CN110488253B - Multi-path delay difference estimation method based on cross-correlation function delay summation - Google Patents
Multi-path delay difference estimation method based on cross-correlation function delay summation Download PDFInfo
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Abstract
The invention discloses a multi-path time delay difference estimation method based on cross-correlation function delay summation, which is used for solving the technical problem that the existing multi-path time delay difference estimation method is poor in robustness under the condition of low signal-to-noise ratio. The technical scheme is that a vertical line array is arranged near the deep sea bottom, and offshore surface target broadband signals are received; calculating a cross-correlation function between broadband signals received by every two hydrophones, and constructing a first type of multi-path delay difference delay summation function according to the linear relation between direct waves between array elements and sea surface reflected wave delay difference to obtain D-D delay difference and SR-SR delay difference between two adjacent hydrophones; and constructing a second type of multi-path delay difference delay summation function by utilizing the characteristic that the phases of the direct wave and the sea surface reflected wave are opposite to each other to obtain the D-SR delay difference at the position of the No. 1 (shallowest) hydrophone. Through the delay summation of the cross-correlation function, the coherent enhancement of the signal delay peak value is realized, and the estimation robustness of the multi-path delay difference under the environment with low signal-to-noise ratio is improved.
Description
Technical Field
The invention relates to a multi-path delay inequality estimation method, in particular to a multi-path delay inequality estimation method based on cross-correlation function delay summation.
Background
In deep sea, when the receiving hydrophones are arranged near the sea bottom, direct wave sound propagation channels between the receiving hydrophones and offshore targets are generally called as reliable sound paths due to the advantages of low propagation loss, medium and short distance shadowless areas, stable channels and the like. The reliable acoustic path is an important acoustic channel for realizing the remote and stable positioning of the deep sea target, and under the condition of the channel, the multipath acoustic signals with strong energy reaching the receiving hydrophone are mainly direct waves (D) and sea surface reflected waves (SR).
The document "Passive localization in The deep ocean based cross-correlation functional mapping, The Journal of The Acoustic Society of America,2016,139(6): EL196-EL 201" discloses a Passive localization method of objects based on cross-correlation function matching. The method performs cross-correlation on broadband signals received by hydrophones at two different depths, and establishes a target positioning cost function by utilizing the corresponding relation between 4 main delay peak values with specific symbol patterns in a cross-correlation function and the position of a sound source. On the positioning fuzzy surface, two side lobe stripes determined by multi-path time delay appear, and the intersection point of the two side lobe stripes is the real position of the target sound source. The method better realizes the steady positioning of the target by the characteristic that the side lobe stripes are intersected at the real position of the target. The key to implementing the positioning method described in the literature is accurate estimation of the target signal multipath delay difference, however, the main problem of the estimation of the hydrophone multipath delay difference is that: 1) under the environment of low signal-to-noise ratio, the difference between the amplitude of a signal peak value and the amplitude of a noise peak value in a cross-correlation function is not large or even lower, so that the multi-path delay difference cannot be accurately extracted; 2) when the distance between the two hydrophones is small, the direct wave delay peak value and the sea surface reflected wave delay peak value in the cross-correlation function cannot be effectively distinguished; 3) the influence of the bottom reflection type signal cannot be eliminated, and a false peak can appear in the cross-correlation function.
Disclosure of Invention
In order to overcome the defect that the existing multi-path time delay difference estimation method has poor robustness under the condition of low signal-to-noise ratio, the invention provides a multi-path time delay difference estimation method based on cross-correlation function delay summation. The method comprises the steps of firstly, placing a vertical linear array near the deep sea bottom, and receiving a target broadband signal on the offshore surface; then, calculating a cross-correlation function between broadband signals received by every two hydrophones, and constructing a first type of multi-path delay difference delay summation function according to the linear relation between direct waves between array elements and sea surface reflected wave delay difference to obtain D-D delay difference and SR-SR delay difference between two adjacent hydrophones; and finally, constructing a second type of multi-path delay difference delay summation function by utilizing the characteristic that the phases of the direct wave and the sea surface reflected wave are opposite to each other, and obtaining the D-SR delay difference at the position of the No. 1 (shallowest) hydrophone. Through the delay summation of the cross-correlation function, the coherent enhancement of the signal delay peak value is realized, and the estimation robustness of the multi-path delay difference under the environment with low signal-to-noise ratio is improved.
The technical scheme adopted by the invention for solving the technical problems is as follows: a multipath time delay difference estimation method based on cross-correlation function delay summation is characterized by comprising the following steps:
step one, vertical line arrayCollecting target broadband signal, and setting sampling rate as f s The array received signal is denoted as x i (N), I ═ 1,2, …, I, N ═ 1,2, …, N. Where the subscript I denotes the hydrophone number, I-1 denotes the shallowest vertical hydrophone, I-I denotes the deepest vertical hydrophone, and n denotes the discrete sample points. When the time length of the collected signal is T, N-T f s 。
Step two, calculating the cross-correlation function of the broadband signals received by the ith hydrophone and the jth hydrophone, and recording the cross-correlation function as R ij (m)，
Where m represents the number of cross-correlation function delay points and requires j > i. And calculating all combination conditions of the cross-correlation functions among different hydrophones to obtain I (I-1)/2 cross-correlation functions in total.
Step three, constructing a first type of multi-path delay difference delay summation function,
in the formula, q represents the delay and summation time delay point number, and the search range is [0, | df |) s /c|]The operator | is absolute value, d is the array element spacing of the vertical linear array, and c is the reference sound velocity. y is 1 (m, q) outputting two delay summation point values q corresponding to the maximum value and the second maximum value, wherein the small value of q represents the average D-D time delay difference between two adjacent hydrophones and is recorded as q D (ii) a The large q value represents the average SR-SR time delay difference between two adjacent hydrophones and is recorded as q SR 。
Step four, constructing a second type of multi-path delay difference delay summation function,
wherein e is a correction factor, q is obtained in step three D And q is SR Determine e ═ q SR -q D 。y 2 (m, q) outputting the value of the number m of the cross-correlation function delay points corresponding to the maximum value position, namely the D-SR delay difference at the position of the No. 1 hydrophone, and recording as q D-SR 。
Under a typical 5000m deep sea Munk sound velocity profile environment, the depth of the vertical line array is greater than 4400m, the number of array elements is greater than 8, the target distance range is 0-30 km, and the target depth range is 20-300 m.
The invention has the beneficial effects that: the method comprises the steps of firstly, placing a vertical linear array near the deep sea bottom, and receiving a target broadband signal on the offshore surface; then, calculating a cross-correlation function between broadband signals received by every two hydrophones, and constructing a first type of multi-path delay difference delay summation function according to the linear relation between direct waves between array elements and sea surface reflected wave delay difference to obtain D-D delay difference and SR-SR delay difference between two adjacent hydrophones; and finally, constructing a second type of multi-path delay difference delay summation function by utilizing the characteristic that the phases of the direct wave and the sea surface reflected wave are opposite to each other, and obtaining the D-SR delay difference at the position of the No. 1 (shallowest) hydrophone. Through the delay summation of the cross-correlation function, the coherent enhancement of the signal delay peak value is realized, and the estimation robustness of the multi-path delay difference under the environment with low signal-to-noise ratio is improved.
The invention adds the cross-correlation function delay obtained between different hydrophones of the vertical linear array, so that the correlation peak values of direct waves and sea surface reflected waves in the cross-correlation function are coherently superposed, and irrelevant noise components are only power average, compared with a double hydrophone, the output signal-to-noise ratio is improved by 10lg [ I (I-1)/2] decibels, and the invention is suitable for multi-path delay difference estimation under the environment with low signal-to-noise ratio. Furthermore, since the method of the present invention requires the delay amount q to be positive, the influence of the sea-bottom reflection wave is avoided in the delay sum output.
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
Drawings
FIG. 1 is a schematic diagram of simulation environment of the method of the present invention, the sea depth is 4390m, the array element spacing of a 16-element vertical linear array is 4m, the depth of No. 1 (shallowest) hydrophone is 4158m, and the depth of No. 16 (deepest) hydrophone is 4218 m; the horizontal distance of the broadband sound source is 10km, and the depth of the sound source is 200 m.
Fig. 2 is a sound velocity profile for simulation, which is a measured sound velocity profile of a certain sea area in the south sea.
Fig. 3 is a time domain target broadband signal for simulation.
Fig. 4 is a time-domain multipath arrival structure of a target broadband signal in a noise-free interference environment, and displayed multipath components of the signal are mainly direct waves (D), sea surface reflected waves (SR), sea bottom reflected waves (BR) and sea surface sea bottom reflected waves (SRBR).
FIG. 5 is a time domain target broadband signal received by a vertical linear array in a low signal-to-noise ratio environment, and multipath components of the signal are submerged by noise.
FIG. 6 is normalized output of the first type of multi-path delay inequality delay sum function of the method of the present invention under the environment of low signal-to-noise ratio, where the q value of the delay point corresponding to the maximum position in the graph is the estimated value of the average SR-SR delay inequality between two adjacent hydrophones, and q is the estimated value of the average SR-SR delay inequality SR 25; the time delay point q value corresponding to the position of the second largest value is an average D-D time delay difference estimated value between two adjacent hydrophones, q D ＝22。
Fig. 7 is normalized output of the second type of multi-transit delay difference delay summation function of the method in the low signal-to-noise ratio environment, where the value of the delay point m corresponding to the maximum position in the graph is the estimated value of the D-SR delay difference at the position of the number 1 hydrophone, and m is 2227.
FIG. 8 is a cross-correlation function result of the No. 1 hydrophone and the No. 16 hydrophone in a low SNR environment, where three vertical dashed lines in the graph correspond to the real positions of the D-D delay difference, the SR-SR delay difference and the D-SR delay difference from left to right, respectively. The signal peaks are overwhelmed by noise.
Detailed Description
Reference is made to fig. 1-8. The invention relates to a multi-path delay inequality estimation method based on cross-correlation function delay summation, which comprises the following steps:
1. the underwater acoustic channel and the target broadband signal are modeled.
The simulation environment is a typical deep sea environment of south sea, the sea depth is 4390m, the sound velocity profile is an actually measured sound velocity profile of a certain sea area, the sound velocity at the depth from 0m to 1660m is a field measured value of a thermohaline depth gauge, and the sound velocity from 1661m to the seabed is obtained according to sound velocity gradient fitting.
The array of 16-element equidistant vertical lines is arranged near the sea bottom, the distance between the array elements is 4m, the depth of the No. 1 array element is 4158m, and the depth of the No. 16 array element is 4218 m. The horizontal distance of the broadband target sound source is 10km, and the depth of the sound source is 200 m. The energetic multipath signals arriving at the vertical linear array from the target location are mainly direct waves (D) and sea surface reflected waves (SR).
In the simulation, a certain explosion sound pulse signal is taken as a target broadband signal, and the intercepted signal duration is 0.05 s. And (3) performing band-pass filtering on the signal, wherein the frequency of a pass band is 100-200 Hz. And (5) normalizing the signal amplitude.
2. The target signal multi-ways to the structure.
The received signal modeling method uses ray model software BELLHOP. From the figure, 4 kinds of multi-path arrival signals are seen, namely direct wave (D), sea surface reflected wave (SR), sea bottom reflected wave (BR) and sea surface sea bottom reflected wave (SRBR). Because the attenuation of the arrival of the sea bottom reflection is large, the arrival amplitudes of the sea bottom reflection wave and the sea surface sea bottom reflection wave are far smaller than those of the direct wave and the sea surface reflection wave. Under the simulation condition, the average D-D time delay difference q between two adjacent hydrophones is taken as a theoretical value D 22, average SR-SR delay difference q SR 25D-SR time delay difference q at No. 1 array element position D-SR ＝2230。
3. And estimating the multipath time delay difference under the environment of low signal-to-noise ratio.
In order to simulate the environment with low signal to noise ratio, Gaussian white noise firstly passes through a band-pass filter with a passband of 100-200 Hz, and then is amplified and superposed with an interference-free multipath signal. Under the condition of low signal-to-noise ratio, a time-domain target broadband signal received by a single hydrophone cannot distinguish a direct wave from a sea surface reflected wave.
Step one, a 16-element vertical linear array collects a target broadband signal with a sampling rate f s 25kHz, the signal acquisition time length T is 0.4s, and the total signal length N is T f s 10000. The array received signal is denoted x i (n), i is 1,2, …,16, n is 1,2, …, 10000. Where the index i denotes the hydrophone number, i 1 denotes the hydrophone with the shallowest vertical line array, and i 16 denotes the deepest vertical line arrayHydrophone, n denotes discrete sampling points.
Step two, calculating the cross-correlation function of the broadband signals received by the ith hydrophone and the jth hydrophone, and recording the cross-correlation function as R ij (m)，
In the formula, m is an integer and represents the time delay point number of the cross-correlation function, and the value range interval of m is [ 03000 ]]. The cross-correlation function of the 1 st and the 2 nd to 16 th broadband signals received by the hydrophones is calculated in turn. Then, with reference to the 2 nd hydrophone, the cross-correlation function with the broadband signal received by the 3 rd to 16 th hydrophones is calculated in turn, and so on, and finally the cross-correlation function with the broadband signal received by the 15 th hydrophone is calculated. By this step, a total of 120 cross-correlation functions R are obtained, I (I-1)/2 ij (m) of the reaction mixture. Each cross-correlation function R ij The signal peak locations in (m) are related to hydrophone serial numbers i and j.
Step three, constructing a first type of multi-path delay difference delay summation function,
in the formula, q represents the number of delay summation time delay points, and the maximum value of the delay summation time delay points does not exceed the maximum time delay amount corresponding to two adjacent hydrophones, namely | df s And/c, wherein the operator | is absolute value, the array element spacing d is 4m, and the reference sound velocity c is 1500 m/s. Thus, the search range for q is [ 067 ]]. According to the relation that the multi-path time delay difference is linearly changed along with the array element spacing, when q is q D Time, cross correlation function R ij (m) all the direct wave delay difference peak delays in the sum are coherently accumulated, at y 1 The (m, q) output theoretically exhibits a global maximum. Similarly, when q is equal to q SR Time, cross correlation function R ij (m) summing and coherently accumulating all the sea surface reflected wave time delay difference peak delays, since the energy of the sea surface reflected wave is lower than that of the direct wave, so that y is the time delay difference peak delay of the sea surface reflected wave 1 Theoretical performance in (m, q) outputIs the global next largest value. And according to the virtual source theory, because the sea surface reflected wave is equivalent to the direct wave emitted from the virtual source position of the sound source, the arrival angle at the vertical line array is slightly larger than that of the direct wave, so that q is equal to the arrival angle of the direct wave SR >q D . However, if the sea surface reflected wave energy is strong, y may be caused due to the influence of the multipath acoustically propagated plane wave assumption error 1 The maximum value of the (m, q) output corresponds to SR-SR delay difference, and the second maximum value corresponds to D-D delay difference. Therefore, in practical application, the D-D time delay difference and the SR-SR time delay difference are distinguished by comparing the magnitude of the q value corresponding to the maximum value and the second maximum value. As can be seen from the figure, q D ＝22，q SR The estimated value of the method of the present invention is equal to the theoretical value mentioned above, 25.
Step four, constructing a second type of multi-path delay difference delay summation function,
wherein the correction factor e is q SR -q D 3 for correcting the D-SR delay difference at each hydrophone position, making it equal to the D-SR delay difference at hydrophone position No. 1, when delay-summing. Since the direct wave is in phase opposition to the sea surface reflected wave, the delayed sum output is multiplied by-1, so y 2 The number m of the time delay points of the cross-correlation function corresponding to the position of the maximum value of the (m, q) output represents the D-SR time delay difference at the position of the No. 1 hydrophone, and as can be seen from the figure, q is the time delay difference of the cross-correlation function corresponding to the position of the maximum value of the (m, q) output D-SR 2227-m. The error between the D-SR delay difference estimated value and the true value at the position of the No. 1 hydrophone obtained by the method is 3. The error is caused because the multi-path delay difference between the hydrophones is not a strict linear relation, and the D-D delay difference and the SR-SR delay difference obtained by the method are only the average delay difference between two adjacent hydrophones, so that the correction factor e is only a statistical average result, and the D-SR delay difference at the position of each hydrophone can be corrected to generate deviation. However, in the simulation, the D-SR delay difference error at the hydrophone position No. 1 is only 0.12ms, and the subsequent target positioning accuracy is not influenced. Theoretically, when the sampling rate isAnd the time delay information represented by each sampling point is small enough, and the D-SR time delay difference estimation error is further reduced.
4. And (5) a result of the multi-path delay difference estimation of the double hydrophones.
For comparison with the method of the present invention, hydrophones # 1 and # 16 receive the broadband signal and cross-correlate, and it can be seen that the signal peaks have been swamped by noise peaks. Under the simulation condition, any multi-path delay difference cannot be distinguished, and the method for estimating the multi-path delay difference of the cross-correlation function of the double hydrophones fails.
Claims (2)
1. A multipath delay difference estimation method based on cross-correlation function delay summation is characterized by comprising the following steps:
step one, collecting target broadband signals by a vertical line array, and setting the sampling rate as f s The array received signal is denoted as x i (N), I ═ 1,2, …, I, N ═ 1,2, …, N; wherein, subscript I represents the hydrophone number, I ═ 1 represents the shallowest hydrophone in the vertical line array, I ═ I represents the deepest hydrophone in the vertical line array, and n represents the discrete sampling point; when the time length of the collected signal is T, N-T f s ；
Step two, calculating the cross-correlation function of the broadband signals received by the ith hydrophone and the jth hydrophone, and recording the cross-correlation function as R ij (m)，
In the formula, m represents the number of time delay points of the cross-correlation function, and j > i is required; calculating all combination conditions of cross-correlation functions among different hydrophones to obtain I (I-1)/2 cross-correlation functions;
step three, constructing a first type of multi-path delay difference delay summation function,
in the formula, q representsDelay and sum time delay point number, the search range is [0, | df s /c|]The operator | is absolute value, d is the array element spacing of the vertical linear array, and c is the reference sound velocity; y is 1 (m, q) outputting two delay summation point values q corresponding to the maximum value and the second maximum value, wherein the small value of q represents the average D-D time delay difference between two adjacent hydrophones and is recorded as q D (ii) a The large q value represents the average SR-SR time delay difference between two adjacent hydrophones and is recorded as q SR ；
Step four, constructing a second type of multi-path delay difference delay summation function,
wherein e is a correction factor, q is obtained in step three D And q is SR Determine e ═ q SR -q D ；y 2 (m, q) outputting the value of the number m of the cross-correlation function delay points corresponding to the maximum value position, namely the D-SR delay difference at the position of the No. 1 hydrophone, and recording as q D-SR 。
2. The method of claim 1, wherein the method comprises: under a typical 5000m deep sea Munk sound velocity profile environment, the depth of the vertical line array is greater than 4400m, the number of array elements is greater than 8, the target distance range is 0-30 km, and the target depth range is 20-300 m.
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