METHOD FOR OBTAINING HORIZONTAL LONGITUDINAL CORRELATION OF DEEP-SEA GREAT-DEPTH SOUND FIELD

Abstract

The present invention relates to a method for obtaining horizontal longitudinal correlation of a deep-sea great-depth sound field. Two testing positions with the same depth and different distances are selected near a deep-sea bottom; time delay differences between a direct wave of a deep sound source in a certain depth reaching two receiving positions and a surface-reflected wave are calculated according to a ray model; one testing position is fixed, and a horizontal spacing between the two positions is continuously changed to recalculate the time delay differences in different positions; and the time delay differences are substituted into a ray theory-based calculation formula of horizontal longitudinal correlation of the deep-sea great-depth sound field to obtain a change rule of the horizontal longitudinal correlation of a target region. The present invention greatly reduces amount of calculation, and is easy in engineering practice.

Claims

1. A method for obtaining horizontal longitudinal correlation of a deep-sea great-depth sound field, comprising the following steps: step 1: determining two receiving positions with the same depth and different distances from a deep sound source near a deep-sea bottom as testing positions, wherein coordinates of the two receiving positions are respectively (z,r) and (z,r+r); z indicates a receiving depth; r indicates a receiving distance; r indicates a horizontal longitudinal spacing of the two receiving positions; the depth wideband deep sound source is indicated by z.sub.s and a center frequency is indicated by .sub.0; step 2: calculating a time delay difference t.sub.r between a direct wave of a wideband deep sound source reaching the receiving position (z,r) and a surface-reflected wave according to a ray model Bellhop, and calculating a time delay difference t.sub.r+r between a direct wave of the wideband deep sound source reaching the receiving position (z,r+r) and the surface-reflected wave according to the ray model Bellhop; and step 3: substituting the time delay differences t.sub.r and t.sub.r+r into a calculation formula of horizontal longitudinal correlation of the sound field, $p\left(r,r+.Math..Math.r\right)=\cos \left(\frac{{}_0}{2}.Math.\left(.Math..Math.t_r-.Math..Math.t_r+{}_r\right)\right)$ to obtain a horizontal longitudinal correlation coefficient of the sound field between two different receiving distances r and r+r when the depth of the sound source is z.sub.s and the receiving depth is z.

2. The method for obtaining the horizontal longitudinal correlation of the deep-sea great-depth sound field according to claim 1, wherein one testing position is fixed; the distance of the other testing position is changed along a horizontal direction, so that a horizontal longitudinal spacing r of the two receiving positions is changed; and then step 2 and step 3 are repeated to obtain a change rule of the correlation of the sound field along with the horizontal longitudinal spacing when a reference receiving distance is r.

3. The method for obtaining the horizontal longitudinal correlation of the deep-sea great-depth sound field according to claim 1, wherein the reference receiving distance r is changed, and then step 2 and step 3 are repeated to obtain the change rule of the correlation of the sound field at different receiving distances.

4. The method for obtaining the horizontal longitudinal correlation of the deep-sea great-depth sound field according to claim 1, wherein a change range of the sound source depth of the wideband deep sound source is 10-1000 m.

5. The method for obtaining the horizontal longitudinal correlation of the deep-sea great-depth sound field according to claim 1, wherein a frequency range of the wideband deep sound source is 10 Hz-5 kHz.

6. The method for obtaining the horizontal longitudinal correlation of the deep-sea great-depth sound field according to claim 1, wherein a receiving distance from the deep sound source to the receiving position is 0-30 km, and the receiving depth is in a range of 1000-10000 m.

Description

DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 shows a sound velocity profile used in simulation.

[0024] FIG. 2 shows an arrival structure of a direct wave and a surface-reflected wave obtained by a ray model.

[0025] FIG. 3 shows a distribution diagram of arrival time delay differences of a direct wave and a surface-reflected wave (receive depth of 4700 m).

[0026] FIG. 4 shows a theoretical calculation result of a correlation coefficient (center frequency of 310 Hz; receiving depth of 4700 m).

[0027] (a) sound source depth of 50 m; (b) sound source depth of 100 m; (c) sound source depth of 150 m; (d) sound source depth of 200 m.

[0028] FIG. 5 shows a modeling calculation result of a correlation coefficient (sound source frequency of 260-360 Hz; receiving depth of 4700 m).

[0029] (a) sound source depth of 50 m; (b) sound source depth of 100 m; (c) sound source depth of 150 m; (d) sound source depth of 200 m.

[0030] FIG. 6 shows a comparison result of theoretical and modeling calculations of correlation lengths at different sound source depths (sound source frequency of 260-360 Hz; receiving depth of 4700 m).

[0031] (a) sound source depth of 50 m; (b) sound source depth of 100 m; (c) sound source depth of 150 m; (d) sound source depth of 200 n.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention is further described in combination with embodiments and drawings.

[0033] FIG. 1 shows a sound velocity profile used in simulation.

[0034] A typical deep-sea Munk profile is adopted for calculating arrival time delay differences of a direct wave and a surface-reflected wave of a sound ray, and a sound velocity is shown in FIG. 1. Because the sound field in a deep-sea direct wave region is mainly contributed by the direct wave and the surface-reflected wave, the effect of a sea-bottom reflected wave on calculation of the correlation is neglected.

[0035] A calculation process is divided into the following five steps:

[0036] step 1: assuming that the depth of the wideband sound source is z.sub.s, and the center frequency is .sub.0, wherein coordinates of the two receiving positions are respectively (z,r) and (z,r+r); z indicates a receiving depth; r indicates a receiving distance; and r indicates a horizontal longitudinal spacing of the two receiving positions;

[0037] step 2: calculating a time delay difference t.sub.r between a direct wave of a wideband deep sound source reaching the receiving position (z,r) and a surface-reflected wave according to a ray model Bellhop, and calculating a time delay difference t.sub.r+r between a direct wave of the wideband deep sound source reaching the receiving position (z,r+r) and the surface-reflected wave according to the ray model Bellhop; and

[0038] step 3: substituting the calculated time delay differences t.sub.r and t.sub.r+r into a calculation formula of horizontal longitudinal correlation of the sound field

[00002]$p\left(r,r+.Math..Math.r\right)=\cos \left(\frac{{}_0}{2}.Math.\left(.Math..Math.t_r-.Math..Math.t_r+{}_r\right)\right)$

to obtain a horizontal longitudinal correlation coefficient of the sound field between two different receiving distances r and r+r when the depth of the sound source is z.sub.s and the receiving depth is z;

[0039] step 4: changing r to obtain a change rule of the correlation of the sound field along with the horizontal longitudinal spacing when a reference receiving distance is r; and

[0040] step 5: changing the reference receiving distance r to obtain the change rule of the correlation of the sound field at different receiving distances.

[0041] FIG. 2 shows an arrival structure of a direct wave and a surface-reflected wave obtained by a ray model.

[0042] FIG. 2 shows an arrival structure of a direct wave and a surface-reflected wave at the receiving distance of 10 km and the receiving depth of 4700 m when the sound source depth is 100 m, wherein the propagation time of the direct wave is 7.1786 s; the propagation time of the surface-reflected wave is 7.2284 s; and the time delay difference between the direct wave and the surface-reflected wave is 0.0498 s. The time delay difference between the direct wave and the surface-reflected wave is called the time delay difference for short.

[0043] FIG. 3 shows a distribution diagram of arrival time delay differences of a direct wave and a surface-reflected wave.

[0044] FIG. 3 shows a distribution result of time delay differences at different sound source depths and different receiving distances when the receiving depth is 4700 m. It can be seen that for a fixed sound source depth, the further the receiving distance is, the slower the change of the time delay differences is; the deeper the sound source depth is, the larger the gradient of the change of the time delay differences along with the distance is. Therefore, the further the receiving distance is, the slower the change of the horizontal longitudinal correlation is, i.e., the larger the period of change is; the deeper the sound source depth is, the quicker the change of the horizontal longitudinal correlation is, i.e., the shorter the period of change is.

[0045] FIG. 4 shows a theoretical calculation result of a correlation coefficient.

[0046] According to the distribution diagram of time delay differences obtained in FIG. 3, the theoretical calculation result of the horizontal longitudinal correlation coefficient of the sound field is shown in FIG. 4, wherein the center frequency 0 is 310 Hz, and the receiving depth is 4700 m. (a) Sound source depth is 50 m; (b) sound source depth is 100 m; (c) sound source depth is 150 m; and (d) sound source depth is 200 m.

[0047] A horizontal axis indicates a receiving distance r as a reference position when the correlation is calculated, and a longitudinal axis indicates a horizontal longitudinal spacing r relative to the reference receiving position.

[0048] FIG. 5 shows a modeling calculation result of a correlation coefficient.

[0049] FIG. 5 gives a change result of the horizontal longitudinal correlation coefficient of the sound field obtained through numerical modeling to verify the accuracy of the theoretical calculation result. The sound source frequency is 260-360 Hz, and the receiving depth is 4700 m. (a) Sound source depth is 50 m; (b) sound source depth is 100 m; (c) sound source depth is 150 m; and (d) sound source depth is 200 m. Compared with FIG. 4, it can be seen that the change rule of the theoretical calculation result and the change rule of the numerical modeling result are consistent, and a change trend of the horizontal longitudinal correlation of the sound field is better predicted.

[0050] FIG. 6 shows a comparison result of theoretical and modeling calculations of correlation lengths at different sound source depths.

[0051] In practical application, a corresponding longitudinal spacing is defined as a correlation length when the correlation coefficient is decreased to 0.707. When the sound source frequency is 260-360 Hz and the receiving depth is 4700 m, a black dotted line in FIG. 6 is a correlation length obtained through numerical modeling, and a black solid line is a correlation length obtained through theoretical prediction. (a) Sound source depth is 50 m; (b) sound source depth is 100 m; (c) sound source depth is 150 m; and (d) sound source depth is 200 m. It can be seen that the theoretical calculation result given by the present invention is consistent with the numerical modeling result, thereby indicating the correctness of the theoretical calculation formula.