A method and system for estimating the bearing of a towed array target based on multi-dimensional null steering

Abstract

The application belongs to the technical field of array signal processing, and particularly relates to a towed array target direction estimation method and system based on multi-dimensional null steering. The application can extract cross-aperture phase drift information according to the towed array movement, perform spatial registration and sequential fusion on non-repeated effective aperture data, construct a multi-dimensional null cancellation discriminant based on the phase cancellation relationship between local aperture projection components, extract target pointing parameters, and obtain target direction results, thereby further improving the direction estimation performance. Meanwhile, the de-coherence algorithm is added to more accurately distinguish multiple targets. The application can accurately estimate the directions of coherent multiple targets in a complex engineering environment with limited towed array size.

Description

Technical Field

[0001] This invention belongs to the field of array signal processing technology, specifically relating to a method and system for estimating the azimuth of a towed array target based on multidimensional null pointing. Background Technology

[0002] Target bearing estimation is a crucial technology in underwater target detection, tracking, and localization, and its accuracy directly impacts the sonar system's ability to detect and identify targets in complex environments. Traditional bearing estimation methods are limited by the physical aperture of the array. When the array size is finite, problems such as wide beamwidth, difficulty in distinguishing coherent multiple targets, and target or environmental noise masking can easily arise. Synthetic aperture technology utilizes the spatial displacement of the towed array caused by the platform's movement to jointly process array data collected at different times. This can create a larger equivalent aperture without increasing the actual number of array elements, thereby improving target bearing resolution. However, in real marine environments, factors such as fluctuations in towed platform speed, changes in array attitude, tow cable deformation, sea surface and seabed reflection, multipath propagation, and the simultaneous presence of multiple targets can easily cause bearing ambiguity and estimation errors. Especially in complex scenarios such as port channels, nearshore waters, and around marine engineering facilities, multipath echo problems often coexist, further increasing the difficulty of obtaining the bearing of towed array targets. Therefore, how to improve the azimuth resolution accuracy of towed arrays for coherent multi-target targets under limited towed array size and complex marine environment conditions has become an urgent technical problem to be solved in underwater target detection engineering applications. Summary of the Invention

[0003] The purpose of this invention is to provide a method and system for estimating the azimuth of towed array targets based on multidimensional null pointing, so as to solve the problem of inaccurate azimuth estimation of coherent multi-target targets in complex engineering environments where the size of the towed array is limited.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A method for estimating the azimuth of a towed array target based on multidimensional null pointing includes:

[0006] Step 1: A towed uniform linear array is used to form multiple time aperture positions in sequence during the continuous movement of the platform. The array received data corresponding to each time aperture position is obtained, and the physical overlapping array element segments formed by the array movement are determined according to the equivalent displacement relationship between adjacent time aperture positions.

[0007] Step 2: Using the received data of overlapping array elements located at the same equivalent spatial coordinates in adjacent time aperture positions, construct a cross-aperture statistic to characterize the phase difference between apertures, and extract the phase drift estimate between adjacent time aperture positions from it.

[0008] Step 3: Select the array received data corresponding to a time aperture position as a global phase reference, accumulate the phase drift estimate between each adjacent time aperture based on this reference, and restore the phase continuity of the array received data at each time aperture position based on the accumulated phase compensation amount.

[0009] Step 4: Retain all array data of the reference time aperture, and extract the newly added non-repeating effective aperture data along the dragging direction from the remaining time aperture data. Merge the non-repeating effective aperture data according to the equivalent array element spatial coordinate order to form equivalent extended aperture array received data.

[0010] Step 5: Construct a statistical correlation structure based on the received data of the equivalent extended aperture array, divide the equivalent extended aperture into multiple sub-apertures that at least partially overlap along the dragging direction, calculate the local correlation matrix based on the received data corresponding to each sub-aperture and perform comprehensive processing to obtain the sub-aperture average covariance matrix used to weaken the influence of coherent targets.

[0011] Step 6: Perform eigenspace decomposition on the sub-aperture average covariance matrix, and select eigenvectors corresponding to the number of incident targets according to the magnitude of the eigenvalues ​​to form the principal subspace of the target signal;

[0012] Step 7: Select multiple pairs of local apertures with different spatial displacement relationships on the equivalent extended aperture array; for the candidate spatial phase parameters, construct the corresponding dimension of null phase cancellation residual based on the cancellation residual between the two local aperture projection components in each pair of local apertures, and fuse the null phase cancellation residuals of multiple dimensions to obtain a multidimensional null phase cancellation discriminant, and then determine the candidate spatial phase parameter corresponding to the local minimum point of the discriminant as the null phase parameter;

[0013] Step 8: Based on the spatial geometric relationship between the null phase parameter, the element spacing, and the incident signal wavelength, obtain the azimuth parameter estimation result of the incident target; when there are multiple incident targets, obtain the azimuth estimation results of multiple targets based on the null phase parameters corresponding to multiple local minima.

[0014] Furthermore, in step one, the equivalent displacement of the dragged uniform linear array between two adjacent time aperture positions is... ,in, Indicates the spacing between array elements. To meet The positive integer represents the number of equivalent displacement matrix element intervals; the first The array received data at each time aperture position is the later Individual metadata and the first The first array received data at each time aperture position Each matrix element data form a physically overlapping matrix element segment on the equivalent spatial coordinates, wherein, Indicates the number of array elements. This indicates the sequence number of the previous time aperture position in the alignment of adjacent time aperture positions. This indicates the total number of time aperture positions.

[0015] Furthermore, in step two, the phase drift estimate for:

[0016]

[0017] in, Indicates the first The time aperture position and the first The cross-aperture complex correlation statistic is calculated based on the physical overlap array elements between time aperture locations. The first term extracted from the phase term of the transaperture complex correlation statistic represents the... The time aperture position and the first Phase drift estimate between time aperture positions Indicates the number of snapshots. Indicates the sequence number of the snapshot. Indicates the element number within the physically overlapping element segment, and , Indicates the first The first time aperture position The array element in the first Data received from each snapshot; .

[0018] Furthermore, in step three, using the array received data corresponding to the 0th time aperture position as a global phase reference, phase continuity recovery is performed on the array received data at each time aperture position, specifically as follows:

[0019]

[0020] in, This represents the cumulative phase compensation amount at the i-th time aperture position relative to the 0th time aperture position. Indicates the first The time aperture position and the first Phase drift estimate between time aperture positions This indicates the cumulative index of the phase drift estimate between adjacent aperture positions. Represents the imaginary unit. Indicates the first The time aperture position at the _ ... The array of snapshots receives data vectors. This indicates the first phase after phase continuity restoration processing. The time aperture position at the _ ... The array of snapshots receives data vectors.

[0021] Furthermore, in step four, the array received data after phase continuity recovery at the 0th time aperture position is used as the reference aperture data, and the equivalent extended aperture array received data vector is formed according to the following formula. :

[0022]

[0023] in, Indicates the first The equivalent extended aperture array received data vector corresponding to each snapshot Indicates the first The time aperture position after phase continuity restoration processing The array element in the first The received data for each snapshot, with the superscript T indicating transpose. The equivalent number of elements of the equivalent extended aperture array satisfies:

[0024]

[0025] in, This represents the total number of equivalent array elements in an equivalent extended aperture array. This represents the number of equivalent displacement array element intervals between adjacent aperture positions at different times.

[0026] Furthermore, in step five, the equivalent extended aperture array is divided along the dragging direction into... A length of The overlapping sub-apertures, and satisfying as well as ;No. The received data vectors corresponding to the overlapping sub-apertures are:

[0027]

[0028] The sub-aperture average covariance matrix for:

[0029]

[0030] in, Indicates the number of incident signals. This represents the number of equivalent array elements contained in each overlapping sub-aperture. This represents the total number of equivalent array elements in an equivalent extended aperture array. Indicates the number of overlapping sub-apertures. Indicates the overlapping sub-aperture number, Indicates the first The overlapping sub-aperture at the ... The received data vector of a snapshot, represents the average covariance matrix of the sub-aperture, and the superscript H indicates the conjugate transpose.

[0031] Furthermore, in step six, the average covariance matrix of the sub-aperture is... Eigenvalue decomposition is performed, and eigenvectors corresponding to the number D of incident signals are selected according to the magnitude of the eigenvalues ​​to form the principal subspace of the target signal. The remaining feature vectors constitute the noise subspace. Wherein, the subscript s represents the identifier subscript of the signal subspace, and the subscript n represents the identifier subscript of the noise subspace.

[0032] Furthermore, in step seven, the multidimensional zero-trap cancellation discriminant... for:

[0033]

[0034] in, Represents the phase parameters of the candidate null space. This represents the total number of dimensions of the zero-trap cancellation residuals. The dimension number representing the zero-trap cancellation residual. Indicates the first The weights corresponding to the zero trap cancellation residuals in the dimension Indicates based on the first The minimum singular value of the dimensional cancellation matrix is ​​used to construct the th Zero-phase residual cancellation, This represents the multidimensional zero-trap cancellation discriminant obtained after weighted fusion of the zero-trap cancellation residuals of each dimension.

[0035] Furthermore, in step eight, the azimuth estimation result of the t-th incident target... for:

[0036]

[0037] in, Indicates the wavelength of the incident signal. Indicates the spacing between array elements. Indicates the number of incident targets. Indicates the incident target number. Indicates the discriminant against multidimensional null traps. The The zero-disturbance phase parameters corresponding to each local minimum point This represents the azimuth estimation result for the t-th incident target.

[0038] A computer system includes a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of a towed array target azimuth estimation method based on multidimensional null pointing.

[0039] The beneficial effects of this invention are as follows:

[0040] To address potential uncertainties that could lead to errors, this invention improves the azimuth resolution of towed arrays without altering existing hardware structures. Simultaneously, by extracting parameters from decoherence and null depletion, it weakens the rank deficiency and near-angle target aliasing caused by coherent multi-target interactions, thereby reducing false peaks and azimuth shifts. Furthermore, this invention utilizes multiple sets of arrays with different preset intervals... Local aperture as a destructive discriminant for multidimensional null traps This invention enables the spatial phase parameters corresponding to the real target to simultaneously generate local minimum responses under multiple local aperture destructive constraints. Compared to orientation estimation methods that rely solely on a single local aperture pair or a single spectral peak search, this invention reduces phase periodic ambiguity caused by a single spatial interval, enhancing orientation discrimination capabilities under near-angle multi-target and coherent multi-target conditions. Attached Figure Description

[0041] Figure 1 This is the overall flowchart of the present invention;

[0042] Figure 2 A schematic diagram of the equivalent expanded aperture construction;

[0043] Figure 3 This is a schematic diagram of null pointing parameter extraction based on local aperture projection cancellation;

[0044] Figure 4 The spectral responses of different orientation estimation methods in coherent dual-target scenarios;

[0045] Figure 5 The spectral responses of different orientation estimation methods in coherent multi-target scenarios;

[0046] Figure 6 This is a magnified view of the spectral response of different orientation estimation methods in a coherent multi-target scenario. Detailed Implementation

[0047] The present invention will now be further described with reference to the accompanying drawings.

[0048] A method and system for estimating the azimuth of a towed array target based on multidimensional null pointing, such as Figure 1 As shown, it includes the following steps:

[0049] Step 1: Use a dragged uniform linear array to spatially sample the narrowband incident target signal, so that the array forms multiple time aperture positions in sequence during the continuous movement of the platform; record the corresponding array received data at each time aperture position, and determine the physical overlapping array element segments formed by the array movement based on the equivalent displacement relationship between adjacent time apertures.

[0050] The equivalent displacement of the dragged uniform linear array between two adjacent time aperture positions is ,in, Indicates the spacing between array elements. To meet The positive integer represents the number of equivalent displacement matrix element intervals; the first The array received data at each time aperture position is the later Individual metadata and the first The first array received data at each time aperture position Each matrix element data form a physically overlapping matrix element segment on the equivalent spatial coordinates, wherein, Indicates the number of array elements. This indicates the sequence number of the previous time aperture position in the alignment of adjacent time aperture positions. This indicates the total number of time aperture positions.

[0051] Step 2: Using the data received by overlapping array elements located at the same equivalent spatial coordinates in adjacent time aperture positions, construct a cross-aperture complex correlation statistic to characterize the phase difference between apertures; based on the phase term of the cross-aperture complex correlation statistic, extract the phase drift estimate between adjacent time aperture positions, thereby obtaining the phase shift relationship between different time aperture data.

[0052]

[0053] in, Indicates the first The time aperture position and the first The cross-aperture complex correlation statistic is calculated based on the physical overlap array elements between time aperture locations. The position of the i-th time aperture, extracted from the phase term of the cross-aperture complex correlation statistic, is related to the position of the i-th time aperture. Phase drift estimate between time aperture positions Indicates the number of snapshots. Indicates the sequence number of the snapshot. Indicates the element number within the physically overlapping element segment, and , Indicates the first The first time aperture position The array element in the first Data received from each snapshot; .

[0054] Step 3: Select the array received data corresponding to one of the time aperture positions as the global phase reference, and use this global phase reference as a benchmark to recursively accumulate the phase drift estimates between adjacent time apertures; based on the accumulated phase compensation amount, perform phase compensation on the array received data corresponding to each time aperture position so that the multiple time aperture data maintain phase continuity under a unified phase reference.

[0055] Using the array received data corresponding to the 0th time aperture position as a global phase reference, phase continuity recovery is performed on the array received data at each time aperture position, specifically as follows:

[0056]

[0057] in, This represents the cumulative phase compensation amount at the i-th time aperture position relative to the 0th time aperture position. Indicates the first The time aperture position and the first Phase drift estimate between time aperture positions This indicates the cumulative index of the phase drift estimate between adjacent aperture positions. Represents the imaginary unit. Indicates the first The time aperture position at the _ ... The array of snapshots receives data vectors. This indicates the first phase after phase continuity restoration processing. The time aperture position at the _ ... The array of snapshots receives data vectors.

[0058] Step 4: After completing the phase continuity restoration, spatial registration is performed on the data of different time apertures according to the equivalent array element spatial coordinates corresponding to each time aperture position; all array element data of the reference time aperture are retained, and non-repeating effective aperture data newly added along the dragging direction is extracted from the remaining time aperture data. The non-repeating effective aperture data is serialized and fused in ascending order of equivalent array element spatial coordinates to form equivalent extended aperture array received data.

[0059] The array received data after phase continuity restoration processing at the first time aperture position is used as the reference aperture data for the equivalent extended aperture, and all data corresponding to the 0th time aperture position are retained. Individual array metadata;

[0060] For the i-th time aperture position, where After phase continuity restoration processing, only q non-repeating effective aperture data points newly added along the dragging direction relative to the aperture position of the previous time are extracted from the array received data. These data points are then serialized and fused with the reference aperture data in ascending order of equivalent array element spatial coordinates to obtain equivalent extended aperture array received data.

[0061]

[0062] in, Indicates the first The equivalent extended aperture array received data vector corresponding to each snapshot Indicates the first The time aperture position after phase continuity restoration processing The array element in the first The received data for each snapshot, with the superscript T indicating transpose. ;in, This represents the total number of equivalent array elements in an equivalent extended aperture array. This represents the number of equivalent displacement array element intervals between adjacent aperture positions at different times.

[0063] Step 5: Construct a statistical correlation structure of the extended aperture based on the received data of the equivalent extended aperture array, and divide the equivalent extended aperture into multiple overlapping sub-apertures with the same length along the drag direction; calculate the local covariance matrix corresponding to each overlapping sub-aperture, and average the multiple local covariance matrices to obtain the average covariance matrix of the sub-apertures used to weaken the influence of coherent targets.

[0064] Data received according to the equivalent extended aperture array Calculate the extended aperture sampling covariance matrix:

[0065]

[0066] The equivalent extended aperture array is divided into K segments of length according to the dragging direction. The overlapping sub-apertures, where D represents the number of incident signals, The length of the overlapping sub-aperture. And satisfy . No. The received data corresponding to each overlapping sub-aperture is represented as follows:

[0067]

[0068] The average covariance matrix of each overlapping sub-aperture is obtained by averaging the received data.

[0069]

[0070] The sub-aperture average covariance matrix is ​​used to reduce the rank deficiency of the covariance matrix caused by coherent incident targets and to restore the effective signal subspace dimension corresponding to the number of incident targets; wherein, Indicates the number of incident signals. This represents the number of equivalent array elements contained in each overlapping sub-aperture. This represents the total number of equivalent array elements in an equivalent extended aperture array. Indicates the number of overlapping sub-apertures. Indicates the overlapping sub-aperture number, Indicates the first The overlapping sub-aperture at the ... The received data vector of a snapshot, represents the average covariance matrix of the sub-aperture, and the superscript H indicates the conjugate transpose.

[0071] Step 6: Perform eigenspace decomposition on the sub-aperture average covariance matrix, and select eigenvectors corresponding to the number of incident targets according to the magnitude of the eigenvalues ​​to form the principal subspace of the target signal; in the principal subspace of the target signal, select local aperture regions with preset spatial displacement relationships along the equivalent array element arrangement direction, and extract the local aperture projection components corresponding to each local aperture region.

[0072] Extended aperture decoherent array signal model:

[0073]

[0074] in, This represents the equivalent array manifold matrix corresponding to the overlapping sub-apertures. Indicates noise power. Represents the identity matrix; , represents the original covariance matrix of the incident signal. Let D represent the equivalent signal covariance matrix, and let D represent the number of incident signals. This represents the spatial phase advance of the t-th incident signal between adjacent equivalent array elements. , Indicates the wavelength of the incident signal. Indicates the first The azimuth parameters of an incident signal, .

[0075] The average covariance matrix of the sub-aperture Eigenvalue decomposition is performed, and eigenvectors corresponding to the number D of incident signals are selected according to the magnitude of the eigenvalues ​​to form the principal subspace of the target signal. The remaining feature vectors constitute the noise subspace. .

[0076] Step 7: Construct a multidimensional null depletion discriminant based on the principal subspace of the target signal. Specifically, G pairs of local apertures are selected on the equivalent extended aperture array. Each pair includes local aperture A and local aperture B, which have the same aperture length and a preset interval. For candidate spatial phase parameters... Phase compensation is applied to the local projection component corresponding to the local aperture B. Based on the cancellation matrix between local apertures A and B after phase compensation, null cancellation residuals of corresponding dimensions are constructed; the null cancellation residuals of multiple dimensions are weighted and fused to obtain a multidimensional null cancellation discriminant. And the multidimensional zero trap cancellation discriminant. The candidate spatial phase parameters corresponding to the local minima are determined as null phase parameters.

[0077] On the equivalent array aperture after phase continuity restoration and equivalent extended aperture reconstruction, at least two local aperture regions are selected along the equivalent array element arrangement direction. These at least two local aperture regions have the same aperture length and a predetermined interval in the equivalent array element spatial coordinates. Taking two of these local aperture regions as examples, denoted as local aperture A and local aperture B respectively, the predetermined interval between them is denoted as... To form a multidimensional null constraint, this embodiment is not limited to a single local aperture pair, but rather selects G sets of local aperture pairs on an equivalent extended aperture array, wherein... . No. The local aperture pairs are respectively denoted as local apertures. and local aperture The two have the same local aperture length and a preset interval in the equivalent element space coordinates. .

[0078] Since target signals from the same incident azimuth reach local apertures A and B, there exists a preset interval in the equivalent array element space coordinates. The deterministic phase advance caused by this means that the same incident target has a phase mapping relationship between different local aperture projection components corresponding to its incident azimuth.

[0079] Furthermore, regarding the candidate spatial phase parameters , for the Local projection components in local aperture pair Apply phase compensation and construct a cancellation matrix:

[0080]

[0081] Construct the first singular value based on the minimum singular value of the cancellation matrix. Null trap cancellation residuals:

[0082]

[0083] in, It represents the smallest singular value of the matrix.

[0084] To reduce phase periodic ambiguity caused by a single local aperture spacing and improve the accuracy of null position under near-angle multi-target conditions, this embodiment will... The local aperture values ​​are weighted and fused with the corresponding zero-traps cancellation residuals to obtain a multidimensional zero-traps cancellation discriminant:

[0085]

[0086] in, Represents the phase parameters of the candidate null space. This represents the total number of dimensions of the zero-trap cancellation residuals. The dimension number representing the zero-trap cancellation residual. Indicates the first The weights corresponding to the zero trap cancellation residuals in the dimension Indicates based on the first The minimum singular value of the dimensional cancellation matrix is ​​used to construct the th Zero-phase residual cancellation, This represents the multidimensional zero-trap cancellation discriminant obtained after weighted fusion of the zero-trap cancellation residuals of each dimension.

[0087] When candidate space phase parameters When the spatial phase parameters are consistent with those of the actual incident target, the cancellation matrices corresponding to multiple local aperture pairs simultaneously tend to be rank deficient, causing multiple null cancellation residuals to decrease simultaneously, thereby enhancing the multidimensional null cancellation discriminant. A stable local minimum occurs.

[0088] Furthermore, a local aperture projection destructive residue is constructed, and a zero-depression destructive discrimination quantity is formed based on the destructive residue. When the candidate spatial phase parameter When matched with the spatial phase parameters of a real incident target, the projection components originating from that real incident target in local apertures A and B satisfy the destructive condition after phase compensation, the destructive residual is reduced, and the null destructive discrimination quantity is reduced. Local minima occur.

[0089] Furthermore, let the search range for candidate spatial phase parameters be... The set of local minima is represented as:

[0090]

[0091] in, Represents the candidate spatial phase parameters The local neighborhood, Let represent the set of local minima of the null destructive discriminant. Then, the null phase parameters corresponding to multiple incident targets can be expressed as:

[0092]

[0093] in, Indicates the number of incident targets. Let represent the null phase parameter corresponding to the t-th incident target. Based on the spatial geometric relationship between each null phase parameter, the element spacing, and the wavelength of the incident signal, the azimuth estimation results for multiple incident targets are obtained:

[0094]

[0095] in, Indicates the wavelength of the incident signal. Indicates the spacing between array elements. Indicates the number of incident targets. Indicates the incident target number. Indicates the discriminant against multidimensional null traps. The The zero-disturbance phase parameters corresponding to each local minimum point Indicates the first The azimuth estimation results of the incident target.

[0096] The above description uses two local aperture regions as an example. In other embodiments, three or more local aperture regions with different preset intervals can be selected, and the cancellation residues between multiple local aperture projection components can be jointly constructed to form a multidimensional zero-dip cancellation discrimination quantity.

[0097] Step 8: Calculate the azimuth parameter estimation result of the incident target based on the spatial geometric correspondence between the null phase parameter, the element spacing and the incident signal wavelength; when there are multiple incident targets, obtain the azimuth estimation results of multiple targets based on the null phase parameters corresponding to multiple local minima.

[0098] For a uniform linear array, the null phase parameter satisfies the following relationship with the target incident azimuth angle:

[0099]

[0100] No. The azimuth estimation results for each incident target are as follows:

[0101]

[0102] This embodiment achieves azimuth estimation for one or more incident targets by acquiring multi-time aperture data of a continuously moving towed array, estimating cross-aperture phase drift, restoring phase continuity under a unified phase reference, constructing an equivalent extended aperture, constructing an overlapping local statistical structure, extracting the target principal subspace, canceling local aperture projections, and converting null phase parameters to target azimuth parameters.

[0103] This embodiment does not require direct azimuth peak search on the original array received data. Instead, it extracts the phase cancellation relationship between local apertures in the principal subspace of the target signal after phase continuity recovery, equivalent extended aperture reconstruction, and overlapping local statistical structure processing. This improves the azimuth estimation capability of the towed array in extracting azimuth parameters under near-angle multi-target and coherent echo conditions.

[0104] A schematic diagram of equivalent extended aperture construction for performing the aforementioned target azimuth estimation method based on equivalent aperture reconstruction and sub-aperture decoherence to extract multidimensional null pointing parameters of a towed matrix, as shown below. Figure 2 As shown:

[0105] With the first The time aperture and the first Taking a single time aperture as an example, the process of restoring phase continuity between adjacent time apertures and constructing an equivalent extended aperture is illustrated. During the continuous motion of the towed array, overlapping array element segments formed by the array motion exist between adjacent time apertures. Based on the received data corresponding to the equivalent spatial coordinates in these overlapping array element segments, a complex correlation statistic is constructed. And the phase drift estimate between adjacent time apertures is obtained from its phase term.

[0106] .

[0107] Furthermore, using the 0th time aperture as the global reference aperture, the phase drift estimates between adjacent time apertures are recursively accumulated to obtain the accumulated phase compensation. The phase continuity of the array received data at each time aperture is restored based on the accumulated phase compensation amount to obtain the phase-restored array received data. and .

[0108] After completing phase continuity restoration, all array data in the reference aperture are retained, and newly added non-repeating effective aperture data along the dragging direction is extracted from the phase restoration data of subsequent time apertures. For example... Figure 2 As shown in the black array element, the newly added non-repeating effective aperture data and the reference aperture retention data are serialized and fused in ascending order of equivalent array element spatial coordinates to form an equivalent extended aperture array.

[0109] This embodiment utilizes overlapping array element segments formed by the continuous motion of the towed array to achieve cross-aperture phase drift estimation, and extracts newly added non-repeating effective aperture data based on the phase continuity recovery, thereby constructing an equivalent extended aperture array without increasing the actual number of array elements, providing an extended aperture data basis for subsequent construction of overlapping sub-aperture statistical structures and extraction of null pointing parameters.

[0110] A schematic diagram illustrating the extraction of null pointing parameters based on local aperture projection cancellation, used to perform the aforementioned target azimuth estimation method based on the extraction of multidimensional null pointing parameters of a towed matrix using equivalent aperture reconstruction and sub-aperture decoherence. Figure 3 As shown:

[0111] Figure 3 The paper illustrates the construction of a multidimensional null destructive discriminant based on the local aperture projection destructive relation. The process is illustrated in the figure using one pair of local apertures, namely local aperture A and local aperture B, as an example. In actual implementation, the equivalent extended aperture array can be selected. The groups have different preset intervals The local aperture pairs are determined, and the null depletion residuals corresponding to each set of local aperture pairs are constructed respectively. .

[0112] for Figure 3 The local projection components of the set of local apertures A and B shown are respectively and The preset interval between the two is For candidate spatial phase parameters For local projection components Apply phase compensation and local projection components Perform cancellation to obtain the zero-trap cancellation discriminant. .when Local minima appear At that time, The null phase parameter was determined, and the target azimuth parameter was further calculated. .

[0113] On the equivalent array after phase continuity restoration and equivalent extended aperture reconstruction, at least two array elements with the same aperture length and a preset interval in the equivalent array element spatial coordinates are selected along the equivalent array element arrangement direction. The figure shows the local aperture regions, with local aperture A and local aperture B as examples.

[0114] For the incident direction is The target signal, due to the presence of a preset interval when it reaches local apertures A and B. The resulting spatial propagation path difference means that the projection components of the same incident target in different local aperture regions have a deterministic phase mapping relationship. Based on the principal subspace of the target signal, the local projection components corresponding to local aperture A and local aperture B are extracted respectively, denoted as... and ,in, This represents the candidate spatial phase parameter.

[0115] Furthermore, phase compensation corresponding to the preset interval is applied to at least one local aperture projection component. Figure 3 Taking the application of phase compensation to the local projection component corresponding to the local aperture B as an example, the phase compensation can be expressed as follows: or After phase compensation, the projected component corresponding to local aperture A is compared with the projected component corresponding to the compensated local aperture B through a destructive comparison, and a null destructive discriminant is constructed based on the residual output between the two. When the candidate spatial phase parameter When matched with the spatial phase parameters corresponding to a real incident target, the projection components originating from that target in local apertures A and B satisfy the phase cancellation condition after phase compensation, the residual output quantity decreases, and the null decoupling discrimination quantity... Local minima occur. Figure 3 The zero-trap decomposition discriminant is shown in the figure. A schematic curve illustrating the variation of the candidate spatial phase parameter, where the true target corresponds to a local minimum on the discriminant curve. .

[0116] Furthermore, the local minimum point The corresponding candidate spatial phase parameters are determined as null phase parameters, and the target azimuth parameters are obtained based on the spatial geometric relationship between the null phase parameters, the element spacing, and the incident signal wavelength. When there are multiple incident targets, multiple local minima can be formed in the null destructive discriminant. By extracting the candidate spatial phase parameters corresponding to each local minima, the target azimuth parameter estimation results for multiple incident targets can be obtained.

[0117] This embodiment utilizes the phase cancellation relationship between different local aperture projection components in the principal subspace of the target signal to construct a null phase cancellation discriminant, and extracts the null phase parameter based on the local minimum position of the discriminant, thereby realizing the target azimuth parameter estimation.

[0118] The method of this invention will be compared and verified from a simulation perspective below, such as... Figure 4 As shown, in Figure 4A target azimuth estimation method based on equivalent aperture reconstruction and sub-aperture solution coherence of towed matrix multidimensional null pointing parameter extraction is referred to as the null pointing parameter extraction method:

[0119] The specific parameters of the simulation environment are as follows:

[0120] A narrowband far-field uniform linear array model is used, with a sound speed of... The center frequency of the signal is The corresponding wavelength is The element spacing is taken as half a wavelength. The original drag array physical array element count is Each adjacent synthetic aperture position is expanded by 4 array elements, constructing a total of [number] apertures. The incident targets are two fully coherent narrowband targets, with true azimuth angles of respectively. and .

[0121] Based on the simulation conditions described above, the performance of this invention was analyzed. Under coherent dual-target conditions, conventional beamforming methods, due to physical aperture limitations, have wide main lobes, making it difficult to distinguish near-angle dual targets. The ETAM synthetic aperture method can compress the main lobe width by expanding the equivalent array aperture, but it still suffers from spectral peak instability under coherent target conditions. The traditional MUSIC method is affected by the rank deficiency of the covariance matrix caused by coherent signals, resulting in decreased target resolution performance. In contrast, the null pointing parameter extraction method proposed in this paper can... and Stable and accurate azimuth estimation results were obtained at the two target locations, verifying the effectiveness of the method in environments with limited towed array size and coherent near-angle dual targets.

[0122] The method of this invention will be compared and verified from a simulation perspective below, such as... Figure 5 , Figure 6 As shown, in Figure 5 , Figure 6 A target azimuth estimation method based on equivalent aperture reconstruction and sub-aperture solution coherence of towed matrix multidimensional null pointing parameter extraction is referred to as the null pointing parameter extraction method:

[0123] The specific parameters of the simulation environment are as follows:

[0124] A narrowband far-field uniform linear array model is used, with a sound speed of... The center frequency of the signal is The corresponding wavelength is The element spacing is taken as half a wavelength. The original towed array has 8 physical elements. Four elements are added at each adjacent synthetic aperture position, resulting in 7 apertures. The incident targets are two fully coherent narrowband targets with true azimuth angles of [missing information]. , .

[0125] Simulation results show that under conditions of limited physical aperture of the towed array, coherent target signals, and close-angle multi-target scenarios, the traditional CBF method struggles to achieve effective resolution due to its wide main lobe. The traditional MUSIC method suffers from spectral peak broadening and estimation instability due to the influence of coherent signals. While the ETAM synthetic aperture method can improve the resolution deficiency caused by limited array aperture, it still cannot completely suppress spectral response fluctuations under coherent multi-target conditions. In contrast, the null pointing parameter extraction method proposed in this invention can generate a stable, sharp, and clearly separated pointing response at the target azimuth, achieving effective estimation of the azimuth of multiple targets. This verifies the effectiveness of this method in improving azimuth estimation under conditions of limited towed array size, low signal-to-noise ratio, and coherent close-angle multi-target scenarios.

[0126] In particular, in some preferred embodiments of the present invention, a computer device is also provided, including a memory and a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the towed array target azimuth estimation method based on multidimensional null pointing described in any of the above embodiments.

[0127] In some other preferred embodiments of the present invention, a computer-readable storage medium is also provided, on which a computer program / instruction is stored, wherein when the computer program is executed by a processor, the steps of the towed array target azimuth estimation method based on multidimensional null pointing described in any of the above embodiments are implemented.

[0128] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the above embodiments of the towed array target azimuth estimation method based on multidimensional null pointing, which will not be repeated here.

[0129] Computer-readable storage media encompass a variety of types, including persistent and non-persistent, portable and fixed. These media store information using different technologies, and the content can be machine instructions, data structures, program modules, or other types of data. Some typical examples of computer storage media include: phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), various types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory and other storage technologies, optical storage media such as CD-ROM and digital video disc (DVD), magnetic storage devices such as magnetic tape and disks, and other non-transferable media used to store information accessible to computing devices. It is important to note that the computer-readable media described herein do not include temporary storage media, such as modulated data signals and carrier waves.

[0130] Those skilled in the art will further recognize that the operation of the module can be achieved using existing technical protocols or programs, without relying on new computer programs themselves. The units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0131] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented in hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0132] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for estimating the azimuth of a towed array target based on multidimensional null pointing, characterized in that, include: Step 1: A towed uniform linear array is used to form multiple time aperture positions in sequence during the continuous movement of the platform. The array received data corresponding to each time aperture position is obtained, and the physical overlapping array element segments formed by the array movement are determined according to the equivalent displacement relationship between adjacent time aperture positions. Step 2: Using the received data of overlapping array elements located at the same equivalent spatial coordinates in adjacent time aperture positions, construct a cross-aperture statistic to characterize the phase difference between apertures, and extract the phase drift estimate between adjacent time aperture positions from it. Step 3: Select the array received data corresponding to a time aperture position as a global phase reference, accumulate the phase drift estimate between each adjacent time aperture based on this reference, and restore the phase continuity of the array received data at each time aperture position based on the accumulated phase compensation amount. Step 4: Retain all array data of the reference time aperture, and extract the newly added non-repeating effective aperture data along the dragging direction from the remaining time aperture data. Merge the non-repeating effective aperture data according to the equivalent array element spatial coordinate order to form equivalent extended aperture array received data. Step 5: Construct a statistical correlation structure based on the received data of the equivalent extended aperture array, divide the equivalent extended aperture into multiple sub-apertures that at least partially overlap along the dragging direction, calculate the local correlation matrix based on the received data corresponding to each sub-aperture and perform comprehensive processing to obtain the sub-aperture average covariance matrix used to weaken the influence of coherent targets. Step 6: Perform eigenspace decomposition on the sub-aperture average covariance matrix, and select eigenvectors corresponding to the number of incident targets according to the magnitude of the eigenvalues ​​to form the principal subspace of the target signal; Step 7: Select multiple pairs of local apertures with different spatial displacement relationships on the equivalent extended aperture array; for the candidate spatial phase parameters, construct the corresponding dimension of null phase cancellation residual based on the cancellation residual between the two local aperture projection components in each pair of local apertures, and fuse the null phase cancellation residuals of multiple dimensions to obtain a multidimensional null phase cancellation discriminant, and then determine the candidate spatial phase parameter corresponding to the local minimum point of the discriminant as the null phase parameter; Step 8: Based on the spatial geometric relationship between the null phase parameter, the element spacing, and the incident signal wavelength, obtain the azimuth parameter estimation result of the incident target; when there are multiple incident targets, obtain the azimuth estimation results of multiple targets based on the null phase parameters corresponding to multiple local minima.

2. The method for estimating the azimuth of a towed array target based on multidimensional null pointing, as described in claim 1, is characterized in that... In step one, the equivalent displacement of the dragged uniform linear array between two adjacent time aperture positions is: ,in, Indicates the spacing between array elements. To meet The positive integer represents the number of equivalent displacement matrix element intervals; the first The array received data at each time aperture position is the later Individual metadata and the first The first array received data at each time aperture position Each matrix element data form a physically overlapping matrix element segment on the equivalent spatial coordinates, wherein, Indicates the number of array elements. This indicates the sequence number of the previous time aperture position in the alignment of adjacent time aperture positions. This indicates the total number of time aperture positions.

3. The method for estimating the azimuth of a towed array target based on multidimensional null pointing, as described in claim 2, is characterized in that... In step two, the phase drift estimate for: in, Indicates the first The time aperture position and the first The cross-aperture complex correlation statistic is calculated based on the physical overlap array elements between time aperture locations. The first term extracted from the phase term of the transaperture complex correlation statistic represents the... The time aperture position and the first Phase drift estimate between time aperture positions Indicates the number of snapshots. Indicates the sequence number of the snapshot. Indicates the element number within the physically overlapping element segment, and , Indicates the first The first time aperture position The array element in the first Data received from each snapshot; .

4. The method for estimating the azimuth of a towed array target based on multidimensional null pointing, as described in claim 3, is characterized in that... In step three, the array received data corresponding to the 0th time aperture position is used as a global phase reference to restore the phase continuity of the array received data at each time aperture position. Specifically: in, This represents the cumulative phase compensation amount at the i-th time aperture position relative to the 0th time aperture position. Indicates the first The time aperture position and the first Phase drift estimate between time aperture positions This indicates the cumulative index of the phase drift estimate between adjacent aperture positions. Represents the imaginary unit. Indicates the first The time aperture position at the _ ... The array of snapshots receives data vectors. This indicates the first phase after phase continuity restoration processing. The time aperture position at the _ ... The array of snapshots receives data vectors.

5. The method for estimating the azimuth of a towed array target based on multidimensional null pointing, as described in claim 4, is characterized in that... In step four, the array received data after phase continuity recovery at the 0th time aperture position is used as the reference aperture data, and the equivalent extended aperture array received data vector is formed according to the following formula. : in, Indicates the first The equivalent extended aperture array received data vector corresponding to each snapshot Indicates the first The time aperture position after phase continuity restoration processing The array element in the first The received data for each snapshot, with the superscript T indicating transpose. The equivalent number of elements of the equivalent extended aperture array satisfies: in, This represents the total number of equivalent array elements in an equivalent extended aperture array. This represents the number of equivalent displacement array element intervals between adjacent aperture positions at different times.

6. The method for estimating the azimuth of a towed array target based on multidimensional null pointing, as described in claim 5, is characterized in that... In step five, the equivalent extended aperture array is divided along the dragging direction into... A length of The overlapping sub-apertures, and satisfying as well as ;No. The received data vectors corresponding to the overlapping sub-apertures are: The sub-aperture average covariance matrix for: in, Indicates the number of incident signals. This represents the number of equivalent array elements contained in each overlapping sub-aperture. This represents the total number of equivalent array elements in an equivalent extended aperture array. Indicates the number of overlapping sub-apertures. Indicates the overlapping sub-aperture number, Indicates the first The overlapping sub-aperture at the ... The received data vector of a snapshot, represents the average covariance matrix of the sub-aperture, and the superscript H indicates the conjugate transpose.

7. The method for estimating the azimuth of a towed array target based on multidimensional null pointing, as described in claim 6, is characterized in that... In step six, the average covariance matrix of the sub-aperture is... Eigenvalue decomposition is performed, and eigenvectors corresponding to the number D of incident signals are selected according to the magnitude of the eigenvalues ​​to form the principal subspace of the target signal. The remaining feature vectors constitute the noise subspace. Wherein, the subscript s represents the identifier subscript of the signal subspace, and the subscript n represents the identifier subscript of the noise subspace.

8. The method for estimating the azimuth of a towed array target based on multidimensional null pointing, as described in claim 7, is characterized in that... In step seven, the multidimensional zero-trap cancellation discriminant... for: in, Represents the phase parameters of the candidate null space. This represents the total number of dimensions of the zero-trap cancellation residuals. The dimension number representing the zero-trap cancellation residual. Indicates the first The weights corresponding to the zero trap cancellation residuals in the dimension Indicates based on the first The minimum singular value of the dimensional cancellation matrix is ​​used to construct the th Zero-phase residual cancellation, This represents the multidimensional zero-trap cancellation discriminant obtained after weighted fusion of the zero-trap cancellation residuals of each dimension.

9. The method for estimating the azimuth of a towed array target based on multidimensional null pointing, as described in claim 8, is characterized in that... In step eight, the azimuth estimation result of the t-th incident target for: in, Indicates the wavelength of the incident signal. Indicates the spacing between array elements. Indicates the number of incident targets. Indicates the incident target number. Indicates the discriminant against multidimensional null traps. The The zero-disturbance phase parameters corresponding to each local minimum point This represents the azimuth estimation result for the t-th incident target.

10. A computer system comprising a memory, a processor, and a computer program stored in the memory, characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 9.

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