Data-driven cetacean tick ranging method, medium and device

Abstract

The present invention relates to a data-driven method, medium and device for measuring the distance between cetaceans and dolphins by clicking. The method belongs to the field of underwater acoustic signal processing. The measured data is obtained to extract the click string from the measured audio data, and the sound propagation loss correction value is obtained according to the measured data. In the subsequent observation of the click sound, the calculated sound propagation loss correction value is used to calculate the actual distance of the click sound. The method of the present invention combines the measured data to achieve effective distance measurement of the click sound. The method can achieve distance measurement using a single hydrophone, is easy for actual engineering operations, and does not require information such as the sensitivity of the hydrophone and the sound source level of the porpoise's click sound.

Description

Technical Field

[0001] The invention belongs to the field of underwater acoustic signal processing, and relates to a data-driven cetacean ticking ranging method, medium and device. Background Art

[0002] In the Yangtze River ecological protection, the Yangtze River porpoise is a freshwater dolphin that lives in the Yangtze River basin. Due to environmental pollution and the impact of human activities, the number of porpoises has dropped sharply and has been listed as a critically endangered species. In order to protect the porpoise, scientists need to conduct long-term monitoring and research on the behavior, habitat, and population of the porpoise. As an important indicator species, the survival status of the Yangtze River porpoise directly reflects the health level of the ecosystem. Accurate monitoring of the activities of porpoises is crucial to the protection of porpoises. Porpoises use ticking sounds to socialize, navigate, and hunt. Based on the method of passive acoustic monitoring of ticking sounds, an effective method has been formed to estimate the direction and number of Yangtze River porpoises. However, there are few practical methods for measuring the distance between Yangtze River porpoises and ticking sounds.

[0003] Acoustic monitoring is an important method in monitoring aquatic animals. Finless porpoises use clicks to echolocate, detect the surrounding environment and capture prey. Using acoustic monitoring equipment, the clicks of finless porpoises can be recorded and analyzed to obtain information about their activities and distribution. Traditional methods for estimating the distance of incident acoustic signals mainly rely on the time difference between multiple hydrophones. However, since the distance between hydrophones in commonly used monitoring systems is usually small (generally within 1 meter), the distance estimation error of the clicks of finless porpoises hundreds of meters away is large [Xu Fu, Hui Junying, Yu Yun. Analysis and correction of the error of passive positioning using the three-point method [J]. Acta Ordnance, 2010, 31(9): 1169-1173]. In addition, although increasing the distance between hydrophones can improve ranging accuracy, the sound of porpoises is highly directional [Erqian Dong, Yu Zhang, Zhongchang Song, Tianye Zhang, Chen Cai, Nicholas X Fang, Physical modeling and validation of porpoises' directional emission via hybrid metamaterials, National Science Review, Volume 6, Issue 5, September 2019, Pages 921–928]. The same ticking signal may not be received by multiple hydrophones at the same time, resulting in ranging failure. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a data-driven cetacean click ranging method, medium and device.

[0005] The invention is realized by the following technical solutions:

[0006] A data-driven cetacean click ranging method, the method comprising the following steps:

[0007] The first step is to obtain measured data. After deploying a single hydrophone to a designated station, the ticking data of finless porpoises is obtained, and manual visual observation is performed or historical manual visual observation information is reviewed and sorted.

[0008] Step 2: Extract tick sound string. Extract the tick sound string from the measured audio data. Extract the maximum tick sound amplitude Amp in the tick sound string as the sound pressure amplitude of this pulse string. Obtain the tick sound pressure amplitude in the tick sound data as Amp_list.

[0009] Step 3: Calculate the sound propagation loss correction value. Calculate the sound propagation loss of each pulse train: TL_m = -20*log10(Amp_list) + TL_adj; TL_adj is the sound propagation loss correction value to be calculated. According to the sound propagation loss, calculate the distance R = 10^(TL_m / 20). Calculate the minimum value of the distance R R_m = min(R). Min(R) is obtained through actual measurement, that is, the minimum distance at which aquatic organisms appear around the hydrophone. Calculate the sound propagation loss correction value TL_adj.

[0010] Step 4: Calculate the ticking distance. In subsequent ticking observations, use the TL_adj calculated in the third step to calculate the acoustic propagation loss of each pulse train collected by the single hydrophone arranged in the first step: TL=-20*log10(Amp)+TL_adj. Then, use R=10^(TL / 20) to calculate the actual ticking distance.

[0011] The present invention also provides a computer-readable storage medium storing a computer program, wherein the computer program is suitable for being loaded by a processor and executing the second to fourth steps of the data-driven cetacean click ranging method.

[0012] A data-driven tick-ranging device for finless porpoises, the device comprising a memory and a processor, the memory storing a computer program, and when the computer program is executed by the processor, the second to fourth steps of the data-driven tick-ranging method for cetaceans are executed.

[0013] The beneficial effects of the present invention compared with the prior art are as follows:

[0014] The method of the present invention uses the basic physical law that the propagation loss of ticking sound in water conforms to the spherical expansion loss, and combines the measured data to achieve effective ranging of ticking sound. The method can achieve ranging using a single hydrophone, is easy to operate in actual engineering, and does not require information such as the sensitivity of the hydrophone and the sound source level of the finless porpoise's ticking sound, providing a new technical means for underwater positioning of cetaceans and dolphins. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a flow chart of the processing steps of the method of the present invention;

[0016] Figure 2 It is the time domain signal diagram of the hydrophone;

[0017] Figure 3 is the hydrophone signal amplitude diagram;

[0018] Figure 4 is the tick amplitude graph;

[0019] Figure 5 It is a logarithmic coordinate tick amplitude graph;

[0020] Figure 6 is the ticking sound propagation loss diagram, where the correction value is 0;

[0021] Figure 7 This is a graph showing how the propagation loss of ticking sound varies with distance;

[0022] Figure 8 This is a graph showing the statistical results of the tick distance. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further explained below by way of embodiments, but the protection scope of the present invention is not limited in any form by the embodiments.

[0024] The current acoustic monitoring method uses hydrophones to record the sound signals of finless porpoises, and then conducts data analysis manually or automatically. Using a single hydrophone, it is currently possible to study the occurrence patterns of finless porpoises and count the number of clicks per unit time. With the help of multiple hydrophones, the direction of the finless porpoise can be estimated, and the number can be counted. However, there is still a lack of effective methods for ranging. For small-sized arrays, passive methods are used to estimate the distance of the incident sound signal. The method that needs to be used is the hyperbolic intersection method. When the target appears outside the area connected by the hydrophone, the positioning accuracy of this method decreases as the wave arrival time and the positioning accuracy error of the hydrophone increase [Xu Fu, Hui Junying, Yu Yun. Analysis and correction of passive positioning errors of three-point method [J]. Acta Armamentarii, 2010, 31(9): 1169-1173], until it does not meet the actual application requirements. If the distance between the hydrophones is increased to the order of 10 meters, it is found through actual experimental tests that the same click cannot be received by the hydrophone at the same time, resulting in positioning failure. The reason is that ticking sound is a directional sound wave [Erqian Dong, Yu Zhang, Zhongchang Song, Tianye Zhang, Chen Cai, Nicholas X Fang, Physical modeling and validation of porpoises' directional emission via hybrid metamaterials, National Science Review, Volume 6, Issue 5, September 2019, Pages 921–928]. If the receiving hydrophones are not in the same beam, the signals cannot be received simultaneously.

[0025] The distance of the finless porpoise from the hydrophone will be reflected in the amplitude of the ticking sound received by the hydrophone. The physical law behind it is the propagation loss. Considering that the ticking sound signal is high frequency and highly directional, generally only the direct sound propagation loss needs to be considered. Then its propagation loss can be described by the following formula:

[0026] TL=20log10(r)+αr

[0027] Where r is the distance and α is the absorption coefficient. For the fresh water in the Yangtze River, at a sound wave frequency of 130kHz, its absorption coefficient can be estimated by the following empirical formula:

[0028] α=0.002×f 2

[0029] Where f is the frequency in MHz. Convert 130kHz to MHz, which is 0.13MHz, and substitute it into the formula to get:

[0030] α=0.0000338dB / m

[0031] For the case of 1000m, the absorption loss is about 0.0338dB, so it can be considered negligible in the detection and ranging of porpoise ticks at the kilometer level.

[0032] In general system deployment, the sound source level of finless porpoises is usually unknown (general measurements can be found in the literature). If relevant information can be statistically analyzed from the observation of ticks over a period of time, it can be used to assist in the distance measurement of ticks. Ticks usually appear in the form of pulse trains, see Figure 2 The amplitude of each click in the pulse train is generally different, representing the change in the azimuth of the finless porpoise's click. It can be assumed that the largest amplitude corresponds to the main axis of the click beam.

[0033] For each pulse train calculator propagation loss,

[0034] TL_m=-20*log10(Amp)+TL_adj

[0035] Among them, the propagation loss correction value TL_adj = SL + SENS_offset, SL is the sound source level of the finless porpoise's ticking sound, SENS_offset is the correction value of the hydrophone sensitivity and preamplification factor, etc. Amp is the maximum amplitude of each ticking sound string. Figure 3 The figure shows the amplitude extracted from the ticking sound. It can be seen that the amplitude increases from small to large, and then decreases from large to small.

[0036] After observing for a period of time, there is a high probability that a finless porpoise will appear near the hydrophone. Based on the historical activity patterns of finless porpoises in the surrounding area, the observation period can be set to 1 week. For the current detection system, the maximum detection distance is generally around 1,000 meters. So the probability that a finless porpoise will appear within 20 meters of the hydrophone at least once is If the number of finless porpoises seen in a week is 1,000, then 4 of them are within 20 meters, so the distance from the hydrophone in a week can be set to 20 meters, that is, R_m = min(R) = 20 meters in the measured data. This data can be obtained from actual measurements in different application scenarios, or from historical data recorded in literature.

[0037] From October 15, 2023 to October 21, 2023, a 7-day continuous observation was carried out in the Nanjing section of the Yangtze River, during which visual observations of Yangtze River finless porpoises were also carried out. Next, we will proceed with the processing and analysis according to the steps, and the flow chart is as follows Figure 1 As shown:

[0038] 1. Measured data and tick string extraction

[0039] The measured audio data is subjected to tick string extraction (for the specific extraction method, see the multi-parameter constrained anti-interference real-time tick detection method, medium and device, CN 118173123 A_), and the maximum amplitude tick amplitude Amp in the tick string is extracted as the sound pressure amplitude of this pulse string. The tick sound pressure amplitude for 7 days is Amp_list. A total of 1696 pulse strings were detected in these 7 days, and the maximum amplitude tick amplitude was extracted for each pulse string, as shown in Figure 4 The sound pressure amplitudes of all clicks are shown. It can be seen that the overall sound pressure amplitude is below 1e-3, with the maximum value around 8e-3. Because the sound pressure power follows an exponential decay, the sound pressure amplitude graph is in line with expectations (see Figure 5 , the y-axis has been changed to logarithmic coordinates).

[0040] 2. Calculate the sound propagation loss correction value

[0041] Calculate the acoustic propagation loss of each pulse train: TL_m = -20*log10(Amp_list) + TL_adj. TL_adj is the acoustic propagation loss correction value to be calculated. Figure 6 The following figure shows the propagation loss value when TL_adj = 0. It can be seen that the minimum value reaches about 42dB, which is not in line with expectations, so correction is required. According to the sound propagation loss, the distance R = 10^(TL_m / 20) is calculated. The minimum value of the distance R is calculated as R_m = min(R). Set R_m = 20 and calculate the sound propagation loss correction value TL_adj = -16.1dB.

[0042] 3. Calculate tick distance

[0043] In the subsequent ticking sound observation, the acoustic propagation loss of each pulse train is calculated using the TL_adj calculated in the previous step: TL = -20*log10(Amp) + TL_adj. Then, the actual ticking sound distance is calculated using R = 10^(TL / 20). Figure 7 The figure shows the calculated sound propagation loss versus distance, where the solid line is the spherical expansion loss curve and the star points are the sound propagation loss values ​​measured over 7 days.

[0044] Continue to perform statistical analysis on the distances measured during these 7 days, such as Figure 8 The figure shows the distance distribution map. It can be seen that the distance where the finless porpoises appear is mainly between 150 meters and 300 meters, which is consistent with the artificial observation of the appearance of finless porpoises, proving the effectiveness of this method.

Claims

1. A data-driven cetacean tick ranging method, characterized in that: The method The following steps are involved: The first step is to obtain measured data. After deploying a single hydrophone to a designated station, the ticking data of finless porpoises is obtained, and manual visual observation is performed or historical manual visual observation information is reviewed and sorted. Step 2: Extract tick sound string. Extract the tick sound string from the measured audio data. Extract the maximum tick sound amplitude Amp in the tick sound string as the sound pressure amplitude of this pulse string. Obtain the tick sound pressure amplitude in the tick sound data as Amp_list. Step 3: Calculate the sound propagation loss correction value. Calculate the sound propagation loss of each pulse train: TL_m = -20*log10(Amp_list) + TL_adj; TL_adj is the sound propagation loss correction value to be calculated. According to the sound propagation loss, calculate the distance R = 10^(TL_m / 20). Calculate the minimum value of the distance R R_m = min(R). Min(R) is obtained through actual measurement, that is, the minimum distance at which aquatic organisms appear around the hydrophone. Calculate the sound propagation loss correction value TL_adj. Step 4: Calculate the ticking distance. In subsequent ticking observations, use the TL_adj calculated in the third step to calculate the acoustic propagation loss of each pulse train collected by the single hydrophone arranged in the first step: TL=-20*log10(Amp)+TL_adj. Then, use R=10^(TL / 20) to calculate the actual ticking distance.

2. A computer-readable storage medium storing a computer program, wherein the computer program is suitable for being loaded by a processor and executing the second to fourth steps of the data-driven cetacean click ranging method according to claim 1.

3. A data-driven tick-ranging device for finless porpoises, the device comprising a memory and a processor, the memory storing a computer program, and when the computer program is executed by the processor, the second to fourth steps of the data-driven tick-ranging method for cetaceans described in claim 1 are executed.

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