DE1132834B - Arrangement for echo sounding - Google Patents

Description

It is known that in echo sounder systems by noises in the water, by reflections of the plumbing pulses on the surface of the water, on the seabed or on layers of mud and on microreflectors in the water, e.g. B. air bubbles or plankton, the target recognition is severely impaired. Such annoying Reflections are commonly referred to as reverberation. A decrease in the reverberation is better Target recognition is of great importance in practice.

The object of the invention is to reduce the reverberation and to ineffective on the electroacoustic transducers affecting acoustic noises of the surrounding water when the acoustic transducer is connected to the receiver.

Soldering pulses are used to solve this problem, with the frequency at the beginning of the pulse is a different one, especially a higher one, than at the end of the pulse, i. i.e., the energy of the solder pulses is swept between an upper and lower frequency value.

It is known per se, in echo sounder systems, the frequency of the echo sounder pulses between an upper one and lower limit to wobble linearly and as a measure for the distance of a reflective object from the echo sounder the difference frequency between the frequency of the reflected pulse and the im The moment of reception of the reflected pulse to use the emitted frequency.

The invention, however, deals with an arrangement for echo sounding with reduced interference reflection, in which plumbing pulses are transmitted and pulses reflected by targets are received, and is characterized in that the frequency contained in the plumbing pulses is frequency-modulated according to a linear time function in such a way that an odd number of modulation half-periods , for example one or three, are omitted for the duration of the transmission pulse, that in the case of a modulation half-period for the duration of the transmission pulse, the difference between the frequencies at the beginning and end of a time interval that is shorter than the duration of the transmission pulse is formed, or that in In the case of more than one, for example three modulation half-periods for the duration of the transmission pulse, the sum of the frequencies at the beginning and end of a time interval, which is equal to the duration of a modulation half-period, is formed that a delay element is switched on at the receiving end, the delay line of which it is equal to that of the selected time interval that an intermediate modulation of delayed and non-ordinate arrangement for echo sounding

Applicant:

Nippon Electric Company Limited,
Minato-ku, Tokyo (Japan)

Representative:

Dipl.-Ing. H. Ciaessen, patent attorney,
Stuttgart-Zuffenhausen, Hellmuth-Hirth-Str. 42

Claimed priority:

Japan April 15 and September 17, 1958
(No. 10 160 and No. 26 636)

Shinpei Nakano, Minato-ku, Tokyo (Japan),
has been named as the inventor

delayed received signals and that the intermediate modulation product by means of a filter for the difference frequency or the sum frequency is filtered out and fed to the display device.

The measures of the invention make it possible to maintain a sufficient signal-to-noise ratio with simple means.
These measures can also be applied to panorama-type echo sounders.

The invention will now be explained in more detail with reference to figures, of which

1 shows an embodiment of the invention as a block diagram,

2 shows an example of a frequency distribution of the solder pulses and

Figures 3, 4 and 5 illustrate the results obtained with the measures of the invention.
The wave used in the invention for echo sounding has a constant, ie linear frequency change with respect to time.

In the block diagram of FIG. 1, a for both

the sending as well as for receiving used electroacoustic transducer 1 when sending by means of a transceiver switch 3 connected to a transmitter 2 and charged with energy, and the

209 618/126

Ultrasonic energy is radiated into the environment. The transmitter 2 is by means of a frequency modulator 10 frequency-modulated as a linear function of time.

In FIG. 2, the frequency (axis of ordinate) of the signals used for sounding is plotted as a function of time (axis of abscissa). The curve part A of Fig. 2 shows that the in the Lotd

3 correspond to the voltage V _(l at the output of the amplifier 5 in FIG. 1. If now, as has been shown in FIG. 2, those voltages are delayed by the time t _s in the delay element 6 (FIG. 1) (voltage V _r at the output of the delay element 6) on the line O ₂ -R drawn stresses. More specifically, from the voltage V _td the voltage V _tn e, _n becomes e _'nl, etc. Each of the voltages is so at the time t _s

pulses contained frequency initially f _s and am
Conclusion / "is. If you now i _s a certain time loading 10 hesitates. If one now be further considering that the seek that is smaller than the pulse width t _w is so emitted wave according to Fig. 2, A is frequency-modulated, and therefore the light reflected from the target pulses V _d related and V _r and V _td and V _tr on

, ....,. , ".,. , ..,. ..., js - j viewed in the lines O ₁ -D and O ₀ -R of FIG. 3,

the change in the unit of time is thus -—, ^ _{if one} ^ J _output ^ _between | _{modulator Vm}

a voltage V _tm as the modulation product, as shown on the line O ₃ -M in FIG. 3, V _tm as the lower sideband representing a constant frequency which is filtered out by means of the filter 8 (FIG. 1)

According to curve A, the frequency runs within the time t _w from the upper value / _s to the lower value / „;

According to curve B , the frequency runs linearly in time t _s , i.e. with a constant frequency change,

from / _s to f _n (change in time unit = --- ~ ^ - ^% )

and then can be 20 while maintaining the same.

..., "/, - f". ,,. ^,,. For the voltages 1 shown in FIG

Change, but with reversed ^^ _{gj uq (} j ^{ö ö} r &

Sign from / "to / _s . In the case of a frequency origin, the temporal origin is irregular. Change according to curve A is the difference in and therefore with the time t _s not in any case of the frequency change according to curve B is related. Therefore, the frequencies at two points are only rarely of the sum · the noise originating output voltages generated curves A and B, which are the time t _s ausein-, since the voltages V _d and V _r, on the other are together constant. are multiplied, and an output voltage

This occurs during the reception time from converter 1 only when both are not zero at the same time energy 30 coming via the transmit / receive switch. The drawn in Fig. 3 on the line O ₃ -M in an amplifier arrangement 5, the Ausneten voltage peaks arise from such noise input voltage V _d directly and via a delay see, of which voltages - undelayed member 6 as voltage V _r an intermediate modulator 7 and delayed by the time t _s - coincidentally still fed the same. The output voltage of the intermittent occur. This means, however, that the ratio modulator 7 is a modulation product of the voltage from the useful voltage to the interference voltage e _nm in the voltages V _d and V _n consisting of different mixtures of the output voltage F _{m of} significantly larger components. One of these components, namely a sideband as the ratio of V _td and e _nl , e _n2 ... etc., is filtered out by means of a filter 8.

(Voltage V _m ) and a display device 9 supplied. took the invention also cause that, if, as shown in Fig. 2, A, the differential 40 echo energy from a target relatively ungefrequenz in any time interval t _s is constant, attenuates to the display device passes, while the filter for the Difference frequency designed, and interference reflections (so-called reverberation) very strong when, as indicated in Fig. 2, B , the sum are attenuated.

frequency during any time interval t _s kon- This is best done by having the

is constant, the filter 8 is tuned to the sum frequency. The display device 9 can, depending on the circumstances, have a target and the false echoes for the two, a cathode ray tube or a
Be headphones.

It will now be the operation of the arrangement according to the invention in relation to the weakening of the Effectiveness of the noises in the surrounding water and the reduction of annoying reflections explained in more detail.

If a target is at a distance r from the transducer and a plumb pulse hits the target, the 55 draws back.

reflected wave V _td after t _e - ~ seconds after

borrowed cases considered that on the one hand the solder pulses are of constant frequency / _s and that on the other hand the frequency changes from f _s to / ".

It should first be noted that the intensity of the echoes from a target do not differ from one another when the intensity of the plumb pulses is constant, regardless of whether the frequency is constant or varies. Let the intensity of the sound field be I _rl

when the speed of propagation of the ultrasonic wave C (in meters per
Second) is called. In Fig. 3, the individual 60 nierbaren manner are superimposed. Let the echo intensity wave trains be plotted as a function of time t during a certain short period of time A _t0

The false echoes are considered next. As stated at the beginning, small Reflectors in the surrounding sonicated field have irregular echoes, d. i.e., the echoes are in undefi-

gen, where t ₀ denotes the time at which the plumb pulse was transmitted and t _c denotes the time at which the echo arrived at the receiver. The echoes arrive successively between time t _e and time t _w . In between, however, numerous noises arise, as is indicated in e _nv e _{n 2 etc.} The different voltages drawn on the line O ₁ -D

within the pulse duration t _w is denoted by A _{1 0} , and it is further assumed that η of such small time segments A _{t 0 are included} in the total duration t _w , the frequencies of which are assumed to be constant, but differ from one another. Then the mixture of false echoes becomes a mixture of wave trains, the phases and amplitudes of which are completely arbitrary.

are borrowed and their frequencies are evenly distributed. If the plumb pulses hit a group of reflectors within a certain angular range that is exposed to sound by the waves, the total reflected sound energy is /,.= η ■ A , ₀ , and the frequency distribution corresponds to the modulation width or the frequency deviation. If one now compares the frequency distribution of the energy in the case that the frequency is

Filters with a bandwidth, as indicated at f _bl , energy passing through only a very small part of the total reflected energy. The ratio of total reflected energy to the energy transmitted by the filter is roughly the same as the one-hatched part of the triangle to the double-hatched part of the triangle in FIG ge

is constant and then not constant, then in the case of io a wobbled frequency is compared to that in the case of a constant

a constant frequency of the frequency given above has decreased noticeably, while

Value I _{r x of} the reflected impulses as the main constituent of the energy reflected by the target itself, almost un-

part of the frequency f _s included, and the waveform remains changed.

there is an amplitude difference, ie if the solder pulses according to curve B (Fig. 2)

Amplitude modulation, and you can swept 15, the filter 8 (Fig. 1) is so out-

therefore, to a certain extent, also placed by sidebands that there is a frequency band f _{b 2} (Fig. 5, right)

speak. In the curve of FIG. 4, the frequency is ~ "" ~ " ~

distribution of the sound intensity, with the frequency on the abscissa axis and the

20th

lets through that of the sum of the frequencies at the beginning and at the end of a predetermined time interval is equivalent to.

Under these conditions, the waves reflected by a target pass through the filter with the passage width f _b2 unhindered, while interference echoes with frequency modulation of the solder pulses according to the energy ratio of the upper sideband and according to the

Ordinate axis the sound intensity is plotted.

In the case of a swept frequency, the echo intensity is also I _{n, as has already been shown}
and the frequency distribution is even of that
Frequency / _s up to the frequency / ". Even with this one
In this case one can be attenuated by sidebands due to the amplitude of the passage width. So it is only possible to speak tudenmodulation, just like in the case of one of the false echoes, a small part of the frequency constant through the filter. through. The drop in false echoes is on the one hand

The frequency distribution of the sound intensity in the case of the modulation width or, in other words, a wobbled frequency, is dependent on the frequency deviation in curve B of FIG. The areas enclosed by curves A and B of the filter provided in the receiver are apparently equal to each other.But how large the frequency deviation may be in practice, depending on the density of the sound intensity, depends on the radiation's own acoustic energy flow can be. shafts of the electroacoustic transducer in one

The observation of the curves shows that the sound-determined frequency deviation of the vibrational intensity that excites it for each individual frequency in the case of a wave decreases. The width of the pass between / „and / _s swept frequency to be selected is smaller curve of the filter, however, depends on the frequency in the case of a constant frequency. shift from the echo pulse due to the

If the sound intensity now turns into electrical tensions by means of an electrical relative speed between observer and target acoustic transducer. One of the advantages of having a constant convert is the electrical energy generated to work 4 ° frequency difference, is that it is proportional to the sound intensity. This electrical energy is then supplied to the receiver and allowed to narrow the bandwidth of the receiver considerably. Since there is usually a relative speed between the observer and his output voltage, the above-described manner to the intermediate modulator 7 changes the receiving frequency in relation to the (Fig. 1) as a voltage, the frequency distribution 45 of which is transmitted frequency in a known manner due to in Fig. 4, B is shown. This already proved the Doppler effect. Since, according to the invention, however, that the frequency distribution of the modulated span- the frequencies of a series of solder pulses, the voltage looks like it is drawn in FIG. experience the same change is the change of

On the ordinate axis of FIG. 5, E _m , the frequency differences are always constant, so that the absolute value plotted from the size of the intermediate modulation product is very small.

gen. The single-hatched triangle L means that, according to the invention, the emitted

Energy distribution for the lower sideband and the frequency changes linearly, the degree of change in the simple hatched triangle H that of the upper can be set in a simple manner so that one can adjust the sideband. an optimum of the signal-to-noise ratio

In the event that the solder pulses according to FIG. 2, A 55 works, as will be explained in more detail below, they are frequency-modulated and the pass frequencies become.

of the filter 8 (Fig. 1) at f _bl (Fig. 5), the one method that does not lead to the desired

Center frequency in any time interval as a difference in the reduction of false echoes would lead to the reference frequency contained in the plumbing pulses, it would be if frequency were selected after the transmission. In this way, the second form of the echo wave coming from 60 of a plumbing impulse with a different target is emitting quite a sequence and the first in the receiver is similar to that of the emitted plumbing impulses, and which delay the time between the two plumbing impulses echoes pass unhindered through the filter, would. This method is not only difficult to apply in practice because the surface of the target is relatively smooth, but it also has no wirist. In contrast, in the case of interfering reflections, this is aimed at reducing interfering echoes. In the case of the lower sideband of the received energy, however, it is provided that the borrowed frequency is distributed from zero to f _s -f “ , as in the frequency deviation of the intended use of the echo sounder fig. 5 is shown, and it is therefore the device to choose accordingly and the time

relation or the delay time of the received signals to the propagation conditions and the surface properties to make the lake freely adjustable accordingly. The time delay itself depends on the linear magnitude of the frequency change not dependent, d. that is, even if the delay is changed, the frequency deviation can be unchanged stay. This is essential for the operation of an echo sounder device, especially since it is known that the Sound propagation in water is subject to strong fluctuations. The size of the fluctuations is even dependent on the distance of the target from the observer. For these reasons, the The time interval between the solder pulses must be as small as possible. For the noises are generally the number the revolutions of the propeller, the period of the waves and the rolling and rolling of the Ship decisive. Since these values are constantly changing, when the time delay occurs on a constant value is set, sometimes coincidence of the signals.

However, according to the invention, the time delay in the receiver depending on the requirements in is made easily adjustable by, for example, the delay chain with taps that are optionally switchable, is provided, or in that the distance between the recording or playback heads a magnetic recording and reproducing device working with an endless tape is changed, and that at the same time the passage width of the filter can be changed accordingly is designed, the best possible operation of the echo sounder can be set.

As shown below, one can easily spot a target among many spurious reflections. As has already been stated, the echo intensity from a target is always constant whether the frequency is constant or not. However, the echo intensity of finely divided micro-reflectors is less in the case of frequency modulation than without this modulation. It is therefore for observation the mode of action in target recognition is very effective, two adjustable, different filters in the Receiver to use, a wide and a narrow, and the solder pulses optionally in the To modulate frequency or not.

For the purpose of display, the following method is very effective. If the solder pulses are frequency-modulated and, as shown in FIG. 5, filters are provided in the receiver for the passbands f _b j and f _bs , the output voltages of which are fed to the separate control grids of a multicolor cathode ray tube, the display can be obtained in one primary color for the target while the false echoes are displayed in a mixed color.

As already shown above, it is not possible to detect targets with underwater sound devices only reduce the noise in the water that falsifies the display, but also the echoes of echoes from micro-reflectors resembling a target to a certain extent switch off those from one Increase the target received echo energy and thereby enable perfect detection.

The measures of the invention are not only directed towards an echo sounder device with a single one Transducer, but also applicable to an echo sounder of the panorama type in which the echoes by means of a number of directional electroacoustic transducers which are scanned in succession will. The solder pulses are frequency modulated in such a way that the difference (or the Sum) during one complete cycle of the scanning device for the number of directed Converter is constant. The received signals are delayed in the manner described above fed to an intermediate modulator, the desired frequency component filtered out, and the output voltages are then fed to the brightness control element of a cathode ray tube, for example, thereby obtaining a map display type image.

Claims (4)

PATENT CLAIMS: 1. An arrangement for echo sounding with reduced spurious reflection, in which plumb pulses are emitted and pulses reflected by targets are received, characterized in that the frequency contained in the plumb pulses is frequency modulated according to a linear time function such that an odd number of modulation half-periods, for example one or three , do not apply to the duration of the transmission pulse (i _w ), so that in the case of a modulation half-period for the duration of the transmission pulse the difference between the frequencies at the beginning and end of a time interval (i _s ) which is smaller than the duration of the transmission pulse (t _w ) , is formed, or that in the case of more than one, for example three modulation half-periods for the duration of the transmission pulse (t _w ), the sum of the frequencies at the beginning and end of a time interval (i _s ), which is equal to the duration of a modulation half-period, is formed that a delay element is switched on at the receiving end, the delay time of which is the same That of the selected time interval is that an intermediate modulation of delayed and non-delayed received signals takes place and that the intermediate modulation product is filtered out by means of a filter for the difference frequency or the sum frequency and fed to the display device. 2. echo sounder system according to claim 1, characterized in that the delay time of the Echo signals variable and the bandwidth of the filter connected downstream of the intermediate modulator is changeable. 3. echo sounder system according to claim 1 and 2, characterized in that a separate display target echoes and false echoes is made possible by the fact that the encoder side between constant frequency and frequency-modulated state is designed to be switchable, that accordingly a synchronous switchover of two dem Intermediate modulator downstream filters with different passage widths is provided and that the output voltages of the filters two separate control organs of a display device are fed. 4. echo sounder system according to claim 3, characterized in that a display device Multicolor cathode ray tube is used, the write beam synchronously in a known manner with the emission of the solder impulses or according to the type of reception of the echo pulses, e.g. B. a directional reception with the help of a number of differently oriented electroacoustic transducers, which are interrogated periodically one after the other be deflected in two coordinates, 10 and their separate control grids the output signals of the two filters. References considered: U.S. Patent No. 2,536,771. 1 sheet of drawings