectrum P of (n) i (k); Sub-step 22: Eliminate out-of-band interference: Calculate the power spectrum P i The position of the maximum value of (k) max Set P to zero i (k max -TH,…,k max Values ​​other than +TH, where TH represents the set range for eliminating out-of-band interference; Sub-step 23: Locate the dual-frequency echo position; this involves the following steps: 1) Finding the peak of the line spectrum: Traversing P i (k), find P i All peak values ​​P of (k) peaks and the x-coordinate k corresponding to the peak value locations , where P peaks and k locations All are arrays; 2) Determine if the number of peaks in the spectral line meets the requirements: Determine P peaks If the length is ≥2, then it is considered that the correct dual-frequency echo cannot be obtained in this frame, and the process proceeds to the next frame. i+1 Processing (n); if yes, then iterate through P. peaks and k locations Find P peaks The maximum value P peaks_max and the second largest value P peaks_secondMax and its corresponding x-coordinate value k locations_max and k locations_secondMax ; 3) Determine whether the peak frequency difference and amplitude of the largest and second largest line spectrum meet the availability requirements. If they do, the location of the echo dual frequency has been found. Step 3: Compare the phases corresponding to the peak points of the two line spectrum peaks, and determine the target distance in the current frame by the phase difference.

2. The method as described in claim 1, characterized in that, In step 2, the frequency difference range is (f d -f th / 2,f d +f th / 2); where f th The length of the set frequency difference range; f d It is the quotient of the frequency difference of the transmitted dual-frequency continuous wave signal and the sampling frequency resolution of the sonar receiver system.

3. The method as described in claim 2, characterized in that, f th Set to 2Hz.

4. The method as described in claim 1, characterized in that, In step 3, determining the target distance of the current frame by phase difference is as follows: by substituting the phase difference corresponding to the current frame into the relationship between the dual-frequency phase difference of the target echo and the target distance, the target distance of the current frame is obtained.

5. The method as described in claim 4, characterized in that, The relationship between the dual-frequency difference of the target echo and the distance is as follows: Among them, R i The target distance in the current frame i. Let f0 be the phase difference between the two frequencies of the target echo, c be the speed of sound in water, and f0 and f1 be the two frequencies at which the sonar transmitter transmits a dual-frequency continuous wave signal to the target.

6. The method as described in claim 1, characterized in that, In step 2, if the number of line spectrum peaks extracted from the power spectrum is less than or equal to 2, it is considered that the current frame cannot obtain the correct dual-frequency echo, and the processing of the next frame begins.

7. The method as described in claim 1, characterized in that, In step 2, if the current frame data does not meet the frequency difference and amplitude requirements based on the frequency difference range and amplitude threshold, it is considered that the current frame cannot obtain the correct dual-frequency echo, and the next frame is processed.

8. The method according to any one of claims 1-7, characterized in that, After step 3, the method further includes: performing fitting interpolation after multi-frame processing to obtain the target distance at each time step.

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