An acoustic tomography flow measurement system and a dual-frequency encoding method for acoustic wave signals used therein

Abstract

The present invention discloses an acoustic layer analysis flow measurement system and a dual-frequency encoding method for acoustic wave signals used therein, wherein the method comprises the following steps: (1) in the river acoustic layer analysis flow measurement system, editing and adjusting a single-frequency M-code signal with a modulation coefficient of 3, wherein the frequency of the single-frequency M-code signal is f Hz, and the duration of one code position is approximately 3 / f seconds; (2) the first half of a code position in the single-frequency M-code signal is modified to two sine waves, and the second half of a code position is modified to one sine wave, so that the modified single-frequency M-code signal becomes a dual-frequency signal; the dual-frequency signal is subjected to a code position specified by a sequence flipped according to the original coding rule of the single-frequency M-code signal, forming a dual-frequency coded signal for transmission; and (3) receiving the dual-frequency coded signal for matched filtering, identifying and separating different signals. The present invention can effectively reduce the peak width of the matched filtering result, reduce mutual interference between signals, and improve the separation and recognition accuracy of different signals.

Description

Technical Field

[0001] The present invention relates to the field of intelligent analysis of river flow measurement data, and in particular to an acoustic tomography flow measurement system and a dual-frequency encoding method of acoustic wave signals used therein. Background Art

[0002] River acoustic tomography flow measurement technology is a brand-new river measurement technology with the advantages of easy installation, minimal impact from river surface conditions, and high accuracy. Acoustic tomography calculates river flow velocity based on the characteristic that sound waves propagate faster downstream than upstream. Therefore, accurately calculating the propagation speed of sound waves in water is the key to acoustic tomography flow measurement. Because sound waves travel through different propagation paths (sound rays) in the water to reach the receiving device, the received signal is a superposition of signals from multiple paths. At the same time, the received signal is also affected by water noise and equipment noise, such as the influence of sandy riverbed weeds and ships on the river surface. This makes it difficult to identify and distinguish the signals of different sound rays, resulting in large errors in the calculation of the sound wave propagation time, which has a significant impact on the subsequent calculation of the river's flow velocity and flow.

[0003] Currently, unmodulated underwater acoustic signals are typically identified by their signal-to-noise ratio. Existing techniques use a template matching filter algorithm to calculate the signal matching value for a coded modulated signal, then locate the signal by finding the maximum value. Because the resulting peak width of a single-frequency coded signal obtained by template matching filtering is relatively wide, sound waves arriving from different paths are superimposed. This wide peak can affect the separation and identification of different signals, leading to errors in the arrival times of the sound waves, and thus affecting subsequent flow velocity and flow calculations.

[0004] The existing patented technology is called a water flow detection system based on acoustic tomography cross-section detection, with application number CN202410695337.2. It receives a reflected signal through a data processing unit, pre-processes the reflected signal to obtain a pre-processed signal; evaluates the quality of the pre-processed signal to obtain an evaluation result, and dynamically adjusts the acoustic signal processing parameters based on the evaluation result to obtain a final pre-processed signal; extracts a pure signal and a noise signal from the pre-processed signal; calculates the variance of the noise signal, traverses all samples of the noise signal, calculates the difference between adjacent samples, and analyzes the final pre-processed signal based on the final pre-processed signal using the initial acoustic signal processing parameters and acoustic tomography technology to calculate the flow velocity distribution and flow rate. This system and method is very difficult to extract pure signals and noise signals. The system processing algorithm sample training is complex and the response is slow, making it not the most effective method. Summary of the Invention

[0005] To overcome the problems of the existing technology, the present invention provides an acoustic tomography flow measurement system and a dual-frequency encoding method for acoustic wave signals used therein, which can effectively reduce the peak width of the matched filtering result, reduce mutual interference between signals, and improve the separation and recognition accuracy of different signals.

[0006] The present invention provides a dual-frequency encoding method for acoustic wave signals applied to an acoustic tomography flow measurement system, comprising the steps of:

[0007] (1) In a river acoustic tomograph flow measurement system, a single-frequency M-code signal with a modulation factor of 3 is edited and adjusted. The frequency of the single-frequency M-code signal is f Hz, and the duration of one code position is 3 / f seconds.

[0008] (2) The first half of a code position in the single-frequency M-code signal is modified into two sine waves, that is, the frequency is 4f / 3; the second half of a code position is modified into one sine wave, that is, the frequency is 2f / 3, so that the single-frequency M-code signal is modified into a dual-frequency signal; the dual-frequency signal is subjected to the coding rule of the original single-frequency M-code signal, and the code positions specified in the sequence are flipped to form a dual-frequency coded signal for transmission;

[0009] (3) Receive the dual-frequency coded signal and perform matched filtering to identify and separate different signals.

[0010] Furthermore, in step (1), the single-frequency M-code signal refers to an M-sequence code, which is a coded signal obtained by flipping a specified code position in a sine wave signal according to a specific sequence; one code position of the single-frequency M-code signal contains 3 sine waves.

[0011] Furthermore, in step (3), the dual-frequency coded signal is received and matched filtered, and the peak width of the filtering result is narrow, and different signals are identified and separated. The narrow peak width will reduce the signal identification error and reduce the coverage between different signals.

[0012] In the specific step (3), the processed signal after the dual-frequency coded signal is subjected to matched filtering weakens the matching degree of non-matching points without reducing the matching degree of matching points, reduces mutual interference between signals, and improves signal matching accuracy.

[0013] The present invention also provides an acoustic tomography flow measurement system with dual-frequency encoding of acoustic wave signals, comprising a host and a plurality of acoustic wave probes, wherein the host comprises:

[0014] A signal editing and adjustment module is used to edit and adjust a single-frequency M-code signal with a modulation coefficient of 3, where the frequency of the single-frequency M-code signal is f Hz, and the duration of one code position is 3 / f seconds;

[0015] a dual-frequency signal processing module, configured to modify the first half of a code position in the single-frequency M-code signal into two sine waves, i.e., a frequency of 4f / 3; and modify the second half of a code position into one sine wave, i.e., a frequency of 2f / 3, thereby converting the modified single-frequency M-code signal into a dual-frequency signal; and flipping the code positions specified in the sequence of the dual-frequency signal according to the original coding rules of the single-frequency M-code signal to form a dual-frequency coded signal;

[0016] The dual-frequency signal filtering module is used to receive the dual-frequency coded signal, perform matched filtering, and identify and separate different signals.

[0017] Furthermore, the signal editing and adjustment module is also used for the single-frequency M-code signal, which refers to an M-sequence code, and is a coded signal obtained by flipping a specified code position in a sine wave signal according to a specific sequence; one code position of the single-frequency M-code signal contains 3 sine waves.

[0018] Furthermore, the dual-frequency signal filtering module is also used to perform matched filtering on the dual-frequency coded signal. The filtering result has a narrow peak width, which can identify and separate different signals. The narrower peak width can reduce the signal recognition error and reduce the coverage between different signals.

[0019] The technical advantages brought by the dual-frequency encoding method and system of the present invention are as follows:

[0020] (1) Compared with the existing single-frequency sound wave signal encoding method, the sound wave signal dual-frequency encoding processing method of the present invention weakens the matching degree of non-matching points without reducing the matching degree of the effective waveform signal matching point, reduces the mutual interference between signals, and especially eliminates the interference of clutter. By matching filtering the dual-frequency coded signal, the peak width of the filtering result is narrow. The narrow peak width will reduce the signal recognition error, reduce the coverage between different signals, and facilitate the identification and separation of different signals, effectively improve the signal matching accuracy, and thus effectively separate different interference clutter signals in the water body, calculate the accurate arrival time of each sound wave signal, and thus analyze the sound line propagation in the water body and the river section, so as to improve the measurement accuracy of river flow rate and flow.

[0021] (2) To overcome the problem of insufficient recognition accuracy in processing single-frequency coded signals, the method and system of the present invention modifies the single-frequency signal based on the M code into a dual-frequency signal. When performing matched filter algorithm calculations, the matching value size of the incorrect matching position is greatly reduced without changing the matching value size of the correct matching position, thereby reducing the possibility of signal recognition errors. The calculation amount is small and the accuracy of the calculation of the arrival time of the underwater sound wave is improved. The optimized and integrated measurement algorithm can obtain flow monitoring data that is more stable, accurate, and fast than existing traditional measurements. The processing speed is 7-9% faster than that of existing single-frequency sound wave signal processing, and the accuracy is improved by 11-13% compared with existing single-frequency signals.

[0022] (3) The system and method of the present invention have wider applicability and overcome the influence of river beaches and riverbed aquatic plants. The dual-frequency signal distortion after dual-frequency coding signal filtering is small and has stronger anti-interference applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of single frequency coded signal.

[0024] Figure 2 Schematic diagram of the dual-frequency coded signal of the present invention.

[0025] Figure 3 It is a partial schematic diagram of the existing technology for matching filtering a single-frequency coded signal.

[0026] Figure 4 The figure is a local schematic diagram of matching filtering of a dual-frequency coded signal using the method of the present invention.

[0027] Figure 5 It is a schematic diagram of the results of matched filtering calculations on single-frequency coded signals using the existing technology.

[0028] Figure 6 The figure is a schematic diagram of the results of matched filtering calculations on a dual-frequency coded signal using the method of the present invention. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the invention will be described clearly and completely below with reference to the accompanying drawings in this embodiment.

[0030] An embodiment of the present invention provides a dual-frequency encoding method for acoustic wave signals applied to an acoustic tomography flow measurement system, comprising: step (1), in the river acoustic tomography flow measurement system, editing and adjusting a single-frequency M-code signal with a modulation coefficient of 3, wherein the frequency of the single-frequency M-code signal is f Hz, and the duration of one code position is approximately 3 / f seconds.

[0031] The dual-frequency coded signal is a modification of the existing single-frequency M-code signal. M-code refers to M-sequence coding, which is a coded signal generated by flipping a specified segment (code position) of a sinusoidal signal according to a specific sequence. M-code signals have high autocorrelation and low cross-correlation, making them highly resistant to noise for signal recognition tasks. The modulation factor refers to the number of sinusoidal waves contained in a code position. A single-frequency M-code signal with a modulation factor of 3 means that one code position of the signal contains three sinusoidal waves. Assuming the signal transmission frequency is f Hz, the duration of one code position is approximately 3 / f seconds.

[0032] Step (2): modify the first half of a code position in the single-frequency M code signal into two sine waves, that is, the frequency is The second half of the code position is modified into a sine wave, that is, the frequency is The single-frequency M-code signal is then modified to become a dual-frequency signal.

[0033] Assume that the M code sequence is {m1,m2,m3,...,m n}(m i =0,1), the dual-frequency signal is expressed in code bits as S={s1,s2,s3,...,s n}, then the dual-frequency signal is flip-encoded according to the M code sequence, and the dual-frequency M code signal is finally obtained

[0034] The flip position of the flip code is determined by the M code sequence, and one sequence determines one flip mode.

[0035] Step (3) receives the dual-frequency coded signal and performs matched filtering to identify and separate different signals. The filtered signal is used in the river acoustic tomography flow measurement process to measure the river flow velocity and flow rate based on the arrival time of the filtered signal. This is prior art and is also disclosed in the applicant's previous patents. It will not be described in detail here.

[0036] The method of the present invention performs matched filtering on the dual-frequency coded signal, resulting in a narrow peak width. Narrow peaks reduce signal recognition errors and reduce overlap between different signals, facilitating the identification and separation of different signals. The processed signal after matched filtering of the dual-frequency coded signal weakens the matching degree of non-matching points, which are often interference clutter, without reducing the matching degree of matching points. This reduces mutual interference between signals and improves signal matching accuracy.

[0037] The following describes the effect of the dual-frequency coded signal in detail with reference to the experimental waveform diagram.

[0038] Taking the acoustic wave measuring probe with a transmitting frequency of 25k as an example, the probe of the system transmits a single frequency coded signal with a modulation coefficient of 3, such as Figure 1 As shown, it is a continuous 25k sine wave, in which a code bit (i.e., a segment) in the middle is flipped due to the M code encoding rule, see the solid line waveform part.

[0039] After being processed and modified by the method of the present invention, it is transformed into a dual-frequency coded signal such as Figure 2 As shown, it is a dual-frequency sine wave with a high frequency band of 33k and a low frequency band of 17k. Figure 2 The dotted line wave in the middle represents the high frequency band, and the solid line represents the low frequency band waveform. It can be seen that the middle code position is due to the reversal of the encoding rule of the M code.

[0040] right Figure 1 The single frequency coded signal is matched filtered to obtain the waveform result as follows Figure 3 As shown. Figure 2 The waveform of the dual-frequency coded signal is obtained by matching the filter. Figure 4 As shown in Figure 2, it can be seen that the peak width of the waveform of the matched filtering result of the single-frequency coded signal is about 100 sampling points, while Figure 4 The peak width of the matched filtering result of the dual-frequency coded signal is significantly narrower than that of the single-frequency coded signal, with only about 25 sampling points. The narrower peak width reduces signal recognition errors and significantly reduces the overlap between different signals, including the actual detection signal, interference signals such as ships on the river surface and riverbed weeds. This helps to identify and separate interference signals, preserving the true and useful detection signal.

[0041] The comparative test results are as follows.

[0042] For a single-frequency signal, assume that the signal strength is 1. Under a background of five times the intensity of white noise, five single-frequency signals are superimposed at the 1000th, 1010th, 1015th, 1030th, and 1050th time points to form a simulated received signal. The received signal data is processed using conventional single-frequency coded signal technology and then matched filtering is performed to obtain the following results: Figure 5 .

[0043] Under the same noise background as above, at the same time point, the dual-frequency signals of the same intensity are superimposed, and then processed using the dual-frequency encoding method of the present invention, and then matched filtering calculation is performed, and the results are as follows: Figure 6 .

[0044] After comparing the experimental waveform data, it can be seen that the matched filtering result of the single-frequency coded signal has only three obvious peak points, located at the 1001st, 1029th and 1052th time points respectively, and two sound wave signals are submerged by other signals; while the matched filtering result of the dual-frequency coded signal processed by the method of the present invention has five obvious peak points, located at the 1000th, 1009th, 1016th, 1030th and 1050th time points respectively, which are almost consistent with the positions of the original signals. It can be proved that the dual-frequency coded signal processed by the method of the present invention has a better effect on the separation and identification of different sound wave signals, and can effectively improve the signal matching accuracy, thereby effectively separating different interfering clutter signals in the water body, calculating the exact arrival time of each sound wave signal, and thus analyzing the sound line propagation in the water body and the river section conditions, thereby improving the measurement accuracy of river flow rate and flow.

[0045] The present invention also provides an acoustic tomography flow measurement system with dual-frequency encoding of acoustic wave signals, which adopts the above-mentioned method of the present invention and includes a host and multiple acoustic wave probes, wherein the host includes: a signal editing and adjustment module for editing and adjusting a single-frequency M-code signal with a modulation coefficient of 3, wherein the frequency of the single-frequency M-code signal is f Hz, and the duration of one code position is 3 / f seconds;

[0046] The dual-frequency signal processing module is used to modify the first half of a code position in the single-frequency M-code signal into two sine waves, that is, the frequency is 4f / 3; and modify the second half of a code position into one sine wave, that is, the frequency is 2f / 3, so that the single-frequency M-code signal is modified into a dual-frequency signal; the dual-frequency signal is subjected to the coding rule of the original single-frequency M-code signal, and the code positions specified in the sequence are flipped to form a dual-frequency coded signal to be transmitted to the probe transmitting end.

[0047] The dual-frequency signal filtering module is used to receive the dual-frequency coded signal transmitted from the probe receiving end, perform matched filtering, and identify and separate different signals. The filtered signal is used in the river acoustic tomography flow measurement process.

[0048] The signal editing and adjustment module is also used to edit the single-frequency M-code signal, which is a coded signal obtained by flipping a specified code position in a sine wave signal according to a specific sequence; one code position of the single-frequency M-code signal contains 3 sine waves.

[0049] The dual-frequency signal filtering module is also used to perform matched filtering on the dual-frequency coded signal. The resulting filtering results in a narrow peak width, enabling identification and separation of different signals. The narrow peak width minimizes signal identification errors and reduces coverage between different signals. This filtering eliminates clutter and interference signals, improving measurement accuracy. The system equipment of the present invention is highly intelligent, capable of remote centralized control, and boasts high data processing efficiency, achieving an 11-13% improvement in accuracy over existing single-frequency signal systems. The software system architecture model is simple, easy to maintain, and highly reliable.

Claims

1. A dual-frequency encoding method for acoustic wave signals applied to an acoustic tomography flow measurement system, characterized in that: Including steps: (1) In a river acoustic tomograph flow measurement system, a single-frequency M-sequence coded signal with a modulation factor of 3 is edited and adjusted. The frequency of the single-frequency M-sequence coded signal is f Hz, and the duration of one code position is 3 / f seconds. (2) The first half of a code position in the single-frequency M-sequence coded signal is modified into two sine waves, that is, the frequency is 4f / 3; the second half of a code position is modified into one sine wave, that is, the frequency is 2f / 3, so that the single-frequency M-sequence coded signal is modified into a dual-frequency signal; the dual-frequency signal is transmitted by flipping the code positions specified in the sequence according to the original coding rules of the single-frequency M-sequence coded signal; (3) Receive the dual-frequency coded signal and perform matched filtering to identify and separate different signals.

2. The dual-frequency encoding method for acoustic wave signals applied to an acoustic tomography flow measurement system according to claim 1, characterized in that: In step (1), The single-frequency M-sequence coded signal refers to an M-sequence code, which is a coded signal obtained by flipping a specified code bit in a sine wave signal according to a specific sequence; one code bit of the single-frequency M-sequence coded signal contains 3 sine waves.

3. The dual-frequency encoding method for acoustic wave signals applied to an acoustic tomography flow measurement system according to claim 1, characterized in that: In step (3), The dual-frequency coded signal is received and matched filtered. The peak width of the filtering result is narrow, and different signals are identified and separated. The narrow peak width will reduce the signal identification error and reduce the coverage between different signals.

4. A dual-frequency encoding method for acoustic wave signals applied to an acoustic tomography flow measurement system according to any one of claims 1 to 3, characterized in that: In step (3), The processed signal after the dual-frequency coded signal is subjected to matched filtering weakens the matching degree of non-matching points without reducing the matching degree of matching points, thereby reducing mutual interference between signals.

5. An acoustic tomography flow measurement system with dual-frequency encoding of acoustic wave signals, comprising a host and a plurality of acoustic wave probes, characterized in that: The host includes A signal editing and adjustment module is used to edit and adjust a single-frequency M-sequence coded signal with a transmission modulation coefficient of 3, where the frequency of the single-frequency M-sequence coded signal is f Hz, and the duration of one code position is 3 / f seconds; a dual-frequency signal processing module, configured to modify the first half of a code position in the single-frequency M-sequence coded signal into two sine waves, i.e., a frequency of 4f / 3; and modify the second half of a code position into one sine wave, i.e., a frequency of 2f / 3, thereby converting the single-frequency M-sequence coded signal into a dual-frequency signal after modification; and to perform flipping of the code positions specified in the sequence of the dual-frequency signal according to the original coding rule of the single-frequency M-sequence coded signal to form a dual-frequency coded signal; The dual-frequency signal filtering module is used to receive the dual-frequency coded signal, perform matched filtering, and identify and separate different signals.

6. The acoustic tomography flow measurement system with dual-frequency encoding of acoustic wave signals according to claim 5, characterized in that: The signal editing and adjustment module is also used for the single-frequency M-sequence coded signal, which refers to M-sequence coding, and is a coded signal obtained by flipping a specified code position in a sine wave signal according to a specific sequence; one code position of the single-frequency M-sequence coded signal contains 3 sine waves.

7. The acoustic tomography flow measurement system with dual-frequency encoding of acoustic wave signals according to claim 5, characterized in that: The dual-frequency signal filtering module is also used to perform matched filtering on the dual-frequency coded signal. The filtering result has a narrow peak width, which can identify and separate different signals. The narrow peak width can reduce the signal recognition error and reduce the coverage between different signals.

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