JP2780157B2 - A method for observing the dynamics of a brackish layer by acoustic waves - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for observing dynamics of a brackish layer in a brackish water region using acoustic reflection.

[0002]

2. Description of the Related Art A brackish water area in which seawater and freshwater are mixed is seen in an inner bay and an estuary, and a part of which is closed is a brackish lake (Nakaumi, Shinji lake, etc.). In this brackish lake, salt water and fresh water have a nearly double-layered structure due to the difference in density, and a salinity jump layer can be seen in areas where the salt content changes rapidly. It is extremely important to know the distribution and movement of saltwater layers in order to secure fishery resources and preserve the environment. For example, there is a problem in that a favorable lake bottom environment is generated due to the flow of salt water, and when a poorly oxygenated salt water body having consumed oxygen enters a fishing ground, damage such as death of fish and shellfish occurs.

[0003] The distribution and movement of the above-mentioned saltwater layer, or the thicknesses of the saltwater layer and the freshwater layer can be almost known by grasping the salinity layer. However, conventionally, since the salt concentration was directly measured by a salt meter, the observation efficiency and the observation accuracy were not good. In order to cope with such a problem, the present inventors have previously developed an underwater acoustic exploration apparatus with a digital recorder in order to grasp the existence and distribution of the salt-cave layer. The detection of the salt-cave layer using this sound wave captures the partial reflection of the sound wave at the boundary where the acoustic impedance (density x sound speed) in the medium is different, like the fish finder and the sound sounder. The digitization enables faithful waveform recording, and the amplitude of the reflected wave can be stored as quantitative data. Try to get an underwater acoustic section.

The present inventors have applied this apparatus to Nakaumi and Lake Shinji, and have been able to ascertain the distribution of the salinity layer and the thickness of the salinity layer. In addition, when used in the Nagara River for performance evaluation in a river, a saltwater wedge that had run up to 16 km upstream from the estuary could be captured. In this developed device, the received reflected wave is digitized and can be processed by a computer, and the digitized reflected wave provides quantitative reflected wave amplitude data. It has been confirmed that the time variation of the salinity layer can be observed accurately by always performing the exploration under the same conditions while keeping the gain of the section constant.

However, such an underwater acoustic search device is installed on a ship and travels in the search area, or the reflected wave is detected at an appropriate measuring point. If the ship fluctuates, it will be difficult to make observations, and if the weather conditions, such as strong winds and typhoons, make it impossible to leave the ship due to bad weather conditions, observation will not be possible. Then, when the weather conditions are not good, there is a high possibility that fluctuations occur in the salinity layer, and it is desired to be able to accurately observe time fluctuations and the like of the salinity layer in relation to the weather conditions. I have. In addition, in order to dynamically capture the temporal and spatial dynamics of the salinity crest, it is necessary to conduct continuous observations at a large number of measurement points. It is necessary to always arrange the underwater acoustic surveying device near the water surface, and it is necessary to install a tower that can withstand wind waves at the bottom of the lake, which is difficult from the viewpoint of economic efficiency and the like.

[0006]

The technical problem of the present invention is that the underwater acoustic sounding device can detect reflected waves at measuring points as appropriate regardless of weather conditions such as strong winds and typhoons. , Which enabled continuous observations at a large number of measuring points by simple means, and as a result, it was possible to dynamically capture the temporal and spatial dynamics of the salinity layer regardless of weather conditions. It is an object of the present invention to provide a method for observing the dynamics of a salinity layer in a water body.

[0007]

According to the present invention, there is provided a method for observing the dynamics of a brackish water layer in a brackish water region, in which a transducer of an underwater acoustic sounding device is fixedly installed at the bottom of a brackish water region. Along with transmitting a sound wave into the water by the transmitter / receiver, receiving a reflected wave reflected at a boundary between two layers having different acoustic impedances in the water, and continuously performing acoustic detection of the boundary by detecting the reflected wave. Thus, the temporal and spatial dynamics of the salt-carrying layer in the brackish water region are captured.

In the method for observing the dynamics of the salt-cave layer,
Based on the temporal and spatial changes of the salinity layer due to the detection of reflected waves, the direction and speed of movement of the salinity layer in the brackish water area can be measured. The vertical pattern of the salinity layer can be measured. Further, in the above dynamic observation method, an acoustic transceiver equipped with a wireless transceiver is connected to the transducer of the underwater acoustic probe, and a signal of a reflected wave detected by the acoustic transceiver is wirelessly collected, and a salt jump is performed. The dynamics of the layer can be measured and displayed in real time.

According to the method for observing the dynamics of a brackish-water salinity layer, a reflected wave partially reflected at a boundary between two layers having different acoustic impedances in water is received by a transducer, and the reflected wave is detected. By performing acoustic surveys of the boundary continuously, it is possible to capture the temporal and spatial dynamics of the salt-carrying layer in brackish waters. That is, since the amplitude of the reflected wave is correlated with the reflection coefficient (amplitude ratio between the incident wave and the reflected wave) caused by the difference in acoustic impedance between the two layers, the acoustic impedance is restored from the amplitude of the reflected wave, and the sound velocity / density is further improved. Is calculated, the relative value of the salt content of the two layers can be obtained.

Further, since the transducer is installed at the bottom of the brackish water area, it is easier to install as compared to the case where it is installed on water, and the transducer is not shaken by waves or the like, and strong wind or Regardless of weather conditions such as typhoons, continuous detection of reflected waves can be performed at many measurement points, amplitude information of the reflected waves is quantitatively grasped, and the temporal record Spatial dynamics can be captured dynamically.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the method for observing the dynamics of a brackish water layer in a brackish water region using acoustic waves according to the present invention can be applied to the water bottom (lake bottom, sea floor, river bottom) in a brackish lake or other brackish water region. In this system, the transmitter / receiver of the underwater acoustic sounding device is fixedly installed, and the salt-carrying layer in the brackish water area is detected, whereby the approximate layer thickness of the saltwater layer and the freshwater layer can be known. Like the fish finder and the sound sounder, the underwater acoustic sounding device transmits sound waves toward the surface of the water at a narrow directional angle using a transducer, and has a different acoustic impedance (density x sound speed) in water. It receives reflected waves that are partially reflected at the boundary between two layers (saline and freshwater layers). Then, the acoustic exploration of the boundary by the detection of the reflected wave is continuously performed at a large number of measuring points, so that the temporal and spatial dynamics of the salt cliff in the brackish water area can be grasped.

Here, an example of the configuration of an underwater acoustic sounding apparatus for carrying out the method of the present invention will be described with reference to the drawings. FIG. 1 shows a basic configuration of the underwater acoustic sounding device. An electrostrictive transducer 1 installed at the bottom of a lake such as a brackish lake, an acoustic transceiver connected thereto, and a received reflected wave signal are transmitted. It is composed of an A / D converter to be digitized and a data recorder (computer) having a system control function.

As shown in FIG. 2, the transducer 1 is preferably provided with a circular iron plate as a pedestal 2 on its lower surface, so that the transducer 1 can be installed at the bottom of a lake. Not only is it easy to fix, but also the sinking of the transducer 1 can be prevented, and stable reflected wave data can always be obtained without being affected by waves and other weather conditions. The data recorder equipped with the system control function controls the transmission time in the transducer 1 and records the A / D-converted signal, and transmits the transmission trigger signal to the transmitter of the acoustic transceiver. After the transmission, the transmission / reception switching circuit converts the received signal of the reflected wave into a high-speed A /
The signal is input to a D converter, and the signal is digitally recorded in a data recorder. The received signal of the reflected wave can be faithfully recorded by digitizing it, and the amplitude of the reflected wave can be stored as quantitative data.

In such an underwater acoustic search device,
When a trigger signal for transmission is sent from the computer constituting the data recording unit to the transmission unit of the acoustic transceiver, a sound wave is transmitted from the transducer 1 toward the lake surface by the signal from the transmission unit, and the sound wave is transmitted to the underwater. Part of the sound wave is reflected at the boundary between two layers (saltwater layer and freshwater layer) having different acoustic impedances, that is, a salinity layer where the acoustic impedance changes rapidly, and the reflected wave is received by the transducer.
Since the amplitude of this reflected wave is correlated with the reflection coefficient caused by the difference in acoustic impedance between the two layers, measurement is always performed with the sound pressure of the sound source and the gain of the receiving unit kept constant. By restoring the impedance, the salinity layer in the brackish water area can be grasped, and the relative value of salinity of the two layers can be obtained by calculating the sound velocity and density from the amplitude.

FIG. 3 shows a plurality (three) of the above-described underwater acoustic sounding apparatuses for carrying out the method for observing the dynamics of a salt cliff according to the present invention.
1 shows a configuration of a dynamic observation device provided with a. The three transducers 1 in this dynamic observation device are installed at the bottom of the lake with the configuration shown in FIG. 2, and are respectively connected to acoustic transceivers installed on the observation tower or the like on the ground or on the lake via cables. Connected. In the acoustic transceiver, the central controller C
After the trigger signal from the data recorder equipped with the PU is sent to the transmission unit, the reception signal of the reflected wave is received by the transmission / reception switching circuit SW in the reception unit, and after the signal is amplified and detected, the data recorder is Is input to the A / D converter in the above, and this is repeated. The signal input to the A / D converter in the data recorder is converted into a digital signal there and digitally recorded in a storage unit such as a magneto-optical disk. Further, the data recorder has a control function of the whole system, and performs time control of transmission in the transducer 1 and the like. Note that a CRT monitor can be connected to the acoustic transceiver or the data recorder so that the time-series observation records can be displayed in color on the CRT monitor simultaneously with the recording of the signal.

According to the dynamic observation device having the above configuration,
Some of the sound waves transmitted from the three transducers 1 installed at the bottom of the lake toward the lake surface are reflected by the salinity-climbing layer where the acoustic impedance in water changes rapidly, and the reflected waves are reflected by the respective transducers. Since it is received, the temporal and spatial change of the salt cliff can be determined by detecting those reflected waves, and based on that, the moving direction and moving speed of the salt stratum in the brackish water area can be measured, Further, the vertical pattern of the salinity layer in the brackish water area can be measured based on the amplitude information of the reflected wave.

Further, as shown in FIG. 4, the dynamic observation device includes a transmitter / receiver 1 installed at a plurality of arbitrary locations on the bottom of a lake.
And a battery-driven acoustic transceiver 3 having a wireless transceiver. This acoustic transceiver 3
As shown in FIG. 5, a radio transmission / reception unit, an A / D conversion unit, a radio transmission / reception unit including an antenna 4 and a battery for operating them are provided. It is assumed that. According to such a dynamic observation device, the signal of the reflected wave detected by the acoustic transceiver is converted into a digital signal by the A / D converter, and then transmitted to the land-based data recording unit wirelessly, thereby forming the salt layer. Movement can be measured and displayed in real time. This data recording unit is the same as the data recording unit in FIG. 3 except that transmission and reception are performed wirelessly.

[0018]

EXAMPLE Next, an example in which the dynamic observation of the salt cliff layer was performed using the dynamic observation device having three underwater acoustic sounding devices shown in FIG. 3 will be described. Each of the three transducers 1 in FIG. 3 was connected to a cable having a total length of 200 m, thereby being connected to a terrestrial acoustic transceiver. The received signal of the reflected wave received by the three-channel receiving unit in the acoustic transceiver is sent as an analog signal to the data recorder,
The data was converted into a digital signal (sampling frequency: 1 MHz) and recorded by the data recorder. At the same time, 3
The time-series observation records of the channels were displayed in color on a CRT monitor. The transducer is an electrostrictive type that outputs a sound wave having a frequency of 200 kHz, and has a directivity angle of about 6 ° at half-duration full angle. The acoustic transceiver has a transmission pulse width of 15 to 110 μs and sensitivity adjustment of 0 to 30 dB.

The observation was performed near the shore of Lake Nakaumi-Donejima, and three transducers were installed at about 200 m offshore from Iejima Port. The transducer was installed offshore as far as possible within the range of the cable, and the acoustic transceiver and data recorder were installed in an observation hut equipped with power supply equipment. In addition to the transducer, three off-line small thermistor water temperature gauges and one current velocimeter were also installed at the bottom of the lake. The point where the transducer was installed is at a depth of about 3.5 m, and usually freshwater is dominant from the water surface to the bottom of the lake, and there is no salinity layer.

FIG. 6 shows an acoustic profile for one week from the start of observation. This is done by transmitting and receiving every 2 minutes and recording and
It is displayed. The thick band at the bottom is the transmission line,
The wavy bands at the top indicate reflections on the water surface. The depth scale is displayed with the lake bottom as 0 m. The record does not show a halocline. Fluctuations in the reflection surface of the water surface reflect the water level and mainly change with the tide. From this, it can be seen that the underwater acoustic sounding device or the dynamic observation device provided with the same also functions as an acoustic water level meter.

FIG. 7 shows a profile of a typical salinity crest in the observation data. The noise visible in the left half of the record is probably due to waves. A salinity crest appears in the water at the center of the record. This indicates that salt water arrived near the transducer at about 8 o'clock on May 11, and the salt-cave layer rose to about 50 m below the water level between 12:00 and 14:00.

The changes in the weather conditions and the temperature of the lake bottom water when the salinity layer arrives are examined as follows. 8 (A) shows the acoustic profile detected by the transducer on April 8, FIG. 8 (B) shows the lake bottom water temperature measured by a thermistor thermometer, and FIG. 8 (C) shows the eastward direction from the observation area. Temperature and wind speed data at Yonago Airport, about 7 km, are shown, and each of these graphs has its time axis aligned. Looking at the acoustic profile, underwater noise increased around 11 o'clock,
It continues until about time. Thereafter, the amplitude of the noise became smaller and disappeared at about 19:00. On the other hand, looking at the wind speed data, the wind intensity peaked at 15:00 (8.7 m / s), decreased to 4.6 m / s at 17:00, and decreased to 2 m / s at 8:00.
m / s or less. From this it is clear that the noise appearing in the acoustic recording correlates with the wind strength.

The height of the salinity layer which appears in the acoustic record from around 16:00 peaks at 18:00. On the other hand, the temperature of the nearby lake bottom rapidly decreased from 16:00,
It has been rising since about 9 o'clock. This indicates that a saltwater mass having a low temperature has arrived, a salt-cliff formation has occurred, and the temperature of the lake bottom has dropped. From these observations, usually near the shallow lake shore where the salinity crest does not appear,
After a strong wind (west wind near the observation area) mainly blown, it was found that the salt mass in the lower part of the lake reached the lake shore.

[0024]

According to the method for observing the dynamics of a brackish water salinity layer according to the present invention described above in detail, detection of a reflected wave by the underwater acoustic sounding device at an appropriate measuring point regardless of weather conditions such as a strong wind or a typhoon. In addition, it is possible to perform continuous observation at a large number of measurement points by simple means, and as a result,
It is possible to dynamically capture the temporal and spatial dynamics of the salt cliff regardless of weather conditions.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of an underwater acoustic search device used in the method of the present invention.

FIG. 2 is a perspective view illustrating a configuration of a transducer.

FIG. 3 is a block diagram of a dynamic observation device including a plurality (three) of underwater acoustic sounding devices for performing the salt cliff dynamic observation method of the present invention.

FIG. 4 is a configuration diagram of a dynamic observation device in which an acoustic transceiver having a wireless transceiver is connected to a transducer installed at the bottom of a lake.

FIG. 5 is a block diagram showing details of an acoustic transceiver in FIG. 4;

FIG. 6 is a graph showing an observed acoustic profile.

FIG. 7 is a graph showing an acoustic profile in which a salinity crest appears in observation data.

FIG. 8A shows an acoustic profile detected by a transducer, FIG. 8B shows a lake bottom water temperature measured by a thermistor thermometer,
(C) shows temperature and wind speed data near the observation area,
It is a graph which shows those time axes together.

[Explanation of symbols]

 1 Transceiver 3 Sound Transceiver

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI G01N 29/18 G01N 29/20 29/20 G01F 23/28 S (72) Inventor Satoshi Suzaki 513-6 Miyashita, Fuji City, Shizuoka Prefecture ( 72) Inventor Shigeo Matsuda 2-12-7, Shirokanedai, Minato-ku, Tokyo (72) Inventor Megumi Anma 6-80-15, Miharu-cho, Yokosuka-shi, Kanagawa-ken (72) Inventor Miro Inuchi 1-3-1 Higashi, Tsukuba-shi, Ibaraki (56) References JP-A-56-72337 (JP, A) JP-A-49-133061 (JP, A) JP-A-6-58912 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G01S 15/88 G01C 13/00 G01D 21/00 G01F 23/28 G01H 15/00 G01N 29/18 G01N 29/20

Claims (4)

(57) [Claims] 1. A transmitter / receiver of an underwater acoustic sounding device is fixedly installed on a water bottom in a brackish water area, and a sound wave is transmitted into the water by the transmitter / receiver, and a boundary between two layers having different acoustic impedances in the water. Receiving the reflected waves reflected by the basin, and continuously detecting the boundary by acoustic detection of the reflected waves, thereby capturing the dynamics of the salt basin in the brackish water area. How to observe layer dynamics. 2. The dynamic observation method according to claim 1,
Acoustic waves characterized by installing transducers at least at multiple points and measuring the direction and speed of movement of the salt formation in the brackish water area based on the temporal changes in the reflected waves detected by those transducers. How to observe the dynamics of the water salinity layer. 3. The dynamic observation method according to claim 1, wherein
A method of observing the dynamics of a brackish-water salinity layer by acoustically measuring a vertical pattern of a salinity layer in a brackish water area based on amplitude information of reflected waves detected by a transducer. 4. The dynamic observation method according to any one of claims 1 to 3, wherein an acoustic transceiver having a wireless transceiver is connected to the transducer of the underwater acoustic probe, and the acoustic transceiver uses the acoustic transceiver. A method for observing the dynamics of a brackish water layer by acoustically collecting the detected reflected wave signals wirelessly and measuring and displaying the dynamics of the saline layer in real time.