A pile driving sonar signal suppression method based on deep sea horizontal array

Abstract

The invention belongs to the field of sonar signal processing, and particularly relates to a method for suppressing pile-driving sonar signals based on a deep-sea horizontal array. The method comprises the following steps: a first step of obtaining an azimuth history diagram of the deep-sea horizontal array; a second step of calculating the background noise of each element in a column vector extracted at any azimuth of the deep-sea horizontal array azimuth history diagram; a third step of comparing the column vector extracted in the second step with the calculated background noise of the element element by element, to obtain a set of new column vectors; a fourth step of traversing all azimuths in the second step to obtain a new azimuth history diagram; a fifth step of performing point-by-point subtraction and modulo-taking on the azimuth history diagram obtained in the fourth step, to output a azimuth history diagram for ultimately suppressing the pile-driving sonar signal. The method proposed by the invention directly suppresses the pile-driving sonar signal on the azimuth history diagram, and does not have the problem of filtering out targets as may occur in a frequency domain filtering method.

Description

Technical Field

[0001] The invention belongs to the field of sonar signal processing, and in particular relates to a pile driving sonar signal suppression method based on a deep sea horizontal array. Background Art

[0002] The azimuth history diagram of a deep-sea horizontal array is a time-delay-azimuth two-dimensional image obtained by beamforming the received signals of each array element of the deep-sea horizontal array at each moment (Reference: Fan Wentao et al. A beam spectrum feature weighted underwater weak target detection method [J]. Signal Processing, 38(1), 2022, pp.195-201.). It is an important way to analyze the temporal changes of target azimuth in sonar array signal processing. In the actual signal processing process of a deep-sea horizontal array, the array usually receives the target signal of interest and interference signals from all directions. When the interference signal is near the azimuth of the target signal and has strong energy, it will have a serious impact on the analysis and judgment of the target azimuth history (i.e., the bright line of the target's azimuth changing with time on the azimuth history diagram). Pile driving sonar signals are a common interference signal faced by deep-sea horizontal arrays. They are usually generated by oil, gas and other drilling platforms in the sea area near the array. Specifically, it refers to the regular impact sound signal generated when the platform moves up and down during drilling. This signal is generally reflected as a periodic pulse signal in a specific direction on the azimuth history diagram. The signal period ranges from seconds to tens of seconds. Its main characteristics are that it lasts for a long time (can last for several hours or even more than several days) and has strong energy, which makes the azimuth history of the target of interest in its direction easily obscured by the pile driving sonar signal, affecting subsequent analysis and judgment.

[0003] There is currently no particularly effective existing technology that can effectively process pile-driving sonar signals. The more commonly used suppression method is to perform frequency domain filtering on the array's received signals. However, since pile-driving sonar signals are mostly broadband signals, this method may also filter out the target frequency during filtering. Summary of the Invention

[0004] In order to better suppress the influence of pile driving sonar signals on the target azimuth course, the present invention proposes a pile driving sonar signal suppression method based on a deep sea horizontal array.

[0005] The technical solution of the present invention is divided into the following steps:

[0006] The first step is to obtain the deep-sea horizontal array azimuth process map.

[0007] In the second step, the background noise of each element in the column vector extracted at any azimuth of the deep-sea horizontal array azimuth history diagram is calculated.

[0008] In the third step, the column vector extracted in the second step is compared element by element with the calculated background noise of the element to obtain a new set of column vectors.

[0009] The fourth step is to traverse all the directions in the second step to obtain a new direction history map.

[0010] In the fifth step, the azimuth history graph obtained in the first step is subtracted point by point from the azimuth history graph obtained in the fourth step, and the azimuth history graph that ultimately suppresses the pile driving sonar signal is output.

[0011] The beneficial result of the present invention is that the proposed method directly suppresses pile driving sonar signals on the azimuth history graph, eliminating the problem of target filtering that may occur with frequency domain filtering methods. The method is simple and easy to operate, has a significant suppression effect on pile driving sonar signals, and is easy to implement in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is an implementation flow chart of the present invention;

[0013] Figure 2 This is the result of actual data testing using the specific implementation methods of the present invention. DETAILED DESCRIPTION

[0014] Figure 1 This is a flow chart of the implementation of the present invention. The specific implementation method includes the following steps:

[0015] The first step is to obtain the deep-sea horizontal array azimuth process map.

[0016] The obtained azimuth history diagram of the deep-sea horizontal array is recorded as X = [X(1), X(2), ..., X(m), ..., X(M)], where the positive integer m represents the azimuth sequence number, M represents the total number of azimuths, and 1≤m≤M. The method of obtaining the azimuth history diagram based on the received signal of the deep-sea horizontal array can be referred to the literature: "Fan Wentao et al. A method for underwater weak target detection based on beam spectrum feature weighting [J]. Signal Processing, 38(1), 2022, pp.195-201.", which will not be repeated here.

[0017] In the second step, the background noise of each element in the column vector extracted at any azimuth of the deep-sea horizontal array azimuth history diagram is calculated.

[0018] The column vector extracted from any position of the deep-sea horizontal array azimuth history diagram (taking the mth position as an example) is x = X(m) = [x(1), x(2), ..., x(n), ..., x(N)] T , N represents the length of the column vector, and the superscript T represents the vector transpose. For the nth (1≤n≤N) element, the background noise p(n) of the element is calculated as follows:

[0019]

[0020] Among them L x represents the length of the vector in the summation symbol, x(nK:n+K) represents the vector consisting of elements nK to n+K of vector x, where K is usually a positive integer not exceeding N / 100. The obtained background noise vector is denoted as p.

[0021] In the third step, the column vector extracted in the second step is compared element by element with the calculated background noise of the element to obtain a new set of column vectors.

[0022] Let the new column vector obtained be c. Since the comparison is element by element, it is obvious that the length of vector c is the same as that of vector p and vector x. Compare each element in the second step with the calculated background noise of the element according to the following formula, and obtain the nth element c(n) of the new vector c:

[0023]

[0024] Where a is the background noise adjustment factor, which can be any value between 1 and 1.5.

[0025] The fourth step is to traverse all the directions in the second step to obtain a new direction history map.

[0026] According to the calculations in the second and third steps, the new azimuth history diagram is obtained as C = [C(1), C(2), ..., C(m), ..., C(M)], where c = C(m) = [c(1), c(2), ..., c(n), ..., c(N)] T .

[0027] In the fifth step, the azimuth history graph obtained in the first step is subtracted point by point from the azimuth history graph obtained in the fourth step, and the azimuth history graph that ultimately suppresses the pile driving sonar signal is output.

[0028] The azimuth history diagram of the final output pile driving suppression sonar signal is denoted as Y, where the dimension of Y is N×M, and Y(n,m)=|X(n,m)-C(n,m)|;

[0029] Figure 2 This is the result of a test using actual data using the specific implementation of the present invention. Figure 2 (a) and Figure 2 The horizontal axis of (b) represents the direction in degrees (°), the vertical axis represents the time in seconds (s), and the color of the color bar represents the noise level of the pixel in the image in dB.

[0030] Figure 2(a) shows the azimuth history of the target of interest before the pile-driving sonar signal is suppressed. The azimuth history of the target of interest is present at approximately -37° and 10°, but a stronger periodic pile-driving sonar signal is present between -30° and 10°. The presence of the pile-driving sonar signal affects the extraction and subsequent analysis of the target's azimuth history. Figure 2 (b) is the output azimuth history graph after pile driving sonar signal suppression processing, where K is 20 and a is 1.3. It can be seen that after processing using the method of the present invention, the output azimuth history graph effectively preserves the target azimuth history information while accurately eliminating periodic pile driving sonar signal peaks. This not only makes the background near the target azimuth history of interest clearer, but also increases the average amplitude of the target azimuth history by approximately 4 dB compared to the pre-processing level.

Claims

1. A method for suppressing pile driving sonar signals based on a deep-sea horizontal array, characterized in that: The method is divided into the following steps: The first step is to obtain the deep-sea horizontal array azimuth history diagram: X = [X(1), X(2), ..., X(m), ..., X(M)], where the positive integer m represents the azimuth sequence number, and M represents the total number of azimuths, 1≤m≤M; The second step is to calculate the background noise of each element in the column vector extracted from any direction of the deep-sea horizontal array azimuth history diagram: Let the column vector extracted from any azimuth of the deep-sea horizontal array azimuth history diagram be x = X(m) = [x(1), x(2), ..., x(n), ..., x(N)] T , N represents the length of the column vector, and the superscript T represents the vector transpose; for the nth element, 1≤n≤N, the background noise p(n) of the element is calculated as follows: Among them L x represents the length of the vector in the summation symbol, x(nK:n+K) represents the vector consisting of the nKth to n+Kth elements of the vector x, and the obtained background noise vector is denoted as p; In the third step, the column vector extracted in the second step is compared element by element with the calculated background noise of the element to obtain a new set of column vectors: Assume that the new column vector obtained is c, and the length of vector c is the same as that of vector p and vector x; compare each element in the second step with the calculated background noise of the element according to the following formula, and obtain the nth element c(n) of the new vector c: Where a is the background noise adjustment factor; Step 4: Traverse all the directions in step 2 to obtain a new direction history map: C = [C(1), C(2), ..., C(m), ..., C(M)], where c = C(m) = [c(1), c(2), ..., c(n), ..., c(N)] T ; In the fifth step, the azimuth history diagram obtained in the first step is subtracted point by point from the azimuth history diagram obtained in the fourth step, and the azimuth history diagram that finally suppresses the pile driving sonar signal is output: Y(n,m)=|X(n,m)-C(n,m)|, where the dimension of Y is N×M.

2. The method for suppressing pile driving sonar signals based on a deep-sea horizontal array according to claim 1, characterized in that: In the second step, the value of K is a positive integer not exceeding N / 100.

3. The method for suppressing pile driving sonar signals based on a deep-sea horizontal array according to claim 1, characterized in that: In the third step, the background noise adjustment factor a takes any value between 1 and 1.5.

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