An acoustic tomography flow measurement system and a forward and reverse code encoding method for acoustic signals applied thereto

Abstract

The present invention discloses a sound tomography flow measurement system and a method for encoding positive and negative codes of acoustic wave signals applied thereto. By using the actually received signal data for matching and through signal positive and negative code conversion, the matching degree of the signal can be effectively improved, and the accuracy of calculating the arrival time of the acoustic wave can be greatly improved. The method includes the steps of: (1) in a river sound tomography flow measurement system, splicing an acoustic wave signal S with a reverse-order flipped signal S' together to form a positive and negative code signal SS, and transmitting the positive and negative code signal SS at the probe transmitting end; (2) at the receiving end, performing matching filtering calculation on the received acoustic wave signal R with a conventional acoustic wave signal S to obtain a filtering result C, and obtaining the time of the maximum point of C as ts; (3) intercepting a matching segment P from the received acoustic wave signal R, performing reverse-order flipping to obtain P', calculating a new matching filtering result, and the arrival time of the acoustic wave signal R.

Description

Technical Field

[0001] The present invention belongs to the field of intelligent processing of river flow monitoring data, and particularly relates to an acoustic tomography flow measurement system and a method for encoding positive and negative codes of acoustic wave signals applied thereto. Background Art

[0002] The river acoustic tomography flow measurement technology has the advantages of easy installation, little influence by the river surface conditions, high accuracy, etc. The acoustic tomography technology calculates the river flow velocity according to the characteristic that the propagation speed of acoustic waves in water is faster in the downstream direction than in the upstream direction. Therefore, accurately calculating the propagation speed and propagation time of acoustic waves in water is the key to acoustic tomography flow measurement. The acoustic tomography flow measurement system sends an encoded acoustic wave signal from an underwater acoustic probe on one side of the river to the other side, and the underwater acoustic probe on the other side obtains the arrival time of the acoustic wave by receiving the acoustic wave signal and identifying it, thereby knowing the propagation speed of the acoustic wave in water and further calculating the river flow velocity.

[0003] Currently, due to some physical condition limitations of the underwater acoustic probe, the conventional acoustic wave signals emitted will be deformed to a certain extent compared with the ideal acoustic wave signals. When the existing technology often uses the ideal signal to perform template matching filtering calculation on the received signal data, the matching degree will decrease and there will be deviations in signal recognition. This will have a great impact on the propagation time of the acoustic wave and the subsequent calculation of the flow velocity.

[0004] The closest existing technology, a coastal acoustic tomography flow measurement method, application number: CN202310314955.3, includes steps of sequentially setting n data acquisition points along the coast; mutually transmitting and receiving acoustic signals between the n data acquisition points to collect cross-correlation data; establishing a two-dimensional flow field between two points through the collected basin data and the reciprocal transmission and acoustic Doppler effect of acoustic waves, and establishing a temperature field between two points through the collected cross-correlation data and the NRLⅡ sound velocity empirical formula. Obtaining the position of the maximum cross-correlation peak through the cross-correlation algorithm, and according to the property of the cross-correlation function, the ratio of it to the sampling rate is the propagation time of the acoustic signal in the direction from the transmitting data acquisition point to the receiving data acquisition point. This method pre-sets equidistant data acquisition points, cannot find the data acquisition point with the strongest signal, has large measurement interference, and needs to build a two-dimensional flow field and a temperature field, resulting in poor signal recognition accuracy. Summary of the Invention

[0005] In order to solve the problem of the decrease in signal recognition accuracy in the existing system and river acoustic tomography flow measurement method, the present invention provides an acoustic tomography flow measurement system and a method for encoding positive and negative codes of acoustic wave signals applied thereto, which use the actually received signal data for matching. Through the conversion of positive and negative codes of the signal, the matching degree and recognition accuracy of the signal can be effectively improved, and the accuracy of calculating the arrival time of the acoustic wave can be greatly improved.

[0006] First, the present invention provides a method for encoding positive and negative codes of acoustic wave signals applied to an acoustic tomography flow measurement system, including the steps:

[0007] (1) In a river acoustic tomography flow measurement system, an acoustic wave signal S is spliced with a reverse-order flipped signal S' to form a positive and negative code signal SS, and the positive and negative code signal SS is transmitted at the probe transmitting end;

[0008] (2) At the receiving end, the received acoustic wave signal R is subjected to matched filtering calculation using a conventional acoustic wave signal S to obtain a filtering result C, and the time of the maximum point of C is obtained as ts;

[0009] (3) A matching segment P is intercepted from the received acoustic wave signal R, and is reverse-order flipped to obtain P', and a new matched filtering result and the arrival time of the acoustic wave signal R are calculated.

[0010] Further, step (3) specifically includes:

[0011] A matching segment P is intercepted from the received acoustic wave signal R, the interception starting point is t0 = ts - dt, if ts < dt, then t0 = 0, and the interception duration is nS; where nS is the length of the positive and negative code signal SS, and dt is a preset time advance amount;

[0012] The segment P is reverse-order flipped to P', and template matching filtering calculation is performed on the acoustic wave signal R using P' as a template to obtain a new matched filtering result C', and the time of the peak point of C' is obtained as ts';

[0013] Calculated by the formula Then t is the arrival time of the acoustic wave signal R, and the obtained arrival time t is used for subsequent flow velocity calculation.

[0014] Further, in step (3): the reverse-order flipping of the segment P is to reverse the encoding order of a segment of acoustic wave signal to obtain the corresponding reverse-order flipped segment P'.

[0015] The positive and negative code encoding method uses the actually received acoustic wave signal R for matching calculation filtering, utilizes the construction of positive and negative codes and the operation of reverse-order flipping the acoustic wave signal, and performs matching on the premise of retaining the characteristics of the actually received acoustic wave signal, improving the signal matching accuracy.

[0016] The acoustic wave signal S is an M-code acoustic wave signal S, and the M-code acoustic wave signal S is spliced with a reverse-order flipped M-code acoustic wave signal S' to form an M-code positive and negative code signal SS; or the acoustic wave signal S is an acoustic wave signal encoded by other codes, including an acoustic wave signal encoded by a Gold sequence or an acoustic wave signal encoded by a quadratic residue sequence.

[0017] Secondly, the present invention also provides an acoustic tomography flow measurement system with forward and reverse code encoding of acoustic signals, comprising: a signal conversion module for splicing an acoustic signal S and a reverse-order flipped signal S' together to form a forward and reverse code signal SS; a forward and reverse code encoding and processing module for performing matched filtering calculation on the received acoustic signal R using a conventional acoustic signal S to obtain a filtering result C, and obtaining the time of the maximum point of C as ts; a signal filtering and processing module for intercepting a matching segment P from the received acoustic signal R, performing reverse-order flipping to obtain P', calculating a new matched filtering result, and the arrival time of the acoustic signal R.

[0018] Further, the signal filtering and processing module further comprises:

[0019] A signal segment intercepting module for intercepting a matching segment P from the received acoustic signal R, the intercepting starting point being t0 = ts - dt, if ts < dt, then t0 = 0, and the intercepting duration being nS; where nS is the length of the forward and reverse code signal SS, and dt is a preset time advance amount;

[0020] A signal segment processing module for reverse-order flipping the segment P to P', performing template matching filtering calculation on the acoustic signal R using P' as a template to obtain a new matched filtering result C', and obtaining the time of the peak point of C' as ts';

[0021] A signal arrival time calculation module for calculating through the formula where t is the arrival time of the acoustic signal R, and the obtained arrival time t is used for subsequent flow velocity calculation.

[0022] The system uses the actually received acoustic signal R for matching calculation and filtering, utilizes the structure of the forward and reverse code and the operation of reverse-order flipping the acoustic signal, and performs matching on the premise of retaining the characteristics of the actually received acoustic signal, thereby improving the signal matching accuracy.

[0023] The acoustic signal S is an M-code acoustic signal S, splicing the M-code acoustic signal S and a reverse-order flipped M-code acoustic signal S' together to form an M-code forward and reverse code signal SS; or the acoustic signal S is an acoustic signal encoded by other codes, including an acoustic signal encoded by a Gold sequence or an acoustic signal encoded by a quadratic residue sequence.

[0024] The following introduces the technical advantages brought by the system and method of the present invention by comparing with the prior art:

[0025] 1) The detection of underwater acoustic wave signals has its particularities and is not as easy as the detection of acoustic wave signals in the atmosphere. There are some physical hardware condition limitations in the underwater acoustic probes of the acoustic tomography flow measurement system, and the acoustic wave signals emitted will have a certain degree of distortion compared to ideal acoustic wave signals. For example, there will be interference such as attenuation, deformation, and superposition. The existing measurement technology uses a conventional acoustic wave signal coding method. When using an ideal waveform signal to perform template matching filtering calculation on the received signal data, the matching degree will decrease and there will be deviations in signal recognition, resulting in a reduction in the accuracy of calculating the arrival time of the acoustic wave.

[0026] Due to the differences in hardware and water body environment, the shapes of the acoustic wave signals emitted by different probes vary. If an ideal waveform signal is used to match the actual signals with differences, it may be difficult to match and the accuracy will decrease. Compared with the existing technology, the method and system of the present invention adopt a newly constructed forward and reverse code signal, use the actually received signal for matching calculation and filtering, utilize the structure of the forward and reverse code and the operation of reversing the signal in reverse order, and perform precise matching on the premise of retaining the characteristics of the actual signal, which can avoid the influence of the error between the ideal waveform signal and the actual signal on the matching result, effectively improve the signal matching accuracy, and thus can accurately calculate the propagation time of the acoustic wave, greatly reducing the error. Through experiments, it is found that the accuracy is improved by 9 - 11% compared with the existing technology.

[0027] 2) The method and system of the present invention are to splice a forward-order signal and a reverse-order signal together to form a forward and reverse code signal for transmission, then intercept a matching segment P from the received acoustic wave signal R, reverse it in reverse order to obtain P', and calculate a new matching filtering result, which can improve the signal matching degree and resolution. Experiments prove that the use of forward and reverse code signals in acoustic tomography flow measurement is helpful for signal recognition, not easily affected by noise, the effective wave peak signals are easy to identify, and the accuracy and stability of estimating the arrival time of the acoustic wave are significantly improved.

[0028] 3) The system of the present invention comprehensively considers the actual situation that the shapes of the acoustic wave signals emitted by multiple different probes vary. Through the forward and reverse code encoding signal, it can well balance the hardware differences of different probes. Finally, the arrival time of the acoustic wave signal calculated by using the special encoding signal filtering formula is more accurate and conforms to the actual hydrological situation. The architecture of the system is simple, reducing a large amount of data sample training, with a calculation amount reduced by about 15% compared with the existing technology, short measurement time, and high stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic flow chart of the forward and reverse code encoding method of the acoustic wave signal of the present invention.

[0030] Figure 2 It is a schematic diagram of an ideal received signal and an actual received signal.

[0031] Figure 3 Schematic diagram of the matching result using the ideal signal and the matching result using the actual received signal.

[0032] Figure 4 Schematic diagram of the waveform of the received signal of the present invention.

[0033] Figure 5 Schematic diagram of the matching filtering processing result using the normal coded signal and the matching filtering processing result using the forward and reverse code signals of the present invention. Specific embodiments

[0034] Next, the technical solutions in the embodiments of the invention will be clearly and completely described in conjunction with the accompanying drawings in this embodiment.

[0035] The present invention provides a forward and reverse code encoding method for acoustic wave signals applied to an acoustic tomography flow measurement system. A forward sequence signal and a reverse sequence signal are spliced together to form a forward and reverse code signal. The river acoustic tomography flow measurement system uses this forward and reverse code signal and performs signal analysis and processing according to a specific signal processing flow, which can improve the signal matching degree and resolution, reduce the possibility of signal recognition errors, and improve the calculation accuracy of the acoustic wave arrival time.

[0036] See the attached Figure 1 , Embodiment 1, the method of the present invention includes:

[0037] Step (1) In the river acoustic tomography flow measurement system, an acoustic wave signal S and a signal S' with reverse order flipping are spliced together to form a forward and reverse code signal SS, and the forward and reverse code signal SS is sent at the probe transmitting end.

[0038] The frequency of the forward and reverse code signal SS remains unchanged, and the waveform is the same as the original acoustic wave signal S. In the actual operation process, the acoustic wave signal S is the M-code acoustic wave signal S. The M-code acoustic wave signal S and an M-code acoustic wave signal S' with reverse order flipping are spliced together to form an M-code forward and reverse code signal SS; or the acoustic wave signal S is an acoustic wave signal encoded by other codes, such as a Gold sequence encoded acoustic wave signal or a quadratic residue sequence encoded acoustic wave signal, and the method of the present invention can be used to convert it into a forward and reverse code signal.

[0039] Step (2) At the receiving end, the received acoustic wave signal R is subjected to matching filtering calculation using the conventional acoustic wave signal S to obtain a filtering result C, and the time of the maximum value point of C is ts.

[0040] If there is no interference considered, the acoustic wave signal R received at the receiving end is the original forward and reverse code signal SS. However, in fact, the river channel situation is complex, and there will be interference such as weakening, deformation, and superposition of waveform signals. Therefore, the acoustic wave signal R received at the receiving end is different from the forward and reverse code signal SS sent at the transmitting end.

[0041] Step (3) intercepts a matching segment P from the received acoustic wave signal R, reverses it in order to obtain P', calculates a new matched filtering result, and the arrival time of the acoustic wave signal R.

[0042] The specific process is as follows. A matching segment P is intercepted from the received acoustic wave signal R. The interception starting point is t0 = ts - dt. If ts < dt, then t0 = 0. The interception duration is nS. Here, nS is the length of the positive and negative code signal SS, and dt is a preset time advance, generally set to one-tenth of nS.

[0043] The segment P is reversed in order to obtain P'. Using P' as a template, template matching filtering calculation is performed on the acoustic wave signal R to obtain a new matched filtering result C'. The time of the peak point of C' is obtained as ts'. Reversing the segment P in order means reversing the encoding order of a segment of the acoustic wave signal to obtain the corresponding reversed segment P'. For example, if the original signal encoding is 12345, the reversed signal encoding is 54321.

[0044] Calculated through the formula Then t is the arrival time of the acoustic wave signal R. The obtained arrival time t is used for subsequent flow velocity calculation.

[0045] The derivation process of the above formula assumes that the acoustic wave signal actually arrives at t, the signal length is nS, and the interception starting point is t0. Then the first t - t0 sampling points actually intercepted are noise points, and the interception end point is located at the last t - t0 points of the actual signal. The intercepted segment P is reversed and then subjected to matched filtering processing again. The maximum value point ts' of the matched filtering result is located at the (t - t0)th point after the starting point t of the actual signal, ts' = t + t - t0. Therefore

[0046] The positive and negative code encoding method of the present invention uses the actually received acoustic wave signal R for matching calculation and filtering. By utilizing the construction of the positive and negative codes and the operation of reversing the acoustic wave signal in order, matching is performed on the premise of retaining the characteristics of the actually received acoustic wave signal, which can avoid the influence of the error between the ideal signal and the actual signal on the matching result, effectively improve the signal matching accuracy, and thus accurately calculate the propagation time of the acoustic wave.

[0047] See the appendix Figures 2 - 5 , and through simulation and comparison of experimental data, the excellent effect of the method of the present invention is proved.

[0048] I. The ideal acoustic wave signal and the actually received acoustic wave signal are as Figure 2 , and it can be seen that the difference in the signal waveforms is relatively obvious.

[0049] Compare the matching result of the ideal received signal with the ideal signal and the matching result of the actual received signal as follows Figure 3 , it can be seen that the matching degree of the actual matching result is slightly lower than the ideal situation, Figure 3 The right waveform diagram in shows that there is a secondary peak behind the highest peak of the actual matching waveform, which will affect the subsequent identification of the arrival time of the sound wave.

[0050] II. In the method of the present invention, the sound wave signal R received by the system receiver is as follows Figure 4 . For Figure 4 The signal is subjected to matched filtering processing using the existing technology normal coding signal, and the result is shown in the small left diagram in Figure 5 , compared with the matched filtering processing using the positive and negative code signals of the present invention, as shown in the small right diagram in Figure 5 .

[0051] It can be seen that at the same sampling point position, the matching degree of the sampling point matching result (the first peak) of the positive and negative code signals is higher than that of the normal coding signal, which is the highest value of the whole result, and there are no other secondary peaks near the matching result, that is, the interference clutter is excluded and is easy to distinguish and filter out, indicating that the result is better, proving that the signal encoded with the positive and negative codes of the present invention helps to effectively measure signal recognition, is not easily affected by noise, and greatly improves the accuracy and stability of the sound wave arrival time estimation. Since theoretically the first peak of the sampling point waveform diagram is the sound wave that reaches through the shortest distance, is least affected by the bottom reflection of the river and has the highest intensity, and the subsequent secondary peaks are signals that have undergone more reflections or other noises, so the highest first peak proves the best signal recognition.

[0052] The present invention also provides an acoustic tomography flow measurement system with positive and negative code encoding of acoustic signals. Using the method of the above embodiment, it includes: a signal conversion module for splicing an acoustic signal S and a reverse-flipped signal S' together to form a positive and negative code signal SS; a positive and negative code encoding processing module for performing matched filtering calculation on the received acoustic signal R with a conventional acoustic signal S to obtain a filtering result C, and obtaining the time of the maximum value point of C as ts; a signal filtering processing module for intercepting a matching segment P from the received acoustic signal R, performing reverse flipping to obtain P', calculating a new matched filtering result, and the arrival time of the acoustic signal R.

[0053] The signal filtering processing module further includes:

[0054] A signal segment intercepting module for intercepting a matching segment P from the received acoustic signal R, the intercepting starting point is t0 = ts - dt, if ts < dt, then t0 = 0, and the intercepting duration is nS; where nS is the length of the positive and negative code signal SS, and dt is a preset time advance amount;

[0055] The signal segment processing module is used to reverse the segment P to P', perform template matching filtering calculation on the acoustic wave signal R with P' as the template, obtain a new matching filtering result C', and obtain the time of the peak point of C' as ts'.

[0056] The signal arrival time calculation module is used to calculate through the formula Then t is the arrival time of the acoustic wave signal R, and the obtained arrival time t is used for subsequent flow velocity calculation.

[0057] The system uses the actually received acoustic wave signal R for matching calculation filtering, utilizes the construction of positive and negative codes and the operation of reversing the acoustic wave signal, and performs matching on the premise of retaining the characteristics of the actually received acoustic wave signal, improving the signal matching accuracy.

[0058] The acoustic wave signal S is the M-code acoustic wave signal S. The M-code acoustic wave signal S is spliced with a reversed M-code acoustic wave signal S' to form the positive and negative code signal SS of the M-code; or the acoustic wave signal S is an acoustic wave signal encoded by other codes, including the acoustic wave signal encoded by the Gold sequence or the acoustic wave signal encoded by the quadratic residue sequence.

[0059] The system of the present invention comprehensively considers the actual situation that the shapes of acoustic wave signals emitted by multiple different probes are different. Through the positive and negative code encoded signals, the hardware differences of different probes can be well balanced. Finally, the arrival time of the acoustic wave signal calculated by the special encoding signal filtering formula on the host is more accurate and conforms to the actual hydrological situation. The system has a simple architecture, reduces a large number of data sample trainings, and has a high degree of intelligent operation.

Claims

1. An encoding method for positive and negative codes of acoustic wave signals applied to an acoustic tomography flow measurement system, characterized in that, Including the steps: (1) In the river acoustic tomography flow measurement system, splice an acoustic wave signal S with a reverse-order flipped signal S' together to form a positive and negative code signal SS, and transmit the positive and negative code signal SS at the probe transmitting end; (2) At the receiving end, perform matched filtering calculation on the received acoustic wave signal R using the conventional acoustic wave signal S to obtain a filtering result C, and obtain the time of the maximum point of C as ts; (3) Intercept a matching segment P from the received acoustic wave signal R, reverse it to get P', calculate a new matched filtering result, and the arrival time of the acoustic wave signal R.

2. The method for encoding positive and negative codes of acoustic wave signals applied to an acoustic tomography flow measurement system according to claim 1, wherein (3) specifically includes: Intercept a matching segment P from the received acoustic wave signal R, the intercept starting point is t0 = ts - dt, if ts < dt, then t0 = 0, and the intercept duration is nS; where nS is the length of the positive and negative code signal SS, and dt is a preset time advance; Reverse the segment P to get P', use P' as a template to perform template matching filtering calculation on the acoustic wave signal R, obtain a new matched filtering result C', and obtain the time of the peak point of C' as ts'; Calculated by formula Then t is the arrival time of the acoustic wave signal R, and the obtained arrival time t is used for subsequent flow velocity calculation.

3. The method for encoding positive and negative codes of acoustic signals applied to an acoustic tomography flow measurement system according to claim 1, characterized in that, In (3): The reverse flipping of the segment P is to reverse the encoding order of a segment of acoustic wave signal to obtain the corresponding reverse-flipped segment P'.

4. The method for encoding positive and negative codes of acoustic wave signals applied to an acoustic tomography flow measurement system according to claim 1, characterized in that The positive and negative code encoding method uses the actually received acoustic wave signal R for matching calculation and filtering, utilizes the construction of positive and negative codes and the operation of reverse flipping of acoustic wave signals, and performs matching on the premise of retaining the characteristics of the actually received acoustic wave signal, thereby improving the signal matching accuracy.

5. The method for encoding positive and negative codes of acoustic wave signals applied to an acoustic tomography flow measurement system according to claim 1 or 2, characterized in that The acoustic wave signal S is an M-code acoustic wave signal S, splice this M-code acoustic wave signal S with a reverse-order flipped M-code acoustic wave signal S' together to form an M-code positive and negative code signal SS; or the acoustic wave signal S is an acoustic wave signal encoded by other codes, including an acoustic wave signal encoded by a Gold sequence or an acoustic wave signal encoded by a quadratic residue sequence.

6. An acoustic tomography flow measurement system with forward and reverse code encoding of acoustic wave signals, characterized in that, Including a signal conversion module for splicing an acoustic wave signal S with a reverse-order flipped signal S' together to form a positive and negative code signal SS; A positive and negative code encoding and processing module for performing matched filtering calculation on the received acoustic wave signal R using the conventional acoustic wave signal S to obtain a filtering result C, and obtaining the time of the maximum point of C as ts; A signal filtering and processing module for intercepting a matching segment P from the received acoustic wave signal R, reversing it to get P', calculating a new matched filtering result, and the arrival time of the acoustic wave signal R.

7. The acoustic tomography flow measurement system with forward and reverse code encoding of acoustic wave signals according to claim 6, characterized in that, The signal filtering and processing module further includes: A signal segment intercepting module for intercepting a matching segment P from the received acoustic wave signal R, the intercept starting point is t0 = ts - dt, if ts < dt, then t0 = 0, and the intercept duration is nS; where nS is the length of the positive and negative code signal SS, and dt is a preset time advance; The signal segment processing module is used to reverse the segment P to obtain P', perform template matching filtering calculation on the acoustic wave signal R with P' as the template, obtain a new matching filtering result C', and obtain the time of the peak point of C' as ts'. The time-of-arrival calculation module is used to calculate through the formula where t is the arrival time of the acoustic wave signal R, and the obtained arrival time t is used for subsequent flow velocity calculation.

8. The acoustic tomography flow measurement system with positive and negative code encoding of acoustic wave signals according to claim 6, characterized in that, The system uses the actually received acoustic wave signal R for matching calculation filtering, utilizes the construction of positive and negative codes and the operation of reversing the acoustic wave signal, and performs matching on the premise of retaining the characteristics of the actually received acoustic wave signal, thereby improving the signal matching accuracy.

9. The acoustic tomography flow measurement system with positive and negative code encoding of acoustic wave signals according to claim 6, wherein The acoustic wave signal S is an M-code acoustic wave signal S, and the M-code acoustic wave signal S is spliced with a reverse M-code acoustic wave signal S' to form a positive and negative code signal SS of M-code; or the acoustic wave signal S is an acoustic wave signal encoded by other codes, including an acoustic wave signal encoded by a Gold sequence or an acoustic wave signal encoded by a quadratic residue sequence.

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