JPH1062466A - System for calculating electric conductivity in bottom of sea by measuring underwater electric field attendant on ship - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate electric conductivity under the bottom of the sea by measuring the underwater electric field caused by the underwater current flowing across the metal products of the bottom of a sailing ship by the electric field sensor on the bottom of the sea and setting the surface of the sea and the bottom of the sea to boundaries to calculate the electric conductivity from the measured value. SOLUTION: Two electrodes are provided on the bottom of a ship 4 straightly advancing on the sea in a definite direction and the waveform of the underwater electric field generated by the underwater current flowing across two electrodes is measured with respect to its horizontal and vertical components by the three-axis electric field sensor 1 provided on the bottom 6 of the sea to be transmitted to a processor 3 by an underwater cable 2. At the same time, the position of the ship 4 is measured by an optical method and the electric conductivity of seawater is measured by a conductivity meter. The processor 3 computes the electric conductivity under the bottom 6 of the sea from the measured value regarding the surface 5 of the sea and bottom 6 of the sea as boundaries and also regarding the mirror image moments to the surface 5 of the sea and the bottom 6 of the sea of the moment of the ship 4 as the electric field formed at a measuring point. By this constitution, work in the sea may be accomplished by only the laying work of the underwater cable 2 and the electric conductivity under the bottom 6 of the sea can be easily measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of measuring electric conductivity under the sea floor when the measurement area is below the sea floor, as a method of measuring electric conductivity underground.

[0002]

2. Description of the Related Art Conventional methods for measuring electric conductivity in the ground include direct methods such as a quadrupole method for measuring electric conductivity using two current supply electrodes and two potential measuring electrodes buried in the ground. There are a method of burying an electrode in the ground, a radio wave method of calculating the electric conductivity in the ground by measuring the polarization state of a medium-short-wave, medium-wave radio wave, and the like.

[0003]

However, when the electric conductivity under the seabed is measured by the conventional electric conductivity measuring method, the method of burying the electrode directly on the ground, such as the quadrupole method, requires that the electrode is buried on the seabed. Operational difficulties arise that must be done. In seawater, the electromagnetic wave intensity is greatly attenuated, so that measurement by the radio method becomes impossible.

The present invention has been made in view of the above problems, and uses a measured value of an underwater electric field generated by an underwater current when a ship is running without performing complicated work on the seabed. It is an object of the present invention to provide a method of obtaining the electric conductivity under the seabed, which can easily measure the electric conductivity under the seabed.

[0005]

In order to achieve the above object, according to the first aspect of the present invention, an underwater electric field generated by an underwater current flowing between metal articles on the bottom of a ship is provided. The electric conductivity under the seabed 6 is obtained by measuring the electric field sensor 1 installed on the seabed 6 and calculating the measured value and considering the sea surface 5 and the seabed 6 as boundaries.

According to a second aspect of the present invention, an underwater electric field generated by an underwater current flowing between metal articles on the bottom of the ship is caused by the electric field sensor 1 installed on the seabed 6 when the ship 4 is sailing. It is characterized in that the electrical conductivity under the seabed 6 is measured from a calculation using the ratio of the maximum amplitude of the horizontal and vertical components of the measured underwater electric field.

[0007] In the method for determining electric conductivity under the seabed according to claim 1 or 2, the metal article on the ship bottom is composed of two electrodes.

According to the present invention, the ship 4 is located in the measurement area.
, An underwater electric field is generated by the underwater current flowing between the metal products on the bottom of the ship 4. This underwater electric field is at sea bottom 6
Is measured by the electric field sensor 1 installed in the. The electric conductivity under the seabed 6 is obtained from the measured value and the calculation considering the sea surface 5 and the seabed 6 as boundaries. In addition, this seabed 6
When determining the lower electric conductivity, if the signal measured by the electric field sensor 1 has little noise and a clear signal, the electric field sensor 1
The calculation can be simplified by directly reading the ratio of the maximum amplitude of the horizontal and vertical components of the underwater electric field measured from the measured value.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a schematic configuration of a measuring system to which a method for obtaining electric conductivity under the seabed according to the present invention is applied.

As shown in FIG. 1, the measurement system includes an electric field sensor 1 installed on the sea floor 6, an underwater cable 2 for transmitting a measurement signal from the electric field sensor 1, and an electric field sensor transmitted via the underwater cable 2. A processing device 3 for receiving and recording the measurement signal 1 and a ship 4 for generating an underwater electric field
And a schematic configuration.

[0011] Here, in a ship in which metal products on the bottom of the ship are arranged in a complicated manner, the method of calculating the ship 4 as a single moment in the measurement method described later may be inappropriate, so that two electrodes are provided on the bottom of the ship. , A single moment is created, and the electrical conductivity below the seabed 6 is determined by a measurement method described later.

The two electrodes provided on the bottom of the marine vessel 4 include metal attached to the hull, such as a screw, and the like.
It can be composed of a dissimilar metal connected to this.

Next, a description will be given of a method of obtaining the electric conductivity under the seabed using the measuring system configured as described above.

First, the horizontal and vertical components of the underwater electric field waveform of a ship 4 traveling straight on the sea in a certain direction are measured by a three-axis electric field sensor 1 installed on the sea floor 6. At this time, the position of the ship 4 is measured at the same time by an optical method or the like,
The electric conductivity of seawater is measured using a conductivity meter or the like.

In the above measurement, coordinate axes are set as shown in FIG. 2 with the seabed 6 immediately below the electric field sensor 1 as the origin, and the position of the electric field sensor 1 (hereinafter, referred to as “measurement point”) is (0, 0,
−z1), the running course of the ship 4 is set in parallel with the x-axis, y = y
0, z = −z0−z1. Further, assuming that the moment of the ship 4 is P = (Px, Py, Pz) and the electric conductivity of seawater is σ1, the components Ex, Ey, Ez of the electric field created by the ship 4 at the measurement points are represented by Equations (1) and (2). , 3

[0016]

(Equation 1)

[0017]

(Equation 2)

[0018]

(Equation 3)

Here, r is the closest distance between the measurement point and the ship 4, and is represented by the following equation.

[0020]

(Equation 4)

Further, t is a parameter defined as follows.

[0022]

(Equation 5)

A1 (t), A2 (t) and A3 (t) are functions defined as follows.

[0024]

(Equation 6)

[0025]

(Equation 7)

[0026]

(Equation 8)

Next, considering the sea surface 5 and the sea bottom 6 as boundaries, the moments P are mirror image moments Is (P) and Ib (P) with respect to the sea surface 5 and the sea bottom 6, and the moments P are Is (P).
Let Ib (Is (P)) be the mirror image moment of
Consider the electric field created by these mirror image moments at the measurement point. Since the underwater electric field intensity due to the electric dipole moment attenuates in proportion to the cube of the distance, the contribution of the mirror image moment other than the above is ignored because it is sufficiently small with respect to the measured value.

The intensity of each image moment and the closest approach distance r
Is as shown in the following table.

[0029]

[Table 1]

Here, k2 and k3 are defined as follows, where σ1, σ2, and σ3 are the electric conductivity of seawater, air, and the seabed 6, respectively.

[0031]

(Equation 9)

By substituting the moment strength and the closest distance shown in Table 1 into Equations 1, 2 and 3, the electric field generated by each mirror image moment at the measurement point is calculated.

The sum of the electric field created at the measurement point by the actual moment and the mirror image moment obtained by the above calculation is calculated,
Find the expression of the electric field at the measurement point considering the boundary.

In the expression of the electric field at the measurement point thus obtained, the electric conductivity σ2 of air is the electric conductivity σ of seawater.
Σ2 = 0, and σ1, y
0, z0, zd, and z1 are known amounts from the measured values.

On the other hand, the quantity k3 determined by the actual moment P and the electric conductivity σ3 below the seabed 6 is an unknown quantity. Therefore, this unknown quantity is obtained from the least squares method and the ratio of the maximum amplitudes of the electric field waveforms Ex and Ez, Exp-p / Exp-p.

First, in Equations 1 and 3, zd and z1 are expressed as z
If negligible as a very small amount with respect to 0, Equations 1 and 3 are coefficients a
The following can be written using 0, a1, a2, c0, c1, c2, and c3.

[0037]

(Equation 10)

[0038]

[Equation 11]

Coefficients a0, a1, a2, c0, c in the above equation
1, c2, and c3 are obtained from the measured values using the least squares method.

The coefficients a0, a1, a2, c thus obtained
The electric field waveforms Ex and Ez are calculated by substituting 0, c1, c2 and c3 into Equations 10 and 11, and the maximum amplitudes Ezp-p and Ex
The ratio of pp, Esp-p / Exp-p, is determined.

Next, assuming that the actual moment P is a moment in the bow and stern direction, and Py = Pz = 0 and y0 = 0, Equations 1, 2, and 3 become as follows.

[0042]

(Equation 12)

[0043]

(Equation 13)

[0044]

[Equation 14]

However, t2, t3 and t4 are as follows.

[0046]

(Equation 15)

[0047]

(Equation 16)

[0048]

[Equation 17]

From Expressions 12 and 14, t that gives the maximum amplitude of Ex and Ez is obtained, and substituted into Expressions 12 and 14 to obtain expressions of the maximum amplitudes Ezp-p and Exp-p.

From the expressions of Exp-p and Exp-p obtained above, Exp-p / Exp-p is calculated, Px is eliminated and Ez-p / Exp-p is calculated.
A relational expression between pp / Exp-p and k3 is obtained.

Ezp-p / Exp-p thus obtained and k3
From the relational expression, k3 that gives the value of the ratio of the maximum amplitude Ezp-p / Exp-p obtained by the least square method is obtained.

The electric conductivity σ3 below the seabed 6 can be obtained by using Equation 9 from k3.

By the way, in the above embodiment, the electric field waveform and the maximum amplitude value of each component are obtained by applying the least square method to the equations (10) and (11). In such a case, these steps can be omitted by directly reading the maximum amplitude value from the measured value.

[0054]

As is apparent from the above description, according to the present invention, the work in seawater requires only the installation work of the electric field sensor and the underwater cable for transmitting the measurement signal from the electric field sensor. Without conducting complicated construction work on the seabed such as the conventional embedding of electrodes, the electric conductivity under the seabed is measured using the measured value of the underwater electric field generated by the weak underwater current when the ship is sailing. It can be easily measured.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a measurement system to which a method for obtaining electric conductivity under the seabed according to the present invention is applied.

FIG. 2 is an explanatory diagram showing the principle of a method for obtaining electric conductivity under the seabed according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electric field sensor, 2 ... Underwater cable, 3 ... Processing device, 4
... vessel, 5 ... sea surface, 6 ... sea bottom.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tokio Kanazawa 40 Kamomochi-cho, Naka-ku, Yokohama-shi, Kanagawa Prefecture Inside Sanba Kogyo Co., Ltd. In company

Claims (3)

[Claims] An underwater electric field generated by an underwater current flowing between metal articles on the bottom of the ship is measured by an electric field sensor (1) installed on the sea floor (6),
A method of obtaining the electric conductivity under the seabed, wherein electric conductivity under the seabed is obtained from the measured value and a calculation considering the sea surface (5) and the seabed as boundaries. 2. A ship (4) is made to sail, and an underwater electric field generated by an underwater current flowing between metal products on the bottom of the ship is subjected to horizontal and vertical components by an electric field sensor (1) installed on the seabed (6). A method for determining the electrical conductivity under the seabed, wherein the electrical conductivity under the seafloor is determined from a calculation using the ratio of the maximum amplitude of the horizontal and vertical components of the measured underwater electric field. 3. The method according to claim 1, wherein the metal article on the bottom of the ship comprises two electrodes.