JPH07270534A - Method for probing stratum of seabed - Google Patents

Abstract

PURPOSE:To obtain a method capable of precisely observing the state of a stratum of the seabed. CONSTITUTION:In a method for probing the stratum of seabed by a multichannel reflection method where ultrasonic waves 6 emitted from the same sound source 3 are received by a multichannel receiver 8, positions of the sound source 3 and the multichannel receiver 8 are computed by receiving GPS position signals from artificial satellites 9a to 9d. The sound source 3 and the multichannel receiver 8 are movable. Reflection waves 7 reflected from the same point and along different routes are taken out and the stratum is discriminated by superposing them on one another, while noise is thereby removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for exploring a seabed, and more particularly to a method for exploring a seabed by the multi-channel reflection method.

[0002]

2. Description of the Related Art FIG. 4 is an explanatory view of multiple reflection, which is a problem in the exploration of the seabed by the conventional multi-channel reflection method. 1 is an observation ship, 2 is the sea surface, 3 is the observation ship 1
Sound sources such as ultrasonic transmitters towed by, 4 and 5 are seafloor strata, 6 are ultrasonic waves from the sound source 3, 7 are reflected waves,
Reference numeral 8 denotes a multi-channel receiver which is also towed by the observation ship 1 and in which a large number of receiving elements for receiving the reflected waves 7 are arranged at regular intervals.

In such a seabed geological survey method,
Accurate position information of the sound source 3 and the multi-channel receiver 8 is required every moment, and conventionally, the position of the observation ship 1 was measured using a radio rangefinder or the like.

[0004]

However, according to the conventional method for exploring the seabed, the position of the observation ship 1 is almost set, and the accurate positions of the sound source 3 and the multi-channel receiver 8 are accurately calculated. It was extremely difficult to obtain information (X, Y, Z), and it was not possible to accurately grasp the stratum condition.

In the conventional method, the ultrasonic wave 6 emitted from the sound source 3 has a certain directivity angle as shown in FIG. If the frequency of ultrasonic waves is increased, the above-mentioned directivity angle becomes sharper and the resolution is improved, which is preferable, but the seabed that can be probed is limited to shallow ones. The corners get wider,
There is a drawback that the resolution becomes coarse.

Further, in the above-mentioned conventional method, since noise due to multiple reflection of the reflected wave 7 is included as shown in FIG. 4, it is necessary to remove it, but this removal is extremely difficult.

The present invention eliminates the above-mentioned drawbacks.

[0008]

A method of exploring a seabed according to the present invention comprises a step of calculating coordinate positions of a towed sound source and a multi-channel receiver by a GPS position signal from an artificial satellite, and from the sound source to the seabed. And transmitting the ultrasonic wave and receiving the ultrasonic wave by the multi-channel receiver.

In the method of exploring the seabed according to the present invention, the step of storing the data received by the multi-channel receiver and the coordinate positions of the sound source and the multi-channel receiver at that time, the sound source and the multi-channel receiver. The step of superimposing the above-mentioned data of different paths reflected from the same point when the object is moved can be further included.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

In the first embodiment of the present invention, as shown in FIG. 1, GPS position signals from four artificial satellites (GPS) 9a to 9d and GP for correcting the GPS position signals are used.
A fixed station 10 and a sound source 3 provided on land for transmitting an S correction signal and a GPS mobile station 11 commonly provided above the multi-channel receiver 8 are used. The GPS position signals from 9a to 9d and the GPS correction signal from the fixed station 10 are received, and the coordinate positions of the sound source 3 and the multi-channel receiver 8 are calculated respectively.

The GPS of the multi-channel receiver 8
The position of the part farther from the mobile station 11 can be calculated by the track and direction and the position of each sensor because the observation ship 1 basically moves straight, but in order to improve the accuracy, an azimuth meter and an inclinometer are used.

According to the first embodiment of the present invention, the coordinate positions of the sound source 3 and the multi-channel receiver 8 are known by using the GPS position signal from the artificial satellite and the GPS correction signal from the fixed station. Therefore, it is possible to significantly improve the positional accuracy as compared with the conventional method.

The GPS correction signal from the fixed station 10 is necessary to correct the orbit error of the artificial satellite and the error due to the ionosphere.

In the second embodiment of the present invention, the reflected waves received by the respective receivers constituting the multi-channel receiver 8 are stored so that the reflected waves from the common reflection point can be superposed.

FIG. 2 shows the result of this superposition, and the reflected wave 7 reflected on the first path is designated as trace 1 and that on the second path is designated as trace 2. Since the noise contained in each trace 1 and 2 has its frequency and amplitude constantly changing,
As shown in b, the reflection from the common reflection point of the stratum 4 has substantially the same frequency and amplitude as A and B. Therefore, the result of the superposition becomes as shown by the trace superposition in FIG. 2, and the noise is removed or reduced, and instead the reflected waves A and B to be obtained are superposed and emphasized.

Conventionally, it was not possible to accurately measure the emission position of each ultrasonic wave, but by using GPS, the positions (X, Y,
Since Z) can be measured, the above-mentioned polymerization treatment becomes possible.

In the third embodiment of the present invention, the formation is accurately obtained from the reflected wave 7 as follows.

FIG. 3 is an explanatory view of a reflected wave reflected from the common reflection point P while the sound source 3 moves from the point A to the point B as the observation ship 1 moves, and as apparent from FIG. Sound source 3
There is a common reflection point P at a half of the distance from when the observation ship 1 is moved to when it is received by the multi-channel receiver 8. This relationship does not change within the range of its directional angle. Absent. That is, when the sound source 3 receives the reflected wave from the common reflection point P at the first position by the first receiving element and then moves the sound source 3 by a distance corresponding to the distance between the receiving elements, Since the channel receiver 8 is also moved, the reflected wave reflected at the reflection angle equal to the incident angle is received by the third reception element of the reception elements.

Therefore, the reflected waves received by the first, third, fifth, ... Receiving elements all indicate the information of the common reflection point P, and by superposing these, the common reflection point P The stratum can be accurately determined.

Therefore, in the third embodiment of the present invention,
While managing the coordinate positions of the sound source 3 and the multi-channel receiver 8 by the GPS position signals as described above, each transmission and reception data is stored and each data related to the P point position is superposed.

In order to simplify the principle, only the reflection on the sea bottom has been described, but in reality underground measurements can also be performed.

As described above, according to the third embodiment of the present invention, the data of all directions of the seabed stratum can be acquired, and the stratum can be clearly discriminated.

The above-mentioned stacking is performed by the method according to the first embodiment of the present invention, the sound source 3 and the multi-channel receiver 8
This was realized because the coordinate position of was able to be managed very accurately.

[0025]

As described above, according to the method for exploring the seabed according to the present invention, there is a great advantage that the state of the seabed layer can be observed extremely accurately regardless of the depth.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of a method for exploring a seabed stratum of the present invention.

FIG. 2 is an explanatory diagram of reflected waves of a second embodiment of the method for exploring a seabed stratum of the present invention.

FIG. 3 is an explanatory view of a third embodiment of the seabed geological survey method of the present invention.

FIG. 4 is an explanatory diagram of multiple reflection, which is a problem of the conventional seabed geological exploration method.

FIG. 5 is an explanatory diagram of a conventional seabed geological exploration method.

[Explanation of symbols]

 1 Observation ship 2 Sea surface 3 Sound source 4 Stratum 5 Stratum 6 Ultrasonic wave 7 Reflected wave 8 Multichannel receiver 9a Artificial satellite 9b Artificial satellite 9c Artificial satellite 9d Artificial satellite 10 Fixed station 11 GPS mobile station

Claims (2)

[Claims] 1. A step of calculating coordinate positions of a towed sound source and a multi-channel receiver by a GPS position signal from an artificial satellite, and an ultrasonic wave is emitted from the sound source toward the seabed, and the multi-channel receiver A method for exploring a seabed, comprising the step of receiving. 2. A step of storing data received by the multi-channel receiver and coordinate positions of the sound source and the multi-channel receiver at that time, and from the same point when the sound source and the multi-channel receiver are moved. The method for exploring a seabed according to claim 1, further comprising the step of superimposing the data of different reflected paths.