JPH03248082A - Sea bottom detector - Google Patents

Abstract

PURPOSE:To accurately sound water by quantizing the intensity of a receiving signal to store the same as time series data and detecting the sea bottom from the correlation of a rectangular wave having pulse width equal to that of the reflected wave from the sea bottom with the time series data. CONSTITUTION:An ROM 2 in which a control program is preliminarily written, an RAM 3, a display control circuit 7, the interface circuit 9 with a key input apparatus 8 and the interface circuit 28 with a tide meter control circuit are connected to the bus of a CPU 1. Ultrasonic transducers 10, 11, 12 are mutually separated by 120 deg. in a horizontal direction to transmit and receive an ultrasonic wave at a fixed dip. A transmission control circuit 15 generates a tone burst wave having definite frequency and definite time width to drive the transducer 11. The receiving signal of the transducer 11 is amplified and filtered to be converted by an intermediate frequency converting circuit 18 and quantized to be written in an echo level memory 21. An intermediate frequency signal is amplified to be converted to a rectangular wave signal by a comparator 25 and frequency is detected to be written in the address of a depth counter memory 27.

Description

DETAILED DESCRIPTION OF THE INVENTION la) Industrial Application Field The present invention relates to a seabed detection device applied to ultrasonic current meters, Doppler sonar, and the like.

(b) Prior Art Conventionally, ultrasonic tidal current meters have been used as fishing electronic devices that measure tidal currents and assist in net maneuvering and boat maneuvering.

The above tidal current meter transmits and receives ultrasonic waves at a constant angle of depression with horizontal pointing directions 120 degrees apart from each other, and determines and sets the ship's moving direction and speed based on the amount of Doppler shift of the seabed reflected waves. This method measures the direction and velocity of the current at a certain depth from the amount of Doppler shift of reflected waves from the depth. Generally speaking, the ultrasonic reflectance of the ocean floor is large compared to schools of fish and other floating objects, so it is more constant than before. Seafloor detection is performed by treating echoes above this level as seafloor reflected waves. Furthermore, since the intensity of seafloor reflected waves generally decreases significantly as the depth increases, so-called TVG correction is performed. Furthermore, a so-called AGC circuit is installed in which a reception gate is provided to capture the reception signal near the seabed detected by the transmission and reception of the previous ultrasonic pulse, and the gain of the amplifier circuit is adjusted according to the strength of the reception signal within the reception gate. It is used.

(C) Problems to be Solved by the Invention However, in conventional equipment that uses the AGC circuit and detects the seabed based on echo data, when relatively large noise enters the receiving gate, the noise causes a gain in the amplifier circuit. As a result, the original level of waves reflected from the ocean floor becomes so small that it may become impossible to detect the ocean floor.

Furthermore, at depth, the level of seafloor reflected waves becomes significantly smaller, approaching the noise level caused by underwater sea noise and circuits. Therefore, the measurable depth is determined by the transmission power of the ultrasonic pulse, and in order to detect the seabed at a deeper depth, it is necessary to transmit and receive ultrasonic pulses with high power. In addition, there were cases in which echoes from schools of garden fish (bottom fish) were mistakenly detected as being on the ocean floor.

For tide meters and Tompler sonar, the accuracy of measuring ground speed is determined by the accuracy of extracting waves reflected from the ocean floor, so one of the technical challenges was how to accurately detect the ocean floor.

An object of the present invention is to provide a seabed detection device that can accurately detect the seabed even at great depths.

(Means for Solving Problem d1) Claim 1 of the present invention is a seabed detection device that detects the seafloor by transmitting ultrasonic pulses into the sea and receiving waves reflected from the seabed, which quantizes the intensity of the received signal. an echo level storage means for storing time-series data as time-series data, and a rectangular wave signal whose pulse width is equal to the expected pulse width of the seabed reflected wave, and the above-mentioned time-series data. The invention is characterized by comprising a seabed detection means for detecting the seabed.

The seabed detection device according to claim 2 of the present invention sets the pulse width of the planned seabed reflected wave according to claim 1 to the emission range of the ultrasonic beam to the virtual seabed at each depth caused by the spread of the ultrasonic beam. , is characterized by being determined by the width in the distance direction with respect to the transducer and the pulse width of the transmitted signal.

A seabed detection device according to a third aspect of the present invention is characterized in that in the seabed detection device according to the first or second aspect, the time series data and the rectangular wave signal are correlated in a direction from the maximum depth to the shallowest depth.

Furthermore, claim 4 of the present invention provides a seabed detection device that detects the seabed by transmitting ultrasonic pulses into the sea and receiving reflected waves from the seabed, in which each received signal is obtained by transmitting and receiving ultrasonic pulses a plurality of times. echo level storage means for quantizing the intensity of the data and storing each as time series data, and averaged echo data generation means for obtaining echo data by sequentially moving average the stored time series data for a plurality of times in the order of occurrence. It is characterized by

(e) Effect In the seabed detection device according to claim 1, first, the intensity of the received signal (echo) is quantized and stored as time series data by the echo level storage means.

The time series data stored in this way is correlated with a rectangular wave signal whose pulse width is equal to the expected pulse width of the seabed reflected wave by the seabed detection means, and the point at which the correlation value is maximum is determined. The sea floor is detected based on

The ultrasonic pulse transmitted into the sea is a 1-in burst wave having a constant frequency and a constant time width, and the pulse width of the seabed reflected wave should also be approximately equal to the pulse width of the transmitted ultrasonic pulse. Therefore, if the received signal includes a seabed reflected wave, the correlation value with the rectangular wave signal will be maximum at the position of the seabed reflected wave.

In this way, instead of directly detecting the seabed based on the level of the received signal, the seafloor reflected waves included in the received signal are detected by correlating them with the signal to be extracted, so the detection level is relatively low. Even if other high-frequency echoes and noise are included, only the waves reflected from the ocean floor can be selectively detected because of the difference in their waveforms.

For example, when a received signal as shown in the upper part of FIG. 7 is obtained, the correlation result with the rectangular wave signal indicated by S is as shown in the lower part of the figure. In this way, for example, the correlation value with the narrow noise N is low, and the correlation value with the seabed reflected wave GE is very large.

In the seabed detection device according to claim 2 of the present invention, the above-mentioned "planned pulse width of the seabed reflected wave" corresponds to the emission range of the ultrasonic beam to the virtual seabed at each depth caused by the spread of the ultrasonic beam, and the transmission and reception wave. The width in the distance direction from the container,
It is determined by the pulse width of the transmission signal.

FIGS. 4 and 5 are diagrams showing the spread of the ultrasonic beam and changes in the pulse width of the waves reflected from the seabed. As shown in Figure 4, the ultrasonic beam transmitted from the ultrasonic transducer has a fixed directivity angle, and the deeper the depth (the wider the radiation range to the seafloor, the greater the distance between the transducer and the seafloor). As for the distance, the width L occurs in the distance direction in proportion to the spread of the radiation range W on the seabed. Therefore, as shown in FIG. 5, the deeper the depth (the wider the pulse width of the seabed reflected wave becomes).

FIGS. 6(A) and 6(B) show examples of correlation results between seafloor reflected waves with different pulse widths and rectangular wave signals. The figure (A) shows the pulse width of the seabed reflected wave when the pulse width of the rectangular wave signal (only the width of the rectangular wave signal is shown in the figure) is equal, and the figure (B) shows the pulse width of the seafloor reflected wave. Cases in which the width and the pulse width of the rectangular wave signal are different are shown. As shown in FIG. 4A, when the correlation is calculated from shallow to deep, the peak of the correlation result appears at only one point behind the seabed position by the pulse width (correlation width) of the rectangular wave signal. Therefore, a place shallower than the peak point of the correlation result by the correlation width can be detected as the seabed. On the other hand, as shown in FIG. 3B, if the pulse width of the seabed reflected wave and the pulse width of the rectangular wave signal are different, the peak of the correlation result will have a width. Therefore, as in the seabed detection device according to claim 2, if the pulse width of the rectangular wave signal to be correlated is changed according to the pulse width of the seabed reflected wave, the correlation result will have a single peak regardless of the depth. can be obtained and the seabed can be detected accurately.

Furthermore, when seeking correlation from deeper to shallower depths,
The above relationship (whether there is a range in the peak of the correlation result or not)
is similar, but in that case, the peak point of the correlation result can be directly determined as the sea floor, as described below.

In the seabed detection device according to claim 3 of the present invention, correlation processing between the time series data and the rectangular wave signal is performed in a direction from the maximum depth to a shallower depth.

In general, it may be difficult to determine the starting depth of the seabed (the starting point of seafloor reflected waves) depending on the quality (condition) of the seabed and the influence of schools of garden fish. For example, as shown in Fig. 8, the waves reflected from a school of garden fish overlap just before the waves reflected from the seabed, making it appear as if they were a single wave reflected from the seabed. On the other hand, ultrasonic pulses will not be reflected from behind the seabed reflected waves (inside the seabed) unless the transmission output is extremely large. Therefore, immediately after the waves reflected from the ocean floor are approximately the sea noise level or the noise level of the equipment. Focusing on this point, the above method enables accurate seabed detection. That is, Fig. 9 (A
), when correlation is taken from the shallowest direction to the maximum depth, the starting depth is mistakenly detected as the pulse width (correlation width) B of the square wave signal from the first peak point of the obtained correlation result. There are cases. On the other hand, if the correlation is taken from the maximum depth to the shallower direction as shown in FIG. 2B, the first (backward) peak point of the correlation result can be correctly detected as the starting depth of the seabed.

In the seabed detection device according to claim 4 of the present invention, the echo level storage means quantizes the intensity of each received signal obtained by transmitting and receiving ultrasonic pulses a plurality of times, and stores each as time series data. Then, the averaged echo data generation means sequentially moves and averages the time-series data for a plurality of times in the order of occurrence to obtain echo data.

FIG. 1θ is an explanatory diagram of the above-mentioned averaging effect. In the figure, (1), (2), (3) . . . represent sequentially stored time series data, with the horizontal axis representing depth and the vertical axis representing echo level. Also, (1 to 4) is (1
) to (4), (2 to 5), (2) to (5), and (3 to 6). ) are (3) to (6)
This is the average of four time series data. By sequentially moving and averaging the received signals in this way, randomly generated noise components are reduced, and the ability to detect seafloor reflected waves is relatively improved. Therefore, accurate seabed detection is possible even at great depths.

Embodiment FIG. 1 shows a block diagram of a tidal current meter which is an embodiment of the present invention.

In Fig. 1, 1 is the CP that controls the entire control of the tidal current meter.
It is U. The bus of this CPU includes a ROM 2 in which a control program is written in advance, a RAM 3 used as various data buffers when executing the control program,
Connected are a VRAM 4 into which display data is written, a display control circuit 7 that performs successive output control of the VRAM 4, an interface circuit 9 with the key human power device 8, and an interface circuit 28 with a tidal current meter control circuit to be described later. Note that the video output circuit 5 generates a video signal from the signal read from the VRAM 4 and outputs it to the CRT 6.

The current meter control circuit connected to the interface circuit 28 will be described below. 10.11 and 1
2 is a direction in which the horizontal direction directions are 120 degrees apart from each other,
This is a transducer that transmits and receives ultrasonic waves at a constant angle of depression. The figure shows a circuit for one channel connected to one of the ultrasonic transducers 11. The transmission control circuit 15 generates a tone burst wave with a constant frequency and a constant time width, and the ultrasonic transducer 11 is driven by the amplifier circuit 14 and the transmission output circuit 13. A received signal from the ultrasonic transducer 11 is amplified by an amplifier circuit 16, a signal in a predetermined band is filtered by a filter 17, and converted to an intermediate frequency by an intermediate frequency conversion circuit 18. Furthermore, the signal is logarithmically compressed by the LOG compression circuit, quantized by the A/D converter 20, and written into the echo level memory 21. The depth counter 22 starts counting up from O every time the transmission control circuit 15 generates a transmission pulse, and selects a write address in the echo level memory 21. On the other hand, the intermediate frequency signal is amplified to a constant amplitude by the amplifier circuit 24, converted to a rectangular wave signal by the comparator 25, frequency detection is performed by digital processing by the frequency detection circuit 26, and the result is selected by the depth counter 22. The frequency data is written to the address of the frequency data memory 27. The CPUI generates a transmission trigger signal to the transmission control circuit 15 via the interface circuit 28, and also reads the contents of the echo level memory 21 and the frequency data memory 27 at a predetermined depth. At that time, T
The VG circuit 23 performs TVG correction on the output data of the echo level memory 21 .

A schematic configuration of the RAM 3 is shown in FIG. In the same figure, M (1, *) □ is the received signal of the ultrasonic transducer pointing toward the bow direction (more precisely, the signal is logarithmically compressed, quantized, and further TVG corrected). is the area to be stored for each predetermined unit depth, and M (
1, *) ) I=M (4, *) Data for the past four times is temporarily stored by H. EA (*)H is an area that stores the result of averaging the above four times of time series data. Further, EC(*)H is an area for storing the correlation result between the data obtained by EAOk) 11 and the rectangular wave signal. Similarly, those with the suffix "R" are 1 point from the bow direction.
An area for storing various data obtained from signals received by an ultrasonic transducer directed toward the starboard rear 20 degrees away.
The area with the suffix "L" is an area for storing various data obtained from the received signal of the ultrasonic transducer pointing toward the port side, 120 degrees away from the bow direction.In addition, there are areas for counters and calculations. There is a working area.

Next, the processing procedure of the CPU is shown in FIGS. 3(A) to 3(C).

As shown in Figure 3 (A), first set the initial value 1 to the number of times 1n of averaging processing of the received signal (see Figure 10).
), and sets the initial value 1 to the counter C (n2). This counter C specifies where in the storage area of the received signal shown in Fig. 2 the data is to be read, and M (C,
*) u, M (C.

depth 0 for 'k)s+ and M(C,*)t, respectively.
Read data from to maximum depth (max) (n3)
. After that, the received signals are averaged several times and stored in the storage area EA.
(*) M, EA (*) R and EA (*) L
(n4). However, when the number of averaging times m is 1, the contents of EA (*) are equal to the contents of M (1, *). Thereafter, the value of counter C is incremented in preparation for the next data reading (n5→n7). However, when C = M, C is returned to the initial value l (n5-
+n6).

Subsequently, in the procedure shown in FIG. 3(B), correlation processing is performed between the averaged data obtained in the above EA (*) and the rectangular wave signal, and the result is written in the storage area EC (*). First, set the maximum value (max) as the depth (n8), and then set the correlation width (
The width of the rectangular wave signal) B is the duration of the transmitted ultrasonic pulse expressed in distance units, and the proportional component a-D of the depth is
(n9) (Figures 4 and 5)
(see figure). After that, the contents of EA (D) to EA (D-B), that is, the data of the storage area EA at each depth from depth DB to depth DB are added (n10). Then, the added value is written into the storage area EC indicated by the depth (nil). This process is sequentially repeated while decreasing the depth by unit depth d until the depth reaches the correlation width B (n l 2 → n 13 → n9 . . . ).

Subsequently, according to the processing procedure shown in FIG. 3(C), the seabed is detected from the correlation results, and the ship's speed relative to the ground is determined. First, the peak point of the obtained correlation value is detected, the values of the peak points are sorted in descending order, and the seabed is detected based on the position with the highest peak value (n14-=n1
5). In addition, as a method of detecting a peak point from a correlation value, as shown in FIG. 11, a location where the value is higher than a certain value or more than the correlation value at a point separated by a correlation width B in the front-rear direction from the position to be detected is extracted, The maximum value within that range can be regarded as the peak point. However, due to the influence of fish schools with eaves, etc.
When the peak of the correlation value has a width, as shown in FIG. 9(B), the deepest position among the peak points is detected as the seabed. After detecting the seabed in this way, the frequency data corresponding to the depth is stored in the frequency data memory (first
27) in the figure, and calculate the speed of the ship relative to the ground and the direction of movement from the Doppler shift of the seabed reflected waves in three directions (n
17). Then, detect the noise level of the received signal and
Set the number of times m of averaging according to the noise level (n
18). For example, when the noise level is very high and the speed of the ship relative to the ground is relatively low, the number of averaging times fL'1 is increased, and when the speed of the ship relative to the ground is high or the noise level is small, the number of averaging times m is decreased. After that, a transmission trigger is generated, and the process waits until all the received signals return, and the process shown above is repeated (1119-1120-'n
3...).

(g) Effects of the Invention According to the invention described in claim 1, even if other echoes or relatively large noise are superimposed on the received signal, only the desired seafloor reflected waves can be accurately detected. can be extracted.

Further, according to the invention according to claim 2, the position of the seabed reflected wave to be extracted can be accurately determined regardless of the depth.

According to the invention according to claim 3, the starting depth of the seabed can be accurately determined based on the quality (condition) of the seabed and the presence of schools of garden fish.

Furthermore, according to the fourth aspect of the present invention, the ability to detect seabed reflected waves is improved, and seabed detection can be easily performed even from weak received signals at great depths.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a tidal current meter that is an embodiment of this invention.
Figure 2 is a schematic configuration diagram of the RAM of the same device, Figure 3 (A) ~
(C) is a flowchart showing the processing procedure of the tidal current meter. Figure 4 is a diagram showing the relationship between the spread of the ultrasonic beam and the width in the distance direction with respect to the transducer, Figure 5 is a diagram showing the relationship between depth and the pulse width of the seabed reflected wave, and Figure 6 is the seabed reflection. FIG. 3 is a diagram showing the relationship between the pulse width of a wave, the width of a rectangular wave signal, and a correlation result. FIG. 7 is a diagram showing an example of a received signal and a correlation result between the received signal and a rectangular wave signal. FIG. 8 is a diagram illustrating an example of a received signal near a seabed reflected wave. FIGS. 9(A) and 9(B) are diagrams for explaining a seabed detection method using different correlation directions. FIG. 10 is a diagram illustrating the averaging process of received signals. FIG. 11 is a diagram illustrating a method of detecting a peak value from correlation results. 10.11.12 = Ultrasonic transducer.

Claims (4)

[Claims] (1) In a seabed detection device that detects the seafloor by transmitting ultrasonic pulses into the sea and receiving seabed reflected waves, an echo level storage means for quantizing the intensity of the received signal and storing it as time series data; Seabed detection means for correlating a rectangular wave signal whose pulse width is equal to the expected pulse width of the seabed reflected wave with the above-mentioned time series data and detecting the seabed using the point at which the correlation value is maximum as a reference. A submarine detection device featuring: (2) The pulse width of the seabed reflected waves planned above is determined by the radiation range of the ultrasonic beam to the virtual seabed at each depth caused by the spread of the ultrasonic beam, the width in the distance direction to the transducer, and the width of the transmitted signal. Claim 1 defined by the pulse width
The seabed detection device described. (3) The seabed detection device according to claim 1 or 2, wherein the correlation between the time series data and the rectangular wave signal is taken from the maximum depth to the shallow direction. (4) In a seabed detection device that detects the seafloor by transmitting ultrasonic pulses into the sea and receiving waves reflected from the seabed, the intensity of each received signal obtained by transmitting and receiving multiple ultrasonic pulses is quantized, Seabed detection characterized by comprising an echo level storage means for storing each time series data as time series data, and an averaged echo data generation means for obtaining echo data by sequentially moving averaging the stored time series data for a plurality of times in the order of occurrence. Device.