Target depth and speed estimation method based on multipath time delay solution

Abstract

The invention provides a target depth and speed estimation method based on multipath time delay solution, and the method comprises the steps: employing a cepstrum analysis method to estimate a multipath time delay value based on a sound signal received by a hydrophone; according to the relation between the multi-path time delay values and the target depth and speed under different reflection conditions, the multi-path time delay values continuously measured for three times are used for resolving the target depth and speed, and target depth ranges and speed ranges under different reflection conditions are obtained through point-by-point resolving; unreasonable data are removed according to a parameter reasonable range determined by actual environment information, and a final target depth range and a final speed range are screened out to serve as estimation results. By using the method, the problem that the realization difficulty of target depth and speed estimation by simultaneously utilizing sea surface and sea bottom multipath time delays or combining sea surface / sea bottom multipath time delays with a pitch angle in a traditional method is large is solved; and even if the target signal is weak, the depth and speed measurement of the target by the underwater unmanned platform can be completed.

Description

Technical Field

[0001] The invention belongs to the fields of underwater acoustic signal processing, sonar technology and acoustic fuze technology, and in particular relates to a target depth and speed estimation method based on multipath time delay solution. Background Art

[0002] The estimation of underwater target depth and speed has always been a key issue for underwater unmanned platforms to identify and locate targets. When acoustic signals propagate in shallow waters, they are affected by reflections from the sea surface and the seabed. Multipath delay speed and depth measurement usually uses the sea surface and seabed multipath delay at the same time or calculates target parameters by combining sea surface / seabed multipath delay with pitch angle. When the target signal is weak and it is difficult to obtain multiple multipath delays, it is difficult to estimate the depth and speed of the target. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a target depth and speed estimation method based on multipath delay solution, which avoids the problem that the traditional method simultaneously uses two multipath delays of the sea surface and the seabed or estimates the target depth and speed through the sea surface / seabed multipath delay combined with the pitch angle, which is difficult to implement; even if the target signal is weak, the underwater unmanned platform can complete the depth and speed measurement of the target.

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

[0005] A method for estimating target depth and speed based on multipath time delay solution, comprising:

[0006] Step 1: Based on the acoustic signal received by the hydrophone, the cepstrum analysis method is used to estimate the delay trajectory caused by the multipath propagation effect of the target sound source to obtain the multipath delay value;

[0007] Step 2: According to the relationship between the multipath delay value and the target depth and speed under different reflection conditions, the target depth and speed are calculated using the multipath delay values ​​measured three times in succession, and the target depth range and speed range under different reflection conditions are obtained by point-by-point calculation;

[0008] Step 3: According to the reasonable range of parameters determined by the actual environmental information, remove the abnormal data of multiple target depth ranges and speed ranges under different reflection conditions, and screen out the final target depth range and speed range as the estimation result.

[0009] Preferably, step 3 is: according to the known sea depth H, judging whether the target depth range estimated in each reflection case is within the known sea depth H, thereby removing outliers and screening out the final target depth range and speed range.

[0010] Preferably, in step 3, if more than two reasonable target depth ranges are retained through screening, further screening is performed according to the speed range.

[0011] Preferably, the different reflection conditions include: sea surface reflection only, sea bottom reflection only, sea surface-sea bottom reflection and sea bottom-sea surface reflection.

[0012] Preferably, in step 2, before solving, the reflection conditions are further screened according to the amplitude corresponding to the multipath delay history in the acoustic signal cepstrum waterfall diagram; if the amplitude is positive, only the seabed reflection is selected; if the amplitude is negative, the different reflection conditions selected include only sea surface reflection, sea surface-seabed reflection and seabed-sea surface reflection.

[0013] Preferably, under different reflection conditions, the relationship between the multipath delay value and the target depth and speed is constructed as follows:

[0014] The multipath delay value τ of sea surface reflection only 1t The relationship between the target depth z and the target speed v is:

[0015]

[0016] The multipath delay value τ of the seabed reflection only 2t The relationship between the target depth z and the target speed v is:

[0017]

[0018] Multipath delay value τ of sea surface-seabed reflection 3t The relationship between the target depth z and the target speed v is:

[0019]

[0020] Multipath delay value τ of seabed-sea surface reflection 4t The relationship between the target depth z and the target speed v is:

[0021]

[0022] Among them, r t is the horizontal distance between the sound source and the receiving point at time t, v is the target speed, T CPA is the moment when the sound source is closest to the receiving point, z0 is the depth of the hydrophone receiving point, c is the speed of sound, and H is the sea depth.

[0023] Preferably, the time delay trajectory generated by the multipath propagation effect of the target sound source estimated by the cepstrum analysis method in step 1 is:

[0024] The hydrophone received signal is processed by framing to obtain a discrete signal sequence;

[0025] Perform FFT operation on the discrete signal sequence to obtain a complex sequence;

[0026] The power spectrum is calculated based on the complex sequence, and the logarithm is taken to obtain the sequence Y(k); the sequence Y(k) is extended and reversally spliced ​​to obtain a new sequence; then the new sequence is inverse Fourier transformed, and the real part is taken to obtain the cepstrum sequence;

[0027] The cepstrum sequence is used to extract the time delay trajectory caused by the multipath propagation effect of the target sound source and obtain the multipath delay value.

[0028] Beneficial effects:

[0029] (1) The present invention calculates the target depth and speed under multiple different assumptions through three consecutive measurements of multipath delay values, and selects reasonable calculation results of target depth and speed in combination with environmental information, thereby avoiding the problem that the traditional method simultaneously uses two types of multipath delays of the sea surface and the seabed, or estimates the target depth and speed through the sea surface / seabed multipath delay combined with the pitch angle, which is difficult to achieve.

[0030] (2) The present invention measures the multipath delay value to calculate the depth and speed of the target. Except for the sea depth, no prior knowledge of other marine environments is required. Only one multipath delay is required, which is conducive to application on underwater unmanned platforms.

[0031] (3) Since no prior knowledge of the ocean environment other than the sea depth is required, and no pitch angle information is required, the underwater unmanned platform can still measure the depth and speed of the target even if the target signal is weak. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The flowchart of the target depth and velocity estimation method based on multipath time delay solution.

[0033] Figure 2 This is the cepstrum waterfall diagram used in the experimental verification;

[0034] Figure 3 This is the multipath delay diagram extracted during the test verification;

[0035] Figure 4 This is the target depth estimation result diagram in the experimental verification;

[0036] Figure 5 This is the target speed estimation result diagram in the test verification;

[0037] Figure 6 This is the target depth estimation error map in the experimental verification;

[0038] Figure 7 Figure 2 is the target velocity estimation error diagram in the experimental verification. DETAILED DESCRIPTION

[0039] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0040] The present invention provides a method for estimating target depth and speed based on multipath time delay solution. The core idea is: using the cepstrum analysis method to estimate the delay trajectory caused by the multipath propagation effect of the target sound source; solving the target depth range and speed range under different reflection conditions by measuring the multipath delay values ​​three times in a row, and finally combining environmental information to screen a reasonable target depth range and speed range as the estimation result.

[0041] It can be seen that this solution avoids the problem that the traditional method uses two multipath delays of the sea surface and the seabed at the same time or estimates the target depth and speed by combining the sea surface / seabed multipath delay with the pitch angle, which is difficult to achieve. In addition to the sea depth, the present invention does not require any prior knowledge of the marine environment, and only requires one multipath delay, which is conducive to application on underwater unmanned platforms.

[0042] Figure 1 The flowchart of the target depth and speed estimation method based on multipath delay solution of the present invention is shown, as shown in the figure, including:

[0043] Step 1: Based on the acoustic signal received by the hydrophone, the cepstrum analysis method is used to estimate the delay trajectory caused by the multipath propagation effect of the target sound source to obtain the multipath delay value.

[0044] Step 2: According to the relationship between the multipath delay value and the target depth and speed under different reflection conditions, the target depth and speed under different reflection conditions are solved using the multipath delay values ​​measured three times in succession. Because the cepstrum analysis obtains N delay measurement values ​​(greater than 3), one depth (speed) can be solved for every 3 measurement values, and N-2 depths (speeds) can be obtained by point-by-point solution, so this step can obtain the target depth range and speed range under different reflection conditions.

[0045] Step 3: According to the reasonable range of parameters determined by the actual environmental information, remove the abnormal data in the multiple target depth ranges and speed ranges obtained under different reflection conditions, and filter out the final target depth range and speed range as the estimation result. In this step, depth information can generally be used to achieve screening. Then this step only needs to determine whether the estimated target depth range under each reflection condition is within the known sea depth H based on the known sea depth H. For unreasonable depth ranges, the depth and speed data are removed. If there are more than one group of remaining depth ranges, the reasonable speed range can be further used for further judgment. For example, the underwater speed will not be too fast. If there are still two reasonable values, continue to track the target.

[0046] The specific embodiments of the present invention are as follows:

[0047] Figure 1 Step 1 in the code is as follows:

[0048] Step S11: filter and amplify the signal received by the hydrophone and then sample it. The sampling frequency is f s .

[0049] Step S12: Estimating multipath delay using cepstrum analysis:

[0050] The hydrophone received signal is processed by framing. The time length of one frame is T0 (unit: s) to obtain a discrete signal sequence x(n), n = 1, 2, ..., N, where N = T0·f s , N is an even number.

[0051] First, perform FFT operation on the sequence x(n), n=1,2,…,N, according to the bandwidth range f L ~f H Get the complex sequence y(k), and Represents rounding up and rounding down respectively; then take the square of the absolute value of y(k) to get the power spectrum P(k); then take the logarithm of P(k) to get the sequence Y(k); then extend Y(k)

[0052]

[0053] In this way, we can get a sequence Y(k) with a length of N / 2, k = 0 to N / 2-1. Reverse Y(k) in time to get Y1(k), and set Y1(0) = 0. After splicing Y1(k) to Y(k), we get a new sequence Z(k) with N points, k = 0 to N-1. Perform an inverse Fourier transform on Z(k), and take its real part to get the cepstrum sequence C(n), n = 0 to N-1.

[0054] Step S13: extracting multipath delay.

[0055] According to the cepstrum sequence, from the cepstrum delay history diagram, according to the sea depth and receiving depth, the peak is searched within a certain delay interval, the delay trajectory caused by the multipath propagation effect of the target sound source is extracted, and the multipath delay measurement value is obtained.

[0056] Figure 1 Step 2 in the code is as follows:

[0057] Step S21: constructing the relationship between the multipath delay value and the target depth and speed under different reflection conditions.

[0058] This embodiment considers four different reflection situations, namely, reflection from the sea surface only, reflection from the seabed only, reflection from the sea surface to the seabed, and reflection from the seabed to the sea surface.

[0059] The time delay value τ of the sea surface reflection only 1t The relationship between the target depth z and the target speed v is:

[0060]

[0061] Among them, r t =v|tT CPA | is the horizontal distance between the sound source and the receiving point at time t, v is the target speed, T CPA It is the moment when the sound source is closest to the receiving point. This parameter is taken as an unknown variable in the solution and has a numerical solution, but it is not the target state that needs attention. z0 is the depth of the receiving point and c is the speed of sound.

[0062] The time delay value τ of the seabed reflection only 2t The relationship between the target depth z and the target speed v is:

[0063]

[0064] Where H is the ocean depth.

[0065] The time delay value τ of the sea surface-seabed reflection 3t The relationship between the target depth z and the target speed v is:

[0066]

[0067] The time delay value τ of the seabed-sea surface reflection 4t The relationship between target depth z and target speed v is:

[0068]

[0069] Step S22: In each selected reflection case, the target depth and speed in the current reflection case are solved by three consecutive multipath delay values. The cepstrum analysis obtains more than three delay measurement values, and one depth and speed can be solved for every three measurement values. The depth range and speed range can be obtained by point-by-point solution.

[0070] The optional reflection situations here include four types: sea surface reflection only, seabed reflection only, sea surface-seabed reflection, and seabed-sea surface reflection. In the preferred scheme, in order to reduce the amount of calculation, the reflection situation can be screened based on some information. Considering that the sea surface reflection coefficient is negative and the seabed reflection coefficient is positive, the positive and negative amplitudes corresponding to the multipath delay process in the acoustic signal inverse spectrum waterfall diagram can be used as identification information. If the amplitude is negative, it means that the multipath must have a sea surface reflection process. If the amplitude is positive, only the seabed reflection process needs to be considered. Based on this, the preferred scheme further screens the reflection situation based on the amplitude corresponding to the multipath delay process in the acoustic signal inverse spectrum waterfall diagram before solving the problem:

[0071] If the amplitude is positive, only the seafloor reflection is selected;

[0072] If the amplitude is negative, the different reflection situations selected include sea surface reflection only, sea surface-bottom seabed reflection and bottom sea surface reflection.

[0073] Depth and velocity are then solved for each reflection case selected.

[0074] Taking the sea surface reflection only as an example, the multipath delay values ​​measured three times in succession are used to list the equations:

[0075]

[0076] where i = 1, 2, ...; τ i , τ i+1 , τ i+2 is the multipath delay value measured at three consecutive moments i, i+1, and i+2; r i 、r i+1 、r i+2 is the horizontal distance between the sound source and the receiving point corresponding to time i, i+1, and i+2. Solving the equations can obtain the target depth and speed in the case of sea surface reflection only.

[0077] Point-by-point solution can obtain the target depth range and speed range.

[0078] Figure 1 Step 3 in the code is as follows:

[0079] Combined with the sea depth information, the reasonable target depth range obtained in step 2 is screened out, and the corresponding speed range is also a reasonable result. If more than one reasonable target depth range is screened out, further judgment is made based on the speed; if none of the results are reasonable or there are still more than one reasonable value, continue to track the target.

[0080] The actual sea depth is known, and the reasonable range of the target depth can be obtained based on the sea depth. For example, if the depth is 100m, the reasonable depth of the target is 0-100m. Step 2 estimates the depth range under various reflection conditions. It can be judged whether the depth range estimate is within the reasonable range. If it exceeds the reasonable range, it is considered an outlier. The depth range (and its target speed range) within the reasonable range is retained as the target depth and speed estimation result.

[0081] The method of the present invention is tested and verified: the sea depth is 100m, there is an underwater sound source with a depth of 15m and a speed of 3.8kn, and the receiving point depth is 60m. The present invention is used to estimate the target depth and speed. The cepstrum waterfall diagram of the received underwater acoustic signal is as follows: Figure 2 As shown in Figure 2, the multipath delay is extracted from the cepstrum waterfall diagram by using the correlation peak tracking search, as shown in Figure 2. Figure 3 As shown. Combined Figure 2 and Figure 3 It can be seen that according to the known delay history, the amplitude corresponding to the delay history is found in the cepstrum waterfall diagram (represented by color), which is the blue area. It can be seen that the amplitude is negative, so only the sea surface reflection, the seabed-sea surface reflection and the sea surface-seabed reflection are considered. The depth and speed of the target are calculated by solving the equation group using the sea surface multipath delay values ​​measured three times in a row, as shown in Figure 4 and Figure 5 As shown, Figure 4 is the depth estimation result, Figure 5 is the speed estimation result. In the case of single reflection from the sea surface, the estimated depth is approximately in the range of 0m to 20.1m, and the estimated speed is approximately in the range of 0m / s to 5.4m / s. In the case of seabed-sea surface reflection, the estimated depth is approximately in the range of 177.4m to 216.4m, and the estimated speed is approximately in the range of 0m / s to 17.7m / s. In the case of sea surface-seabed reflection, the estimated depth is approximately in the range of -30.2m to -21.4m, and the estimated speed is approximately 0m / s to 5.7m / s. Combined with the information that the sea depth is 100m, it can be seen that the depth of underwater targets can only be in the range of 0-100m. The estimated depths in the cases of seabed-sea surface reflection and sea surface-seabed reflection do not conform to the actual situation. Therefore, it can be judged that the extracted multipath delay should be the delay result of sea surface reflection only. Calculate the absolute error of depth estimation and the absolute error of speed estimation, and the results are as follows Figure 6 and Figure 7 As shown, the absolute error of depth estimation is approximately in the range of 0.04m to 15.00m, and the absolute error of velocity estimation is approximately in the range of 0.01m / s to 3.55m / s, which can meet application requirements and demonstrate the feasibility of the method.

[0082] 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 method for estimating target depth and speed based on multipath delay solution, characterized in that: include: Step 1: Based on the acoustic signal received by the hydrophone, the cepstrum analysis method is used to estimate the delay trajectory caused by the multipath propagation effect of the target sound source to obtain the multipath delay value; Step 2: According to the relationship between the multipath delay value and the target depth and speed under different reflection conditions, the target depth and speed are calculated using the multipath delay values ​​measured three times in succession, and the target depth range and speed range under different reflection conditions are obtained by point-by-point calculation; Step 3: According to the reasonable range of parameters determined by the actual environmental information, remove the abnormal data of multiple target depth ranges and speed ranges under different reflection conditions, and screen out the final target depth range and speed range as the estimation result.

2. The method according to claim 1, characterized in that The step 3 is: according to the known sea depth H, judging whether the target depth range estimated in each reflection case is within the known sea depth H, thereby removing outliers and screening out the final target depth range and speed range.

3. The method according to claim 2, characterized in that In step 3, if more than two reasonable target depth ranges are retained through screening, further screening is performed according to the speed range.

4. The method according to claim 1, characterized in that The different reflection situations include: sea surface reflection only, sea bottom reflection only, sea surface-sea bottom reflection and sea bottom-sea surface reflection.

5. The method according to claim 4, characterized in that In step 2, before solving, the reflection conditions are further screened according to the amplitude corresponding to the multipath delay process in the acoustic signal cepstrum waterfall diagram; if the amplitude is positive, only the seabed reflection is selected; if the amplitude is negative, the different reflection conditions selected include only sea surface reflection, sea surface-seabed reflection and seabed-sea surface reflection.

6. The method according to claim 4, characterized in that Under different reflection conditions, the relationship between the multipath delay value and the target depth and speed is constructed as follows: The multipath delay value τ of sea surface reflection only 1t The relationship between the target depth z and the target speed v is: The multipath delay value τ of the seabed reflection only 2t The relationship between the target depth z and the target speed v is: Multipath delay value τ of sea surface-seabed reflection 3t The relationship between the target depth z and the target speed v is: Multipath delay value τ of seabed-sea surface reflection 4t The relationship between the target depth z and the target speed v is: Among them, r t is the horizontal distance between the sound source and the hydrophone receiving point at time t, v is the target speed, T CPA is the moment when the sound source is closest to the receiving point, z0 is the depth of the hydrophone receiving point, c is the speed of sound, and H is the sea depth.

7. The method according to any one of claims 1 to 6, characterized in that: The time delay trajectory generated by the multipath propagation effect of the target sound source estimated by the cepstrum analysis method in step 1 is: The hydrophone received signal is processed by framing to obtain a discrete signal sequence; Perform FFT operation on the discrete signal sequence to obtain a complex sequence; The power spectrum is calculated based on the complex sequence, and the logarithm is taken to obtain the sequence Y(k); the sequence Y(k) is extended and reversally spliced ​​to obtain a new sequence; then the new sequence is inverse Fourier transformed, and the real part is taken to obtain the cepstrum sequence; The cepstrum sequence is used to extract the time delay trajectory caused by the multipath propagation effect of the target sound source and obtain the multipath delay value.

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