A line spectrum detection method based on uniform linear array element cross spectrum

Abstract

The application relates to a line spectrum detection method based on inter-spectrum of elements of a uniform linear array, and aims to solve the problem that a traditional beam forming line spectrum detector cannot effectively detect a near-field line spectrum target in the presence of a far-near mixed source. The process is as follows: step one, performing FFT (fast Fourier transform) on array receiving signals to obtain frequency domain receiving data; step two, based on the frequency domain receiving data obtained in step one, starting from an element at one end of the array, calculating the inter-spectrum of adjacent elements in sequence to obtain element inter-spectrum output; step three, based on the inter-spectrum output obtained in step two, summing the inter-spectrum output of each element and taking a modulus value to obtain a to-be-detected power spectrum diagram; and step four, performing line spectrum detection on the to-be-detected power spectrum diagram to obtain frequency information of the line spectrum.

Description

Technical Field

[0001] This invention relates to a line spectrum detection method based on the cross spectrum of elements of a uniform linear array. Background Technology

[0002] The power spectrum of underwater target radiated noise consists of a broadband continuous spectrum and a low-frequency narrowband line spectrum. Due to the higher intensity per unit bandwidth of its low-frequency line spectrum components, the detection of low-frequency line spectrum signals is crucial for passive target detection. Array-based line spectrum detection methods can achieve spatial processing gain, improve the signal-to-noise ratio of the line spectrum signal, and thus enhance the detection capability of weak targets. A common approach is to use broadband beamforming and then accumulate the spatial spectrum outputs at each frequency point of the target's azimuth; this is called additive beamforming. The most common method is conventional beamforming (CBF) line spectrum detectors, which effectively improve line spectrum detection capability compared to single-element arrays. However, CBF line spectrum detectors require four-dimensional display, necessitating the simultaneous observation of multiple three-dimensional windows to achieve multi-target analysis. Furthermore, when both near-field and far-field targets coexist, conventional far-field beamforming cannot focus on near-field targets, and additive beamforming can lead to the loss of near-field weak line spectrum targets. Near-field focusing beamforming, on the other hand, requires near-field scanning, which significantly increases computational complexity for large-aperture arrays.

[0003] A literature search revealed several research articles on array signal processing detection methods for line spectrum targets:

[0004] Reference [1] (Chen Yang, Wang Zijuan, Zhu Daizhu, Yu Yun, Hui Junying. A line spectrum target detection method based on frequency variance weighting [J]. Acta Acustica, 2010, 35(1): 76-80.) proposes a line spectrum target detection method based on frequency variance weighting, which uses the peak frequency variance of each azimuth frequency domain to weight the azimuth spectrum output by CBF. The smaller the frequency variance of the line spectrum, the larger the azimuth spectrum weighting coefficient, and the larger the output value of the azimuth beam. The advantage of this method is that it only requires a three-dimensional window, avoiding the difficulty of traditional line spectrum detection requiring four-dimensional display, and can detect weak line spectrum targets in the background of strong interference from multiple targets and strong coherent interference from the same beam. However, this method is based on the results of far-field CBF and cannot solve the problem of near-field line spectrum target detection.

[0005] Reference [2] (Chen Yang, Zhao Anbang, Wang Zijuan, et al. Instantaneous frequency variance weighted guided minimum variance beamforming detector [J]. Journal of Harbin Engineering University, 2011, 32(6): 730-735.) applies the instantaneous frequency variance weighted method proposed in Reference [1] to the guided minimum variance beamforming detector. It utilizes the characteristics of narrow main lobe and low side lobe of minimum variance beamforming to improve the detection performance of weak line spectrum targets under strong interference, but it cannot solve the problem of near-field line spectrum target detection.

[0006] Reference [3] (Chen Xinhua, Bao Xizhong, Li Qihu, et al. Research on target detection method of unknown frequency underwater acoustic signal [J]. Acta Ordnance et al., 2012, 33(4): 471-475.) proposes a target detection method of unknown frequency line spectrum. It utilizes the characteristic that the maximum value of the noise frequency beam output is random while the maximum value of the target frequency beam output is basically unchanged, and statistically analyzes the azimuth estimation results of each frequency point at multiple times, thereby realizing the detection of targets of unknown frequency line spectrum. This method can achieve the same detection performance as when the frequency is known, but it still cannot solve the problem of mixed sources. Summary of the Invention

[0007] The purpose of this invention is to solve the problem that traditional beamforming line spectrum detectors cannot effectively detect near-field line spectrum targets in the presence of mixed near-field and far-field sources, and to propose a line spectrum detection method based on the cross spectrum of elements of a uniform linear array.

[0008] The specific process of a line spectrum detection method based on the cross spectrum of elements of a uniform linear array is as follows:

[0009] Step 1: Perform FFT on the array received signal to obtain frequency domain received data;

[0010] FFT stands for Fast Fourier Transform;

[0011] Step 2: Based on the frequency domain received data obtained in Step 1, starting from the array element at one end of the array, calculate the cross spectrum of adjacent array elements in sequence to obtain the array element cross spectrum output.

[0012] Step 3: Based on the cross-spectral output obtained in Step 2, sum the cross-spectral outputs of each array element and take the modulus value to obtain the power spectrum diagram to be measured.

[0013] Step 4: Perform line spectrum detection on the power spectrum to be tested to obtain the frequency information of the line spectrum.

[0014] Preferably, in step one, the array received signal is subjected to FFT to obtain frequency domain received data;

[0015] The specific process is as follows:

[0016] Step 11: Define the array receiving signal model, such as... Figure 7 ;

[0017] The array receiving signal model is as follows:

[0018] for A uniform linear array, with the direction of the array as... The axis is selected, with the array center as the reference point, which is the origin of the coordinate system, and the perpendicular direction to the array is... axis;

[0019] The target angle is the angle between the target's incident direction and... The included angle of the axis, the element number follows The axis coordinates increase sequentially as follows: ;

[0020] Considering the spherical wave model, when the target is located in the near-field or far-field region, the target angle is... At that time, the first The time delay of the data received by the array element relative to the reference point is expressed as:

[0021]

[0022] in, For the first The delay of data received by the array element relative to the reference point;

[0023] For the first Number Array Element Axis coordinates;

[0024] The distance from the target to the reference point; To achieve the goal of The distance between the array elements;

[0025] The speed of sound underwater is taken as 1500 m / s;

[0026] Step 1 and 2: Perform FFT on the time-domain signal received by each array element to obtain the frequency-domain signal received by each array element.

[0027] No. The frequency domain signal received by the array element is represented as follows:

[0028]

[0029] in, For the first The frequency domain signal received by the array element; The frequency of the target signal;

[0030] The frequency domain signal received at the reference point; The imaginary unit, .

[0031] Preferably, the process of obtaining the near-field region and the far-field region is as follows:

[0032] When the distance from the target to the reference point satisfy At that time, the target is considered to be in the near field zone;

[0033] When the distance from the target to the reference point satisfy At that time, the target was considered to be in the very near field area;

[0034] When the distance from the target to the reference point satisfy At that time, the target is considered to be in the far field region;

[0035] in, For array aperture, , The number of array elements. The spacing between array elements;

[0036] The wavelength of the source radiation signal is the target.

[0037] Preferably, in step two, based on the frequency domain received data obtained in step one, the cross spectrum of adjacent array elements is calculated sequentially, starting from the array element at one end of the array, to obtain the array element cross spectrum output.

[0038] The specific process is as follows:

[0039] Calculate the mutual spectrum of array elements starting from array element 0;

[0040] Based on the Frequency domain signal received by the array element With the Frequency domain signal received by the array element Calculate the first Cross-spectral output of array elements ; indicates as:

[0041]

[0042] in, For the first The frequency domain signal received by the array element;

[0043] To Find the conjugate; To Find the absolute value;

[0044] The direction is Target signal arrives The receiving phase of the array element; The direction is Target signal arrives The receiving phase of the array element.

[0045] Preferably, the orientation is Target signal arrives The receiving phase of the array element Represented as:

[0046]

[0047] in, Wave number; ; The frequency of the target signal; The speed of sound underwater is taken as 1500 m / s;

[0048] For the first Number Array Element Axis coordinates.

[0049] Preferably, the orientation is Target signal arrives The receiving phase of the array element Represented as:

[0050] .

[0051] Preferably, the

[0052] in, The distance between array elements.

[0053] Preferably, in step three, based on the cross-spectral output obtained in step two, the cross-spectral outputs of each array element are summed and the modulus is taken to obtain the power spectrum to be measured.

[0054] The specific process is as follows:

[0055] Based on the cross-spectral output obtained in step two The cross-spectral outputs of each array element are summed and the modulus is taken to obtain the power spectrum of the target array. ; indicates as:

[0056]

[0057] in, The cross-spectral output obtained in step two; This is the cross-spectral output for the 0th array element; This is the cross-spectral output for the first array element; This is the cross-spectral output for the second array element; For the first The cross-spectral output of the array elements.

[0058] Preferably, step four involves analyzing the power spectrum to be measured. Line spectrum detection is performed to obtain the frequency information of the line spectrum;

[0059] The specific process is as follows:

[0060] Step 41: Extract the power spectrum of the target power Continuous spectrum background ;

[0061] Step 42, against a continuous spectrum background Add a fixed detection threshold To obtain the new threshold value ;

[0062] Step 4.3: Process the power spectrum of the target power using the local peak detection method. Medium greater than the new threshold In this part, the power spectrum to be measured is selected. The local maxima points that are greater than the new threshold are selected, and the frequencies corresponding to the local peaks are the frequencies corresponding to the line spectrum components.

[0063] Preferably, the new threshold value Represented as:

[0064] .

[0065] The beneficial effects of this invention are as follows:

[0066] This invention proposes a line spectrum target detection method applicable to situations with mixed far-field and near-field sources. Addressing the problem that traditional line spectrum detectors based on far-field beamforming cannot effectively detect near-field line spectrum targets in mixed-source scenarios, this invention utilizes the phase characteristics of the cross-spectral results of target array elements in the near-field region to propose a mixed-source line spectrum detection method. This invention achieves spatial gain acquisition of targets in all directions in both the far-field and near-field regions by calculating the cross-spectrum of signals received from adjacent array elements and then calculating the power spectrum to be measured based on the cross-spectrum.

[0067] Compared to traditional beamforming line spectrum detectors, this invention possesses significant technical advantages. Leveraging the characteristic that the cross-spectral directivity of array elements is insensitive to both target azimuth and distance, this invention overcomes the limitation of traditional far-field beamforming methods, which are only applicable to far-field line spectrum target detection. Simultaneously, it avoids the cumbersome large-range range scanning operations required for near-field target detection. This invention, through an array element cross-spectral directivity algorithm, directly sums and moduloes the cross-spectral data of the array elements, thus obtaining stable and reliable spatial processing gain for targets at any unknown azimuth. The overall algorithm is simple in principle, has low computational complexity, supports single-shot signal processing, and only requires a three-dimensional viewport to complete the observation and identification of the entire target line spectrum, significantly improving detection efficiency and engineering practicality. Attached Figure Description

[0068] Figure 1 This is a flowchart of the processing of the present invention;

[0069] Figure 2 The angular dimension normalized directional image of cross-spectral beamforming of array elements;

[0070] Figure 3 To generate a range-dimensional normalized directional image for cross-spectral beamforming of array elements;

[0071] Figure 4 A comparison of power spectrum diagrams obtained by various line spectrum detection methods for a single-frequency target in the positive lateral direction far field.

[0072] Figure 5 A comparison of power spectrum diagrams obtained by various line spectrum detection methods for a near-field single-frequency target in the positive transverse direction;

[0073] Figure 6 A comparison of power spectrum diagrams obtained by various line spectrum detection methods under the condition of mixed near-field and far-field sources;

[0074] Figure 7 This is a structural diagram of the array receiving signal model. Detailed Implementation

[0075] Specific implementation method one: Combining Figure 1 This embodiment describes a line spectrum detection method based on the cross spectrum of elements in a uniform linear array. The specific process is as follows:

[0076] Step 1: Perform FFT on the array received signal to obtain frequency domain received data;

[0077] FFT stands for Fast Fourier Transform;

[0078] Step 2: Based on the frequency domain received data obtained in Step 1, starting from the array element at one end of the array, calculate the cross spectrum of adjacent array elements in sequence to obtain the array element cross spectrum output.

[0079] Step 3: Based on the cross-spectral output obtained in Step 2, sum the cross-spectral outputs of each array element and take the modulus value to obtain the power spectrum diagram to be measured.

[0080] Step 4: Perform line spectrum detection on the power spectrum to be tested to obtain the frequency information of the line spectrum.

[0081] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that step one involves performing an FFT on the array received signal to obtain frequency domain received data.

[0082] The specific process is as follows:

[0083] Step 11: Define the array receiving signal model, such as... Figure 7 ;

[0084] The array receiving signal model is as follows:

[0085] for A uniform linear array, with the direction of the array as... The axis is selected, with the array center as the reference point, which is the origin of the coordinate system, and the perpendicular direction to the array is... axis;

[0086] The coordinate system is a two-dimensional rectangular coordinate system, and the direction of the array is... The axis, the vertical direction of the array is axis;

[0087] The target angle is the angle between the target's incident direction and... The included angle of the axis, the element number follows The axis coordinates increase sequentially as follows: ;

[0088] Considering the spherical wave model, when the target is located in the near-field or far-field region, the target angle is... At that time, the first The time delay of the data received by the array element relative to the reference point can be uniformly expressed as:

[0089]

[0090] in, For the first The delay of data received by the array element relative to the reference point;

[0091] For the first Number Array Element Axis coordinates;

[0092] The distance from the target to the reference point; To achieve the goal of The distance between the array elements;

[0093] The speed of sound underwater is typically taken as 1500 m / s;

[0094] Step 1 and 2: Perform FFT on the time-domain signal received by each array element to obtain the frequency-domain signal received by each array element.

[0095] No. The frequency domain signal received by the array element is represented as follows:

[0096]

[0097] in, For the first The frequency domain signal received by the array element; The frequency of the target signal;

[0098] The frequency domain signal received at the reference point; The imaginary unit, .

[0099] The other steps and parameters are the same as in Specific Implementation Method 1.

[0100] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the process of obtaining the near-field region and the far-field region is as follows:

[0101] When the influence of third-order and higher small quantities on the time delay of the received data of each array element relative to the reference point can be ignored after Taylor expansion, the target is said to be in the near field region. Reference [4] (KT Selvan and R. Janaswamy. Fraunhofer and Fresnel Distances: Unified derivation for aperture antennas. IEEE Antennas and Propagation Magazine, 2017; 59(4): 12-15.) derived the range of the near field region; when the distance from the target to the reference point satisfy At that time, the target is considered to be in the near field zone;

[0102] When the distance from the target to the reference point satisfy At that time, the target was considered to be in the very near field area;

[0103] When the distance from the target to the reference point satisfy At that time, the target is considered to be in the far field region;

[0104] in, For array aperture, , The number of array elements. The spacing between array elements;

[0105] The wavelength of the source radiation signal is the target.

[0106] Other steps and parameters are the same as in specific implementation method one or two.

[0107] Specific Implementation Method Four: This implementation method differs from one of the specific implementation methods one to three in that, in step two, based on the frequency domain received data obtained in step one, the cross spectrum of adjacent array elements is calculated sequentially starting from one element of the array to obtain the array element cross spectrum output.

[0108] The specific process is as follows:

[0109] Calculate the mutual spectrum of array elements starting from array element 0;

[0110] Based on the Frequency domain signal received by the array element With the Frequency domain signal received by the array element Calculate the first Cross-spectral output of array elements ; indicates as:

[0111]

[0112] in, For the first The frequency domain signal received by the array element;

[0113] To Find the conjugate; To Find the absolute value;

[0114] For direction Target signal arrives The receiving phase of the array element; For direction Target signal arrives The receiving phase of the array element.

[0115] The other steps and parameters are the same as those in one of the specific implementation methods one to three.

[0116] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the orientation is... Target signal arrives The receiving phase of the array element Represented as:

[0117]

[0118] in, Wave number; ; The frequency of the target signal; The speed of sound underwater is typically taken as 1500 m / s;

[0119] For the first Number Array Element Axis coordinates.

[0120] The other steps and parameters are the same as those in one of the specific implementation methods one to four.

[0121] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the orientation is... Target signal arrives The receiving phase of the array element Represented as:

[0122] .

[0123] The other steps and parameters are the same as those in one of the specific implementation methods one to five.

[0124] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that the...

[0125] in, The distance between array elements.

[0126] The other steps and parameters are the same as those in one of the specific implementation methods one to six.

[0127] Specific Implementation Method Eight: This implementation method differs from any of the specific implementation methods one to seven in that, in step three, based on the cross-spectral output obtained in step two, the cross-spectral outputs of each array element are summed and the modulus value is taken to obtain the power spectrum to be measured.

[0128] The specific process is as follows:

[0129] The result obtained in step two Viewed as a reconstruction The meta array receives data and processes it. By performing appropriate phase compensation, beam output can be obtained. ; indicates as:

[0130]

[0131] in, Pre-formed beam direction;

[0132]

[0133] From this, we can obtain the normalized directivity function for array element cross-spectral beamforming. ; indicates

[0134]

[0135] Figure 2 and Figure 3 Normalized directivity (i.e., the decibel value of normalized power output) of an M-element uniform linear array with a half-wave spacing of 0.5 m is presented in the angular and range dimensions. Generally, a target is considered detectable when the beam output energy is 3 dB higher than the sidelobes. It can be seen that the beam output energy is higher than 3 dB in all directions and at all ranges. This means that the cross-spectral beamforming output of the array elements is insensitive to angle and range; therefore, no compensation is needed. The power spectrum with spatial gain can be obtained by directly accumulating the cross-spectral outputs of the array elements and taking the modulus.

[0136] Based on the cross-spectral output obtained in step two The cross-spectral outputs of each array element are summed and the modulus is taken to obtain the power spectrum of the target array. ; indicates as:

[0137]

[0138] in, The cross-spectral output obtained in step two; This is the cross-spectral output for the 0th array element; This is the cross-spectral output for the first array element; This is the cross-spectral output for the second array element; For the first The cross-spectral output of the array elements.

[0139] In addition, by Figure 3 It can be seen that the beam output power decreases as the distance between the target and the array decreases. This is because the target enters the extremely near-field region, and the second-order or higher nonlinear time delay of the spherical wave target cannot be ignored. At this time, the target is no longer located in the near-field region. The cross-spectral beamforming of the array elements based on the near-field received signal model experiences a decrease in spatial gain due to model mismatch. The extremely near-field range increases with the increase of the array aperture, but overall, the beam output power is still higher than -3dB for each distance.

[0140] The other steps and parameters are the same as those in any of the specific implementation methods one to seven.

[0141] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that step four involves examining the power spectrum under test. Line spectrum detection is performed to obtain the frequency information of the line spectrum;

[0142] The specific process is as follows:

[0143] Step 41: Utilizing bidirectional Filtering method, dual-pass window method, and sorting truncation method for extracting the power spectrum of the target power. Continuous spectrum background ;

[0144] Step 42, against a continuous spectrum background Add a fixed detection threshold To obtain the new threshold value ;

[0145] Step 4.3: Process the power spectrum of the target power using the local peak detection method. Medium greater than the new threshold In this part, the power spectrum to be measured is selected. The local maxima points that are greater than the new threshold are selected, and the frequencies corresponding to these local peaks are the frequencies corresponding to the line spectrum components.

[0146] The other steps and parameters are the same as those in one of the specific implementation methods one to eight.

[0147] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that the new threshold value is... Represented as:

[0148] .

[0149] The other steps and parameters are the same as those in any of the specific implementation methods one to nine.

[0150] Example:

[0151] Implementation Case 1:

[0152] Given a single-frequency line spectrum target with an input spectral signal-to-noise ratio of 5dB, the target is processed according to the array element cross-spectral line spectrum detection steps proposed in this invention:

[0153] First, following step one, perform FFT calculation on the received time-domain data; then, following step two, based on the frequency-domain received data obtained in step one, calculate the cross-spectrum of adjacent array elements sequentially starting from one side of the array; then, following step three, based on the array element cross-spectrum obtained in step two, process the corresponding frequency points within the processing bandwidth... The cross-spectral outputs of the elements are summed and then moduloed to obtain the power spectrum of the target. This spectrum is then compared with the power spectrum obtained by directly performing FFT on a single array element and the power spectrum obtained by the CBF line spectrum detector with azimuth compensation for the real target. The results are as follows when the target is a 400Hz far-field target. Figure 4 As shown, the result is as follows when the target is a 300Hz near-field target. Figure 5 As shown; finally, line spectrum target detection is performed, and the final line spectrum detection result can be obtained by measuring the frequency information.

[0154] The invention will now be further described with reference to the accompanying drawings. (Comparison) Figure 4 and Figure 5 Therefore, for far-field line spectrum targets, compared to single-element line spectrum detectors, array-element cross-spectral line spectrum detectors obtain the following spatial gain: decibels, while the spatial gain obtained by the CBF line spectrum detector is Decibels. This is because cross-spectral calculations change the noise distribution from a complex Gaussian distribution to... Distribution, and then through After noncoherent superposition, the output signal-to-noise ratio is improved compared to the input signal-to-noise ratio. The gain of the CBF line spectrum detector decreases significantly for near-field line spectrum targets. This is because the linear phase compensation model based on the far-field plane wave assumption mismatches the near-field received signal, causing the phases of the received signals of each array element to be misaligned, or even resulting in phase cancellation. However, the cross-spectral line spectrum detector can still obtain the target signal at this time. Decibels of spatial gain.

[0155] Implementation Case 2:

[0156] Two far-field single-frequency line spectrum targets are set with frequencies of 100Hz and 400Hz, and input spectral level signal-to-noise ratios of 10dB and 5dB, respectively. Two near-field single-frequency line spectrum targets are located at distances of 200m and 100m from the array, with frequencies of 80Hz and 300Hz, and input spectral level signal-to-noise ratios of 7dB and -15dB, respectively. The array element cross-spectral line spectrum detection steps proposed in this invention are used for processing, and the results are compared with the power spectrum obtained by directly performing FFT on a single array element and the power spectrum obtained by the CBF line spectrum detector with compensation in the positive lateral direction. The results are as follows: Figure 6 As shown, in the case of multiple targets, the array element cross-spectral line spectrum detector can achieve [the following]: line spectrum signals from all directions in both the far-field and near-field regions. The spatial gain is obtained in decibels, but the CBF line spectrum detector can only obtain the maximum spatial gain for far-field line spectrum targets in the positive transverse direction at 100Hz, and the gain for far-field and near-field targets in other unknown directions is significantly reduced. For near-field weak targets at 300Hz, only the array element cross-spectral line spectrum detector can achieve detection. Therefore, the array element cross-spectral line spectrum detection method proposed in this invention can effectively improve the detection performance of near-field weak line spectrum targets in mixed source situations, without requiring prior knowledge of the target direction and distance, and only requiring three-dimensional display.

[0157] This invention may have other embodiments. Without departing from the spirit and essence of this invention, those skilled in the art can make various corresponding changes and modifications according to this invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A line spectrum detection method based on the cross spectrum of elements of a uniform linear array, characterized in that: The specific process of the method is as follows: Step 1: Perform FFT on the array received signal to obtain frequency domain received data; FFT stands for Fast Fourier Transform; Step 2: Based on the frequency domain received data obtained in Step 1, starting from the array element at one end of the array, calculate the cross spectrum of adjacent array elements in sequence to obtain the array element cross spectrum output. Step 3: Based on the cross-spectral output obtained in Step 2, sum the cross-spectral outputs of each array element and take the modulus value to obtain the power spectrum diagram to be measured. Step 4: Perform line spectrum detection on the power spectrum to be tested to obtain the frequency information of the line spectrum.

2. The line spectrum detection method based on the cross spectrum of elements of a uniform linear array according to claim 1, characterized in that: Step one involves performing an FFT on the array received signal to obtain frequency domain received data. The specific process is as follows: Step 11: Define the array receiving signal model; The array receiving signal model is as follows: for A uniform linear array, with the direction of the array as... The axis is selected, with the array center as the reference point, which is the origin of the coordinate system, and the perpendicular direction to the array is... axis; The target angle is the angle between the target's incident direction and... The included angle of the axis, the element number follows The axis coordinates increase sequentially as follows: ; Considering the spherical wave model, when the target is located in the near-field or far-field region, the target angle is... At that time, the first The time delay of the data received by the array element relative to the reference point is expressed as: in, For the first The delay of data received by the array element relative to the reference point; For the first Number Array Element Axis coordinates; The distance from the target to the reference point; To achieve the goal of The distance between the array elements; The speed of sound underwater is taken as 1500 m / s; Step 1 and 2: Perform FFT on the time-domain signal received by each array element to obtain the frequency-domain signal received by each array element. No. The frequency domain signal received by the array element is represented as follows: in, For the first The frequency domain signal received by the array element; The frequency of the target signal; The frequency domain signal received at the reference point; The imaginary unit, .

3. The line spectrum detection method based on the cross spectrum of elements of a uniform linear array according to claim 2, characterized in that: The process of acquiring the near-field region and the far-field region is as follows: When the distance from the target to the reference point satisfy At that time, the target is considered to be in the near field zone; When the distance from the target to the reference point satisfy At that time, the target was considered to be in the very near field area; When the distance from the target to the reference point satisfy At that time, the target is considered to be in the far field region; in, For array aperture, , The number of array elements. The spacing between array elements; The wavelength of the source radiation signal is the target.

4. The line spectrum detection method based on the cross spectrum of elements of a uniform linear array according to claim 3, characterized in that: Step two involves calculating the cross spectrum of adjacent array elements sequentially, starting from the array element at one end of the array, based on the frequency domain received data obtained in step one, to obtain the array element cross spectrum output. The specific process is as follows: Calculate the mutual spectrum of array elements starting from array element 0; Based on the Frequency domain signal received by the array element With the Frequency domain signal received by the array element Calculate the first Cross-spectral output of array elements ; indicates as: in, For the first The frequency domain signal received by the array element; To Find the conjugate; To Find the absolute value; The direction is Target signal arrives The receiving phase of the array element; The direction is Target signal arrives The receiving phase of the array element.

5. The line spectrum detection method based on the cross spectrum of elements of a uniform linear array according to claim 4, characterized in that: The orientation is Target signal arrives The receiving phase of the array element Represented as: in, Wave number; ; The frequency of the target signal; The speed of sound underwater is taken as 1500 m / s; For the first Number Array Element Axis coordinates.

6. The line spectrum detection method based on the cross spectrum of elements of a uniform linear array according to claim 5, characterized in that: The orientation is Target signal arrives The receiving phase of the array element Represented as: 。 7. The line spectrum detection method based on the cross spectrum of elements of a uniform linear array according to claim 6, characterized in that: The in, The distance between array elements.

8. The line spectrum detection method based on the cross spectrum of elements of a uniform linear array according to claim 7, characterized in that: In step three, based on the cross-spectral output obtained in step two, the cross-spectral outputs of each array element are summed and the modulus is taken to obtain the power spectrum to be measured. The specific process is as follows: Based on the cross-spectral output obtained in step two The cross-spectral outputs of each array element are summed and the modulus is taken to obtain the power spectrum of the target array. ; indicates as: in, The cross-spectral output obtained in step two; This is the cross-spectral output for the 0th array element; This is the cross-spectral output for the first array element; This is the cross-spectral output for the second array element; For the first The cross-spectral output of the array elements.

9. The line spectrum detection method based on the cross spectrum of elements of a uniform linear array according to claim 8, characterized in that: Step four: Power spectrum under test Line spectrum detection is performed to obtain the frequency information of the line spectrum; The specific process is as follows: Step 41: Extract the power spectrum of the target power Continuous spectrum background ; Step 42, against a continuous spectrum background Add a fixed detection threshold To obtain the new threshold value ; Step 4.3: Process the power spectrum of the target power using the local peak detection method. Medium greater than the new threshold In this part, the power spectrum to be measured is selected. The local maxima points that are greater than the new threshold are selected, and the frequencies corresponding to the local peaks are the frequencies corresponding to the line spectrum components.

10. The line spectrum detection method based on the cross spectrum of elements of a uniform linear array according to claim 9, characterized in that: The new threshold Represented as: 。

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