CN104820218B - Shallow sea bottom single-parameter inversion method based on frequency domain autocorrelation - Google Patents
Shallow sea bottom single-parameter inversion method based on frequency domain autocorrelation Download PDFInfo
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- CN104820218B CN104820218B CN201510275387.6A CN201510275387A CN104820218B CN 104820218 B CN104820218 B CN 104820218B CN 201510275387 A CN201510275387 A CN 201510275387A CN 104820218 B CN104820218 B CN 104820218B
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Abstract
The invention provides a shallow sea bottom single parameter inversion method based on frequency domain autocorrelation. Which comprises the following steps: s1, carrying out frequency domain autocorrelation processing on an acoustic signal received by a hydrophone; s2, acquiring a frequency shift amount corresponding to the normalized frequency domain autocorrelation coefficient reduced to 0.5; and S3, obtaining a single-parameter value through inversion by utilizing the relation between the frequency shift quantity and the single parameter of the shallow sea bottom. The method can quickly acquire the single submarine parameter, reduces the submarine acoustic parameter from multi-dimension to one-dimension, greatly simplifies the inversion process, avoids the problems of different sensitivities and the like caused by multi-dimension optimization and coupling among parameters, can well describe the shallow submarine reflection property in a large range by the inverted single parameter, and can be applied to underwater sound field prediction, submarine sediment classification and the like.
Description
Technical Field
The invention relates to the field of shallow sea bottom acoustic parameter inversion, in particular to a shallow sea bottom single parameter inversion method based on frequency domain autocorrelation.
Background
In a shallow sea environment, the influence of submarine earth sound parameters on sound transmission characteristics is great, and the submarine earth sound parameters play a decisive role in sound transmission. The submarine ground sound parameters are necessary prior information for analyzing and calculating a shallow sound field, and the acquisition of the submarine ground sound parameters has important significance for application of shallow sound field prediction, sonar performance optimization, matching field positioning, submarine bottom material classification and the like.
The traditional method for acquiring the submarine geophone parameters mainly adopts a direct measurement method represented by submarine sampling. The methods can obtain more accurate ground sound parameter values, but have some insurmountable defects: (1) expensive, time consuming and labor intensive; (2) the obtained ground sound parameters have obvious locality, only discrete point values can be obtained, and if the sampling data are less, the ground sound parameters cannot comprehensively represent the large-scale sea bottom parameters; (3) the influence of external conditions is large, and the sample is easy to disturb, such as the sample loses the original conditions of temperature, pressure and the like on the seabed.
In recent years, due to the development of signal processing technology and the intersection of underwater sound physics and multiple disciplines, the earth sound parameter acoustic inversion technology is developed rapidly. The method for inverting the earth sound, namely the method for obtaining the indirect earth sound parameters by indirectly measuring underwater sound signals and reversely pushing seabed environment information can continuously obtain the seabed sediment characteristics of the shallow sea in a large scale, and has the advantages of economy, high efficiency, continuous and rich obtained results and the like.
Most of common geoacoustic inversion methods are based on multi-parameter seabed models to perform seabed acoustic parameter inversion, and in the multi-parameter inversion process, the coupling among parameters is a problem which needs to be considered by an inversion designer. A typical example is the coupling of sound source depth to propagation distance in matched field processing. Some methods determine the correct result in the optimization process at the expense of computational effort, but this does not fundamentally solve the problem. Especially when the parameters of the local acoustic model have complex coupling relations as the inversion result, the estimation error of one parameter can cause continuous errors like domino effect.
Similar to the coupling between parameters, the sensitivity between parameters is a difficult problem to avoid in the inversion of the sea bottom multidimensional acoustic parameters, for example, when near-field reflected acoustic signals are processed, the sensitivity of the sediment density is far lower than the sediment sound velocity. For the problems, the method represented by step inversion can also obtain the result which is in accordance with the true value, but the parameter sensitivity belongs to the inherent physical property of the earth-sound model and is difficult to eliminate fundamentally.
Therefore, in recent years, domestic acoustic researchers have proposed using the rate of change F of the undersea reflection loss with grazing angle at small grazing anglesdb(dB/rad) to describe the seabed, and a shallow seabed single-parameter model is established, and the single-parameter model can better describe an underwater sound field in a large scale.
The invention is provided on the basis of the single-parameter model.
Disclosure of Invention
The invention aims to solve the problems of complex measurement, large multidimensional optimization calculation amount, uncertainty caused by coupling among parameters and the like of the current multidimensional parameter inversion method, and provides a corresponding single-parameter inversion method by analyzing time-frequency correlation characteristics contained in submarine acoustic echoes starting from reducing inversion parameter dimensions. Book (I)The invention provides a shallow sea bottom single parameter inversion method based on frequency domain autocorrelation, which comprises the following steps: s1, calculating a normalized frequency domain autocorrelation function of a received acoustic signal; s2, calculating a frequency shift amount corresponding to the normalized frequency domain autocorrelation function reduced to 0.5, and marking as delta fH(ii) a And S3, calculating the single parameter.
Further, in step S1, the normalized frequency domain autocorrelation function of the received acoustic signal is calculated according to the following formula:
wherein p (f) is the Fourier transform of the acoustic signal, Δ f is the frequency shift, and < represents the mean value.
Further, in step S3, the single parameter is calculated according to the following formula:
wherein, cwIs the sound velocity in the sea water, and H is the sea depth.
According to the shallow sea bottom single-parameter inversion method based on frequency domain autocorrelation, the inversion parameter dimension is reduced from multi-dimension to one-dimension, so that the physical quantity to be measured is small, multi-dimension optimization is not needed, the calculated quantity is reduced, the signal processing process is simple, rapid inversion can be carried out, and the inversion result is stable. The single parameter obtained by inversion can better describe an underwater sound field, and can be applied to classification of submarine sediments, matching field positioning and the like.
Drawings
FIG. 1 is a flow chart of a shallow sea bottom single parameter inversion method based on frequency domain autocorrelation of the present invention;
FIG. 2 is a schematic waveform diagram of an acoustic signal received by a hydrophone array;
FIG. 3 is a graph of normalized frequency domain autocorrelation function as a function of the amount of frequency shift;
FIG. 4 is a graph comparing the acoustic propagation attenuation prediction values of the present invention with experimental values and prediction values obtained by a conventional algorithm at a center frequency of 1000 Hz.
Detailed Description
The invention is described in detail below with reference to the drawings and preferred embodiments.
Referring to fig. 1, the steps of the shallow sea bottom single parameter inversion method based on frequency domain autocorrelation of the present invention are described in detail as follows.
Step S1, performing frequency domain autocorrelation processing on the acoustic signal received by the hydrophone array (refer to fig. 2, which is a schematic diagram of experimental data of the acoustic signal received by the hydrophone array, in this example, the hydrophone array includes four hydrophones, 1# -4 #), and obtaining a normalized frequency domain autocorrelation function according to the following formula (1):
fourier transforming the acoustic signal received by the hydrophone to a frequency domain, and then carrying out normalized autocorrelation processing:
where ρ is|p|(Δ f) is the normalized frequency autocorrelation function, p (f) is the Fourier transform of the acoustic signal, Δ f is the corresponding frequency shift when taken at any fixed value, and < > represents the mean value.
And step S2, acquiring the frequency shift amount corresponding to the normalized frequency domain autocorrelation function when the normalized frequency domain autocorrelation function is reduced to 0.5. Referring to fig. 3, a normalized frequency domain autocorrelation function variation Line with frequency shift amount can be obtained from formula (1)f。ΔfHDefined as the amount of frequency shift when the autocorrelation function drops to 0.5, can be represented by the LinefObtaining the frequency shift quantity delta fHThe value of (a).
Step S3, using frequency shift quantity and shallow sea bottom single parameter FdbThe relation between the two is inverted to obtain a single parameter FdbThe value is obtained.
Under the condition of the shallow sea approximate uniform water layer, a shallow sea bottom single parameter F can be obtained through a series of theoretical deductionsdbFrequency shift amount delta f when autocorrelation coefficient of normalized frequency domain is reduced to 0.5HThe relational expression between:
wherein, cwIs the sound velocity in the sea water, and H is the sea depth. According to the formula (2), the single parameter F to be inverted can be obtained from the frequency shift quantitydbThe value is obtained.
The principle of the shallow sea bottom single parameter inversion method based on frequency domain autocorrelation of the present invention is described in detail below.
When the multipath spread loss is not considered, the normalized autocorrelation coefficient can be expressed as:
where τ is the time required for the field intensity to decrease by 1/e.
Due to Δ fHTo normalize the frequency shift when the autocorrelation coefficient drops to 0.5, thus:
from the perspective of ray geometry, for τ and single parameter FdBThe relational expression between them is derived. Under the condition of shallow sea uniform water layer, considering the condition that a seabed single-parameter model generally discusses that reflected sound which is greatly glancing after sound rays are contacted with the seabed for multiple times is negligible, and pulse time delay delta t of n times of contact of the direct wave with the seabednThe sound source depth and the receiver depth can be ignored, expressed approximately as:
wherein, cwThe sound velocity of the seawater, H is the depth of the sea, and r is the distance between the receiver and the sound source. Small glancing angle for nth subsea contact for shallow sea levellingCan be approximately expressed as:
therefore, the nth subsea contact subsea reflection loss BLnCan be composed of a single parameter FdBExpressed as:
the total seafloor reflection loss BL is expressed as:
simultaneous equations (5) and (8) can be obtained:
for a shallow sea near uniform water layer, the signal energy is a function of Δ tnExponentially decays, so, based on equation (9), the pulse delay τ when the sound field intensity decreases by 1/e can be expressed as:
substituting the formula (10) into the formula (4) to finally obtain a single-parameter frequency domain inversion expression:
the formula (2) can be obtained by converting the above formula (11) into a main term.
The shallow sea bottom single-parameter inversion method based on the frequency domain autocorrelation adopts a shallow sea bottom single-parameter model, inverts shallow sea bottom single parameters based on the normalized frequency domain autocorrelation, obtains an inversion result which is stable, has small physical quantity required to be measured in practical application, has low requirement on measurement conditions, is simple in signal processing, can perform quick inversion, and can be applied to the fields of shallow sea sound propagation prediction, seabed sediment classification and the like.
Referring to FIGS. 2-4, an embodiment of the present invention is described that utilizes the shallow sea acoustic experimental data of the east Chinese sea region with inversion frequencies of 1000-2000 Hz, all averaged over one-third octave.
Step S1, performing autocorrelation processing on the acoustic signals received by the hydrophones of the hydrophone array in the experiment in the frequency domain to obtain a normalized frequency autocorrelation function. Fig. 2 shows the acoustic signals of an explosive source received by # 1 to # 4 hydrophones at a distance of 4.65Km from the explosive source.
Step S2, obtaining the frequency shift quantity delta f corresponding to the normalized frequency domain autocorrelation function when the normalized frequency domain autocorrelation function is reduced to 0.5H. FIG. 3 is a Line showing the relationship between the frequency domain autocorrelation function of the acoustic signals received by 1# -4 # hydrophones and the variation of the offset delta f at a distance of 4.65Km from the explosive sound source and at a center frequency of 2000Hzf. From the variation graph, the frequency shift Δ f when the frequency domain autocorrelation function is reduced to 0.5 can be obtainedHThe value of (c).
Step S3, using frequency shift amount Δ fHSingle parameter F with shallow sea bottomdbThe relation between the two is inverted to obtain a single parameter FdbThe value of (c). According to shallow sea bottom single parameter FdbThe relational expression between the two, namely the formula (2), finally obtains the seabed single parameter value F to be inverted under different frequenciesdbThe final inversion results are shown in table 1:
TABLE 1 sea-bottom single parameter of east sea experiment sea area
Acoustic propagation loss prediction is the most effective way to check the correctness of the inversion results. Fig. 4 is a comparison graph of the propagation prediction value and the experimental value of the single-parameter inversion result of the present invention and the acoustic propagation prediction value of the conventional algorithm, and it can be seen that the seafloor single-parameter inversion method of the present invention is better in accordance with the experimental value, which indicates that the seafloor single-parameter inversion method of the present invention is effective.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (1)
1. A shallow sea bottom single parameter inversion method based on frequency domain autocorrelation is characterized by comprising the following steps:
s1, calculating a normalized frequency domain autocorrelation function of the received acoustic signal, specifically, calculating the normalized frequency domain autocorrelation function of the received acoustic signal according to the following formula:
wherein p (f) is the Fourier transform of the acoustic signal, Δ f is the frequency shift amount, < represents the mean value, < is the frequency of the acoustic signal, < Δ f is the frequency shift amount, | | represents the amplitude;
s2, calculating a frequency shift amount corresponding to the normalized frequency domain autocorrelation function reduced to 0.5, and marking as delta fH；
S3, calculating the single parameter, wherein the calculation formula of the single parameter is as follows:
wherein, cwIs the sound velocity in the sea water, and H is the sea depth.
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| CN110542919A (en) * | 2019-07-10 | 2019-12-06 | 自然资源部第三海洋研究所 | Sea sand resource detection method based on electric spark source seismic data inversion |
| CN110389335B (en) * | 2019-07-25 | 2022-09-02 | 西北工业大学 | Underwater sound propagation loss reliable calculation method based on ocean background field |
| CN111458008B (en) * | 2020-04-16 | 2021-03-26 | 浙江大学 | Ocean earth sound parameter inversion method based on single fixed hydrophone and single mobile sound source |
| CN112270140B (en) * | 2020-09-29 | 2023-10-17 | 北京遥测技术研究所 | Far-field inversion near-field distribution method for explosion shock wave overpressure prediction |
| CN113009419B (en) * | 2021-02-25 | 2021-11-09 | 中国科学院声学研究所 | Target depth estimation method based on frequency domain cross-correlation matching |
| CN116660996B (en) * | 2023-07-24 | 2023-10-13 | 山东科技大学 | Drifting type shallow sea local earth sound parameter prediction method based on deep learning |
| CN116859460B (en) * | 2023-09-04 | 2023-11-21 | 自然资源部第一海洋研究所 | Submarine physical property parameter inversion method suitable for elastic wave near-field reflection |
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