A non-directional wave height spectrum inversion method for small aperture bistatic high frequency radar

Abstract

The application discloses a non-directional wave height spectrum inversion method of a small-aperture bistatic high-frequency radar. First, Fourier transform is used to transform original data of the small-aperture bistatic high-frequency radar into wide-beam ocean echoes, then first-order ocean echoes are extracted from the wide-beam ocean echoes, and the energy of the first-order ocean echoes is calculated; then second-order ocean echoes meeting the signal-to-noise ratio condition and the Doppler angle frequency condition are extracted from the wide-beam ocean echoes, and the second-order ocean echoes are divided by the energy of the first-order ocean echoes to obtain normalized second-order ocean echoes; then a conversion matrix for mapping the non-directional wave height spectrum into the normalized second-order ocean echoes is constructed by using a sea current flow rate, a sea current direction and a direction distribution factor of the sea waves; and finally, the non-directional wave height spectrum is calculated from the normalized second-order ocean echoes in a reverse mapping manner. The application has the advantages of high calculation efficiency, high calculation precision, cross-platform software deployment and the like.

Description

Technical Field

[0001] This invention belongs to the field of marine remote sensing technology of small-aperture bistatic high-frequency radar, specifically relating to an undirected wave hyperspectral inversion method for small-aperture bistatic high-frequency radar. Background Technology

[0002] Since 2000, bistatic high-frequency radar has become a research hotspot in the field of high-frequency radar marine remote sensing. Compared with traditional monostatic high-frequency radar, bistatic high-frequency radar has the following three advantages: First, for the same sea surface conditions, the separate transmitting and receiving geometry allows bistatic high-frequency radar to observe the sea surface from multiple directions; second, bistatic high-frequency radar has a larger detection range; third, bistatic high-frequency radar can deploy multiple receiving stations while sharing a single transmitting station, making multi-station networking of bistatic high-frequency radar more convenient. Furthermore, due to the shared transmitting site, the manufacturing and maintenance costs of bistatic high-frequency radar networks are lower.

[0003] Despite the numerous advantages of the new bistatic high-frequency radar system, the aperture size of its receiving antenna array remains a compromise issue in practical applications. Flat land areas near the coast are typically small, lacking sufficient space to install large-aperture radar receiving antenna arrays; therefore, bistatic high-frequency radars usually employ small-aperture receiving antenna arrays. This type of bistatic high-frequency radar equipped with a small-aperture receiving antenna array is simply referred to as a small-aperture bistatic high-frequency radar. The ocean echoes acquired by small-aperture bistatic high-frequency radars are wide-beam ocean echoes. Since wide-beam ocean echoes can be considered as the superposition of multiple narrow-beam ocean echoes from different incoming directions, and there is mutual coupling between the narrow-beam ocean echoes and ocean currents, directly extracting the unidirectional wave height spectrum from wide-beam ocean echoes with high precision is quite challenging. Currently, no publicly reported method exists for inverting the unidirectional wave height spectrum from wide-beam ocean echoes of small-aperture bistatic high-frequency radars. To address these challenges, this invention proposes a feasible scheme for inverting the unidirectional wave height spectrum, filling a relevant gap. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an undirected wave hyperspectral inversion method for small-aperture bistatic high-frequency radar. Since the proposed scheme only involves two mature numerical computation methods—Newton's method and singular value decomposition of matrices—and there are many related numerical algorithm implementation modules, the proposed scheme has advantages in practical applications, including fast computation speed, high computational accuracy, and ease of deployment on various computing platforms.

[0005] To achieve the above objectives, the present invention provides a method for unidirectional wave hyperspectral inversion of a small-aperture bistatic high-frequency radar, comprising the following steps: Step 1: Perform a Discrete Fourier Transform on the original high-frequency radar data matrix to obtain the wide-beam ocean echo. ; Step 2: Search for the maximum value point of the wide-beam ocean echo obtained in Step 1, i.e., the peak point of the first-order ocean echo region of the wide-beam. And record the index of the peak point. ; Step 3, from the index obtained in Step 2 Starting from point A, continuously search to the left for points that satisfy the peak value. The difference between them is less than or equal to The index of the left endpoint of the first-order ocean echo region of the wide-beam was determined by measuring ocean echo points of 1 decibel. ; Step 4, from the index obtained in Step 2 Starting from point A, continuously search to the right for points that satisfy the peak value. The difference between them is less than or equal to The index of the right endpoint of the first-order ocean echo region of the wide-beam was determined by measuring ocean echo points of 1 decibel. ; Step 5: Determine the wide-beam first-order ocean echo region jointly identified in Steps 3 and 4. The first-order ocean echo energy of the wide-beam ocean was calculated by summing up the wide-beam ocean echoes within the range. ; Step 6, first determine the radar operating frequency. Gravitational acceleration speed of light Calculated Bragg angular frequency Then, select M points on each side of the row vector of the wide-beam ocean echo obtained in step 1 to estimate the noise level. ; Step 7: Search for wide-beam second-order ocean echo regions that satisfy the signal-to-noise ratio and Doppler angular frequency conditions; Step 8: Divide the wide-beam second-order ocean echo obtained in Step 7 by the wide-beam first-order ocean echo energy obtained in Step 5. Normalized wide-beam second-order ocean echo was calculated. ; Step 9: The azimuth range of the incoming wave covered by the receiving antenna array of the small-aperture bistatic high-frequency radar. Discretize the data, and then calculate the two-way distance based on the elliptical equidistant lines of the bistatic high-frequency radar. The straight-line distance between the bistatic high-frequency radar transmitting station and the receiving station Calculate the azimuth of each incoming wave The scattering azimuth of the corresponding angle element Angle of incidence and scattering angle ; Step 10, considering the magnitude of the ocean current velocity Ocean current direction When the wide-beam ocean echo obtained in step 1 is affected, the direction factor of the waves is taken into account. For each incoming wave azimuth obtained in step 9 Calculate an L-row, Q-column transformation matrix. ; Step 11, using the J transformation matrices obtained in step 10 , , , and the direction factor of the waves At average angle J values ​​at position , , , The normalized transformation matrix is ​​obtained. ; Step 12, normalize the transformation matrix obtained in step 11. Perform singular value decomposition and decompose values ​​less than 10 ... After setting the singular values ​​to 0, the normalized transformation matrix is ​​calculated. pseudo-inverse matrix ; Step 13: Use matrix multiplication to transform the pseudo-inverse matrix obtained in Step 12. Multiply by the normalized wide-beam second-order ocean echo obtained in step 8 Calculate the undirected wave height spectrum .

[0006] Furthermore, the discrete Fourier transform performed on the original high-frequency radar data matrix in step 1 yields the following wide-beam ocean echo in Doppler spectrum form: (1) In the formula, the wide-beam ocean echo is represented by a row vector of N points, where N is the number of sampling points. The index of the row vector element.

[0007] Based on the radar's Doppler sampling period T and the number of sampling points N, the row vector composed of Doppler angular frequencies is calculated using the sampling theorem as follows: (2) In the formula, each Doppler angular frequency Points with ocean echoes One-to-one correspondence.

[0008] Furthermore, the index of the left endpoint of the wide-beam first-order ocean echo region in step 3. The calculation method is as follows: ① Initialize the index as ; ② Let the index Subtract 1; ③ Judgment conditions Check if the condition is met. If it is met, return to step ②; otherwise, proceed to step ④. ④ End the search and output the results. .

[0009] Furthermore, the index of the right endpoint of the wide-beam first-order ocean echo region in step 4. The calculation method is as follows: ① Initialize the index as ; ② Let the index Add 1; ③ Judgment conditions Check if the condition is met. If it is met, return to step ②; otherwise, proceed to step ④. ④ End the search and output the results. .

[0010] Furthermore, the calculation method for the wide-beam first-order ocean echo energy in step 5 is as follows: (3) In the formula, For wide-beam first-order ocean echo energy, For index n Corresponding wide-beam ocean echo.

[0011] Furthermore, the Bragg angular frequency in step 6 The calculation method is as follows: (4) In the formula, For radar operating frequency, It is the acceleration due to gravity. It is the speed of light.

[0012] noise level The calculation method is as follows: (5) In the formula, For index n The corresponding wide-beam ocean echo, where M is the number of selected points and N is the number of sampling points.

[0013] Moreover, there are two ways to implement step 7. Method 1: from the left end point of the wide-beam first-order ocean echo region obtained in step 3. Starting from the left, search for a noise level higher than that obtained in step 6. higher decibels and Doppler angular frequency satisfy the inequality The wide-beam second-order ocean echo region is implemented as follows: ① Initialize the index as Initialize an empty array Index; ② Let the index Subtract 1; ③ Judgment conditions Check if the condition is met. If it is met, continue with step ④; otherwise, proceed with step ⑤. ④ Judgment conditions If true, then set the current index. Add it to the Index array and return ②; otherwise, do nothing and return ② directly. ⑤ End the search. At this point, the Index array contains L indices. , , , , , , The wide-beam second-order ocean echo region was defined, in which Since it's an index, we can simply output the array Index.

[0014] Method 2: From the right end point of the wide-beam first-order ocean echo region obtained in step 4 Starting from the point, search to the right for a noise level higher than that obtained in step 6. higher decibels and Doppler angular frequency satisfy the inequality The wide-beam second-order ocean echo region is implemented as follows: ① Initialize the index as Initialize an empty array Index. ② Let the index Add 1; ③ Judgment conditions Check if the condition is met. If it is met, continue with step ④; otherwise, proceed with step ⑤. ④ Judgment conditions If true, then set the current index. Add it to the Index array and return ②; otherwise, do nothing and return ② directly. ⑤ End the search. At this point, the Index array contains L indices. , , , , , , The wide-beam second-order ocean echo region was defined, in which Since it's an index, we can simply output the array Index.

[0015] Furthermore, the normalized wide-beam second-order ocean echo calculated in step 8 for: (6) In the formula, , ... , For index , , , , Corresponding wide-beam ocean echo, This refers to the first-order ocean echo energy of a wide-beam wave.

[0016] Furthermore, in step 9, the location coordinates of the bistatic high-frequency radar transmitting station are first used as... The coordinates of the receiving station are Calculate the position coordinates of the j-th angle element. The calculation formula is as follows: (7) (8) In the formula, Let j be the discretized azimuth of the incoming wave. The distance between the two-way elliptical equidistant lines of a bistatic high-frequency radar. This represents the straight-line distance between the bistatic high-frequency radar transmitting and receiving stations.

[0017] Two sets of position coordinates can be obtained from equations (7) and (8). It is necessary to discard an extra set of position coordinates based on the positional relationship between the j-th angle element and the transmitting and receiving stations of the bistatic high-frequency radar, and only retain the position coordinates that are consistent with the actual situation.

[0018] Then, the incident vector is calculated based on the vector coordinates. angle of incidence and scattering vector scattering angle The scattering azimuth angle of the j-th angle element is obtained. The calculation method is as follows: (9) Finally, J scattering azimuth angles corresponding one-to-one with the azimuth of the incoming wave are obtained. , , , , .

[0019] Furthermore, the j-th transformation matrix in step 10 The specific calculation method is as follows: ①The range of ocean wave frequencies by Discretize the interval as Wave frequency , , , , , , ,in Indicates an index; ② Initialize row index ; ③ Row Index Add 1; ④ Initialize column indexes ; ⑤ Column Index Add 1; ⑥ Calculate the first The wave number corresponding to each wave frequency And according to the magnitude of the ocean current. Ocean current direction and the result obtained in step 7 indexes Solve using Newton's method At zero point, the direction of the waves is obtained. ,Right now: (10) In the formula, Wave number For the direction of the waves, For index The corresponding Doppler angular frequency, For the speed of the ocean current, According to the direction of the ocean current, It is the Bragg angular frequency. It is the acceleration due to gravity. The incident vector The angle of incidence, Scattering vector The scattering angle; ⑦ Based on the direction factor of ocean waves In the direction of the waves The value at the location And the coupling coefficient of second-order ocean echoes. Calculate the j-th transformation matrix In the OK Elements in a column The calculation formula is as follows: (11) ⑧ Judgment conditions and Check if the equality is true. If true, proceed to step 9; otherwise, return to step 5. ⑨ Judgment conditions and Check if the equality holds. If it does, proceed to step 10; otherwise, return to step 3. ⑩ End the loop and transform the matrix. The calculation results are output.

[0020] Furthermore, in step 11, the J transformation matrices obtained in step 10 are first... , , , The transformation matrix is ​​summed by adding the results, and then the incident angle obtained in step 9 is calculated. and scattering angle average angle And simultaneously calculate the direction factor of the waves. At average angle Value at location Then calculate J values. , , , The sums of the direction factors are obtained by adding them together. Finally, the sum of the transformation matrices is divided by the sum of the direction factors to obtain the normalized transformation matrix. The specific calculation method is as follows: (12) In the formula, The direction of the incoming wave The corresponding transformation matrix, The direction of the incoming wave The incident angle of the corresponding angle element, The direction of the incoming wave The scattering angle of the corresponding angle element.

[0021] Furthermore, the specific calculation method in step 13 is as follows: (13) In the formula, For the spectrum of boundless waves, Normalized transformation matrix The pseudo-inverse matrix, This is a normalized wide-beam second-order ocean echo.

[0022] Compared with the prior art, the present invention has the following advantages: The solution provided by this invention directly extracts the omnidirectional wave height spectrum from the wide-beam ocean echo of a small-aperture bistatic high-frequency radar. On the one hand, it can overcome the disadvantage of large footprint of using a large-aperture receiving antenna array; on the other hand, it can omit the necessary step of digital beamforming technology used in previous omnidirectional wave height spectrum inversion methods, thus reducing the amount of computation in the omnidirectional wave height spectrum inversion process. Attached Figure Description

[0023] Figure 1 This is a flowchart of an embodiment of the present invention.

[0024] Figure 2 This refers to the wide-beam ocean echo in this embodiment of the invention.

[0025] Figure 3 This is the inversion result of the undirected wave height spectrum in an embodiment of the present invention. Detailed Implementation

[0026] This invention provides a method for inverting the undirected wave height spectrum of a small-aperture bistatic high-frequency radar. This method overcomes the problem that the coupling effect between ocean currents and narrow-beam ocean echoes with different azimuths is difficult to directly decouple in wide-beam ocean echoes by considering the influence of ocean currents on the wide-beam ocean echoes received by the small-aperture bistatic high-frequency radar. By combining the direction factor of the waves, a transformation matrix that is a linear mapping from the undirected wave height spectrum to the wide-beam ocean echo is directly constructed. Finally, the undirected wave height spectrum is solved from the wide-beam ocean echo through the inverse mapping (i.e., the pseudo-inverse matrix of the transformation matrix).

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0028] like Figure 1 As shown, the process of this embodiment of the invention includes the following steps: Step 1: Perform a Discrete Fourier Transform on the original high-frequency radar data matrix to obtain the wide-beam ocean echo in Doppler spectrum form, as shown below: (1) In the formula, the wide-beam ocean echo is the row vector of N points, where N is the number of sampling points. In this embodiment, N=1024. The index of the row vector element.

[0029] Based on the radar's Doppler sampling period T (T=0.5s in this embodiment) and the number of sampling points N (N=1024 in this embodiment), the row vector composed of Doppler angular frequencies is calculated using the sampling theorem as follows: (2) In the formula, each Doppler angular frequency Points with ocean echoes One-to-one correspondence.

[0030] The wide-beam ocean echo obtained in step 1 is as follows: Figure 2 The continuous curve is shown in the figure.

[0031] Step 2: Search for the maximum value point of the wide-beam ocean echo obtained in Step 1, i.e., the peak point of the first-order ocean echo region of the wide-beam. And record the index of the peak point. .

[0032] The index of the peak points searched in this embodiment .

[0033] Step 3, from the index obtained in Step 2 Starting from point A, continuously search to the left for points that satisfy the peak value. The difference between them is less than or equal to The index of the left endpoint of the first-order ocean echo region of the wide-beam was determined by measuring ocean echo points of 1 decibel. The specific implementation method is as follows: ① Initialize the index as ; ② Let the index Subtract 1; ③ Judgment conditions Check if the condition is met. If it is met, return to step ②; otherwise, proceed to step ④. ④ End the search and output the results. .

[0034] Index of the left endpoint of the wide-beam first-order ocean echo region in this embodiment The left endpoint found by the search is Figure 2 The rhombus shape in the middle.

[0035] Step 4, from the index obtained in Step 2 Starting from point A, continuously search to the right for points that satisfy the peak value. The difference between them is less than or equal to The index of the right endpoint of the first-order ocean echo region of the wide-beam was determined by measuring ocean echo points of 1 decibel. The specific implementation method is as follows: ① Initialize the index as ; ② Let the index Add 1; ③ Judgment conditions Check if the condition is met. If it is met, return to step ②; otherwise, proceed to step ④. ④ End the search and output the results. .

[0036] Index of the right endpoint of the wide-beam first-order ocean echo region in this embodiment The right endpoint found in the search is Figure 2 The square in the middle.

[0037] Step 5: Determine the wide-beam first-order ocean echo region jointly identified in Steps 3 and 4. The wide-beam ocean echoes within the range are accumulated to calculate the first-order ocean echo energy of the wide-beam, i.e. (3) In the formula, For wide-beam first-order ocean echo energy, For index n Corresponding wide-beam ocean echo.

[0038] This embodiment focuses on the wide-beam first-order ocean echo region. The wide-beam ocean echoes within the range [289, 321] are accumulated to obtain the first-order wide-beam ocean echo energy. .

[0039] Step 6, first determine the radar operating frequency. Gravitational acceleration speed of light Calculate the Bragg angular frequency Then, select M points on each side of the row vector of the wide-beam ocean echo obtained in step 1 to estimate the noise level. The specific calculation method is as follows: (4) In the formula, For radar operating frequency, It is the acceleration due to gravity. It is the speed of light.

[0040] (5) In the formula, For index n The corresponding wide-beam ocean echo, where M is the number of selected points and N is the number of sampling points.

[0041] In this embodiment, the radar operating frequency MHz, gravitational acceleration speed of light m / s, the Bragg angular frequency is calculated. rad / s. From the row vector of the wide-beam ocean echo obtained in step 1, select M=15 points on each side to calculate the noise level. , Figure 2 The estimation results of the noise level are shown using a horizontal dashed line.

[0042] Step 7: Search for wide-beam second-order ocean echo regions that satisfy the signal-to-noise ratio and Doppler angular frequency conditions.

[0043] There are two ways to implement this step. Method 1: From the left end point of the wide-beam first-order ocean echo region obtained in step 3. Starting from the left, search for a noise level higher than that obtained in step 6. higher decibels and Doppler angular frequency satisfy the inequality Method 2: From the right end point of the wide-beam second-order ocean echo region obtained in step 4. Starting from the point, search to the right for a noise level higher than that obtained in step 6. higher decibels and Doppler angular frequency satisfy the inequality Wide-beam second-order ocean echo region.

[0044] In this embodiment, method one was selected for implementation, and its specific implementation method is described below: ① Initialize the index as Initialize an empty array Index; ② Let the index Subtract 1; ③ Judgment conditions Check if the condition is met. If it is met, continue with step ④; otherwise, proceed with step ⑤. ④ Judgment conditions If true, then set the current index. Add it to the Index array and return ②; otherwise, do nothing and return ② directly. ⑤ End the search. At this point, the Index array contains L indices. , , , , , , The wide-beam second-order ocean echo region was defined, in which Since it's an index, we can simply output the array Index.

[0045] The specific implementation method of method two is explained as follows: ① Initialize the index as Initialize an empty array Index. ② Let the index Add 1; ③ Judgment conditions Check if the condition is met. If it is met, continue with step ④; otherwise, proceed with step ⑤. ④ Judgment conditions If true, then set the current index. Add it to the Index array and return ②; otherwise, do nothing and return ② directly. ⑤ End the search. At this point, the Index array contains L indices. , , , , , , The wide-beam second-order ocean echo region was defined, in which Since it's an index, we can simply output the array Index.

[0046] In this embodiment, the final number of indices obtained in step 7 is L=70, and the wide-beam second-order ocean echo region is as follows: Figure 2 As indicated by the asterisk in the image.

[0047] Step 8, use the index obtained in step 7. , , , , The corresponding wide-beam second-order ocean echo energy divided by the wide-beam first-order ocean echo energy obtained in step 5 Normalized wide-beam second-order ocean echo was calculated. as follows: (6) In the formula, , ... , For index , , , , The corresponding wide-beam second-order ocean echo, This refers to the first-order ocean echo energy of a wide-beam wave.

[0048] The normalized wide-beam second-order ocean echo obtained in this embodiment It is a column vector with 70 rows and 1 column.

[0049] Step 9: First, the azimuth range of the incoming wave covered by the receiving antenna array of the small-aperture bistatic high-frequency radar. Discretize the data, with a discrete interval of 1 / 2. The discretized J incoming wave azimuths are , , , , , , , where index Then, based on the two-way distance of the elliptical equidistant lines of the bistatic high-frequency radar... The straight-line distance between the bistatic high-frequency radar transmitting station and the receiving station Calculate the azimuth of each incoming wave The scattering azimuth of the corresponding angle element Angle of incidence and scattering angle The specific calculation method is as follows: First, the location coordinates of the bistatic high-frequency radar transmitter station are used as follows: The coordinates of the receiving station are Calculate the position coordinates of the j-th angle element. The specific calculation method is as follows: (7) (8) In the formula, Let j be the discretized azimuth of the incoming wave. The distance between the two-way elliptical equidistant lines of a bistatic high-frequency radar. This represents the straight-line distance between the bistatic high-frequency radar transmitting and receiving stations.

[0050] Two sets of position coordinates can be obtained from equations (7) and (8). It is necessary to discard an extra set of position coordinates based on the positional relationship between the j-th angle element and the transmitting and receiving stations of the bistatic high-frequency radar, and only retain the position coordinates that are consistent with the actual situation.

[0051] Then, the incident vector is calculated based on the vector coordinates. angle of incidence and scattering vector scattering angle The calculation results are saved, and finally the scattering azimuth angle of the j-th angle element is calculated. The calculation method is as follows: (9) Through calculation, J scattering azimuth angles corresponding one-to-one with the azimuth of the incoming wave can be obtained. , , , , .

[0052] In this embodiment, the azimuth range of the incoming wave The discrete interval is After discretization, J=121 incoming wave azimuths are obtained. , , , , , , Two-way distance of the elliptical equidistant line of a bistatic high-frequency radar km, the straight-line distance between the bistatic high-frequency radar transmitting station and the receiving station km.

[0053] Step 10, considering the magnitude of the ocean current velocity Ocean current direction When the wide-beam ocean echo obtained in step 1 is affected, the direction factor of the waves is taken into account. For each incoming wave azimuth obtained in step 9 Calculate an L-row, Q-column transformation matrix. , where the j-th transformation matrix The specific calculation method is as follows: ①The range of ocean wave frequencies by With an interval of 0.005 Hz, discretized as follows Wave frequency , , , , , , ,in Indicates an index.

[0054] ② Initialize row index ; ③ Row Index Add 1; ④ Initialize column indexes ; ⑤ Column Index Add 1; ⑥ Calculate the first The wave number corresponding to each wave frequency And according to the magnitude of the ocean current. Ocean current direction and the result obtained in step 7 indexes Solve using Newton's method At zero point, the direction of the waves is obtained. ,Right now: (10) In the formula, Wave number For the direction of the waves, For index The corresponding Doppler angular frequency, The speed of the ocean current (in this embodiment) m / s), In the direction of ocean currents (in this embodiment) ), It is the Bragg angular frequency. It is the acceleration due to gravity. The incident vector The angle of incidence, Scattering vector The scattering angle.

[0055] ⑦ Based on the direction factor of ocean waves In the direction of the waves The value at the location And the coupling coefficient of second-order ocean echoes. Calculate the j-th transformation matrix In the OK Elements in a column The calculation formula is as follows: (11) ⑧ Judgment conditions and Check if the equality is true. If true, proceed to step 9; otherwise, return to step 5. ⑨ Judgment conditions and Check if the equality holds. If it does, proceed to step 10; otherwise, return to step 3. ⑩ End the loop and transform the matrix. The calculation results are output.

[0056] Step 11, first convert the J transformation matrices obtained in step 10 into... , , , The transformation matrix is ​​summed by adding the results, and then the incident angle obtained in step 9 is calculated. and scattering angle average angle And simultaneously calculate the direction factor of the waves. At average angle Value at location Then calculate J values. , , , The sums of the direction factors are obtained by adding them together. Finally, the sum of the transformation matrices is divided by the sum of the direction factors to obtain the normalized transformation matrix. The specific calculation method is as follows: (12) Step 12, normalize the transformation matrix obtained in step 11. Perform singular value decomposition and decompose values ​​less than 10 ... After setting the singular values ​​to 0, the normalized transformation matrix is ​​calculated. pseudo-inverse matrix .

[0057] Step 13: Use matrix multiplication to transform the pseudo-inverse matrix obtained in Step 12. Multiply by the normalized wide-beam second-order ocean echo obtained in step 8 Calculate the undirected wave height spectrum The specific calculation method is as follows: (13) The above undirected wave high spectrum It is a Q-row, 1-column column vector, which also represents the inversion result of the undirected wave height spectrum.

[0058] Figure 3 The inversion results of the undirected wave height spectrum and the actual undirected wave height spectrum are presented simultaneously. Through comparison... Figure 3 As can be seen from the two curves, the proposed solution can accurately invert the undirected wave height spectrum.

[0059] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for unidirectional wave hyperspectral inversion of a small-aperture bistatic high-frequency radar, characterized in that, Includes the following steps: Step 1: Perform a Discrete Fourier Transform on the original high-frequency radar data matrix to obtain the wide-beam ocean echo. ; Step 2: Search for the maximum value point of the wide-beam ocean echo obtained in Step 1, i.e., the peak point of the wide-beam first-order ocean echo region. And record the index of the peak point. ; Step 3, from the index obtained in Step 2 Starting from point A, continuously search to the left for points that satisfy the peak value. The difference between them is less than or equal to The index of the left endpoint of the first-order ocean echo region of the wide-beam was determined by measuring ocean echo points of 1 decibel. ; Step 4, from the index obtained in Step 2 Starting from point A, continuously search to the right for points that satisfy the peak value. The difference between them is less than or equal to The index of the right endpoint of the first-order ocean echo region of the wide-beam was determined by measuring ocean echo points of 1 decibel. ; Step 5: Determine the wide-beam first-order ocean echo region jointly defined in Steps 3 and 4. The first-order ocean echo energy of the wide-beam ocean was calculated by summing up the wide-beam ocean echoes within the range. ; Step 6, first determine the radar operating frequency. Gravitational acceleration speed of light Calculated Bragg angular frequency Then, select M points on each side of the row vector of the wide-beam ocean echo obtained in step 1 to estimate the noise level. ; Step 7: Search for wide-beam second-order ocean echo regions that satisfy the signal-to-noise ratio and Doppler angular frequency conditions; Step 8: Divide the wide-beam second-order ocean echo obtained in Step 7 by the wide-beam first-order ocean echo energy obtained in Step 5. Normalized wide-beam second-order ocean echo was calculated. ; Step 9: The azimuth range of the incoming wave covered by the receiving antenna array of the small-aperture bistatic high-frequency radar. Discretize the data, and then calculate the two-way distance based on the elliptical equidistant lines of the bistatic high-frequency radar. The straight-line distance between the bistatic high-frequency radar transmitting station and the receiving station Calculate the azimuth of each incoming wave The scattering azimuth angle of the corresponding angle element Angle of incidence and scattering angle ; First, the location coordinates of the bistatic high-frequency radar transmitter station are used as follows: The coordinates of the receiving station are Calculate the position coordinates of the j-th angle element. The calculation formula is as follows: （7） （8） In the formula, The j-th incoming wave direction after discretization; Two sets of position coordinates can be obtained from equations (7) and (8). It is necessary to discard an extra set of position coordinates based on the positional relationship between the j-th angle element and the transmitting and receiving stations of the bistatic high-frequency radar, and only retain the position coordinates that are consistent with the actual situation. Then, the incident vector is calculated based on the vector coordinates. angle of incidence and scattering vector scattering angle The scattering azimuth angle of the j-th angle element is obtained. The calculation method is as follows: （9） Finally, J scattering azimuth angles corresponding one-to-one with the azimuth of the incoming wave are obtained. , , , , ; Step 10, considering the magnitude of the ocean current velocity Ocean current direction When the wide-beam ocean echo obtained in step 1 is affected, the direction factor of the waves is taken into account. For each incoming wave azimuth obtained in step 9 Calculate an L-row, Q-column transformation matrix. ; Step 11, using the J transformation matrices obtained in step 10 , , , and the direction factor of the waves At average angle J values ​​at position , , , The normalized transformation matrix is ​​obtained. ; First, transform the J transformation matrices obtained in step 10... , , , The transformation matrix is ​​summed by adding the results, and then the incident angle obtained in step 9 is calculated. and scattering angle average angle And simultaneously calculate the direction factor of the waves. At average angle Value at location Then calculate J values. , , , The sums of the direction factors are obtained by adding them together. Finally, the sum of the transformation matrices is divided by the sum of the direction factors to obtain the normalized transformation matrix. The specific calculation method is as follows: （12） In the formula, The direction of the incoming wave The corresponding transformation matrix, The direction of the incoming wave The incident angle of the corresponding angle element, The direction of the incoming wave The scattering angle of the corresponding angle element; Step 12, normalize the transformation matrix obtained in step 11. Perform singular value decomposition and decompose values ​​less than 10 ... After setting the singular values ​​to 0, the normalized transformation matrix is ​​calculated. pseudo-inverse matrix ; Step 13: Use matrix multiplication to transform the pseudo-inverse matrix obtained in Step 12. Multiply by the normalized wide-beam second-order ocean echo obtained in step 8 Calculate the undirected wave height spectrum .

2. The method for unidirectional wave hyperspectral inversion of a small-aperture bistatic high-frequency radar as described in claim 1, characterized in that: In step 1, the discrete Fourier transform of the original high-frequency radar data matrix is ​​performed, and the resulting wide-beam ocean echo in Doppler spectrum form is as follows: （1） In the formula, the wide-beam ocean echo is represented by a row vector of N points, where N is the number of sampling points. The index of the row vector element; Based on the radar's Doppler sampling period T and the number of sampling points N, the row vector composed of Doppler angular frequencies is calculated using the sampling theorem as follows: （2） In the formula, each Doppler angular frequency Points with ocean echoes One-to-one correspondence.

3. The method for unidirectional wave hyperspectral inversion of a small-aperture bistatic high-frequency radar as described in claim 1, characterized in that: Index of the left endpoint of the wide-beam first-order ocean echo region in step 3 The calculation method is as follows: ① Initialize the index as ; ② Let the index Subtract 1; ③ Judgment conditions Check if the condition is met; if it is, return to step ②. Otherwise, proceed to step ④; ④ End the search and output the results. .

4. The method for unidirectional wave hyperspectral inversion of a small-aperture bistatic high-frequency radar as described in claim 1, characterized in that: Index of the right endpoint of the wide-beam first-order ocean echo region in step 4 The calculation method is as follows: ① Initialize the index as ; ② Let the index Add 1; ③ Judgment conditions Check if the condition is met; if it is, return to step ②. Otherwise, proceed to step ④; ④ End the search and output the results. .

5. The method for unidirectional wave hyperspectral inversion of a small-aperture bistatic high-frequency radar as described in claim 1, characterized in that: Bragg angular frequency in step 6 The calculation method is as follows: （4） In the formula, For radar operating frequency, It is the acceleration due to gravity. The speed of light; noise level The calculation method is as follows: （5） In the formula, For index n The corresponding wide-beam ocean echo, where M is the number of selected points and N is the number of sampling points.

6. The method for unidirectional wave hyperspectral inversion of a small-aperture bistatic high-frequency radar as described in claim 1, characterized in that: There are two ways to implement step 7. Method 1: From the left end point of the wide-beam first-order ocean echo region obtained in step 3. Starting from the left, search for a noise level higher than that obtained in step 6. higher decibels and Doppler angular frequency satisfy the inequality The wide-beam second-order ocean echo region is implemented as follows: ① Initialize the index as Initialize an empty array Index; ② Let the index Subtract 1; ③ Judgment conditions Is it valid? If so, continue with step ④. Otherwise, proceed to step ⑤; ④ Judgment conditions If true, then set the current index. Add it to the Index array and return ②; otherwise, do nothing and return ② directly. ⑤ End the search. At this point, the Index array contains L indices. , , , , , , The wide-beam second-order ocean echo region was defined, in which Since it's an index, we can simply output the array Index; Method 2: From the right end point of the wide-beam first-order ocean echo region obtained in step 4 Starting from the point, search to the right for a noise level higher than that obtained in step 6. higher decibels and Doppler angular frequency satisfy the inequality The wide-beam second-order ocean echo region is implemented as follows: ① Initialize the index as Initialize an empty array Index. ② Let the index Add 1; ③ Judgment conditions Is it valid? If so, continue with step ④. Otherwise, proceed to step ⑤; ④ Judgment conditions If true, then set the current index. Add it to the Index array and return ②; otherwise, do nothing and return ② directly. ⑤ End the search. At this point, the Index array contains L indices. , , , , , , The wide-beam second-order ocean echo region was defined, in which Since it's an index, we can simply output the array Index.

7. The method for unidirectional wave hyperspectral inversion of a small-aperture bistatic high-frequency radar as described in claim 1, characterized in that: Step 8 calculates the normalized wide-beam second-order ocean echo. for: （6） In the formula, , ... , For index , , , , Corresponding wide-beam ocean echo, This refers to the first-order ocean echo energy of a wide-beam wave.

8. The method for unidirectional wave hyperspectral inversion of a small-aperture bistatic high-frequency radar as described in claim 1, characterized in that: The j-th transformation matrix in step 10 The specific calculation method is as follows: ①The range of ocean wave frequencies by Discretize the interval as Wave frequency , , , , , , ,in Indicates an index; ② Initialize row index ; ③ Row Index Add 1; ④ Initialize column indexes ; ⑤ Column Index Add 1; ⑥ Calculate the first The wave number corresponding to each wave frequency And according to the magnitude of the ocean current. Ocean current direction and the result obtained in step 7 indexes Solve using Newton's method At zero point, the direction of the waves is obtained. ,Right now: （10） In the formula, Wave number For the direction of the waves, For index The corresponding Doppler angular frequency, For the speed of the ocean current, According to the direction of the ocean current, It is the Bragg angular frequency. It is the acceleration due to gravity. The incident vector The angle of incidence, Scattering vector The scattering angle; ⑦ Based on the direction factor of ocean waves In the direction of the waves The value at the location And the coupling coefficient of second-order ocean echoes. Calculate the j-th transformation matrix In the OK Elements in a column The calculation formula is as follows: （11） ⑧ Judgment conditions and Check if the equality holds; if it does, proceed to step 9. Otherwise, return ⑤; ⑨ Judgment conditions and Check if the equality holds; if it does, proceed with step 10. Otherwise, return ③; ⑩ End the loop and transform the matrix. The calculation results are output.

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