JPH06341838A - Doppler shift correction pulse-type fishing-net depth meter - Google Patents

Abstract

PURPOSE:To precisely measure depth by eliminating the influence of the Doppler effect by the relative velocity between a transmitter attached to a fishing net anal a wave receiver suspended from a fishing vessel in a fishing-net depth meter. CONSTITUTION:The relative velocity (v) between a transmitter 1 and a wave receiver 2 is detected by a relative-velocity detection means 6 on the basis of prepulses received by the wave receiver 2, the frequency F' of main pulses which are received by the wave receiver 2 and which are detected by a main- pulse-frequency detector 5 is corrected by the relative velocity (v) by a correction and operation means 7 so as to remove the Doppler effect, the corrected frequency is sent to a fishing-net-depth display means 8 as in conventional cases, and a fishing-net-depth which is not affected by the Doppler effect is displayed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for correcting an error due to Doppler shift of a fishing net depth gauge using a frequency-modulated ultrasonic pulse whose frequency is changed according to the magnitude of water pressure.

[0002]

2. Description of the Related Art Conventionally, as to the depth of a fishing net, a transmitter 1 is attached to the bottom of the fishing net as shown in FIG. 5, and an ultrasonic wave generated by the transmitter 1 is received by a receiver 2 suspended below the bottom of the ship. It was done by wave. The transmitter 1 receives a frequency called prepulse as shown in FIG. 6 ultrasonic pulses P ₁ of the fixed known, P _2, P _3, the frequency modulation frequency is changed by ...... and subsequently the depth i.e. water pressure thereto The ultrasonic pulse (main pulse) F ₁ , F ₂ , ... That is, the water pressure is converted into frequency and transmitted. The pre-pulse is a signal for synchronizing on the receiving side.

The prepulse and frequency-modulated ultrasonic wave are received by the receiver 2
The received signal is guided to a receiver inside the ship, and the depth of the net bottom is known by detecting the frequency of the frequency-modulated ultrasonic signal. When the network is large, a plurality of sets may be used such as the transmitter 1'and the wave receiver 2 '. In this case, the frequencies are separated from each other in order to avoid mutual interference.

[0004]

However, since the fishing net moves up, down, and moves under the influence of tidal current, the transmitter also moves in the same manner, and the fishing boat also performs pitching and rolling due to the waves. Therefore, the suspended wave receiver also swings. As a result, the relative positional relationship between the transmitter and the wave receiver fluctuates with time, and a relative velocity (to be represented by v) occurs between the two.

Therefore, the frequency-modulated ultrasonic wave transmitted from the transmitter 1 is affected by the Doppler effect, and the frequency of the ultrasonic wave received by the wave receiver 2 is changed from the frequency when the transmitter transmits the wave. There is a problem in that this causes a shift, which reduces the accuracy of depth measurement.

In view of the above problems of the prior art, an object of the present invention is to provide a fishing net depth gauge capable of accurately measuring the fishing net depth by correcting the Doppler shift.

[0007]

The present invention has the following means for achieving the above object. That is, the Doppler shift correction pulse-type fishing net depth meter of the present invention is a frequency-modulated ultrasonic pulse whose frequency changes according to the magnitude of water pressure (referred to as main pulse) and an ultrasonic pulse for synchronization whose frequency is fixed (pre-pulse). An underwater transmitter for transmitting the ultrasonic wave to the water at a predetermined cycle; a receiver for receiving the ultrasonic pulse emitted from the underwater transmitter; and an ultrasonic pulse for synchronization (prepulse) from the receiver. ) A pulse-type fishing net depth consisting of a receiver that knows the depth at which the underwater transmitter is located by receiving a signal and synchronizing and receiving a frequency-modulated ultrasonic pulse (main pulse) signal and detecting the frequency. Relative speed calculation to detect the Doppler frequency from the synchronizing ultrasonic pulse (pre-pulse) signal and calculate the relative speed between the underwater transmitter attached to the fishing net and the wave receiver A Doppler shift correction pulse type fishing net depth meter, which comprises: a step; and a correction operation unit that performs an operation for correcting the frequency of the frequency-modulated ultrasonic pulse (main pulse) signal with the relative speed and the underwater sound speed. Is.

[0008]

The operation of the present invention having the above-mentioned means will be described below. The present invention is, in comparison with a conventional fishing net depth meter, a relative speed v between a submersible transmitter and a receiver for detecting a Doppler frequency from a synchronizing ultrasonic pulse (pre-pulse) signal on the receiving side. It is characterized in that it has a speed calculation means and a correction calculation means for correcting the frequency of the frequency-modulated ultrasonic signal based on the relative speed.

First, the relative velocity calculating means will be described.
If the known fixed frequency of the pre-pulse is f, and the frequency subjected to the Doppler shift due to the movement of the relative speed v is f ′, and the underwater sound velocity is V, the formula 1 is established by the Doppler effect.

[0010]

[Equation 1]

The relative velocity v can be obtained from Equation 1 as shown in Equation 2.

[0012]

[Equation 2]

That is, the relative velocity calculating means calculates the relative velocity v by detecting the frequency f of the received pre-pulse and performing the calculation of Equation 2. Next, the correction calculation means calculates the relative speed v.
Is used to correct the frequency of the received frequency modulated ultrasonic signal. Now, let the frequency of the frequency-modulated ultrasonic wave transmitted from the transmitter be F, and let it be the frequency that is received by the wave receiver after being subjected to Doppler shift and detected by the frequency detecting means in the receiver as F '. For example, Equation 3 holds due to the Doppler effect.

[0014]

[Equation 3]

From the formula 3, the frequency F not subjected to the Doppler shift can be obtained as the formula 4.

[0016]

[Equation 4]

That is, the frequency F without Doppler shift is calculated by performing the operation of the equation 4 on the frequency F'with Doppler shift detected by the frequency detecting means in the receiver.
Is obtained, and the Doppler shift is corrected.
After the frequency F is obtained in this way, by converting it to the depth as in the conventional case, an accurate fishing net depth without the influence of the Doppler shift due to the relative speed can be obtained.

[0018]

Embodiments of the depth gauge of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the depth gauge of the present invention. The transmitter 1 repeatedly transmits a prepulse having a frequency f and a main pulse having a frequency F. The wave receiver 2 receives these ultrasonic pulses, but at the time of reception, if there is a relative velocity v between the transmitter 1 and the wave receiver 2, it undergoes a Doppler shift due to this, Frequency f
Shifts to f'and the frequency F shifts to F '. These ultrasonic pulses are converted into electric signals by the wave receiver and then amplified by the receiving amplifier 4 to a required level. The amplified signal is branched into two and one of them is sent to the main pulse frequency detector 5, where the frequency F'of the main pulse is detected. The process up to this point is the same as the conventional technique.

The other branched signal is sent to the relative speed detecting means 6 newly provided in the present invention. First, the prepulse frequency detector 9 detects the prepulse frequency f '. The detected frequency f ′ is sent to the speed calculator 10. In addition to the frequency f ′, the speed calculator 10
The frequency f of a known fixed pre-pulse and the similarly known underwater sound velocity V are input, and the relative velocity v is calculated by the above-mentioned formula 2.

The relative velocity v thus obtained is sent to the correction calculation means 7. In addition to the correction pulse calculating means 7, the main pulse frequency detector 5 outputs the main pulse frequency F ′ and the underwater sound velocity V.
Is input, and using these, the frequency F before undergoing the Doppler shift of the main pulse is calculated by the above-mentioned formula 4.
Is calculated. The frequency F thus calculated is sent to the fishing net depth display means similar to the conventional one, and the influence of the Doppler shift is removed and corrected, and the fishing net depth is displayed.

FIG. 2 is a block diagram showing a specific example 1 of the prepulse frequency detector 9. The operation will be described with reference to the waveform chart of FIG. FIG. 4A shows a reception pulse appearing at the output of the reception amplifier 4. This received pulse is shown in Figure 2.
Are input to the pre-pulse detection unit 11 and the shaping unit 12. Then, the pre-pulse detection unit 11 outputs a pre-pulse timing pulse as shown in FIG. This timing pulse is sent to the shaping unit 12.

In the shaping section 12, the input frequency f '
The pre-pulse and the pre-pulse timing pulse output the gate having the wavelength f'of one wavelength width. For example, when the prepulses P ₁ and P ₂ of the frequency f ′ are enlarged, the figure becomes as shown in FIG. 4C. Then, the gate having the time width corresponding to the first wavelength of each prepulse is output as shown in (d). This gate is added to the frequency counting section 14 and also sent to the latch timing generator 13. From the oscillator circuit 15 to the frequency counting unit 14, as shown in FIG.
(E), a clock signal having a known frequency much higher than the frequency of the pre-pulse is added, and the number of clocks is counted during the gate width time. This counting is performed at the timings shown in (f) and (g) of FIG.

Let this count value be m. The count value m is sent to the latch unit 16 and is latched in the latch unit 16 by the latch timing signal output from the latch timing generator 13 after the counting is completed. The latched count value m is input to the frequency output unit 17 and is output as a frequency f'from there.

Now, assuming that the frequency of the oscillation circuit 15 is f ₀ , the time per clock is 1 / f ₀ . Therefore, if the clock count value in the gate width time is m, the gate width time is m / f ₀ . Since this time is one wavelength of the pre-pulse frequency f ', its reciprocal f ₀ / m is the frequency f'. That is, the frequency output unit 17 outputs the frequency f'of the pre-pulse by calculating f ₀ / m.

FIG. 3 is a block diagram showing a specific example 2 of the pre-pulse frequency detector 9. This is a configuration in which when the relative speed is changing and the prepulses P ₁ and P ₂ have different frequencies, the average of the two is calculated and treated as the prepulse frequency f ′. When compared with the operation of FIG. 2, the pre-pulse detection unit 11, the shaping unit 12,
The operations of the frequency counting unit 14 and the oscillator circuit 15 are the same as those in FIG. It is now assumed that the clock count value of the prepulse P ₁ is m ₁ and the clock count value of the prepulse P ₂ is m ₂ .

The count value m ₁ is latched by the latch section 16a, and the count value m ₂ is latched by the latch section 16b.
This is in addition to the case of FIG.
3'receives the output of the pre-pulse detector 11 ((b) of FIG. 4) and outputs the latch timing signal to the latch unit 16a.
This is done by alternately sending to b.

The latched count values m ₁ and m ₂ are sent to the frequency output section 17 '. As described in the explanation of FIG. 2, the frequency for the count value m ₁ is f ₀ / m ₁ , and the count value m _1
Since the frequency for ₂ is f ₀ / m ₂ , the average frequency number f'of both is expressed by Equation 5.

[0028]

[Equation 5]

The frequency output unit 17 'outputs the pre-pulse frequency f'by performing the operation of Equation 5.

[0030]

As described above, the fishing net depth gauge of the present invention utilizes the pre-pulse for synchronization to make a relative relation between the underwater transmitter attached to the fishing net and the receiver suspended from the fishing boat. The speed is calculated, and the Doppler shift that occurs in the frequency of the main pulse for depth measurement is corrected and removed based on this relative speed to determine the depth. However, there is an advantage that even if the wave receiver sways due to rolling or pitching of a fishing boat, the fishing net depth can be accurately measured without being affected by the Doppler effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a depth gauge of the present invention.

FIG. 2 is a block diagram showing a specific example 1 of the pre-pulse frequency detector in the embodiment of the present invention.

FIG. 3 is a block diagram showing a specific example 2 of the pre-pulse frequency detector in the embodiment of the present invention.

FIG. 4 is an operation timing waveform diagram of the pre-pulse frequency detector in the example of the present invention.

FIG. 5 is a situation diagram in which a fishing net depth gauge is used.

FIG. 6 is a diagram showing a prepulse and a main pulse emitted from a transmitter of a depth gauge.

[Explanation of symbols]

 1 transmitter 1'transmitter 2 receiver 2'receiver 3 receiver 4 receiver amplifier 5 main pulse frequency detector 6 relative speed detection means 7 correction calculation means 8 fishing net depth display means 9 pre-pulse frequency detector 10 speed calculation Device 11 Pre-pulse detection unit 12 Shaping unit 13 Latch timing generator 13 'Latch timing generator 14 Frequency counting unit 15 Oscillation circuit 16 Latch unit 16a Latch unit 16b Latch unit

Claims (1)

[Claims] 1. An underwater transmitter that transmits a frequency-modulated ultrasonic pulse whose frequency changes according to the magnitude of water pressure and an ultrasonic pulse for synchronization whose frequency is known and fixed to the water at a predetermined cycle; A receiver for receiving the ultrasonic pulse generated by the detector; a synchronizing ultrasonic pulse signal is received from the receiver for synchronization, and a frequency-modulated ultrasonic pulse signal is received to detect its frequency A receiver for knowing the depth at which the underwater transmitter is located by; and a pulse type fishing net depth gauge comprising: a Doppler frequency detected from the ultrasonic pulse signal for synchronization, and an underwater transmitter attached to the fishing net and Relative velocity calculating means for calculating a relative velocity between the wave receivers; and correction computing means for performing a computation for correcting the frequency of the frequency-modulated ultrasonic pulse signal with the relative velocity and the underwater sound velocity. Doppler shift correction pulsed fishing net depth gauge characterized.