JPH01212383A - Sonar - Google Patents

Abstract

PURPOSE:To discriminate the kinds of fish on the basis of the difference in reflection loss from schools of fish, by accurately correcting an absorption damping component being a function of frequency in the damping characteristics of an ultrasonic wave in water. CONSTITUTION:Control circuits 6, 7 allow oscillation circuits 8, 9 to generate frequency signals lasting for a definite time and the output signals of the circuits 8, 9 are amplified by power amplifiers 10, 11 and vibrators 22, 23 are driven through duplexer circuits 12, 13. Ultrasonic pulses respectively having predetermined frequencies are transmitted from the vibrators 22, 23. The vibrators 22, 23 receive reflected waves from a submerged object to be detected to generate super-voltages and the signals thereof are supplied to amplifier circuits 14, 15 through the circuits 12, 13. Further, amplifier circuit 16, 17 amplify the output signals of the circuits 14, 15 at the mu-factor corresponding to the output levels of D/A converters 20, 21. A/D converters 18, 19 supply receiving signal level data to an I/O port 5. A CPU 3 outputs control data to the converters 20, 21 through an I/O port 4 to perform the correction of the damping of an ultrasonic wave in water.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an underwater detection device that detects underwater targets by transmitting ultrasonic pulses underwater and receiving reflected signals from underwater targets.

(bl Conventional Technology) Conventionally, for example, vertical fish finders have been used for seafloor sounding and fish detection. In devices that detect underwater by transmitting and receiving ultrasonic pulses, it is necessary to correct the attenuation characteristics of ultrasonic waves underwater. A so-called TVG circuit is provided.

The attenuation characteristics of ultrasonic waves in water are generally expressed by the following equation.

TL=20βOg,. 2R+2αR...tl)TL
=40βOg+oR+2αR・・・・(2) TL: Propagation attenuation (dB) R: Distance (Km) α: Absorption attenuation rate (dB/Km) Here, equation (1) is for seafloor sounding, and equation (2) is for fish detection. This is the case. Furthermore, in both equations, the former term is attenuation due to diffusion, and the latter term is attenuation due to absorption.

Conventionally, correction is performed by increasing the gain of the receiving section by an amount inversely proportional to the attenuation amount TL as time passes after the ultrasonic pulse is transmitted.

(C1 Problem to be solved by the invention However, in the conventional underwater detection device, there was a problem to be solved in the following points. In other words, the propagation attenuation TL depends on whether the target to be detected is the seabed or a school of fish. In addition, even if it is a school of fish, the above equation (2) does not hold depending on its density.Furthermore, when the distance to be detected is long, the range of change in the correction amount becomes large, but the S/
In cases where correction can only be made within a certain range due to the relationship with the N ratio, this method uses two types of ultrasonic pulses with different frequencies to identify the type of target to be detected, such as the type of fish. It is effective to compare the reflection intensity from the target. This invention does not necessarily require the above-mentioned +11 formula or (2) to identify the type of detected target.
) In view of the fact that it is not necessary to completely correct the amount of attenuation according to the equation, the present invention aims to provide an underwater detection device that solves the conventional purpose by correcting only the amount of attenuation related to absorption attenuation α, which is a function of frequency. be.

(Means for Solving Problem d1) The underwater detection device of the present invention is an underwater detection device that transmits ultrasonic pulses underwater, receives reflected signals from underwater targets, and determines the position and reflection intensity of the underwater targets. Attenuation correction data generation means for generating data for correcting absorption attenuation for each elapsed time after transmission of an underwater ultrasonic pulse for two types of ultrasonic waves with different frequencies; and the two types of ultrasonic waves with different frequencies. The present invention is characterized in that a correction means is provided for correcting the reception level for each pulse using correction data generated by the attenuation correction data generation means as time elapses after transmission of the ultrasonic pulse.

(e) Function In the underwater detection device of the present invention, the attenuation correction data generation means generates data for correcting absorption attenuation for each elapsed time after transmission of an underwater ultrasonic pulse for two types of ultrasonic waves having different frequencies. The correction means corrects the received signal level for each of two types of ultrasonic pulses having different frequencies using the correction data generated by the attenuation correction data generation means as time elapses after the ultrasonic pulse is transmitted. Here, the absorption attenuation is expressed by the term 2αR in the above equation (1) or (2), and is proportional to the distance R. The absorption attenuation coefficient α is a coefficient determined by the frequency of the ultrasonic wave. Therefore, by correcting this absorption attenuation term, the amount of attenuation with respect to the travel distance of the ultrasonic pulse, that is, the elapsed time after the ultrasonic pulse is transmitted, becomes equal regardless of the frequency of the ultrasonic pulse. Therefore, the proportional relationship between the received signal levels due to the transmission and reception of two different types of ultrasonic pulses remains unchanged, making it possible to observe the frequency characteristics of the detected target. Note that even when detecting over a long distance, the variation width of the absorption attenuation term is relatively small (f) Embodiment FIG. 1 is a block diagram of an underwater detection device that is an embodiment of the present invention. In the figure, 3 is a CPU that controls the entire device through program processing, 1 is a ROM that stores the program in advance, and 2 is a RAM that is used as a working area when executing the program. 4 and 5
is an I10 port, to which an input/output device to be described later is connected. 24 is a memory for storing display data; 25 is a display control circuit for generating a display signal from the display data; and 26 is a CRT for displaying the detection results as an image.

Control circuits 6 and 7 generate frequency signals that last for a certain period of time from oscillation circuits 8 and 9. Power amplifiers 10 and 11 amplify the output signals of oscillation circuits 8 and 9, and drive vibrators 22 and 23 via transmission/reception switching circuits 12 and 13. As a result, the vibrators 22 and 23
Ultrasonic pulses of predetermined frequencies are transmitted from each.

The vibrators 22 and 23 generate an electromotive force upon receiving the reflected wave from the underwater detection object, and the signals are supplied to the amplifier circuits 14 and 15 via the transmission/reception switching circuits 12 and 13.

Furthermore, the amplifier circuits 16 and 17 are connected to the amplifier circuits 14 and 1.
5 is amplified with an amplification factor corresponding to the output level of D/A comparators 20 and 21. 18 and 19
is an A/D converter, which supplies received signal level data to the I10 port 5. CPU3 is I10 boat 4
By outputting control data to the D/A converters 20 and 21 via the D/A converters 20 and 21, absorption and attenuation of ultrasonic waves in water, which will be described later, is corrected, and data of the received signal is read via the I10 boat 5.

FIG. 2 shows a specific example of the amplifier circuits 16 and 17 shown in FIG. This circuit amplifies the input signal si using a FET to obtain an output signal SO. At this time, the gain of the FET is varied by the voltage of the control signal sc given from the D/A converters 20 and 21 shown in FIG. There is.

FIG. 3 shows the waveform of the signal a''-e shown in FIG. 1. In this way, the control circuit 6 generates the signal a.

As a result, the signal is supplied from the power amplifier IO to the vibrator 22 via the transmission/reception switching circuit 12. This allows C
As shown in the waveform below, received signals such as fish school echoes and seafloor echoes can be obtained. At the same time, as shown in signal d, D/
The A converter 20 generates a voltage signal that is proportional to the time elapsed after the ultrasonic pulse is transmitted. As a result, the output signal e of the amplifier circuit 16 becomes a received signal whose absorption and attenuation has been corrected.

Next, the processing procedure of the CPU 3 shown in FIG. 1 is shown in FIG. First, immediately after power is turned on, a correction data table is created (nl). This is a table that stores in advance the amount of correction for each elapsed time after the transmission of an ultrasonic pulse, and is used to receive and correct reflected waves through real-time processing. FIG. 4 shows an example of this correction data table. The figure shows specific areas of RAM2, including GHl”GHn and GL
l-GLn is correction data given to D/A converters 20 and 21 shown in FIG. 1 each time the received signal is sampled. This correction data is obtained by the following formula.

G=KX (0,11f +22f”/(4100+f
2) +0.0O0238f”) x 2 x (75
0/1000) t...(3) Here, f is the frequency of the ultrasonic wave (K)lz), t is the elapsed time (seconds) after transmitting the ultrasonic pulse, and K is a constant determined by the circuit configuration.

In the above equation, 750/1000 is the sound speed of ultrasonic waves in water (Km/sec), and (750/1000) T
corresponds to R in formula (1) or formula (2).

If the frequencies of the two types of ultrasound waves used are constant (
3) The value in parentheses in the equation can also be set as a constant in advance.

After creating the correction data table in this way, the timer T is reset as shown in FIG. 5, and a transmission control signal is output to the control circuits 6 and 7 (n2→n3). Subsequently, at each sampling timing, correction data is sequentially read out from the already determined correction data table and output to the D/A converters 20 and 21 (n4). Furthermore, λ/
The output data of the D converters 18 and 19 is read and temporarily stored (n5). Furthermore, display data is created from this read data and written into the memory 24 (n6).

After that, the timer T is incremented, and the value becomes the maximum value T.
Repeat the reception process until reaching M (n7-n8→n4
-...). Timer T
Reset again and transmit the next ultrasonic pulse (n
8-n2-n3).

The embodiments described above are examples in which a variable gain amplifier circuit is used to correct the absorption and attenuation of ultrasonic waves in water, but the correction can be performed by arithmetic processing as described below.

FIG. 6 is a block diagram of an underwater detection device according to another embodiment. Unlike the underwater detection device shown in FIG. 1, there are no D/A converters 20 and 21, and the amplifier circuits 16' and 17' are logarithmic amplifier circuits.

FIG. 7 shows the signals a and b shown in FIG.
The data C and d processed by . As shown in the figure, 4-bit data is obtained which is converted into decibels according to the level of the received signal. For this data, as shown in C, a decibel value that corrects absorption attenuation is generated as time passes after ultrasonic pulse transmission, and by adding this value, received data d with absorption attenuation corrected can be obtained. .

The processing procedure of the CPU shown above is shown in FIG. First, the timer T is reset and a transmission control signal is output to the control circuits 6 and 7 (nl→n2). Next, the output data of the A/D converters 18 and 19 is read, the correction data (see C in FIG. 7) is calculated from the value of the timer T, and the correction data is added to the received data, so that the corrected received data ( d) in FIG. 7 is determined (n3 to n5).

Furthermore, display data is created and written into the display memory 24. After that, the timer T is incremented and the reception process is repeated until the value reaches the maximum number of incoming calls (n?-
n8-=n3-...), and after completing the reception process for a certain period of time, the next ultrasonic pulse is transmitted (n8-'n1
→n2).

In each of the embodiments, an ultrasonic pulse transmitting/receiving circuit is provided for each frequency used, but it is also possible to use a part of the circuit.

(g) Effects of the Invention As described above, according to the present invention, among the attenuation characteristics of ultrasonic waves in water, the absorption attenuation component, which is a function of frequency, is accurately corrected. When using this method for underwater detection, the attenuation characteristics are the same, making it possible to identify the species of fish based on the difference in reflection loss, for example. Moreover, since the correction change width of absorption attenuation is relatively small, underwater detection over long distances is possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an underwater detection device according to an embodiment of the present invention, and FIG. 2 is a specific circuit diagram of specific blocks in FIG. 1. FIG. 3 is a waveform diagram of the main part of FIG. 1. FIG. 4 is a diagram showing the configuration of a specific area of the RAM, and FIG. 5 is a flowchart showing the processing procedure of the CPU. 6 to 8 are diagrams relating to other embodiments of the underwater detection device, in which FIG. 6 is a block diagram, and FIG. 7 shows signals and data of each part thereof,
Figure 8 shows the processing procedures of the CPU. Figure 2, Figure 3, Figure 4, Figure 5, Figure 8.

Claims (1)

[Claims] (1) In an underwater detection device that transmits an ultrasonic pulse underwater and receives a reflected signal from an underwater target to determine the position and reflection intensity of the underwater target, every time elapsed after the ultrasonic pulse was transmitted underwater. an attenuation correction data generating means that generates data for correcting the absorption attenuation of two types of ultrasonic waves having different frequencies; an underwater detection device comprising: correction means for correcting a reception level using correction data generated by the attenuation correction data generation means;