Dual-frequency phase-comparison underwater acoustic ranging method

Abstract

The invention provides a dual-frequency phase-comparison underwater acoustic ranging method, which comprises the following steps that: step 1, a sonar transmitter transmits a dual-frequency continuous wave signal to a target, and a sonar receiver receives a target echo; 2, for one frame of data of the target echo, two line spectrum peak values with the maximum amplitude and the second maximum amplitude in a power spectrum are searched, and a frequency difference is obtained; according to the frequency difference range and the amplitude threshold, carrying out availability confirmation on the two line spectrum peak values; and 3, comparing phases corresponding to peak points of the peak values of the two line spectrums, and determining a target distance of the current frame through a phase difference. According to the method, the continuous wave system sonar is matched with the multi-frequency phase comparison technology for target distance measurement, the precision of phase measurement is higher than that of time delay measurement, and the sensitivity of the phase difference of double-frequency signals to random noise is low, so that the influence of a multi-path effect and noise can be effectively reduced, and the accuracy and reliability of distance measurement are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of underwater acoustic detection and sonar technology, and specifically relates to a dual-frequency phase comparison underwater acoustic ranging method. Background Art

[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 of the target. These methods usually have problems such as resolution limitation, large measurement blind spots caused by duty cycle, signal distortion caused by multipath effect and 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 comparison underwater acoustic ranging method, which can improve the ranging accuracy.

[0004] In order to solve the above technical problems, the present invention is implemented as follows.

[0005] A dual-frequency phase comparison 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 target echo data, find the two line spectrum peaks with the largest and second largest amplitudes in the power spectrum and obtain the frequency difference; confirm the availability of the two line spectrum peaks based on the frequency difference range and amplitude threshold;

[0008] Step 3: Compare the phases corresponding to the peak points of the two line spectrum peaks, and determine the target distance of the current frame through 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: the power spectrum of the target echo of the i-th frame is denoted as P i (k), k is the frequency, the power spectrum P i (k) The frequency corresponding to the maximum peak is recorded as k max , set the power spectrum P to zero i (k) P i (k max -TH,k max -TH+1,…,k max ,…,k max +TH-1,k max +TH) to eliminate out-of-band interference; TH represents the half 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 is 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: 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 to obtain the target distance of the current frame.

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

[0014]

[0015] Among them, R i is the target distance of the current frame i, is the dual-frequency phase difference of the target echo, c is the speed of sound in water, f 0 and f 1 The two frequencies at which the sonar transmitter transmits dual-frequency continuous wave signals 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 process proceeds to the next frame.

[0017] Preferably, in step 2, if it is determined that the current frame data does not meet the frequency difference and amplitude requirements according to the frequency difference range and the amplitude threshold, it is considered that the current frame cannot obtain the correct dual-frequency echo, and the next frame is processed.

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

[0019] Beneficial effects:

[0020] (1) The present invention utilizes continuous wave sonar equipment in conjunction with multi-frequency phase comparison technology to perform 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 is less sensitive to random noise, which effectively reduces the influence of noise. Therefore, the present invention can significantly improve the accuracy and reliability of ranging, and is particularly suitable for use in short-range ranging situations in water.

[0021] (2) A single transmitter and receiver are used to realize the dual-frequency phase comparison ranging function. The equipment is not complicated and easy to implement.

[0022] (3) The present invention constructs a frequency difference range using the quotient of the frequency difference of the dual-frequency continuous wave signal and the sampling frequency resolution of the sonar receiver system, thereby ensuring that the line spectrum peak used for distance calculation is the echo of the transmitted dual-frequency signal rather than non-target peaks such as noise, thereby improving the accuracy of ranging.

[0023] (4) In a preferred embodiment, the present invention performs fitting interpolation through multi-frame measurement to obtain the target distance at each moment, thereby achieving tracking of the target trajectory.

[0024] (5) In a preferred embodiment, an operation of filtering out-of-band interference is added to reduce the amount of data processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart of the dual-frequency phase comparison underwater acoustic ranging method of the present invention;

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

[0027] Figure 3 This is a schematic diagram of the distance solution results. DETAILED DESCRIPTION

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

[0029] Continuous wave sonar equipment is simple and light, with high speed measurement resolution. Therefore, in recent years, there has been further research on continuous wave sonar, but simple continuous wave sonar is mainly used to measure the speed and angle of moving targets. The present invention uses continuous wave sonar equipment in conjunction with multi-frequency phase comparison technology to measure target distance. Since the accuracy of phase measurement is higher than that of time delay measurement, the phase difference of dual-frequency signals is less sensitive to random noise, thus effectively reducing the impact of multipath effects and noise, and can significantly improve the accuracy and reliability of ranging, and effectively improve the underwater acoustic ranging effect. It is particularly suitable for use in short-range ranging occasions in water.

[0030] Figure 1 The flowchart of the dual-frequency phase comparison underwater acoustic ranging method provided by the present invention is as follows: Figure 1 As shown, the method comprises 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 processing.

[0032] In this step, the sonar transmitter transmits a dual-frequency continuous wave signal x to the target. T , consisting of two frequencies f 0 and f 1 A single frequency continuous sine wave signal and Composition, regulations 0 <f 1 , and The expression is

[0033]

[0034] Among them, f 0 and f 1 is the transmitting frequency of dual-frequency continuous wave, and It is the initial phase of the dual-frequency continuous wave.

[0035] The sonar transmitter transmits a dual-frequency continuous wave signal to the target x T for and The superposition expression is:

[0036]

[0037] The sonar receiver receives the first frame of target echo as p 1 (n)(n=1,…,M-1,M); M is the length of a frame of data. Frames overlap partially, usually 50%, then the target echo p of the second frame 2 The value of n in (n) is Similarly, the target echo p in the i-th frame i The value range of n in (n) is:

[0038]

[0039] In the formula, the symbol Indicates rounding down.

[0040] Step 2: For a frame of target echo data, find the two line spectrum peaks with the largest and second largest amplitudes in the power spectrum and obtain the frequency difference; according to the frequency difference range and amplitude threshold, confirm the availability of the two line spectrum peaks and remove data whose frequency difference and amplitude do not meet the requirements.

[0041] This step 2 includes the following sub-steps:

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

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

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

[0045] Sub-step 23: Find the echo dual-frequency position. This is divided into the following steps:

[0046] 1) Find the peak of the line spectrum: traverse P i (k), find P i All peak values ​​P of (k) peaks The horizontal coordinate k corresponding to the peak value locations , where P peaks and k locations All are arrays.

[0047] 2) Determine whether the number of line spectrum peaks meets the requirements: Determine whether P peaks Is the length of ≥2, that is, whether there are 2 or more peaks; if not, it is considered that this frame cannot obtain the correct dual-frequency echo, and the next frame p is entered i+1 (n) processing. If yes, then traverse P peaks and k locations , find P peaks The maximum value P peaks_max and the next largest value P peaks_secondMax and its corresponding horizontal coordinate value k locations_max and k locations_secondMax .

[0048] 3) Determine whether the frequency difference and amplitude of the maximum and second largest line spectrum peaks meet the availability requirements. If they meet the availability requirements, it is determined that the echo dual-frequency position is found. Specifically, this step determines whether the frequency difference and amplitude of the two line spectrum peaks are suitable for ranging according to the set frequency difference range and amplitude threshold.

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

[0050] The frequency difference judgment condition is based on the frequency difference threshold f d OK, f d The physical meaning is the digital frequency difference of dual frequencies, and the expression is:

[0051]

[0052] Among them, f 0 and f 1 Represents the frequency of the dual-frequency continuous wave signal emitted by the sonar transmitter, f s is the sampling frequency of the system, M represents the length of each frame of data, i.e., the number of Fourier transform points. Then the above formula (5) 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 construction frequency difference range is: (f d -f th / 2,f d +f th / 2); where f th is the length of the set frequency difference range. In this embodiment, f th Set to 2Hz. Then the frequency difference limit is: (f d -1)<|k locations_max -k locations_secondMax |<(f d +1).

[0053] The amplitude judgment condition is that the line spectrum peak is greater than the set amplitude threshold A 0 The physical meaning is that 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. It should be understood here that the peak points of the two line spectrum peaks are greater than the set amplitude threshold A. 0 For example, 0 You can choose 3-6 decibels.

[0054] Then, to determine whether the maximum and second largest line spectrum peak frequency difference and amplitude meet the requirements is to determine whether the following formula (6) is established:

[0055]

[0056] If the result is no, it is considered that the current frame cannot obtain the correct dual-frequency echo, and the next frame p is entered. i+1 If the result is yes, the frequencies k of the two line spectrum peaks are compared. locations_max and k locations_secondMax , where the smaller one is considered to be the transmitting frequency f 0 The frequency of the echo signal after the continuous wave of the target is reflected, denoted as k 0 , where the larger one is considered to be the transmitting frequency f 1 The frequency of the echo signal after the continuous wave of the target is reflected, denoted as k 1 .

[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 of the i-th frame is calculated i The Fourier transform of (n) is k 0 and k 1 Phase at frequency and That is, the phase difference is:

[0059]

[0060] Phase Difference Substitute the current frame target distance R i Phase Difference The relationship between R i 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 current frame target distance R i , calculate the target distance R of the next frame according to steps 2-3 i+1 , until the end. Figure 1 This is the power spectrum of multi-frame echo FFT analysis.

[0064] Step 5: After multi-frame processing, the target distance at each moment is obtained through fitting interpolation.

[0065] After calculating the target distance R of all frames i (i=1,…,N-1,N), assuming that there are N frames of data in total, due to the influence of noise and interference, some frames cannot estimate the correct value. In this case, interpolation and fitting are needed to obtain the target distance results R_interp at each time point. i (i=1,…,N-1,N), Figure 2 The distance settlement result R for each frame i And the interpolation result R_interp i .

[0066] The above specific embodiments only describe the design principle of the present invention. The shapes and names of the components in the description may be different and are not limited. Therefore, those skilled in the art in the field of the present invention may modify or replace the technical solutions recorded in the above embodiments; and these modifications and replacements do not deviate from the creative purpose 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 comparison 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 target echo data, find the two line spectrum peaks with the largest and second largest amplitudes in the power spectrum and obtain the frequency difference; confirm the availability of the two line spectrum peaks based on the frequency difference range and amplitude threshold; Step 3: Compare the phases corresponding to the peak points of the two line spectrum peaks, and determine the target distance of the current frame through the phase difference.

2. The method according to claim 1, characterized in that In step 2, before finding the peak values ​​of the two line spectra, the out-of-band interference is further filtered out: the power spectrum of the target echo of the i-th frame is denoted as P i (k), k is the frequency, the power spectrum P i (k) The frequency corresponding to the maximum peak is recorded as k max , set the power spectrum P to zero i (k) P i (k max -TH,k max -TH+1,…,k max ,…,k max +TH-1,k max +TH) to eliminate out-of-band interference; TH represents the half length of the set out-of-band interference elimination range.

3. The method according to 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 is 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.

4. The method according to claim 3, characterized in that f th Set to 2Hz.

5. The method according to claim 1, characterized in that In step 3, the target distance of the current frame is determined by the phase difference: 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.

6. The method according to claim 5, characterized in that The relationship between the target echo dual-frequency difference and the distance is: Among them, R i is the target distance of the current frame i, is the dual-frequency phase difference of the target echo, c is the speed of sound in water, and f0 and f1 are the two frequencies at which the sonar transmitter transmits dual-frequency continuous wave signals to the target.

7. The method according to 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 process proceeds to the next frame.

8. The method according to claim 1, characterized in that In step 2, if the current frame data is determined not to meet the frequency difference and amplitude requirements according to the frequency difference range and the amplitude threshold, it is considered that the current frame cannot obtain the correct dual-frequency echo, and the next frame is processed.

9. The method according to any one of claims 1 to 8, characterized in that: After step 3, the method further includes: performing fitting interpolation after processing multiple frames to obtain the target distance at each moment.

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