JPH03215773A - Underwater detecting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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.

(+1) 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.

(1v) 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 (1v) 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 (11), if the target object moves within a short period of time, such as a school of fish, correlation processing cannot be performed effectively. In the case of (iii), there is a limit depending on the seabed depth. 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 present invention, a plurality of transmission pulses are made into a group of transmission pulse trains, and a transmission pulse train generation section that generates this transmission pulse train at regular intervals is used. a buffer memory that temporarily stores the data of each received signal from underwater obtained based on the data, and a section width corresponding to the transmission timing of each of the plurality of transmission pulses for the received signal data stored in this buffer memory. a sampling means for setting autocorrelation points having an autocorrelation point, and sampling the received signal data existing at each autocorrelation point while shifting these autocorrelation points for each sampling period of the received signal data; For received signal data, set upper and lower thresholds, and if all sampled received signal data exists within this threshold, all these received signal data are added and output, and if the received signal data is within the threshold and an autocorrelation calculation section that outputs zero data when there is no received signal data at least one.

Function> In the underwater detection device of the present invention, from the transmission pulse train generation section,
A plurality of transmission pulses are made into a group of transmission pulse trains, and this transmission pulse train is generated at regular intervals. The data of each received signal from underwater obtained based on the transmission pulse train generated by the transmission pulse train generator is temporarily stored in a buffer memory. Subsequently, the sampling means sets autocorrelation points having interval widths corresponding to the transmission timings of each of the plurality of transmission pulses for the received signal data stored in the buffer memory, and sets these autocorrelation points to the received signal data. The received signal data present at each autocorrelation point is sampled while shifting every sampling period. Next, the autocorrelation calculation section sets upper and lower thresholds for each received signal data sampled by the sampling means, and if all the sampled received signal data exists within these thresholds, these All the received signal data are added and outputted, and if even one received signal data does not exist within the threshold value, zero data is outputted. Therefore, while noise without autocorrelation is removed, the level of the signal component from the target object with autocorrelation is increased, improving the S/N ratio.

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

In the same figure, the symbol I indicates the entire underwater detection device, and 2
4 is a transducer that transmits and receives ultrasonic waves, and 4 is a transmission pulse train generator that uses a plurality of transmission pulses with a fixed interval of 8 T as a group of transmission pulse trains, and generates a signal s(t) of this transmission pulse train at regular intervals Ts. and 6 are this transmission pulse train generation section 2.
This is a transmitting side amplifier that amplifies the signal s(t) of the transmitted pulse train from the transmitter.

8 is a receiving side amplifier that amplifies the received signal x(t) obtained by receiving the reflected wave from the water at the transducer 2; IO is an A/D converter that digitizes this received signal x(t); I2
is a buffer memory that temporarily stores each digitized received signal data x(i).

Further, l4 is a CPU, and this CPU 14 performs processing on the received signal data stored in the buffer memory l2.
Autocorrelation points having interval widths corresponding to the transmission timings of each of the plurality of transmission pulses are set, and while these autocorrelation points are shifted every sampling period τ of the received signal data, reception signals existing at each autocorrelation point are calculated. A sampling means 15 that samples signal data, and upper and lower thresholds are set for each received signal data sampled by this sampling means 15, and when all the sampled received signal data exists within these thresholds. is provided with an autocorrelation calculating section 16 that adds all of these received signal data and outputs the result, and outputs zero data if even one received signal data does not exist within the threshold value.

18 is a display memory for storing the output of the CPU 14 as image data, and 20 is a CRT.

Next, we will discuss the operation of the underwater detection device l with the above configuration in the second section.
This will be explained with reference to the flowchart shown in the figure and the time chart shown in FIG.

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 ΔTt, ΔT, and ΔT<ΔT,
The three pulses pl-p3) are defined as a group of transmission pulse trains, and this transmission pulse train is generated at regular intervals Ts taking into consideration the seabed depth. Note that each of the above transmission pulses p,
The transmission time intervals ΔT1 and ΔT of ~p3 are both set in advance to be sufficiently smaller than the period Ts of the transmission pulse train. That is, ΔT1, Δ'1', <<'r
It is s.

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 ΔT1 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 e1 with time intervals 8T1 and 8T, corresponding to the transmitted pulse train.
~e, is included. And these received signals x(t)
is amplified by the receiving side amplifier 8, and then the A/D converter 10
The signal is denotated at every predetermined sampling interval τ and is temporarily stored in the buffer memory l2 as received signal data x(i).

For example, if the number of sampling points from immediately after transmission of a transmission pulse train to just before transmission of the next transmission pulse train is N, the reception signal data stored in the buffer memory is x(
i), i=1, 2,...N.

Subsequently, the received signal data x(i) stored in this buffer memory 12 is taken into the CPU 14. C.P.
The sampling means 15 in U14 includes a buffer memory l.
Regarding the received signal data x(i) stored in 2, the time width ΔT, ΔT, of each transmission timing of the transmission pulse is
The sampling width n+(-ΔTl/τ) corresponding to nt
Three autocorrelation points a with (-ΔT x/ r ),
~a3 and these autocorrelation points alq at, a
, are shifted by the sampling interval τ of the received signal data x(i), and the received signal data present on each autocorrelation point aa, , a3 is sampled. That is, the sampling means 15 first sets i=1 and x(
1), x(t+r++), and X(1+n++nJ) are sampled.

Then, the three sampled data x(1),
1+nl), x( 1 + n+ + nt), when the autocorrelation calculation unit 16 in the next stage completes the autocorrelation calculation, next, i is increased by 1 to i=2, and X(2), x(
2 + n+) and X( 2 + n+ + nt) are sampled. From then on, the same operation is performed for i=
Repeat until H. This operation is shown in steps ①, ②, and ① of the flowchart in FIG.

The next-stage autocorrelation calculation section 16 calculates each received signal data x(i) and x(i) sampled by the sampling means l5.
+n. ), x(i+n+ + nt),
Perform the following calculation. First, one received signal data x(i)
, ± around the level of this data x(i)
Upper and lower thresholds xmax = x(i
)+Δx1xmin=x(i) - ΔX are set respectively (step ■), and the level of other sampled received signal data x(i+r++), x(i+n4+nt) is within the range of these thresholds XfflaX, xmin. It is determined whether it is included (steps ■, ■). All sampled received signal data x(i), x(i+
n. ), x(i+n+ + n2) is the threshold xm
If it exists within the range of ax and xmin, all of these received signal data are added and output. That is,
If the output data is y(i), then y(D-x(i)+x
(i+ n+) + X(+ + rl+ + nt)
(Step ■). On the other hand, the threshold xma
If even one sampled received signal data does not exist within x, xmin, the output data is set to zero.

That is, y(i)=0 (step ■). Therefore, the output data y(i) obtained in the autocorrelation calculation unit l6 is the received signal data x(i), x(++n+
), x(i + nl + nt), there is a locally large peak in one place as shown in Figure 4(a), and if there is no correlation even in one place, the figure shows ( As shown in b), the level becomes zero. Therefore, noise without autocorrelation is removed and only data y(i) based on reflected waves from the target object is obtained. And C.P.
The calculation output y(t) of U14 is stored as image data in display memory l8, and then displayed as an image on CRT20.

In this embodiment, the transmission pulse train is composed of three transmission pulses p, -pi, but is not limited to this, and may be a pulse train of a larger number.

Furthermore, in this example, the transmission time intervals ΔTl and ΔT of the respective transmission pulses p, .about.p are different from each other, but they may be the same time interval ΔT.

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

(1) 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.

(ii) 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 4 show embodiments of the present invention, in which FIG. 1 is a block diagram of an underwater detection device, FIG. 2 is a flowchart for explaining the autocorrelation calculation operation for received signal data, and FIG. 4 is a time chart for explaining the autocorrelation calculation for received signal data, and FIG. 4 is an explanatory diagram showing the output signal level obtained by the autocorrelation calculation section depending on the presence or absence of autocorrelation of the received signal data. DESCRIPTION OF SYMBOLS 1... Underwater detection device, 2... Transducer/receiver, 3... Transmission pulse train generation section, 9... Addition section, l2... Buffer memory, l4... CPU, 15... Sampling Means, 16... autocorrelation calculation unit.

Claims (1)

[Claims] (1) A transmission pulse train generation unit that forms a group of transmission pulse trains from a plurality of transmission pulses and generates this transmission pulse train at regular intervals; a buffer memory for temporarily storing data of the received signal; and for the received signal data stored in the buffer memory, setting an autocorrelation point having an interval width corresponding to the transmission timing of each of the plurality of transmission pulses; A sampling means for sampling the received signal data existing at each autocorrelation point while shifting these autocorrelation points every sampling period of the received signal data, and a sampling means for sampling the received signal data present at each autocorrelation point, and A threshold is set, and if all sampled received signal data exists within this threshold, all these received signal data are added and output, and even if there is only one received signal data within the threshold, An underwater detection device comprising: an autocorrelation calculation section that outputs zero data when the data does not exist.