SU1693379A1 - Method of determining sea-way sea surface knoll and device - Google Patents

Abstract

The invention relates to hydrophysical measurements and can be used to measure the elevation spectra of a rippling sea surface. The purpose of the invention is to expand the field of application by increasing the wave band of the wave being analyzed. In accordance with the invention, acoustic waves radiate with a constant power spectral density, the modulation frequency is determined at the measured power spectral density of the received radiation, and its time dependence is determined and the spectrum of the elevations of sea-surface disturbances is judged by the spectrum of the time dependence of the modulation frequency of the power spectral density of the received radiation. The introduction of a correlometer, a threshold unit and a memory unit to the device provides an exception to the received signal of a powerful low-frequency component that is not associated with the spectrum under study, which expands the wave band of the waveform being analyzed. 2 sec. f-ly, 1 silt, С / С

Description

The invention relates to hydrophysical measurements and can be used to measure the elevation spectra of a rippling sea surface.

The aim of the invention is to expand the scope by increasing the wave band of the wave being analyzed.

The drawing shows a block diagram of a device for determining the spectrum of elevations of disturbances of the sea surface.

The device contains a generator 1, an acoustic wave emitter 2 connected to it, an acoustic radiation receiver 3, an amplifier 4 connected to it, and a spectrum analyzer 5. The output of amplifier 4 is connected in series with a correlometer 6, threshold unit 7 and memory block 8, the output of which is connected to

spectrum analyzer 5. In order to synchronize the measurement cycles of the modulation frequency, the second output of the correlometer 6 is connected to the second input of the memory block 8. The generator 1 is made in the form of a white noise generator.

The essence of the method for determining the spectrum of waves of the sea surface is the use of the frequency modulation spectrum of broadband acoustic radiation received in the marine environment at a distance from the source. Modulation occurs as a result of the interference of acoustic waves reflected from the sea surface with direct waves, i.e. such that propagate along the beam connecting the source to the receiver. So, with radiation during ti-t2

ABOUT

43

with

W

X o

n the fi -fa frequency band of acoustic waves with a constant power spectral density Go by a source located at one point in the marine environment with coordinates Z Z0, Ј 0, where Z is the vertical coordinate, Z0 is the horizontal coordinate. Acoustic radiation received at another point in the marine environment with coordinates Z Zi, r R has a power spectral density G (t, f) defined by the expression

G (t, r) + m cos (2 t (t)), (1)

where t is time;

f is the frequency of the acoustic wave;

m is the reflection coefficient of the acoustic wave from the sea surface;

r (t) is the delay in the arrival of the acoustic wave reflected from the sea surface relative to the direct wave.

From the geometry of the course of direct and reflected waves

G: Ј (X0 - Xl),

(2)

Where

Xi - (Zo-Zi + R2;

X0 v / (z7 + Zi + 2 Ј2 + R2;

C is the speed of sound in the marine environment.

Since in practice it is always possible to fulfill the condition R Z0; Zi | (t), the relation (2) takes the form

r (t)

 Ј (t) (Zo + Zi) + Z0

CR

(3)

From relation (1) with regard to relation (3), it can be seen that the spectral power density of the received acoustic radiation due to the interference of the direct and reflected acoustic EOLN is frequency modulated. The frequency r (t) of this modulation is equal to the delay time r (t) of the arrival of the reflected wave relative to the direct wave and is directly proportional to the magnitude of the elevation (t) of the analyzed sea-surface wave. Therefore, by selecting the frequency r (t) of the modulation of the spectral density G (t, f) of the power of the received radiation and registering it, you can determine the spectrum Gj- (Q) of the obtained time dependence r (t) the spectrum Gz (Q) of the elevations of sea-surface disturbances from the ratio

g / g - Gg (0 7 7, Sin Q (2 -tlh

G (Q) Gr (Q) -Z0

/

/ (Z0 + Zi); Gr (Q)

(four)

 J r (t) exp (-iQt) dt G, R / 2,

0.5

where b2 is the sea wave frequency.

In order to obtain information about the elevation spectrum of all wavelengths of the waves being analyzed, it is necessary to radiate and record acoustic waves during the time interval ti-t.2, which is longer than the time interval T determined by the ratio

, -.

-T uTmYamax,

g

where g is the acceleration of free fall, Amax is the greatest of the wavelengths of the wave being analyzed,

The device for determining the range of elevations of the sea surface as follows.

With the help of generator 1 and radiator 2,

installed in the marine environment, emit acoustic waves.

Receiver 3 receives acoustic radiation. The output signal of the receiver, carrying information about the received acoustic radiation, through the amplifier 4 is fed to the correlometer 6, with which the spectral density of the received power is measured, which determines the value of the correlation function of the signal realization, and the maximum correlation function the modulation frequency, equal to the delay of the reflected wave relative to the direct wave, is measured. Using the threshold unit 7, the measured modulation frequency is extracted against the background of the signal caused by the noise of the marine environment, and the measured modulation frequencies are accumulated using the memory unit 8. In order to provide useful information for all wavelengths of the wave being analyzed, including the longest waves, the time dependence T (t) is taken for a time longer than the interval T. The output signal c

memory unit 8 is fed to a processor, with which the spectrum Gf (Q) of the time dependence r (m) is determined. The desired spectrum is determined from the measured spectrum Gj- (Q) in accordance with relation (4).

spectrum G, (Q) wave elevations of the sea surface.

Claims (2)

Thus, the invention provides an exclusion in the spectrum of the received signal of a powerful low frequency component that is not associated with the spectrum under study, which makes it possible to expand the wave band of the analyzed waves. Claim 1. A method for determining the wave spectrum of a sea surface, which consists in placing an emitter and receiver of acoustic waves in a marine environment, emit an acoustic wave, receive a direct wave and reflected from the sea surface, measure the received power spectral density. radiation, according to which a controlled parameter is judged, characterized in that, in order to expand the field of application, acoustic waves emit with a constant power spectral density, determine the frequency of modulation of the power spectral density of the received radiation, and the spectrum of sea-surface wave elevations is determined by its time dependence. 2. A device for detecting the spectrum of sea-wave elevations, containing a generator, an acoustic wave emitter connected to it, an acoustic wave receiver connected to it, an amplifier and a spectrum analyzer that is equipped with series-connected correlometers connected to the amplifier, a threshold unit and a memory unit, a second input connected to the output of the correlometer, an output with a spectrum analyzer, and the generator is designed as a white noise generator.