Distance estimation method using ice layer Schlte wave and airwave time delay

Abstract

The invention belongs to the field of polar acoustic detection, and provides a distance estimation method using ice layer Schlte wave and airwave time delay, comprising the following steps: arranging a geophone or a microphone on an ice surface to detect an acoustic wave signal; determining the arrival time of the air wave and the ice layer Schlte wave according to the time-frequency spectrum; calculating the sound velocity of the airwave according to the room temperature; calculating the sound velocity c2 of the Schlte wave according to the acoustic parameters of the ice layer; and determining the sound source distance according to the time delay and distance relationship. The method can be realized by arranging one collection device on the ice surface, and is convenient, effective and low in cost; the energy of the Schlte wave and the air wave is relatively high, so that the problem of relatively low signal-to-noise ratio of other sound waves can be effectively solved; finally, the effectiveness of the method is verified through an external field test.

Description

Technical Field

[0001] The invention belongs to the field of polar acoustic detection and relates to a passive distance measurement method, in particular to a distance estimation method using the time delay between ice layer Scholte waves and air waves. Background Art

[0002] Global warming has become a universal consensus of human society. At the same time, the Arctic amplification effect reveals that the degree of warming in the Arctic region is more prominent than in other regions. Existing research shows that the Arctic region has rich energy resources and important strategic value. As the Arctic sea ice melts, people will increase their activities in the Arctic, such as tourism, resource exploration, and scientific research.

[0003] Some experiments often require activities such as drilling through the polar ice and performing on-ice operations. Researching the location technology of ice sound sources is one of the important research directions to ensure personnel safety, monitor sea ice movement noise, and other potential needs.

[0004] Among the latest invention patents of similar technologies, CN115166817B "A method for ice acoustic positioning based on the slowness difference characteristics of ice layer modal groups", CN113687308B "A method for locating earthquake sources on ice based on bending waves" and CN115236592B "A method for ice acoustic positioning based on single-element time-frequency curve matching" propose methods for distance estimation using the dispersion characteristics of low-frequency bending waves (Lamb wave A0 mode) in ice layers. CN113359183B "A method for locating earthquake sources for polar ice layers" proposes to determine the location of sound sources using the time delays of longitudinal plate waves (Lamb wave S0 mode) and horizontally polarized shear waves (SH mode) in ice layers. There is also a method for positioning using the time delays of longitudinal and shear waves in ice layers. Due to the strong environmental noise and background interference in the Arctic, the above methods are easily interfered by noise, resulting in greater difficulty in detecting acoustic signals.

[0005] Research has found that ice floating on the ocean is affected by seawater, and ice sound sources can excite strong Scholte waves. At low frequencies, they appear as bending waves with dispersion effects, and at high frequencies, they propagate at a relatively stable speed, also known as Quasi-Scholte waves. Therefore, studying the method of using ice Scholte waves for distance estimation can avoid the above problems to a certain extent. Summary of the invention

[0006] In view of the above existing research and technology, the technical problem to be solved by the present invention is to provide a distance estimation method using the time delay between the Scholte wave of the ice layer and the air wave.

[0007] In order to solve the above technical problems, a distance estimation method using the time delay of ice layer Scholte waves and air waves of the present invention comprises the following steps:

[0008] Step 1: Place a geophone or microphone on the ice surface to detect sound wave signals. The energy of air waves excited by sound sources on the ice is often relatively strong, so using a geophone can better record the Scholte waves in the ice layer and also receive the vibration signals caused by air waves.

[0009] Step 2: Determine the arrival time of the air wave and the ice layer Scholte wave based on the time-frequency spectrum;

[0010] The duration of air waves is longer than that of Scholte waves. The arrival time is determined according to the time of the wavefront in the time-frequency spectrum of the air wave, which is set as t1. The wavefront of the air wave refers to the front part of the wave during propagation, and is the first air wave to arrive at the detector.

[0011] The speed of the Scholte wave in the ice layer is faster than that of the air wave. Since the Scholte wave has a dispersion effect in the low frequency band, the propagation speed is related to the frequency, while the high-frequency Scholte wave has no dispersion effect and the propagation speed is stable. Therefore, the arrival time is determined here according to the time-frequency spectrum of the higher-frequency Scholte wave, which is set as t2.

[0012] By performing time-frequency analysis on the signal collected in step 1, the arrival times t1 and t2 of the two sound waves can be accurately obtained, and the time delay t=t1-t2 between the air wave and the ice layer Scholte wave can be calculated.

[0013] Step 3: Calculate the speed of sound of air waves based on room temperature; the relationship between room temperature and the speed of sound of air waves is:

[0014] c1=331.6+0.6T

[0015] Where T is the room temperature in degrees Celsius. Assuming the room temperature is minus 20 degrees Celsius, the speed of sound of the air wave is about c1 = 320 m / s.

[0016] Step 4: Calculate the sound velocity c2 of the Scholte wave based on the acoustic parameters of the ice layer;

[0017] The densities of ice and water are ρ and ρ respectively. L The longitudinal and transverse wave velocities of ice are c s and c t , the longitudinal wave speed of seawater is c L , the characteristic equation of Scholte wave is as follows:

[0018]

[0019] Solving this equation can solve c in the above equation, and we can get the sound speed of Scholte wave c2=c;

[0020] Step 5: Determine the distance of the sound source based on the relationship between time delay and distance; Based on the time delay t calculated in step 2, the air wave sound speed c1 calculated in step 3, and the sound speed c2 of the Scholte wave calculated in step 4, the distance of the sound source is obtained as:

[0021] R = t×c1×c2 / (c2-c1).

[0022] Beneficial effects of the invention: The invention proposes a distance estimation method using the time delay of Scholte waves and air waves in the ice layer. The method can be realized by arranging a collection device on the ice surface. The method is convenient, effective and low-cost. The energy of Scholte waves and air waves is relatively high, which can effectively overcome the problem of low signal-to-noise ratio of other sound waves. Finally, the effectiveness of the method was verified through field tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a sound source distance estimation flow chart in the present invention;

[0024] Figure 2 It is the field experiment acquisition signal in the present invention;

[0025] Figure 3 is the signal time-frequency spectrum in the present invention;

[0026] Figure 4 It is the corresponding relationship between time delay and distance in the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0028] like Figure 1 As shown, the present invention comprises the following steps:

[0029] like Figure 2 As shown, step 1 arranges a seismic detector or microphone on the ice surface to detect the sound wave signal. The distance of the sound source in the ice experiment is set to 200m. The energy of the air wave excited by the sound source on the ice is often relatively strong. Therefore, the use of the seismic detector can better record the Scholte wave in the ice layer and also receive the vibration signal caused by the air wave.

[0030] like Figure 3 As shown, step 2 determines the arrival time of the air wave and the ice layer Scholte wave according to the time-frequency spectrum;

[0031] The duration of air waves is longer than that of Scholte waves. The arrival time is determined by the time of the wavefront in the time spectrum of the air wave, which is set as t1. The wavefront of the air wave refers to the front part of the wave when the air wave propagates, and is the first air wave to arrive at the detector. Figure 3 Determined, t1=0.672s.

[0032] The speed of the Scholte wave in the ice layer is faster than that of the air wave. Since the Scholte wave has a dispersion effect in the low frequency band, the propagation speed is related to the frequency, while the high frequency Scholte wave has no dispersion effect and the propagation speed is stable. Therefore, the arrival time is determined here according to the time-frequency spectrum of the higher frequency Scholte wave, which is set as t2. Figure 3 Determined, t2=0.196s.

[0033] By performing time-frequency analysis on the signal collected in step 1, the arrival times t1 and t2 of the two sound waves can be accurately obtained, and the time delay between the air wave and the ice layer Scholte wave t=t1-t2=0.476s can be calculated.

[0034] Step 3: Calculate the speed of sound of air waves based on room temperature; the relationship between room temperature and the speed of sound of air waves is:

[0035] c1=331.6+0.6T

[0036] Where T is the room temperature in degrees Celsius. The room temperature is about -20 degrees Celsius, so the speed of sound of the air wave is about c1 = 320 m / s.

[0037] Step 4: Calculate the sound velocity c2 of the Scholte wave based on the acoustic parameters of the ice layer;

[0038] The densities of ice and water are ρ and ρ respectively. L The longitudinal and transverse wave velocities of ice are c s and c t , the longitudinal wave speed of seawater is c L , the characteristic equation of Scholte wave is as follows:

[0039]

[0040] The density of ice and water is ρ = 900 kg / m 3 and ρ L =1000kg / m 3 The longitudinal and transverse wave velocities of ice are c s =3800m / s and c t =1900m / s, the longitudinal wave speed of seawater is c L =1500m / s, solving this equation can solve the above equation c = 1270m / s, and get the sound speed of Scholte wave c2 = 1270m / s;

[0041] Step 5: Determine the distance of the sound source based on the relationship between time delay and distance; based on the time delay t=0.476s calculated in step 2, the air wave sound speed c1=320m / s calculated in step 3, and the sound speed of the Scholte wave c2=1270m / s calculated in step 4, the sound source distance is:

[0042] R=t×c1×c2 / (c2-c1)=203.6m

[0043] The calculated results are consistent with the actual distance of the sound source.

[0044] like Figure 4 As shown, the corresponding relationship between the time delay and distance calculated based on all experimental data is given, which shows that the time delay between the air wave and the Scholte wave is proportional to the distance from the sound source.

[0045] As shown in Table 1, for all experimental data, the distance estimation statistics are performed according to step 5, and the accuracy of the method is verified, with a relative error of less than 5%.

[0046] Table 1 All experimental results verified

[0047]

[0048] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A distance estimation method using the time delay of ice Scholte waves and air waves, characterized in that: The following steps are involved: Step 1: Place a seismic detector or microphone on the ice surface to detect the sound wave signal; Step 2: Determine the arrival time of the air wave and the ice layer Scholte wave based on the time-frequency spectrum; The arrival time is determined according to the time of the wavefront in the time spectrum of the air wave, which is set as t1. The wavefront of the air wave refers to the front part of the wave when the air wave propagates, and is the air wave that arrives at the detector first. The time-frequency spectrum of the Scholte wave determines the arrival time, which is set as t2; Calculate the time delay between the air wave and the ice layer Scholte wave t = t1-t2; Step 3: Calculate the speed of sound of air waves based on room temperature; Step 4: Calculate the sound velocity c2 of the Scholte wave based on the acoustic parameters of the ice layer; Step 5: Determine the distance of the sound source based on the relationship between time delay and distance; Based on the time delay t calculated in step 2, the air wave sound speed c1 calculated in step 3, and the sound speed c2 of the Scholte wave calculated in step 4, the distance of the sound source is obtained as: R = t×c1×c2 / (c2-c1).

2. A distance estimation method using the time delay of ice layer Scholte waves and air waves according to claim 1, characterized in that: The relationship between room temperature and air wave speed in step 3 is: c1=331.6+0.6T Where T is room temperature in degrees Celsius.

3. The distance estimation method using the time delay of ice layer Scholte wave and air wave according to claim 1 is characterized in that: Step 4: The densities of ice and water are ρ and ρ respectively. L The longitudinal and transverse wave velocities of ice are c s and c t , the longitudinal wave speed of seawater is c L , the characteristic equation of Scholte wave is as follows: Solving this equation can solve c in the above equation and obtain the sound speed of Scholte wave c2=c.

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