A sonar array spatial gain measurement method based on modular hierarchical measurement

Abstract

The present invention relates to a sonar array spatial gain measurement method of analog-digital hierarchical measurement. The gain measurement method is decomposed into two levels, namely, array element gain and directional gain. The hierarchical measurement is performed using an analog measurement system composed of standard instruments and a digital measurement system of a sonar receiving unit. The sum of the two levels of gain is the acoustic array spatial gain. The method includes the following steps: arranging test equipment; measuring array element gain; measuring directional gain; and spatial gain. The obtained array element gain and directional gain are added together to obtain the acoustic array spatial gain. The gain measurement method of the present invention decomposes the sonar array spatial gain components, respectively uses an analog measurement system and a digital measurement system to measure the array element gain and directional gain, and finally synthesizes the total spatial gain of the array. This method can avoid the final measurement result deviation caused by the differences in filtering, amplification, AD acquisition quantization error and other conditions in different measurement systems during the direct measurement of input and output signal-to-noise ratios.

Description

Technical Field

[0001] The invention relates to the technical field of underwater acoustic measurement, and in particular to a sonar array spatial gain measurement method of modular hierarchical measurement. Background Art

[0002] The concept of acoustic array spatial gain refers to the difference between the signal-to-noise ratio of the output beam signal of the acoustic array multi-channel received signal after beamforming and the signal-to-noise ratio of the signal in the free field of space (input signal-to-noise ratio). As can be seen from the concept, if you want to measure the spatial gain of the acoustic array, you only need to obtain the input signal-to-noise ratio and the beam output signal-to-noise ratio. However, in the current mainstream sonar information processing system, the beam data signal-to-noise ratio is generally calculated from the digital signal after amplification, filtering, and collection by the sonar's own receiving system; for the spatial input signal signal-to-noise ratio in the free field, it must be measured using a non-directional transducer, and the acoustic array's own array elements are generally directional. At this time, it is necessary to use a standard hydrophone equipped with a matching acoustic measurement equipment for measurement. It can be seen that the measurement of input and output requires two different measurement systems, and these two measurement systems are generally not exactly the same, so there is a deviation in the spatial gain obtained by this method. Summary of the invention

[0003] To this end, the technical problem to be solved by the present invention is to overcome the problem in the prior art that the measurement of input and output requires two different measurement systems that cannot be exactly the same, and the obtained spatial gain has deviations, thereby providing a sonar array spatial gain measurement method with modular hierarchical measurement.

[0004] In order to solve the above technical problems, the present invention provides a sonar array spatial gain measurement method of analog-digital hierarchical measurement, wherein the gain measurement method is decomposed into two levels: array element gain and directional gain, and hierarchical measurement is performed using an analog measurement system composed of standard instruments and a digital measurement system of a sonar receiving unit, respectively. The sum of the two levels of gain is the sonar array spatial gain, and the method comprises the following steps:

[0005] Step S1: Arrange the test equipment so that the i-th array element of the acoustic array is horizontally pointed to the transmitting transducer. The horizontal distance R between the two meets the far-field measurement condition. The standard hydrophone of the same depth is arranged 1m away from the acoustic array and connected to the transmitting transducer through an acoustic transmitting device. The single-frequency pulse signal with a center frequency of F can be emitted, which is the signal to be measured.

[0006] Step S2: Use the analog measurement system to measure the gain of the array element. First, the transmitting transducer is not transmitting, and the standard hydrophone is connected to the analog measurement system. The filter frequency and bandwidth of the measurement system are adjusted to make the frequency of the signal to be measured within the measurement frequency band. The dial reading of the measurement amplifier is observed to calculate the noise level NL1.

[0007] Step S3: After the noise measurement is completed, the transmitting transducer starts to transmit the signal to be measured with the specified sound source level SL, calculates the signal source level SL'1 arriving at the acoustic array, and then calculates the array element input signal-to-noise ratio SNR1;

[0008] Step S4: connect the i-th array element signal to the analog measurement system, and measure the array element receiving signal source level SL'2 and the array element receiving noise level NL2 respectively according to the method of steps 2-3, and similarly calculate the array element output signal-to-noise ratio SNR2, and finally calculate the array element gain G1;

[0009] Step S5: Use the digital measurement system to measure the directivity gain. First, connect the array element signal back to the original position, start the sonar receiving processing program, use the debugging PC and the sonar's own digital signal processor to form a digital measurement system, and record and save the i-th array data and the j-th beam data with the same pointing direction in real time;

[0010] Step S6: Use simulation analysis tools to analyze the stored array data and beam data. zy_n 、x zy_s 、x bs_n 、x bs_n , calculate their respective mean square values ​​σ zy_n , σ zy_s , σ bs_n , σ bs_s ;

[0011] Step S7: Calculate the array data signal-to-noise ratio SNR3 and the beam output signal-to-noise ratio SNR4, then calculate the directivity gain G2, add G1 and G2 to calculate the sonar array spatial gain.

[0012] In one embodiment of the present invention, the test equipment adopts a cylindrical acoustic array, whose array element structure is a longitudinal oscillator, the array frequency is F, m elements are arranged horizontally, n elements are arranged vertically, and k beams are pre-formed horizontally.

[0013] In one embodiment of the present invention, the analog measurement system adopts a small signal receiving and measuring system composed of a BK2636 measurement amplifier, a BK1617 filter and an oscilloscope.

[0014] In one embodiment of the present invention, the digital measurement system can directly use the sonar digital signal processing platform to read and record the internal data through the debugging PC, and perform analysis and calculation in an offline processing manner.

[0015] In one embodiment of the present invention, the acoustic emission device in step S1 uses a 33521A function generator and a BK2713 instrument amplifier.

[0016] In one embodiment of the present invention, the mean square value in step S6 may reflect the power level of the received data.

[0017] The above technical solution of the present invention has the following advantages over the prior art: the gain measurement method described in the present invention, by decomposing the spatial gain components of the sonar array, adopts an analog measurement system and a digital measurement system to measure the element gain and the directional gain respectively, and finally synthesizes the total spatial gain of the array. This method can avoid the deviation of the final measurement result caused by the differences in filtering, amplification, AD acquisition quantization error and other conditions in different measurement systems during the direct measurement of the input and output signal-to-noise ratio, and the method of the present invention can be applied to the static performance measurement test of various types of acoustic arrays in environments such as anechoic pools and lakes. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings.

[0019] Figure 1 It is a schematic diagram of the working principle of the sonar array spatial gain measurement method of the modulus hierarchical measurement of the present invention;

[0020] Figure 2 is a layout diagram of the test equipment of the present invention;

[0021] Figure 3 It is a schematic diagram of noise and signal sampling in array data and beam data according to the present invention. DETAILED DESCRIPTION

[0022] like Figure 1 As shown, this embodiment provides a sonar array spatial gain measurement method of analog-digital hierarchical measurement, in which the gain measurement method is decomposed into two levels: array element gain and directivity gain. The hierarchical measurement is performed using an analog measurement system composed of standard instruments and a digital measurement system of a sonar receiving unit. The sum of the two levels of gain is the sonar array spatial gain.

[0023] Furthermore, the sonar acoustic array receives underwater space signals through various array elements. Due to the design principle of the array elements' amplification or self-vibration, they have spatial directivity, that is, when a single array element receives an incident signal, it can obtain a certain gain, which is defined as the array element gain in this method. Multiple array elements are arranged in space according to certain rules or specified coordinates, and the received signals of each array element are phase-shifted, weighted, and summed through software algorithms to pre-form a receiving beam. In the beamforming process, gain is also brought about, which is defined as directivity gain in this method.

[0024] The measurement of the array element gain is to measure the non-directional hydrophone receiving signal and the array element receiving signal facing the incident signal through an analog measurement system built by the instrument, and obtain the input signal-to-noise ratio SNR1 and the array element output signal-to-noise ratio SNR2. The difference between the two is the array element gain.

[0025] The measurement of directivity gain is to use the digital signal processor in the sonar receiving system as a digital measurement system to measure the array element digital signal after receiving preprocessing and the beam digital signal after beam forming, respectively, to obtain the beam input signal-to-noise ratio SNR1 and the beam output signal-to-noise ratio SNR2, and the difference between the two is the directivity gain;

[0026] The spatial gain is the sum of the obtained array element gain and the directional gain, which is the spatial gain of the acoustic array. The measurement of the two-stage gain uses the same measurement system to measure the input and output signals, with the same processing and filtering environment, which can avoid the errors caused by inconsistent measurement systems. The spatial gain obtained by hierarchical measurement and summation is more accurate. In addition, since the processing gain is the relative value of the input and output signal-to-noise ratio, it is invariant within the same frequency band, and a transmission signal that is conducive to measurement can be designed for testing, which has high operability.

[0027] The steps include:

[0028] Step S1: Figure 2 As shown in the figure, the test equipment is arranged so that the i-th array element of the acoustic array is horizontally pointed to the transmitting transducer. The horizontal distance R between the two meets the far-field measurement condition. At the same water depth H, a standard hydrophone of the same depth is arranged 1m away from the acoustic array and connected to the transmitting transducer through an acoustic transmitting device. A single-frequency pulse signal with a center frequency of F can be emitted, which is the signal to be measured.

[0029] Step S2: Use the analog measurement system to measure the gain of the array element. First, the transmitting transducer is not transmitting. The standard hydrophone is connected to the analog measurement system. The filter frequency and bandwidth of the measurement system are adjusted to make the frequency of the signal to be measured within the measurement frequency band. The dial reading of the measurement amplifier is observed. The noise level NL1 is calculated according to formula (1):

[0030]

[0031] Where:

[0032] U n It is the effective value of the receiving noise voltage read by the measurement amplifier, unit: V;

[0033] M0 is the receiving sensitivity of the standard hydrophone in the measurement frequency band, unit: dB;

[0034] F is the frequency of the signal to be measured, unit: Hz.

[0035] Step S3: After the noise measurement is completed, the transmitting transducer starts to transmit the signal to be measured with the specified sound source level SL, and calculates the signal source level SL'1 arriving at the acoustic array, as shown in Formula 2, and then calculates the array element input signal-to-noise ratio SNR1, as shown in Formula 3:

[0036] SL'1=SL-20lgR (2)

[0037] SNR1=SL'1-NL1 (3)

[0038] Where R represents the horizontal distance between the transmitting transducer and the acoustic array, unit: m.

[0039] Step S4: Connect the i-th array element signal to the analog measurement system, and measure the array element receiving signal source level SL'2 and the array element receiving noise level NL2 according to the method in steps 2-3, and similarly calculate the array element output signal-to-noise ratio SNR2. Finally, the array element gain G1 can be calculated:

[0040] G1=SNR2-SNR1 (4)

[0041] Step S5: Use the digital measurement system to measure the directivity gain. First, connect the array element signal back to the original position, start the sonar receiving processing program, use the debugging PC and the sonar's own digital signal processor to form a digital measurement system, and record and save the i-th array data and the j-th beam data with the same pointing direction in real time;

[0042] Step S6: Use simulation analysis tools to analyze the stored array data and beam data. The noise and signal collection methods in the digital data are as follows: Figure 3 As shown, for the sampled data segment x zy_n 、x zy_s 、x bs_n 、x bs_n , calculate their respective mean square values ​​σ zy_n , σ zy_s , σ bs_n , σ bs_s , according to formula (5):

[0043]

[0044] Step S7: Calculate the array data signal-to-noise ratio SNR3 and the beam output signal-to-noise ratio SNR4 according to formula (6), and then calculate the directivity gain G2 according to formula (7). Add G1 and G2 to calculate the spatial gain of the sonar array:

[0045]

[0046] G2=SNR4-SNR3 (7)

[0047] Furthermore, when the sonar array is of irregular shape, its spatial gain may be unevenly distributed in the horizontal direction. In this case, the main working sectors can be divided and measurements can be carried out separately.

[0048] The test equipment adopts a cylindrical acoustic array, whose array element structure is a longitudinal oscillator, the array frequency is F, m elements are arranged horizontally, n elements are arranged vertically, and k beams are pre-formed horizontally.

[0049] The analog measurement system adopts a tiny signal receiving and measuring system composed of a BK2636 measurement amplifier, a BK1617 filter and an oscilloscope.

[0050] The digital measurement system can directly use the sonar digital signal processing platform to read and record internal data through a debugging PC, and perform analysis and calculation in an off-line processing manner.

[0051] In step S1, the acoustic emission device uses a 33521A function generator and a BK2713 instrument amplifier.

[0052] The mean square value in step S6 can reflect the power level of the received data.

[0053] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A sonar array spatial gain measurement method using analog-digital hierarchical measurement, wherein the gain measurement method is decomposed into two levels: array element gain and directional gain, and hierarchical measurement is performed using an analog measurement system composed of standard instruments and a digital measurement system of a sonar receiving unit, respectively. The sum of the two levels of gain is the sonar array spatial gain, and the method is characterized in that: The steps include: Step S1: Arrange the test equipment so that the i-th array element of the acoustic array is horizontally pointed to the transmitting transducer. The horizontal distance R between the two meets the far-field measurement condition. The standard hydrophone of the same depth is arranged 1m away from the acoustic array and connected to the transmitting transducer through an acoustic transmitting device. The single-frequency pulse signal with a center frequency of F can be emitted, which is the signal to be measured. Step S2: Use the analog measurement system to measure the gain of the array element. First, the transmitting transducer is not transmitting, and the standard hydrophone is connected to the analog measurement system. The filter frequency and bandwidth of the measurement system are adjusted to make the frequency of the signal to be measured within the measurement frequency band. The dial reading of the measurement amplifier is observed to calculate the noise level NL1. Step S3: After the noise measurement is completed, the transmitting transducer starts to transmit the signal to be measured with the specified sound source level SL, calculates the signal source level SL'1 arriving at the acoustic array, and then calculates the array element input signal-to-noise ratio SNR1; Step S4: connect the i-th array element signal to the analog measurement system, and measure the array element receiving signal source level SL'2 and the array element receiving noise level NL2 respectively according to the method of steps 2-3, and similarly calculate the array element output signal-to-noise ratio SNR2, and finally calculate the array element gain G1; Step S5: Use the digital measurement system to measure the directivity gain. First, connect the array element signal back to the original position, start the sonar receiving processing program, use the debugging PC and the sonar's own digital signal processor to form a digital measurement system, and record and save the i-th array data and the j-th beam data with the same pointing direction in real time; Step S6: Use simulation analysis tools to analyze the stored array data and beam data. zy_n 、x zy_s 、x bs_n 、x bs_n , calculate their respective mean square values ​​σ zy_n , σ zy_s , σ bs_n , σ bs_s ; Step S7: Calculate the array data signal-to-noise ratio SNR3 and the beam output signal-to-noise ratio SNR4, then calculate the directivity gain G2, add G1 and G2 to calculate the sonar array spatial gain.

2. The sonar array spatial gain measurement method of the modulus hierarchical measurement according to claim 1 is characterized in that: The test equipment adopts a cylindrical acoustic array, whose array element structure is a longitudinal oscillator, the array frequency is F, m elements are arranged horizontally, n elements are arranged vertically, and k beams are pre-formed horizontally.

3. The sonar array spatial gain measurement method of the modulus hierarchical measurement according to claim 2 is characterized in that: The analog measurement system adopts a tiny signal receiving and measuring system composed of a BK2636 measurement amplifier, a BK1617 filter and an oscilloscope.

4. The sonar array spatial gain measurement method of the modulus hierarchical measurement according to claim 2 is characterized in that: The digital measurement system can directly use the sonar digital signal processing platform to read and record internal data through a debugging PC, and perform analysis and calculation in an off-line processing manner.

5. The sonar array spatial gain measurement method of modular hierarchical measurement according to claim 4 is characterized in that: In step S1, the acoustic emission device uses a 33521A function generator and a BK2713 instrument amplifier.

6. The sonar array spatial gain measurement method of modular hierarchical measurement according to claim 4 is characterized in that: The mean square value in step S6 can reflect the power level of the received data.

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