CN107870034B - Underwater acoustic velocity measurement method based on phase difference - Google Patents
Underwater acoustic velocity measurement method based on phase difference Download PDFInfo
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Abstract
The invention discloses underwater sound based on phase differenceA method for fast measurement includes using dual AD sampling modules to synchronously and respectively pre-sample emission signals x1(t) and pre-sampled received signal x2(t) collecting to obtain two paths of discrete sampling sequences x1(n) and x2(n), then two discrete sampling sequences x1(n) and x2(n) performing cross-spectrum processing and cross-correlation calculation, and decomposing the measurement of the propagation time of the acoustic wave signal in the distance d into the sum of the phase difference in a single period and the whole period number, so that the measurement accuracy of the propagation time of the acoustic wave signal can be realized by improving the calculation accuracy of the phase difference in the single period; the method has the advantages that the propagation time of the sound wave signal is obtained by accurately calculating the phase difference and the whole period number of the sound wave signal in a single period, and on the basis of time-guaranteeing measurement, the method is simple in measurement process, high in measurement precision and low in cost.
Description
Technical Field
The invention relates to an underwater acoustic velocity measurement method, in particular to an underwater acoustic velocity measurement method based on phase difference.
Background
At present, the conventional underwater sound velocity measurement method mainly comprises an empirical formula method and a direct measurement method. The empirical formula method is used for calculating based on parameters obtained by measuring the temperature, salinity and depth in the marine environment to obtain the acoustic velocity of water sound. Although the empirical formula method has high accuracy in measuring the sound velocity, in the method, corresponding instruments are firstly adopted to obtain the temperature, the salinity and the depth in the marine environment, and then the parameters are obtained from the instruments to perform calculation, so that the measurement process is complex, the time for obtaining the sound velocity is long, the hysteresis ratio is obvious, and the underwater sound velocity of the current sea area cannot be obtained in real time.
The direct measurement method mainly utilizes the propagation characteristic of sound waves in seawater, sound wave signals are acquired through an analog-to-digital converter and then directly transmitted to a processor, the processor calculates the propagation time of the sound waves, and then the underwater sound velocity is obtained through calculation. The method has the advantages of simple measurement process, short time for obtaining the sound velocity, negligible hysteresis and capability of obtaining the underwater sound velocity of the current sea area in real time. However, in this method, the accuracy of the digital measurement of the propagation time directly restricts the accuracy of the sound velocity. Although increasing the acquisition frequency of the analog-to-digital converter can improve the measurement accuracy of the propagation time to some extent, the analog-to-digital converter with higher acquisition frequency has higher cost, and the acquisition frequency of the analog-to-digital converter in the state of the art is relatively limited, so that the measurement accuracy of improving the sound velocity in this way is relatively limited.
Disclosure of Invention
The invention aims to solve the technical problem of providing a phase difference-based underwater acoustic velocity measurement method which is simple in measurement process, high in measurement precision and low in cost on the basis of time-guaranteeing measurement.
The technical scheme adopted by the invention for solving the technical problems is as follows: a phase difference-based underwater acoustic velocity measurement method is characterized by comprising the following steps:
placing a transmitting transducer and a receiving transducer in the measured seawater at intervals, and recording the distance between the transmitting transducer and the receiving transducer as d, wherein d is more than or equal to 10cm and less than or equal to 20 cm;
second, using signal generator to generate frequency f0Sine wave signal of f01MHz, the sine wave signal is denoted as se (t), where t is the time domain time;
amplifying the power of the sine wave signal by 4-8 times through a power amplifier to obtain a driving signal, and recording the driving signal as s (t);
fourthly, attenuating the driving signal s (t) through an attenuation circuit, wherein the attenuation multiple is 8-16 to obtain a pre-sampling emission signal, and recording the pre-sampling emission signal as x1(t); and driving the transmitting transducer by the driving signal s (t), wherein the transmitting transducer emits a sound wave signal, the receiving transducer receives the sound wave signal and converts the sound wave signal into a receiving electrical signal, the receiving electrical signal is amplified by 4-8 times and then is subjected to filtering treatment to obtain a pre-sampling receiving signal, and the pre-sampling receiving signal is recorded as x2(t)；
Adopting two-way AD sampling module to respectively pre-sample emission signal x1(t) and pre-sampled received signal x2(t) collecting, wherein the sampling frequency of the two-way AD sampling module is fs,20MHz≤fsLess than or equal to 80MHz, and transmitting signal x by pre-sampling1(t) taking a sample to obtain a discrete sample sequence denoted as x1(n) for the pre-sampled received signal x2(t) taking a sample to obtain a discrete sample sequence denoted as x2(N), N is a discrete serial number, N is 0,1,2,3, …, N-1, N is an integer of 2000 or more and 2500 or less;
sixthly, discrete sampling sequence x1(n) and a discrete sampling sequence x2(n) cross-spectrum processing, discrete sampling sequence x1The frequency spectrum of (n) is denoted X1(k) Discrete sampling sequence x2The frequency spectrum of (n) is denoted X2(k) Discrete sample sequence x1(n) and a discrete sampling sequence x2The cross spectrum of (n) is marked as Y (k), and k is a discrete sampling sequence x1(n) and a discrete sampling sequence x2(N) a sequence number of a frequency domain, where k is 0,1,2,3, …, N ' -1, where N ' is a number of points of a discrete sampling sequence participating in FFT operation, and a value of N ' is 128 or 256; the specific process is as follows:
sixthly, 1, respectively adopting FFT calculation to obtain discrete sampling sequence x1(n) frequency spectrum X1(k) And a discrete sample sequence x2(n) frequency spectrum X2(k)；
Sixthly-2 adopts the formulaCalculating to obtain x1(n) and x2(n) a cross-spectrum Y (k), whereinIs X1(k) The symbol x is a conjugate operator, and the symbol x is an inner product operator;
seventhly, calculating cross spectrum Y (k) at frequency point f0Phase angle ofThe specific process is as follows:
seventhly-1 sets an intermediate parameter, which is marked as k0By the formula k0＝[f0/fs(N'-1)]Calculating cross spectrum Y (k) middle frequency point f0Corresponding k0The term "[ 2 ]]"is the operator of rounding, symbol/is the operator of dividing;
seventhly-2 adopting arctangent function to solve phase angle phi0I.e. byIm(Y(k0) Is Y (k)0) Imaginary part of Re (Y (k)0) Is Y (k)0) The real part of (a);
calculating the whole period number M of sound wave signal propagation, and the specific process is as follows:
[ 1 ] discrete sampling sequence x1(n) and a discrete sampling sequence x2The cross-correlation function of (n) is denoted as R (r) and adopts the formulaCalculating to obtain corresponding cross-correlation function values, wherein L is an integer which is more than or equal to 100 and less than or equal to 200, r is 0,1,2,3, …, and N-L;
(viii) the cross-correlation function with the largest cross-correlation function value calculated in the step (viii) -2 is denoted as r (q), and q is an integer which is not less than 0 and not more than N-L;
-3 according to the formula M ═ qf0/fs]Calculating to obtain M, symbol "[ alpha ]]"is the operator of rounding, symbol/is the operator of dividing;
ninthly, recording the time of the acoustic signal passing through the distance d as T, and adopting a formulaCalculating to obtain T;
and (c) calculating the sound speed c by using the formula c ═ d/T.
Compared with the prior art, the method has the advantages that the pre-sampling transmitting signals x are synchronously and respectively subjected to pre-sampling by adopting the double-path AD sampling module1(t) and Pre-samplingReceived signal x2(t) collecting to obtain two paths of discrete sampling sequences x1(n) and x2(n), then two discrete sampling sequences x1(n) and x2(n) performing cross-spectrum processing and cross-correlation calculation, and decomposing the measurement of the propagation time of the sound wave signal in the distance d into the sum of the phase difference and the whole period number in a single period, thereby improving the calculation accuracy of the phase difference in the single period and measuring the propagation time of the sound wave signal.
Drawings
FIG. 1 is an error curve for measuring absolute errors of travel times at different SNR according to the method of the present invention;
FIG. 2 is an error curve of the absolute error of sound velocity measured by the method of the present invention under different SNR.
Detailed Description
The invention is described in further detail below with reference to the accompanying examples.
Example (b): a phase difference-based underwater acoustic velocity measurement method comprises the following steps:
placing a transmitting transducer and a receiving transducer in the measured seawater at intervals, and recording the distance between the transmitting transducer and the receiving transducer as d, wherein d is more than or equal to 10cm and less than or equal to 20 cm;
second, using signal generator to generate frequency f0Sine wave signal of f01MHz, the sine wave signal is denoted as se (t), where t is the time domain time;
amplifying the power of the sine wave signal by 4-8 times through a power amplifier to obtain a driving signal, and recording the driving signal as s (t);
fourthly, attenuating the driving signal s (t) through an attenuation circuit, wherein the attenuation multiple is 8-16 to obtain a pre-sampling emission signal, and recording the pre-sampling emission signal as x1(t); and driving the transmitting transducer by using the driving signal s (t), wherein the transmitting transducer transmitsGenerating a sound wave signal, receiving the sound wave signal by the receiving transducer, converting the sound wave signal into a receiving electric signal, amplifying the receiving electric signal by 4-8 times, filtering the wave to obtain a pre-sampling receiving signal, and recording the pre-sampling receiving signal as x2(t)；
Adopting two-way AD sampling module to respectively pre-sample emission signal x1(t) and pre-sampled received signal x2(t) collecting, wherein the sampling frequency of the two-way AD sampling module is fs,20MHz≤fsLess than or equal to 80MHz, and transmitting signal x by pre-sampling1(t) taking a sample to obtain a discrete sample sequence denoted as x1(n) for the pre-sampled received signal x2(t) taking a sample to obtain a discrete sample sequence denoted as x2(N), N is a discrete serial number, N is 0,1,2,3, …, N-1, N is an integer of 2000 or more and 2500 or less;
sixthly, discrete sampling sequence x1(n) and a discrete sampling sequence x2(n) cross-spectrum processing, discrete sampling sequence x1The frequency spectrum of (n) is denoted X1(k) Discrete sampling sequence x2The frequency spectrum of (n) is denoted X2(k) Discrete sample sequence x1(n) and a discrete sampling sequence x2The cross spectrum of (n) is marked as Y (k), and k is a discrete sampling sequence x1(n) and a discrete sampling sequence x2(N) a sequence number of a frequency domain, where k is 0,1,2,3, …, N ' -1, where N ' is a number of points of a discrete sampling sequence participating in FFT operation, and a value of N ' is 128 or 256; the specific process is as follows:
sixthly, 1, respectively adopting FFT calculation to obtain discrete sampling sequence x1(n) frequency spectrum X1(k) And a discrete sample sequence x2(n) frequency spectrum X2(k)；
Sixthly-2 adopts the formulaCalculating to obtain x1(n) and x2(n) a cross-spectrum Y (k), whereinIs X1(k) Of a conjugated complex sequence of (A), a symbolSymbol x is the conjugate operator, symbol x is the inner product operator;
seventhly, calculating cross spectrum Y (k) at frequency point f0Phase angle ofThe specific process is as follows:
seventhly-1 sets an intermediate parameter, which is marked as k0By the formula k0＝[f0/fs(N'-1)]Calculating cross spectrum Y (k) middle frequency point f0Corresponding k0The term "[ 2 ]]"is the operator of rounding, symbol/is the operator of dividing;
seventhly-2 adopting arctangent function to solve phase angle phi0I.e. byIm(Y(k0) Is Y (k)0) Imaginary part of Re (Y (k)0) Is Y (k)0) The real part of (a);
calculating the whole period number M of sound wave signal propagation, and the specific process is as follows:
[ 1 ] discrete sampling sequence x1(n) and a discrete sampling sequence x2The cross-correlation function of (n) is denoted as R (r) and adopts the formulaCalculating to obtain corresponding cross-correlation function values, wherein L is an integer which is more than or equal to 100 and less than or equal to 200, r is 0,1,2,3, …, and N-L;
(viii) the cross-correlation function with the largest cross-correlation function value calculated in the step (viii) -2 is denoted as r (q), and q is an integer which is not less than 0 and not more than N-L;
-3 according to the formula M ═ qf0/fs]Calculating to obtain M, symbol "[ alpha ]]"is the operator of rounding, symbol/is the operator of dividing;
ninthly, recording the time of the acoustic signal passing through the distance d as T, and adopting a formulaCalculating to obtain T;
and (c) calculating the sound speed c by using the formula c ═ d/T.
The method of the invention is simulated in a Matlab platform, the sound velocity is assumed to be 1500 m/s, the method is adopted for measurement when the SNR is respectively 20dB, 30dB and 40dB, the absolute error of the measured propagation time is shown in figure 1, and the absolute error of the measured sound velocity is shown in figure 2.
Analyzing fig. 1 and 2 may conclude that: along with the improvement of the SNR, the measurement error is obviously reduced, and the precision is improved. When the SNR is 40dB, the absolute error of the measurement of the propagation time is less than 0.674 multiplied by 10-9Seconds, i.e., 0.674 nanoseconds; and the corresponding sound velocity measurement absolute error is less than 0.012 m/s. In actual measurement, the propagation distance of the acoustic signal is only 10 cm-20 cm, and the SNR (signal to noise ratio) of the environment is>40dB is easy to meet, and high-precision sound velocity measurement can be obtained by measuring by the method.
Claims (1)
1. A phase difference-based underwater acoustic velocity measurement method is characterized by comprising the following steps:
placing a transmitting transducer and a receiving transducer in the measured seawater at intervals, and recording the distance between the transmitting transducer and the receiving transducer as d, wherein d is more than or equal to 10cm and less than or equal to 20 cm;
second, using signal generator to generate frequency f0Sine wave signal of f01MHz, the sine wave signal is denoted as se (t), where t is the time domain time;
amplifying the power of the sine wave signal by 4-8 times through a power amplifier to obtain a driving signal, and recording the driving signal as s (t);
fourthly, attenuating the driving signal s (t) through an attenuation circuit, wherein the attenuation multiple is 8-16 to obtain a pre-sampling emission signal, and recording the pre-sampling emission signal as x1(t); and driving the transmitting transducer by the driving signal s (t), wherein the transmitting transducer transmits a sound wave signal, the receiving transducer receives the sound wave signal and converts the sound wave signal into a receiving electrical signal, and the receiving electrical signal is amplified 4Filtering after 8 times to obtain pre-sampled received signal, and recording the pre-sampled received signal as x2(t)；
Adopting two-way AD sampling module to respectively pre-sample emission signal x1(t) and pre-sampled received signal x2(t) collecting, wherein the sampling frequency of the two-way AD sampling module is fs,20MHz≤fsLess than or equal to 80MHz, and transmitting signal x by pre-sampling1(t) taking a sample to obtain a discrete sample sequence denoted as x1(n) for the pre-sampled received signal x2(t) taking a sample to obtain a discrete sample sequence denoted as x2(N), N is a discrete serial number, N is 0,1,2,3, …, N-1, N is an integer of 2000 or more and 2500 or less;
sixthly, discrete sampling sequence x1(n) and a discrete sampling sequence x2(n) cross-spectrum processing, discrete sampling sequence x1The frequency spectrum of (n) is denoted X1(k) Discrete sampling sequence x2The frequency spectrum of (n) is denoted X2(k) Discrete sample sequence x1(n) and a discrete sampling sequence x2The cross spectrum of (n) is marked as Y (k), and k is a discrete sampling sequence x1(n) and a discrete sampling sequence x2(N) a sequence number of a frequency domain, where k is 0,1,2,3, …, N ' -1, where N ' is a number of points of a discrete sampling sequence participating in FFT operation, and a value of N ' is 128 or 256; the specific process is as follows:
sixthly, 1, respectively adopting FFT calculation to obtain discrete sampling sequence x1(n) frequency spectrum X1(k) And a discrete sample sequence x2(n) frequency spectrum X2(k)；
Sixthly-2 adopts the formulaCalculating to obtain x1(n) and x2(n) a cross-spectrum Y (k), whereinIs X1(k) The symbol x is a conjugate operator, and the symbol x is an inner product operator;
seventhly, calculating cross spectrum Y (k) at frequency point f0Phase angle ofThe specific process is as follows:
seventhly-1 sets an intermediate parameter, which is marked as k0By the formula k0＝[f0/fs(N'-1)]Calculating cross spectrum Y (k) middle frequency point f0Corresponding k0The term "[ 2 ]]"is the operator of rounding, symbol/is the operator of dividing;
seventhly-2 adopting arctangent function to solve phase angle phi0I.e. byIm(Y(k0) Is Y (k)0) Imaginary part of Re (Y (k)0) Is Y (k)0) The real part of (a);
calculating the whole period number M of sound wave signal propagation, and the specific process is as follows:
[ 1 ] discrete sampling sequence x1(n) and a discrete sampling sequence x2The cross-correlation function of (n) is denoted as R (r) and adopts the formulaCalculating to obtain corresponding cross-correlation function values, wherein L is an integer which is more than or equal to 100 and less than or equal to 200, r is 0,1,2,3, …, and N-L;
(viii) the cross-correlation function with the largest cross-correlation function value calculated in the step (viii) -2 is denoted as r (q), and q is an integer which is not less than 0 and not more than N-L;
-3 according to the formula M ═ qf0/fs]Calculating to obtain M, symbol "[ alpha ]]"is the operator of rounding, symbol/is the operator of dividing;
ninthly, recording the time of the acoustic signal passing through the distance d as T, and adopting a formulaCalculating to obtain T;
and (c) calculating the sound speed c by using the formula c ═ d/T.
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| CN104634878A (en) * | 2014-12-16 | 2015-05-20 | 北京林业大学 | Wood damage monitoring method based on acoustic emission technique |
| CN105572650A (en) * | 2015-12-15 | 2016-05-11 | 宁波大学 | Broadband multiple correlation flow velocity measurement method |
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| JPS6296878A (en) * | 1985-10-24 | 1987-05-06 | Tech Res & Dev Inst Of Japan Def Agency | Sonic wave propagation simulating system |
| CN104634878A (en) * | 2014-12-16 | 2015-05-20 | 北京林业大学 | Wood damage monitoring method based on acoustic emission technique |
| CN105572650A (en) * | 2015-12-15 | 2016-05-11 | 宁波大学 | Broadband multiple correlation flow velocity measurement method |
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