Method for determining effective sound velocity in deep sea

Abstract

The present invention discloses a method for determining an effective sound velocity in the deep sea. The method is applied to an apparatus for determining an effective sound velocity in the deep sea having a transmission point, a receiving point, and an underwater mobile carrier. The transmission point is installed on the sea surface such that the depth of the transmission point is unchanged. The receiving point is installed on the underwater mobile carrier such that the depth of the receiving point changes with movement of the underwater mobile carrier. The underwater mobile carrier can measure a sound velocity profile between the transmission point and the receiving point and a horizontal distance between the transmission point and the receiving point.

Claims

1. A method for determining an effective sound velocity in the deep sea, comprising: a transmission point depth at a moment k and a receiving point depth at the moment k; wherein the transmission point is installed on the sea surface, a depth of the transmission point is unchanged, the receiving point is installed on an underwater mobile carrier, a depth of the receiving point changes with movement of the underwater mobile carrier, the underwater mobile carrier measures a sound velocity between the transmission point and the receiving point; receiving a receiving point depth at a moment k+1 and measuring a horizontal distance between the transmission point and the receiving point by the underwater mobile carrier; determining a pitch angle between the transmission point and the receiving point according to the transmission point depth, the receiving point depth at the moment k+1, and the horizontal distance between the transmission point and the receiving point by means of trigonometry; obtaining a sound velocity profile between the transmission point and the receiving point at the moment k+1; obtaining a difference between the receiving point depth at the moment k and the receiving point depth at the k+1 moment; determining an arithmetic average sound velocity variable quantity and a mean square arithmetic average sound velocity variable quantity according to the receiving point depth at the moment k+1, the receiving point depth at the moment k, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, and the sound velocity profile between the transmission point and the receiving point at the moment k+1; obtaining a depth difference between the receiving point and the transmission point at the moment k; determining an arithmetic average sound velocity at the moment k+1 and a mean square average sound velocity at the moment k+1 according to a depth difference between the receiving point and the transmission point at the moment k+1, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, an arithmetic average sound velocity at the moment k, a mean square average sound velocity at the moment k, the arithmetic average sound velocity variable quantity, and the mean square arithmetic average sound velocity variable quantity; determining an n-order sound velocity function variable quantity (n=2,3,4) according to the sound velocity profile between the transmission point and the receiving point at the moment k+1, the receiving point depth at the moment k, the receiving point depth at the moment k+1, and the arithmetic average sound velocity at the moment k+1; determining an n-order sound velocity function (n=2,3,4) at the moment k+1 according to the n-order sound velocity function variable quantity, the depth difference between the receiving point and the transmission point at the moment k+1, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, the sound velocity profile between the transmission point and the receiving point at the moment k+1, and the arithmetic average sound velocity; calculating an n-order sound velocity coefficient (n=2,3,4) at the moment k+1 according to a pitch angle at the moment k+1; and determining an effective sound velocity at the moment k+1 according to the n-order sound velocity coefficient at the moment k+1, the n-order sound velocity function corresponding to the n-order sound velocity coefficient at the moment k+1, and the arithmetic average sound velocity at the moment k+1.

2. The method for determining an effective sound velocity in the deep sea according to claim 1, wherein the obtaining a difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1 comprises: determining the difference between the receiving point depth at the moment k and the receiving point depth at the moment k according to the receiving point depth at the moment k and the receiving point depth at the moment k+1 by using a formula Δz.sub.k=z.sub.B,k+1−z.sub.B,k, wherein Δz.sub.k is the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1; z.sub.B,k is the receiving point depth at the moment k; and z.sub.B,k+1 is the receiving point depth at the moment k+1.

3. The method for determining an effective sound velocity in the deep sea according to claim 2, wherein the obtaining a depth difference between the receiving point and the transmission point at the moment k comprises: determining the depth difference between the receiving point and the transmission point at the moment k according to the receiving point depth at the moment k and the transmission point depth at the moment k by using a formula z.sub.ABk=z.sub.B,k−z.sub.A, wherein z.sub.ABk, is the depth difference between the receiving point and the transmission point at the moment k; z.sub.A is the transmission point depth; and z.sub.B,k is the receiving point depth at the moment k.

4. The method for determining an effective sound velocity in the deep sea according to claim 3, wherein the determining an arithmetic average sound velocity variable quantity and a mean square arithmetic average sound velocity variable quantity according to the receiving point depth at the moment k+1, the receiving point depth at the moment k, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, and the sound velocity profile between the transmission point and the receiving point at the moment k+1 comprises: respectively determining the arithmetic average sound velocity variable quantity and the mean square arithmetic average sound velocity variable quantity according to the receiving point depth at the moment k+1, the receiving point depth at the moment k, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, and the sound velocity profile between the transmission point and the receiving point at the moment k by using a formula ΔV.sub.k=∫.sub.z.sub.B,k.sup.z.sup.B,k.sup.+Δz.sup.kc(z)dz and a formula ΔW.sub.k=∫.sub.z.sub.B,k.sup.z.sup.B,k.sup.+Δz.sup.kc.sup.2(z)dz, wherein ΔV.sub.k is the arithmetic average sound velocity variable quantity; ΔW.sub.k is the mean square arithmetic average sound velocity variable quantity; z.sub.B,k+Δz.sub.k is the receiving point depth at the moment k+1; z.sub.B,k is the receiving point depth at the moment k; Δz.sub.kis the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1; and c(z) is the sound velocity profile between the transmission point and the receiving point at the moment k+1.

5. The method for determining an effective sound velocity in the deep sea according to claim 4, wherein the determining an arithmetic average sound velocity at the moment k+1 and a mean square average sound velocity at the moment k+1 according to a depth difference between the receiving point and the transmission point at the moment k+1, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, an arithmetic average sound velocity at the moment k, a mean square average sound velocity at the moment k, the arithmetic average sound velocity variable quantity, and the mean square arithmetic average sound velocity variable quantity comprises: obtaining a sound velocity profile at the moment k; determining the arithmetic average sound velocity at the moment k and the mean square average sound velocity at the moment k according to the sound velocity profile c(z) at the moment k, the transmission point depth z.sub.A, and the receiving point depth Z.sub.B,k; and determining the arithmetic average sound velocity at the moment k+1 and the mean square average sound velocity at the moment k+1 according to the depth difference between the receiving point and the transmission point at the moment k+1, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, the arithmetic average sound velocity at the moment k, the mean square average sound velocity at the moment k, the arithmetic average sound velocity variable quantity, and the mean square arithmetic average sound velocity variable quantity by using a formula ${\stackrel{\_}{v}}_{k+1}=\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}z\left[\mathrm{ABk}\right)\mathrm{vk}+\Delta \mathrm{Vk}$ and a formula ${\stackrel{\_}{w}}_{k+1}=\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}\left[z_{\mathrm{ABk}}{\stackrel{\_}{w}}_k+\Delta W_k\right],$ wherein v.sub.k+1 is the arithmetic average sound velocity at the moment k+1; w.sub.k+1 is the mean square average sound velocity at the moment k+1; z.sub.ABk is the depth difference between the receiving point and the transmission point at the moment k+1; v.sub.k is the arithmetic average sound velocity at the moment k; w.sub.k is the mean square average sound velocity at the moment k; ΔV.sub.k is the arithmetic average sound velocity variable quantity; and ΔW.sub.k is the mean square arithmetic average sound velocity variable quantity.

6. The method for determining an effective sound velocity in the deep sea according to claim 5, wherein the determining an n-order sound velocity function variable quantity (n=2,3,4) according to the sound velocity profile between the transmission point and the receiving point at the moment k+1, the receiving point depth at the moment k, the receiving point depth at the moment k+1, and the arithmetic average sound velocity at the moment k+1 comprises: determining the n-order sound velocity function variable quantity (n=2,3,4) according to the sound velocity profile between the transmission point and the receiving point at the moment k+1, the receiving point depth at the moment k, the receiving point depth at the moment k+1, and the arithmetic average sound velocity at the moment k+1 by using a formula $Q_k={\int }_{z_{B,k}}^{z_{B,k+1}}{\left(\frac{c\left(z\right)-{\stackrel{\_}{v}}_{k+1}}{{\stackrel{\_}{v}}_{k+1}}\right)}^n\mathrm{dz},$ wherein Q.sub.k is the n-order sound velocity function variable quantity; c(z) is the sound velocity profile between the transmission point and the receiving point at the moment k+1; z.sub.B,k is the receiving point depth at the moment k; z.sub.B,k+1 is the receiving point depth at the moment k+1; and v.sub.k+1 is the arithmetic average sound velocity at the moment k+1.

7. The method for determining an effective sound velocity in the deep sea according to claim 6, wherein the determining an n-order sound velocity function (n=2,3,4) at the moment k+1 according to the n-order sound velocity function variable quantity, the depth difference between the receiving point and the transmission point at the moment k+1, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, the sound velocity profile between the transmission point and the receiving point at the moment k+1, and the arithmetic average sound velocity comprises: determining the n-order sound velocity function (n=2,3,4) at the moment k+1 according to the n-order sound velocity function variable quantity, the depth difference between the receiving point and the transmission point at the moment k+1, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, the sound velocity profile between the transmission point and the receiving point at the moment k+1, and the arithmetic average sound velocity by using a formula $J_n^{k+1}=\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}\left[{\int }_{z_A}^{z_{B,k}}{\left(\frac{c\left(z\right)-{\stackrel{\_}{v}}_{k+1}}{{\stackrel{\_}{v}}_{k+1}}\right)}^n\mathrm{dz}+Q_k\right],$ wherein I.sub.n.sup.k+1 is the n-order sound velocity function corresponding to the n-order sound velocity coefficient at the moment k+1; Q.sub.k is the n-order sound velocity function variable quantity; z.sub.ABk is the depth difference between the receiving point and the transmission point at the moment k+1; Δz.sub.k is the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1; c(z) is the sound velocity profile between the transmission point and the receiving point at the moment k+1; and v.sub.k+1 is the arithmetic average sound velocity at the moment k+1.

8. The method for determining an effective sound velocity in the deep sea according to claim 7, wherein the calculating an n-order sound velocity coefficient (n=2,3,4) at the moment k+1 according to a pitch angle at the moment k+1 comprises: calculating a second-order sound velocity coefficient, a third-order sound velocity coefficient, and a fourth-order sound velocity coefficient according to the pitch angle at the moment k+1 by using formulas: C.sub.2.sup.k+1=1−½cot.sup.2β.sub.k+1; C.sub.3.sup.k+1=−C.sub.2.sup.k+1−1/2cot.sup.4β.sub.k+1; and C.sub.4.sup.k+1=1/2cot.sup.4β.sub.k+1 (3−5cot.sup.2β.sub.k+1)+C.sub.2.sup.k+1, C.sub.4.sup.k+1J.sub.4.sup.k+1) wherein β.sub.k+1 is the pitch angle at the moment k+1, and C.sub.2.sup.k+1, C.sub.3.sup.k+1, c.sub.4.sup.k+1 are respectively the second-order sound velocity coefficient, the third-order sound velocity coefficient, and the fourth-order sound velocity coefficient.

9. The method for determining an effective sound velocity in the deep sea according to claim 8, wherein the determining an effective sound velocity at the moment k+1 according to the n-order sound velocity coefficient at the moment k+1, the n-order sound velocity function corresponding to the n-order sound velocity coefficient at the moment k+1, and the arithmetic average sound velocity at the moment k+1 comprises: determining the effective sound velocity at the moment k+1 according to a formula v.sub.e.sup.k+1=v.sub.k+1(1−C.sub.2.sup.k+1J.sub.2.sup.k+1−C.sub.3.sup.k+1J.sub.3.sup.k+1−C.sub.4.sup.k+1J.sub.4.sup.k+1), wherein v.sub.e.sup.k+1 is the effective sound velocity at the moment k+1; v.sub.k+1 is the arithmetic average sound velocity at the moment k+1; J.sub.2.sup.k+1, J.sub.3.sup.k+1, J.sub.4.sup.k+1 are respectively a second-order sound velocity function, a third-order sound velocity function, and a fourth-order sound velocity function; and C.sub.2.sup.k+1, C.sub.3.sup.k+1, and C.sub.4.sup.k+1 are respectively the second-order sound velocity coefficient, the third-order sound velocity coefficient, and the fourth-order sound velocity coefficient.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) To describe the technical solutions in the embodiments of the present invention or in the prior art more clearly, the following briefly introduces the accompanying drawing required for describing the embodiments. Apparently, the accompanying drawings in the following description show merely some embodiments of the present invention, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

(2) FIG. 1 is a flowchart of a method for determining an effective sound velocity in the deep sea according to an embodiment of the present invention.

(3) FIG. 2 is a schematic diagram of an apparatus for determining an effective sound velocity in the deep sea according to an embodiment of the present invention;

DETAILED DESCRIPTION

(4) The following clearly and completely describes the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are merely a part rather than all of the embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

(5) An objective of the present invention is to provide a method for determining an effective sound velocity in the deep sea, so as to rapidly and accurately determine an effective sound velocity.

(6) To make the foregoing objective, features, and advantages of the present invention clearer and more comprehensible, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

(7) FIG. 1 is a flowchart of a method for determining an effective sound velocity in the deep sea according to an embodiment of the present invention. The method for determining an effective sound velocity in the deep sea is provided, where the method is applied to an apparatus for determining an effective sound velocity in the deep sea. As shown in FIG. 2, the apparatus includes a transmission point 1, a receiving point 2, and an underwater mobile carrier 3. The transmission point 1 is installed on the sea surface and the depth of the transmission point is unchanged. The receiving point 2 is installed on the underwater mobile carrier 3 and the depth of the receiving point changes with movement of the underwater mobile carrier 3. The underwater mobile carrier 3 can measure a sound velocity profile between the transmission point 1 and the receiving point 2 and a horizontal distance between the transmission point and the receiving point 2. As shown in FIG. 1, the method includes the following steps:

(8) Step 101. Obtain a transmission point depth at a moment k and a receiving point depth at the k moment.

(9) Step 102. Obtain a receiving point depth at a moment k+1 and the horizontal distance between the transmission point and the receiving point.

(10) Step 103. Determine a pitch angle between the transmission point and the receiving point according to the transmission point depth, the receiving point depth at the moment k+1, and the horizontal distance between the transmission point and the receiving point.

(11) Step 104. Obtain a sound velocity profile between the transmission point and the receiving point at the moment k+1.

(12) Step 105. Obtain a difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1.

(13) Step 106. Determine an arithmetic average sound velocity variable quantity and a mean square arithmetic average sound velocity variable quantity according to the receiving point depth at the moment k+1, the receiving point depth at the k moment, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, and the sound velocity profile between the transmission point and the receiving point at the moment k+1.

(14) Step 107. Obtain a depth difference between the receiving point and the transmission point at the moment k.

(15) Step 108. Determine an arithmetic average sound velocity at the moment k+1 and a mean square average sound velocity at the moment k+1 according to a depth difference between the receiving point and the transmission point at the moment k+1, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, an arithmetic average sound velocity at the moment k, a mean square average sound velocity at the moment k, the arithmetic average sound velocity variable quantity, and the mean square arithmetic average sound velocity variable quantity.

(16) Step 109. Determine an n-order sound velocity function variable quantity (n=2,3,4) according to the sound velocity profile between the transmission point and the receiving point at the moment k+1, the receiving point depth at the moment k, the receiving point depth at the moment k+1, and the arithmetic average sound velocity at the moment k+1.

(17) Step 110. Determine an n-order sound velocity function (n=2,3,4) at the moment k+1 according to the n -order sound velocity function variable quantity, the depth difference between the receiving point and the transmission point at the moment k+1, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, the sound velocity profile between the transmission point and the receiving point at the moment k+1, and the arithmetic average sound velocity.

(18) Step 111. Calculate an n-order sound velocity coefficient (n=2,3,4) at the moment k+1 according to a pitch angle at the moment k+1.

(19) Step 112. Determine an effective sound velocity at the moment k+1 according to the n-order sound velocity coefficient at the moment k+1, the n-order sound velocity function corresponding to the n-order sound velocity coefficient at the moment k+1, and the arithmetic average sound velocity at the moment k+1.

(20) Step 105 specifically includes:

(21) determining the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1 according to the receiving point depth at the moment k and the receiving point depth at the moment k+1 by using a formula Δz.sub.k=z.sub.B,k+1−z.sub.B,k, where

(22) 66 .sub.k is the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1; z.sub.B,k is the receiving point depth at the moment k; and z.sub.B,k+1 is the receiving point depth at the moment k+1.

(23) Step 107 specifically includes:

(24) determining the depth difference between the receiving point and the transmission point at the moment k according to the receiving point depth at the moment k and the transmission point depth at the moment k by using a formula Z.sub.ABk=z.sub.B,k−Z.sub.A, where

(25) z.sub.ABk is the depth difference between the receiving point and the transmission point at the moment k; z.sub.A is the transmission point depth; and z.sub.B,k is the receiving point depth at the moment k.

(26) Step 106 specifically includes:

(27) respectively determining the arithmetic average sound velocity variable quantity and the mean square arithmetic average sound velocity variable quantity according to the receiving point depth at the moment k+1, the receiving point depth at the moment k, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, and the sound velocity profile between the transmission point and the receiving point at the moment k by using a formula ΔV.sub.k=∫.sub.z.sub.B,k.sup.z.sup.B,k.sup.+Δz.sup.kc(z)dz and a formula ΔW.sub.k=∫.sub.z.sub.B,k.sup.z.sup.B,k.sup.+Δz.sup.kc.sup.2 (z)dz, where

(28) ΔV.sub.k is the arithmetic average sound velocity variable quantity; ΔW.sub.k is the mean square arithmetic average sound velocity variable quantity; z.sub.B,k+Δz.sub.k is the receiving point depth at the moment k+1; z.sub.B,k is the receiving point depth at the moment k; Δz.sub.k is the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1; and c(z) is the sound velocity profile between the transmission point and the receiving point at the moment k+1.

(29) Step 108 specifically includes:

(30) obtaining a sound velocity profile at the moment k;

(31) determining the arithmetic average sound velocity at the moment k and the mean square average sound velocity at the moment k according to the sound velocity profile c(z) at the moment k, the transmission point depth z.sub.A, and the receiving point depth z.sub.B,k; and

(32) determining the arithmetic average sound velocity at the moment k+1 and the mean square average sound velocity at the moment k+1 according to the depth difference between the receiving point and the transmission point at the moment k+1, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, the arithmetic average sound velocity at the moment k, the mean square average sound velocity at the moment k, the arithmetic average sound velocity variable quantity, and the mean square arithmetic average sound velocity variable quantity by using a formula

(33) ${\stackrel{\_}{v}}_{k+1}=\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}z\left[\mathrm{ABk}\right)\mathrm{vk}+\Delta \mathrm{Vk}$
and a formula

(34) ${\stackrel{\_}{w}}_{k+1}=\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}\left[z_{\mathrm{ABk}}{\stackrel{\_}{w}}_k+\Delta W_k\right],$
where

(35) v.sub.k+1 is the arithmetic average sound velocity at the moment k+1; w.sub.k+1 is the mean square average sound velocity at the moment k+1; z.sub.ABk is the depth difference between the receiving point and the transmission point at the moment k+1; v.sub.k is the arithmetic average sound velocity at the moment k; w.sub.k is the mean square average sound velocity at the moment k; ΔV.sub.k is the arithmetic average sound velocity variable quantity; and ΔW.sub.k is the mean square arithmetic average sound velocity variable quantity.

(36) Step 109 specifically includes:

(37) determining the n-order sound velocity function variable quantity (n=2,3,4) according to the sound velocity profile between the transmission point and the receiving point at the moment k+1, the receiving point depth at the moment k, the receiving point depth at the moment k+1, and the arithmetic average sound velocity at the moment k+1 by using a formula

(38) $Q_k={\int }_{z_{B,k}}^{z_{B,k+1}}{\left(\frac{c\left(z\right)-{\stackrel{\_}{v}}_{k+1}}{{\stackrel{\_}{v}}_{k+1}}\right)}^n\mathrm{dz},$
where

(39) Q.sub.k is the n-order sound velocity function variable quantity; c(z) is the sound velocity profile between the transmission point and the receiving point at the moment k+1; z.sub.B,k is the receiving point depth at the moment k; z.sub.B,k+1 is the receiving point depth at the moment k+1; and v.sub.k+1 is the arithmetic average sound velocity at the moment k+1.

(40) Step 110 specifically includes:

(41) determining the n-order sound velocity function (n=2,3,4) at the moment k+1 according to the n-order sound velocity function variable quantity, the depth difference between the receiving point and the transmission point at the moment k+1, the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1, the sound velocity profile between the transmission point and the receiving point at the moment k+1, and the arithmetic average sound velocity by using a formula

(42) $J_n^{k+1}=\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}\left[{\int }_{z_A}^{z_{B,k}}{\left(\frac{c\left(z\right)-{\stackrel{\_}{v}}_{k+1}}{{\stackrel{\_}{v}}_{k+1}}\right)}^n\mathrm{dz}+Q_k\right],$
where

(43) ∫.sub.n.sup.k+1 is the n-order sound velocity function corresponding to the n-order sound velocity coefficient at the moment k+1; Q.sub.k is the n-order sound velocity function variable quantity; z.sub.ΔBk is the depth difference between the receiving point and the transmission point at the moment k+1; Δz.sub.k is the difference between the receiving point depth at the moment k and the receiving point depth at the moment k+1; c(z) is the sound velocity profile between the transmission point and the receiving point at the moment k+1; and v.sub.k+1 is the arithmetic average sound velocity at the moment k+1.

(44) Step 111 specifically includes:

(45) calculating a second-order velocity coefficient, a third-order sound velocity coefficient, and a fourth-order sound velocity coefficient according to the pitch angle at the moment k+1 by using formulas: C.sub.2.sup.k+1=1−½cot.sup.2β.sub.k+1; C.sub.3.sup.k+1=−C.sub.2.sup.k+1=½cot.sup.4β.sub.k+1; and C.sub.4.sup.k+1=⅛cot.sup.4β.sub.k+1(3−5cot.sup.2β.sub.k+1)+C.sub.2.sup.k+1, where

(46) β.sub.k+1 is the pitch angle at the moment k+1, C.sub.2.sup.k+1, C.sub.3.sup.k+1, and C.sub.4.sup.k+1, are respectively the second-order sound velocity coefficient, the third-order sound velocity coefficient, and the fourth-order sound velocity coefficient.

(47) Step 112 specifically includes:

(48) determining the effective sound velocity at the moment k+1 according to a formula v.sub.e.sup.k+1=v.sub.k+1(1−C.sub.2.sup.k+1J.sub.2.sup.k+1−C.sub.3.sup.k+1−C.sub.4.sup.k+1J.sub.4.sup.k+1), where

(49) v.sub.e.sup.k+1 is the effective sound velocity at the moment k+1; v.sub.k+1, is arithmetic average sound velocity at the moment k+1; J.sub.2.sup.k+1, J.sub.3.sup.k+1, and J.sub.4.sup.k+1 are respectively a second-order sound velocity function, a third-order sound velocity function, and a fourth-order sound velocity function, and C.sub.2.sup.k+1, C.sub.3.sup.k+1, and C.sub.4.sup.k+1 are respectively the second-order sound velocity coefficient, the third-order sound velocity coefficient, and the fourth-order sound velocity coefficient.

(50) Integral operations of Formula (2) and Formula (4) are converted from whole integral to local integral in a depth change area, to reduce an integral calculation amount of Formula (2) and Formula (4), so as to reduce a calculation amount of the effective sound velocity v.sub.e. Only in this way, in an underwater acoustic positioning system, when a depth of the transmission point or the receiving point changes, a corresponding effective sound velocity v.sub.e can be calculated very rapidly, and then a measured propagation time is converted into a slant distance between the transmission point and the receiving point, and finally implements real-time underwater positioning.

(51) In the present invention, it is assumed that a position of a sound source is near a sea surface and is stationary; a position of a receiving point is below the position of the sound source and the position can be moved; when both the sound source and the receiving point change, a specific method of the present invention is obtained through the following derivation method.

(52) (1) Calculate an arithmetic average sound velocity v.sub.k+1 at the moment k+1 through the arithmetic average sound velocity v.sub.k at the moment k.

(53) From the moment k to the moment k+1, the corresponding depth difference Δz.sub.k of the receiving point is as follows:
Δz.sub.k=z.sub.B,k+1−z.sub.B,k   (5)

(54) The corresponding depth difference z.sub.ABk between the receiving point and the transmission point at the moment k is as follows:
z.sub.ABk=z.sub.B,k−z.sub.A   (6)

(55) The following formulas can be obtained through Formula (2a), Formula (2b), and Formula (6):
∫.sub.z.sub.A.sup.z.sup.B,kc(z)dz=z.sub.ABkv.sub.k   (7a):
∫.sub.z.sub.A.sup.z.sup.B,kC.sup.2(z)dz=z.sub.ABkw.sub.k   (7b)

(56) At the moment k+1, the arithmetic average sound velocity v.sub.k+1, and the mean square arithmetic average sound velocity Δw.sub.k+1 are respectively as follows:

(57) 0$\begin{array}{cc}{\stackrel{\_}{v}}_{k+1}=\frac{1}{z_{B,k+1}-z_A}{\int }_{z_A}^{z_{B,k+1}}c\left(z\right)\mathrm{dz}=\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}\left[z_{\mathrm{ABk}}{\stackrel{\_}{v}}_k+{\int }_{z_{B,k}}^{z_{B,k}+\Delta z_k}c\left(z\right)\mathrm{dz}\right]& \left(8a\right)\\ {\stackrel{\_}{w}}_{k+1}=\frac{1}{z_{B,k+1}-z_A}{\int }_{z_A}^{z_{B,k+1}}{c}^2\left(z\right)\mathrm{dz}=\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}\left[z_{\mathrm{ABk}}{\stackrel{\_}{w}}_k+{\int }_{z_{B,k}}^{z_{B,k}+\Delta z_k}{c}^2\left(z\right)\mathrm{dz}\right]& \left(8b\right)\end{array}$

(58) For the receiving point, from the moment k to the moment k+1, let the arithmetic average sound velocity variable quantity ΔV.sub.k and the mean square arithmetic average sound velocity variable quantity ΔW.sub.k respectively satisfy the following:
ΔV.sub.k=∫.sub.z.sub.B,k.sup.z.sup.B,k.sup.+Δz.sup.kc(z)dz   (9a)
ΔW.sub.k=∫.sub.z.sub.B,k.sup.z.sup.B,k.sup.+Δz.sup.kc.sup.2(z)dz   (9b)

(59) In this way, Formula (8) changes to

(60) $\begin{array}{cc}{\stackrel{\_}{v}}_{k+1}=\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}\left[z_{\mathrm{ABk}}{\stackrel{\_}{v}}_k+\Delta V_k\right]& \left(10a\right)\\ {\stackrel{\_}{w}}_{k+1}=\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}\left[z_{\mathrm{ABk}}{\stackrel{\_}{w}}_k+\Delta W_k\right]& \left(10b\right)\end{array}$

(61) In this case, an integral operation of Formula (2) is converted from original whole integral of the transmission point to the receiving point to local integral corresponding to a change of the receiving point depth, greatly reducing an integral calculation amount.

(62) (2) Calculate J.sub.n.sup.k (n=2,3,4) at the moment k+1 through J.sub.n.sup.k (n=2,3,4) at the moment k.

(63) The following formula can be obtained through Formula (4) and Formula (7):

(64) $\begin{array}{cc}{\int }_{z_A}^{z_{B,k}}{\left(\frac{c\left(z\right)-{\stackrel{\_}{v}}_k}{{\stackrel{\_}{v}}_k}\right)}^n\mathrm{dz}=\left(z_{B,k}-z_A\right)J_n^k=z_{\mathrm{ABk}}{J}_n^k,n=2,3,4& \left(11\right)\end{array}$

(65) At the moment k+1, an n-order J function J.sub.n.sup.k+1 (n=2,3,4) is as follows:

(66) $\begin{array}{cc}\begin{array}{cc}{J}_n^{k+1}=& \frac{1}{z_{B,k+1}-z_A}{\int }_{z_A}^{z_{B,k+1}}{\left(\frac{c\left(z\right)-{\stackrel{\_}{v}}_{k+1}}{{\stackrel{\_}{v}}_{k+1}}\right)}^n\mathrm{dz}\\ =& \frac{1}{z_{\mathrm{ABk}}+\Delta z_k}[{\int }_{z_A}^{z_{B,k}}{\left(\frac{c\left(z\right)-{\stackrel{\_}{v}}_{k+1}}{{\stackrel{\_}{v}}_{k+1}}\right)}^n\mathrm{dz}+\\ & {\int }_{z_{B,k}}^{z_{B,k+1}}{\left(\frac{c\left(z\right)-{\stackrel{\_}{v}}_{k+1}}{{\stackrel{\_}{v}}_{k+1}}\right)}^n\mathrm{dz}]\end{array}& \left(12\right)\end{array}$

(67) For the receiving point, from the moment k to the moment k+1, let an n-order J function variable quantity Q.sub.k satisfy the following:

(68) $\begin{array}{cc}{Q}_k={\int }_{z_{B,k}}^{z_{B,k+1}}{\left(\frac{c\left(z\right)-{\stackrel{\_}{v}}_{k+1}}{{\stackrel{\_}{v}}_{k+1}}\right)}^n\mathrm{dz},n=2,3,4& \left(13\right)\end{array}$

(69) In this case, Formula (12) changes to:

(70) $\begin{array}{cc}{J}_n^{k+1}=\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}\left[{\int }_{z_A}^{z_{B,k}}{\left(\frac{c\left(z\right)-{\stackrel{\_}{v}}_{k+1}}{{\stackrel{\_}{v}}_{k+1}}\right)}^n\mathrm{dz}+Q_k\right],n=2,3,4& \left(14\right)\end{array}$

(71) A function ƒ(v.sub.k) is defined as follows:

(72) $\begin{array}{cc}f\left({\stackrel{\_}{v}}_k\right)={\left(\frac{c\left(z\right)-{\stackrel{\_}{v}}_k}{{\stackrel{\_}{v}}_k}\right)}^n,n=2,3,4& \left(15\right)\end{array}$

(73) A integral of the function ƒ(v.sub.k) is as follows:

(74) $\begin{array}{cc}{f}^{\prime }\left({\stackrel{\_}{v}}_k\right)=\frac{n}{{\stackrel{\_}{v}}_k^2}c\left(z\right)-\frac{n}{{\stackrel{\_}{v}}_k^3}{c}^2\left(z\right)& \left(16a\right)\\ f^{″}\left({\stackrel{\_}{v}}_k\right)=-\frac{2n}{{\stackrel{\_}{v}}_k^3}c\left(z\right)+\frac{3n}{{\stackrel{\_}{v}}_k^4}{c}^2\left(z\right)& \left(16b\right)\\ f^{\mathrm{\prime \prime \prime }}\left({\stackrel{\_}{v}}_k\right)=\frac{6n}{{\stackrel{\_}{v}}_k^4}c\left(z\right)-\frac{12n}{{\stackrel{\_}{v}}_k^5}{c}^2\left(z\right)& \left(16c\right)\\ f^{\left(4\right)}\left({\stackrel{\_}{v}}_k\right)=-\frac{24n}{{\stackrel{\_}{v}}_k^5}c\left(z\right)+\frac{60n}{{\stackrel{\_}{v}}_k^6}{c}^2\left(z\right)& \left(16d\right)\end{array}$

(75) According to the Taylor expansion, a function ƒ(v.sub.k+1) at the moment k+1 is as follows:
ƒ(v.sub.k+1)≈ƒ(v.sub.k)+ƒ′(v.sub.k).Math.Δv+½ƒ″(v.sub.k).Math.Δv.sup.2 +⅙ƒ′″(v.sub.k).Math.Δv.sup.3+ 1/24ƒ.sup.(4))v.sub.k).Math.Δvv.sup.4   (17)
Δv.sub.k=v.sub.k+1−v.sub.k   (18)

(76) Substitute Formula (16a-d) is substituted into Formula (17) to conduct a series of algebraic operations, and the function ƒ(v.sub.k+1) at the moment k+1 may be simplified to:

(77) $\begin{array}{cc}f\left({\stackrel{\_}{v}}_{k+1}\right)\approx f\left({\stackrel{\_}{v}}_k\right)+\left(\frac{1}{1}.Math.\frac{n.Math.\Delta \stackrel{\_}{v}}{{\stackrel{\_}{v}}_k^2}-\frac{1}{2}.Math.\frac{2n-\Delta {\stackrel{\_}{v}}^2}{{\stackrel{\_}{v}}_k^3}+\frac{1}{6}.Math.\frac{6n.Math.\Delta {\stackrel{\_}{v}}^3}{{\stackrel{\_}{v}}_k^4}-\frac{1}{24}.Math.\frac{24n.Math.\Delta {\stackrel{\_}{v}}^4}{{\stackrel{\_}{v}}_k^5}\right)c\left(z\right)+\left(-\frac{1}{1}.Math.\frac{n.Math.\Delta \stackrel{\_}{v}}{{\stackrel{\_}{v}}_k^3}+\frac{1}{2}.Math.\frac{3n-\Delta {\stackrel{\_}{v}}^2}{{\stackrel{\_}{v}}_k^4}-\frac{1}{6}.Math.\frac{12n.Math.\Delta {\stackrel{\_}{v}}^3}{{\stackrel{\_}{v}}_k^5}+\frac{1}{24}.Math.\frac{60n.Math.\Delta {\stackrel{\_}{v}}^4}{{\stackrel{\_}{v}}_k^6}\right)c^2\left(z\right)& \left(19\right)\end{array}$

(78) To further simplify Formula (19), let

(79) $\begin{array}{cc}{\Phi }_k=\frac{1}{1}.Math.\frac{n.Math.\Delta \stackrel{\_}{v}}{{\stackrel{\_}{v}}_k^2}-\frac{1}{2}.Math.\frac{2n-\Delta {\stackrel{\_}{v}}^2}{{\stackrel{\_}{v}}_k^3}+\frac{1}{6}.Math.\frac{6n.Math.\Delta {\stackrel{\_}{v}}^3}{{\stackrel{\_}{v}}_k^4}-\frac{1}{24}.Math.\frac{24n.Math.\Delta {\stackrel{\_}{v}}^4}{{\stackrel{\_}{v}}_k^5}& \left(20\right)\\ {\Psi }_k=-\frac{1}{1}.Math.\frac{n.Math.\Delta \stackrel{\_}{v}}{{\stackrel{\_}{v}}_k^3}+\frac{1}{2}.Math.\frac{3n-\Delta {\stackrel{\_}{v}}^2}{{\stackrel{\_}{v}}_k^4}-\frac{1}{6}.Math.\frac{12n.Math.\Delta {\stackrel{\_}{v}}^3}{{\stackrel{\_}{v}}_k^5}+\frac{1}{24}.Math.\frac{60n.Math.\Delta {\stackrel{\_}{v}}^4}{{\stackrel{\_}{v}}_k^6}& \left(21\right)\end{array}$

(80) In this case, a function ƒ(v.sub.k+1) at the moment k+1 is as follows:
ƒ(v.sub.k+1)≈ƒ(v.sub.k)+Φ.sub.k.Math.c(z)+Ψ.sub.k.Math.c.sup.2(z)   (22)

(81) Formula (22) is substituted into Formula (12), and the n-order J function J.sub.n.sup.k+1(n=2,3,4) at the moment k+1 is as follows:

(82) 0$\begin{array}{cc}\begin{array}{cc}{J}_n^{k+1}=& \frac{1}{z_{\mathrm{ABk}}+\Delta z_k}\left[{\int }_{z_A}^{z_{B,k}}f\left({\stackrel{\_}{v}}_{k+1}\right)\mathrm{dz}+Q_k\right]\\ =& \frac{1}{z_{\mathrm{ABk}}+\Delta z_k}[{\int }_{z_A}^{z_{B,k}}f\left({\stackrel{\_}{v}}_k\right)\mathrm{dz}+{\int }_{z_A}^{z_{B,k}}{\Phi }_k.Math.c\left(z\right)\mathrm{dz}+\\ & {\int }_{z_A}^{z_{B,k}}{\Psi }_k.Math.c^2\left(z\right)\mathrm{dz}+Q_k]\\ =& \frac{1}{z_{\mathrm{ABk}}+\Delta z_k}{\int }_{z_A}^{z_{B,k}}f\left({\stackrel{\_}{v}}_k\right)\mathrm{dz}+\frac{{\Phi }_k}{z_{\mathrm{ABk}}+\Delta z_k}{\int }_{z_A}^{z_{B,k}}c\left(z\right)\mathrm{dz}+\\ & \frac{{\Psi }_k}{z_{\mathrm{ABk}}+{\mathrm{\Delta z}}_k}{\int }_{z_A}^{z_{B,k}}{c}^2\left(z\right)\mathrm{dz}+\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}{Q}_k\end{array}& \left(23\right)\end{array}$

(83) J.sub.n.sup.k+1 Formula (7) and Formula (11) are substituted into Formula (23), and the n-order J function J.sub.n.sup.k+1 (n=2,3,4) at the moment k+1 is as follows:

(84) $\begin{array}{cc}{J}_n^{k+1}=\frac{1}{z_{\mathrm{ABk}}+\Delta z_k}\left[z_{\mathrm{ABk}}{J}_n^k+{\Phi }_k{Z}_{\mathrm{ABk}}{\stackrel{\_}{v}}_k+{\Psi }_k{z}_{\mathrm{ABk}}{\stackrel{\_}{w}}_k+Q_k\right],n=2,3,4& \left(24\right)\end{array}$

(85) In this case, an integral operation of Formula (4) is converted from original whole integral of the transmission point to the receiving point to local integral of Formula (13) corresponding to a change of the receiving point depth, greatly reducing an integral calculation amount.

(86) Each embodiment of the present specification is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same and similar parts between the embodiments may refer to each other.

(87) Several examples are used for illustration of the principles and implementation methods of the present invention. The description of the embodiments is used to help illustrate the method and its core principles of the present invention. In addition, those skilled in the art can make various modifications in terms of specific embodiments and scope of application in accordance with the teachings of the present invention. In conclusion, the content of this specification shall not be construed as a limitation to the invention.