JPH03215772A - Underwater detecting device - Google Patents

Abstract

PURPOSE:To obtain a received signal equivalent to a signal obtained by increasing transmission power substantially and to improve the S/N by generating sent pulses which are different in transmission time intervals at constant intervals as a sent pulse train. CONSTITUTION:A sent pulse train generation part 4 generates the sent pulses which differ in transmission time interval as the sent pulse train, which is sent out of a transmitter/receiver 2 at the constant intervals matching the depth of the sea bottom. A reflected wave from the sea is received by the transmitter/ receiver 2, amplified 8 and A/D-converted 10, and stored temporarily in a buffer memory 12 and then transferred to a cross-correlation arithmetic part 14. The arithmetic part 14 perform cross-correlation arithmetic operation between the received signal from the memory 12 and the sent pulse train generated by the generation part 4. Then the obtained cross-correlation signal has a large peak locally only when there is cross-correlation. For the purpose, the level of the cross-correlation signal is compared by a level comparison part 16 with a specific threshold value and only a signal larger than the threshold value is extracted and outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to underwater detection devices such as scanning sonar and fish finders, and particularly relates to techniques for improving the S/N ratio.

<Prior art> Signals received by a transducer include waves reflected from target objects such as schools of fish and the seabed, as well as waves reflected from minute underwater objects other than the target, engine noise, and other ships. This includes various noise signals such as ultrasonic waves generated from detectors. If such noise is displayed on the display, it will be very difficult to see the reflected information from the target object, so remove the noise and improve the S/N.
Improving the ratio becomes essential.

Conventionally, the following methods have been adopted to improve the S/N ratio.

(1) The power of the ultrasonic waves transmitted from the transducer is increased, thereby relatively increasing the level of the signal component from the target object included in the received signal.

(1l) A so-called correlation process is performed in which the received signal is delayed by one period or several periods using a delay circuit or the like to match the next received signal and remove noise components.

(iii) increasing the number of transmissions per unit time;
This increases the information density of the received signal.

(iv) By increasing the pulse width of the transmission pulse from the transducer and correspondingly increasing the time during which the reception signal can be received, noise components are removed by taking a moving average of the reception signal.

Problems to be Solved by the Invention> However, each of the conventional methods (1) to (iv) above has the following problems. That is, in the case of (i), if the transmission power is extremely increased, cavitation will occur, making it impossible to receive the reflected wave from the target object. In the case of (I1), if the target object moves within a short period of time, such as a school of fish, correlation processing cannot be performed effectively. (Mountain), it is limited by the depth of the ocean floor. In other words, if the transmission period is short, the reflected waves from the target object such as a school of fish obtained from the current transmission and the reflected waves from the seafloor obtained from the previous transmission will be received in the same manner. When the received signal is displayed as an image, a virtual image appears. Therefore, the transmission period T must satisfy at least the relationship T≧2D/v (where D is the depth of the seabed and ■ is the speed of sound), and there is a limit to how short the transmission period T can be. In case (iv), the distance resolution decreases.

Means for Solving the Problems> The present invention has been made in view of the above circumstances, and it is possible to obtain a received signal equivalent to substantially increasing the transmission power, thereby increasing the S The purpose is to improve the /N ratio.

Therefore, in the underwater detection device according to the first invention, a plurality of transmission pulses having different transmission time intervals are treated as a group of transmission pulse trains, and a transmission pulse train generation section that generates this transmission pulse train at regular intervals; a buffer memory for temporarily storing each received signal from underwater obtained based on the transmitted pulse train generated by the part; and calculation of cross-correlation between the received signal stored in this buffer memory and the transmitted pulse train. and a level comparison unit that compares the level of the cross-correlation signal calculated by the cross-correlation calculation unit with a threshold value and outputs a signal having a level equal to or higher than the threshold value. The composition is 1 piece.

Further, in the underwater detection device according to the second invention, a plurality of transmission pulses having different transmission frequencies are set as a group of transmission pulse trains, and a transmission pulse train generation section generates the transmission pulse train at regular intervals, and the transmission pulse train generation section bandpass filters that individually pass each received signal from underwater according to its frequency, which is obtained based on the transmitted pulse train generated by the transmission pulse train; The configuration includes: each delay circuit that individually provides a delay time corresponding to the pulse transmission timing; and an adder circuit that adds and outputs each received signal delayed by these delay circuits.

<Operation> In the underwater detection device of the first invention, a plurality of transmission pulses having different transmission time intervals are made into a group of transmission pulse trains from the transmission pulse train generation section, and this transmission pulse train is generated at regular intervals. Then, each received signal from underwater obtained based on the transmission pulse train generated by the transmission pulse train generator is temporarily stored in the sofa memory. Subsequently, the cross-correlation calculating section calculates the cross-correlation between the received signal stored in the buffer memory and the transmitted pulse train. As mentioned above, since the transmission time intervals of each transmission pulse constituting a group of transmission pulse trains are set in advance to be different from each other, the cross-correlation signal obtained in the cross-correlation calculation is localized only when there is a cross-correlation. shows a large peak. Therefore, the level of this cross-correlation signal is compared with a predetermined threshold by a level comparison section,
Only signals above the threshold are extracted and output. Therefore, noise without cross-correlation is removed and the level of the signal component from the target object is relatively increased.

On the other hand, in the underwater detection device of the second invention, a plurality of transmission pulses having different transmission frequencies are made into a group of transmission pulse trains from the transmission pulse train generation section, and this transmission pulse train is generated at regular intervals. Then, each received signal from the water having a different frequency obtained based on the transmission pulse train generated by the transmission pulse train generating section is individually passed through a band pass filter. Next, each received signal that has passed through these bandpass filters is individually given a delay time corresponding to the transmission timing of each transmission pulse by a delay circuit, and then each of the signals delayed by these delay circuits is The received signals are added together in an adder circuit and output. Therefore, the level of the signal component from the target object is relatively increased.

<Embodiments> Embodiment 1 FIG. 1 is a block diagram of an underwater detection device according to the first invention.

In the figure, reference numeral 1 indicates the entire underwater detection device;
2 is a transducer that transmits and receives ultrasonic waves, and 4 is a transmission time interval (
ΔT in FIG. , ΔT, ) are treated as a group of transmission pulse trains, and a transmission pulse train generation unit 6 generates a signal s(t) of the transmission pulse train at regular intervals Ts. This is a transmission side amplifier that amplifies the signal s(t) of the transmission pulse train.

8 is a receiving side amplifier that amplifies the received signal x(t) obtained by receiving the reflected wave from the water with the transducer 2; 10 is an A/D converter that digitizes this received signal x(t); 12
is a buffer memory that temporarily stores each digitized received signal. In addition, l4 is the reception signal x(t) stored in the buffer memory l2 and the transmission pulse train signal s(
A cross-correlation calculation unit (CPU) that calculates the cross-correlation of both data of t), l6 compares the level of the cross-correlation signal yU) calculated by the cross-correlation calculation unit 14 with the threshold value Lsh, and calculates the threshold value. A level comparison section outputs a signal having a level equal to or higher than Lsh, 18 is a display memory that stores the output of the level comparison section as image data, and 20 is a CRT.

Next, the operation of the underwater detection device 1 having the above configuration will be explained with reference to FIG. 2.

When transmitting ultrasonic waves underwater, the transmission pulse train generator 4 generates a plurality of transmission pulses with different transmission time intervals (in this example, the transmission time intervals are ΔTl, ΔT, ΔT, <ΔTt).
The three pulses p1 to p3) having the relationship shown in FIG. Note that the transmission time intervals ΔT of each of the above-mentioned transmission pulses pI-1)3 are set in advance so as to be sufficiently smaller than the period Ts of the transmission pulse train. That is, ΔT ls ΔT,
<<Ts.

The signal s(t) of this transmission pulse train is amplified by the transmission side amplifier 6 and then applied to the transducer 2. therefore,
The transducer 2 emits a group of three ultrasonic pulses into the water at time intervals of ΔT and ΔT at regular intervals Ts.

On the other hand, the reflected wave from the water is received by the transducer 2 again and output as a received signal x(t). When the target object is present, the received signal x(t) has three peaks el with time intervals ΔT1, ΔT, corresponding to the transmitted pulse train.
-e3 is included. And these received signals x(t)
is amplified by the receiving side amplifier 8, and then the A/D converter 10
The data is digitized and temporarily stored in the buffer memory l2. Subsequently, the received signal x of this buffer memory 12
The data of (t) is transferred to the cross-correlation calculation unit l4.

The cross-correlation calculation unit 14 performs a cross-correlation calculation between the received signal x(t) from the buffer memory 12 and the signal s(t) of the transmission pulse train generated by the transmission pulse train generation unit 4.

That is, the signal s(t) of the transmitted pulse train and the received signal x(
The cross-correlation signal yU) based on the cross-correlation with t) is generally given by the following equation.

y(D=Σs(i)・x(i+ Company D.IO j=0, 1, 2,... (N-n) where N is the received signal x obtained within one period Ts of the transmission pulse train The number of samplings for (t) (1 Ts/τ,
τ is the sampling interval), n is a group of transmitted pulse sequences s (
Number of samplings within period ΔTo of t) (=ΔT/τ)
Therefore, x(i+D is the period from immediately after the transmission of the transmission pulse train to immediately before the transmission of the next transmission pulse train (=Ts
−ΔT0).

Conceptually, this cross-correlation calculation converts the signal s(t) of a transmission pulse train having a transmission interval width of ΔTo into the reception signal x(t
) is shifted in units of sampling intervals within the range of j=0 to (N - n), and the mutual correlation is calculated. For example, when shifting the transmission pulse train signal s(t) to the right with respect to the reception signal x(t),
In the state indicated by the symbol ■ in FIG. 2, there is one correlation between p3 and el, so a 1-level pulse is output as the cross-correlation signal yU). The same applies to cases ① and ②. On the other hand, in the state of code ■, I)+ and e1, p, and e,
Since there are three correlations between , p3 and e3 at the same time, a three-level pulse is output as the cross-correlation signal y (D. There is only one correlation between codes ■ and ■, and therefore,
A 1-level pulse is output as the cross-correlation signal y (D).

As shown in FIG. 3(a), when the transmission time intervals L of the transmission pulses generated by the transmission pulse train generator are the same, the cross-correlation signal obtained by the cross-correlation calculation is as shown in FIG. 3(b). As shown in Figure 2, it gradually increases and decreases to form a mountain-shaped peak, which results in a decrease in distance resolution.
In the present invention, the transmission time interval Δ of each transmission pulse pl-p3
T. , ΔT, is ΔT,≠ΔT, so the cross-correlation signal y (D obtained in the cross-correlation calculation is
As shown in C), a locally large peak is shown at one location where there is a cross-correlation. For this reason, next
Cross-correlation signal y(D
, the level comparator 16 compares the level of the signal y (D) with a predetermined threshold Lsh, and extracts and outputs only the signals that are equal to or higher than the threshold Lsh. Noise is removed and only the signal y(t) based on the reflected wave from the target object is obtained.

Then, the signal y(t) that has passed through the level comparison section l6 is
After being stored as image data in the display memory l8, C
The image is displayed on RT20.

Note that in this embodiment, the transmission pulse train is composed of three transmission pulses p1 to p3, but is not limited to this, and may be a pulse train of a larger number.

Embodiment 2 FIG. 4 is a block diagram of an underwater detection device according to a second invention, and parts corresponding to those in FIG. 1 are given the same reference numerals.

In the figure, reference numeral 1 indicates the entire underwater detection device of this embodiment, and reference numeral 3 indicates different transmission frequencies. 5. A transmission pulse train generation unit that generates a transmission pulse train at fixed intervals Ts, forming a group of transmission pulse trains from a plurality of transmission pulses;
- 5n are band pass filters that individually pass each received signal x(t) from the water obtained based on the transmission pulse train generated by the transmission pulse train generator 3 according to its frequency, and 71 to 7n are each band. Each delay circuit individually gives a delay time corresponding to the transmission timing of each transmission pulse to each received signal that has passed through the pass filters 5, . An adder circuit l5 that adds and outputs the received signals is an arithmetic control unit that takes in the output of the adder circuit 9 and transfers it to the subsequent display memory l8. The other configurations are similar to those shown in FIG.

In the underwater detection device 12 of this embodiment, as shown in FIG. Pulses) p+-pn are used as a group of transmission pulse trains, and this transmission pulse train is generated at regular intervals Ts taking into consideration the seabed depth.

? In this example, the transmission time intervals ΔT of each transmission pulse I)+−pn constituting the transmission pulse train are all constant;
And, the transmission time interval 8T is the generation period Ts of the transmission pulse train.
It is set in advance to be sufficiently small compared to . That is, ΔT<<TS.

On the other hand, the reflected wave of the ultrasonic wave emitted into the water from the transducer 2 based on this transmission pulse train is received by the transducer 2 again and output as a received signal x(t). The received signal x(t
) have different frequencies at each time interval ΔT corresponding to the transmission pulse train when viewed in time series. and,
After this received signal x(t) is amplified by the receiving side amplifier 8, it is applied to band pass filters 51-5n.

Each of the bandpass filters 51 to 5n receives each received signal x(t
) is set in advance according to its frequency, so the received signal based on the first transmitted pulse p+ (frequency f. Transmission pulse pt (frequency rt)
The received signal based on
The received signal obtained based on (frequency fn) is coded 5n
The signals are individually passed through bandpass filters shown in . Therefore, noise components having different frequencies are removed by each of the bandpass filters 5, to 5n.

Next, a delay time corresponding to the transmission timing of each transmission pulse p1 to pn is individually given to each received signal that has passed through each of these bandpass filters 51 to 5n by delay circuits 7 to 7n-1. . That is, the received signal obtained based on the first transmitted pulse p+ (frequency f,) is processed by the delay circuit 71 with a delay time of nΔT, and the received signal obtained based on the next transmitted pulse pt (frequency f,). is the delay time indicated by the symbol 7, and the delay time of (n-1)8T is given and outputted as a delay time opposite to the transmission timing of the transmission pulses p, ~pn, respectively. Ru. Therefore, the received signals that have passed through each delay time 7I to 7n are all aligned in phase at this point, so next,
The respective received signals delayed by these delay circuits 7, to 7n-, are added by an adder circuit 9 and output. Therefore, the level of the received signal based on the reflected wave from the target object is relatively increased. Then, this received signal is displayed as an image on the CRT 20 via the A/D converter 10, the arithmetic control section 15, and the display memory 18 in sequence.

Note that, in this example, the transmission time intervals ΔT of the respective transmission pulses p, to pn are all set to be the same, but they may be set to different time intervals. In this case, it is necessary to appropriately set the delay times in the delay circuits 71 to 7n depending on the transmission time interval.

<Effect of the invention> According to the present invention, the following effects can be obtained.

(i) Since this is essentially equivalent to increasing the power of the transmitted signal and increasing the level of the signal component from the target object, the S/N ratio is improved.

(11) Since the power of the transmitted signal is not directly increased, there is no risk of occurrence of cavitation.

(iii) Since the pulse width of each transmission pulse constituting the transmission pulse train is short, the distance resolution does not deteriorate.

(1v) Since the transmission time interval of each transmission pulse that makes up the transmission pulse train is sufficiently short compared to the movement of a target object such as a ship or a school of fish, it is possible to Compared to the case of performing correlation processing,
Not easily affected by movement of the target object, etc.

[Brief explanation of drawings]

1 to 3 show an embodiment corresponding to Embodiment 1 according to the first invention, and FIGS. 4 and 5 show an embodiment corresponding to Embodiment 2 according to the second invention, respectively. So, the first
FIG. 2 is a block diagram of the underwater detection device, FIG. 2 is an explanatory diagram of a cross-correlation calculation operation between a transmitted pulse train and a received signal, and FIG. 3 is an explanatory diagram of a cross-correlation calculation signal obtained by the cross-correlation calculation. Also, Figure 4 is a block diagram of the underwater detection device.
FIG. 5 is an explanatory diagram of a transmission pulse train. 1,,1,... Underwater detection device, 2... Transmitter/receiver, 3
, 4 - Transmission pulse train generator, 5. ~5n...Band pass filter, 71~7n...Delay circuit, 9...Addition circuit, 12...Buffer memory, l4...Cross correlation calculation unit, l6...Level comparison unit.

Claims (2)

[Claims] (1) A plurality of transmission pulses with different transmission time intervals are treated as a group of transmission pulse trains, and a transmission pulse train generation unit generates this transmission pulse train at regular intervals; and a transmission pulse train generation unit that generates this transmission pulse train at regular intervals; and a buffer memory that temporarily stores each received signal obtained from underwater; a cross-correlation calculation section that calculates a cross-correlation between the reception signal stored in the buffer memory and the transmitted pulse train; and this cross-correlation calculation section. An underwater detection device comprising: a level comparison section that compares the level of the cross-correlation signal calculated in step 1 with a threshold value and outputs a signal having a level equal to or higher than the threshold value. (2) A plurality of transmission pulses having different transmission frequencies are treated as a group of transmission pulse trains, and a transmission pulse train generation unit that generates this transmission pulse train at regular intervals, and a transmission pulse train generated by the transmission pulse train generation unit generate a transmission pulse train. bandpass filters that individually pass each received signal from underwater according to its frequency; and a delay time corresponding to the transmission timing of each transmission pulse for each received signal that has passed through these bandpass filters. What is claimed is: 1. An underwater detection device comprising: delay circuits that individually apply the signals; and an addition circuit that adds and outputs the received signals delayed by the delay circuits.