Method and system for accurately estimating inclination angle of interference baseline of wide-swath altimeter

Abstract

The invention discloses a method and system for accurately estimating the inclination angle of an interference baseline of a wide-swath altimeter, and the method comprises the steps: setting a search range based on a satellite rolling angle as an initial value of the inclination angle of the interference baseline, and selecting N inclination angles in the search range; sea surface height inversion is carried out on observation data of right side view and left side view of the altimeter, averaging is carried out in the azimuth direction, one-dimensional height vectors of right side view and left side view are obtained, each vector comprises height values corresponding to M range gates, then a right side view matrix and a left side view matrix are obtained, and the sizes of the right side view matrix and the left side view matrix are both N * M; differential operation is carried out in the column direction, and a right side parallax matrix and a left side parallax matrix are obtained; calculating the absolute value of the sum of the two difference matrixes to obtain an absolute value matrix; searching a minimum value of each column, and taking a corresponding inclination angle as a preliminary estimation value of each range gate; performing error correction to obtain a corrected inclination angle estimation value; and averaging all the corrected inclination angle estimated values of the range gates to obtain a final interference baseline inclination angle estimated value.

Description

Technical Field

[0001] This invention belongs to the field of spaceborne microwave remote sensing technology, specifically relating to a method and system for accurately estimating the inclination angle of the interferometric baseline of a wide-swath altimeter. Background Technology

[0002] Spaceborne radar altimeters are crucial marine microwave remote sensing instruments. Mounted on satellites, they can precisely measure global sea level height with centimeter-level accuracy. Wide-swath altimeters, a new type of spaceborne radar altimeter developed in recent years, are exemplified by the Tiangong-2 3D imaging altimeter and the SWOT satellite Ka-band radar interferometer. Employing short baseline interferometry with small incident angles, they achieve high-resolution, wide-swath sea level measurements, with observation swaths ranging from tens to hundreds of kilometers. This significantly improves the altimeter's observation efficiency and meets the observation needs of sub-mesoscale ocean phenomena. To achieve high-precision sea level measurement, wide-swath altimeters require accurate knowledge of the interferometric baseline inclination angle, with errors needing to be less than arcseconds, and in some cases even reaching 10 arcseconds. -2 The inclination angle is on the order of arcseconds. Generally, the inclination angle of the interferometric baseline of a wide-swath altimeter is equal to the roll angle of the satellite attitude, which can be measured in real time by the satellite attitude measurement instrument. However, the measurement accuracy is difficult to meet the altimeter's requirements for inclination error, requiring calibration or estimation using other methods. For example, external calibration can be used, but this method has high requirements for ground control points, is often difficult to implement, and cannot be frequently revisited. Alternatively, multiple parameters, including the interferometric baseline inclination angle, can be estimated using altimeter observation data, but this method is complex, computationally intensive, and easily affected by other parameters. Wide-swath altimeters are divided into single-side-looking and double-side-looking systems, with the development trend being from single-side-looking to double-side-looking. The two methods mentioned above are applicable to both single-side-looking and double-side-looking wide-swath altimeters. Another method applicable to wide-span altimeters with two-sided views estimates the inclination angle based on the characteristic that the inclination error of the interferometric baseline is exactly opposite in the left and right views. However, this method is only suitable for ideal conditions, i.e., when the sea surface to be observed is calm and wave-free, and the sea surface height trends on both sides are consistent. In reality, ideal conditions rarely exist, and this estimation method will introduce a non-negligible error. For the new generation of wide-span altimeters, its accuracy is insufficient and it cannot be applied in practice. Therefore, there is an urgent need for a method to accurately estimate the inclination angle of the interferometric baseline of wide-span altimeters. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and to propose a method for accurately estimating the inclination angle of the interferometric baseline of a wide-width altimeter. This method is easy to implement and has high accuracy in practical applications.

[0004] In view of this, the present invention proposes a method for accurately estimating the inclination angle of the interferometric baseline of a wide-span altimeter, comprising: Step 1: Based on the satellite roll angle measured by the satellite attitude measurement instrument, the initial value of the interferometric baseline tilt angle is used as the center. The search range is set with this initial value as the center, and N tilt angles are selected within the search range. Step 2: Perform sea surface height inversion on the right-side and left-side altimeter observation data respectively. Average the obtained two-dimensional sea surface height along the azimuth direction to obtain a one-dimensional height vector for the right-side view and a one-dimensional height vector for the left-side view. Each vector contains height values ​​corresponding to M range gates. Arrange the one-dimensional height vectors for the right-side view corresponding to N dip angles into a right-side view matrix of size N×M. Arrange the one-dimensional height vectors for the left-side view corresponding to N dip angles into a left-side view matrix of size N×M. Step 3: Perform difference operations along the column direction on the right view matrix and the left view matrix respectively to obtain the right view difference matrix and the left view difference matrix; calculate the absolute value of the sum of the right view difference matrix and the left view difference matrix to obtain the absolute value matrix; Step 4: Search for the minimum value in each column of the absolute value matrix, and use the corresponding tilt angle value as the preliminary estimate of each distance gate; Step 5: Perform error correction on the preliminary estimate of each distance gate to obtain the corrected tilt angle estimate; Step 6: Average the corrected tilt angle estimates for all distance gates to obtain the final interferometric baseline tilt angle estimate.

[0005] Preferably, the initial value in step 1 is The search scope is Select within the search range N Angle values , i =1,2,… N , .

[0006] Preferably, the right-side view matrix obtained in step 2 is denoted as... The left-side view matrix is ​​denoted as ,in, This represents the j-th distance gate. j =1,2,…M.

[0007] Preferably, the right-side disparity matrix in step 3 and the left-side disparity matrix They are respectively:

[0008]

[0009] in, This is the element in the (i+1)th row and jth column of the right-hand disparity matrix. This is the element in the (i+1)th row and jth column of the left-hand disparity matrix.

[0010] Preferably, step 5 yields the corrected tilt angle estimate. for:

[0011] in, This is the preliminary estimate of the j-th distance gate obtained in step 4. The difference in average sea level model height at the j-th distance gate, For the j-th distance gate, The altitude of the satellite orbit. For the Earth's radius, Let be the altimeter viewpoint corresponding to the j-th distance gate.

[0012] Preferably, step 6 yields the final estimated value of the interferometric baseline tilt angle. for: .

[0013] On the other hand, the present invention provides a system for accurately estimating the inclination angle of a wide-span altimeter interferometer baseline, characterized in that it comprises: The initial module is used to set the search range based on the satellite roll angle measured by the satellite attitude measurement instrument as the initial value of the interferometric baseline tilt angle, and select N tilt angles within the search range using this initial value as the center; The inversion and averaging modules are used to invert sea surface height from the right-side and left-side altimeter observation data, respectively. The inverted two-dimensional sea surface height is averaged along the azimuth direction to obtain a one-dimensional height vector from the right-side and left-side views. Each vector contains height values ​​corresponding to M range gates. The one-dimensional height vectors from the right-side views corresponding to N dip angles are arranged into a right-side view matrix of size N×M, and the one-dimensional height vectors from the left-side views corresponding to N dip angles are arranged into a left-side view matrix of size N×M. The difference and calculation module is used to perform difference operations along the column direction on the right view matrix and the left view matrix respectively to obtain the right view difference matrix and the left view difference matrix; and to calculate the absolute value of the sum of the right view difference matrix and the left view difference matrix to obtain the absolute value matrix. The estimation module is used to search for the minimum value in each column of the absolute value matrix and use the corresponding tilt angle value as the initial estimate of each distance gate. The correction module is used to correct the error of the initial estimate of each distance gate to obtain the corrected tilt angle estimate. The output module is used to average the corrected tilt angle estimates of all distance gates to obtain the final interferometric baseline tilt angle estimate.

[0014] Compared with the prior art, the advantages of the present invention are: The method is easy to implement, has high estimation accuracy, and can independently estimate the tilt angle of the interference baseline among multiple interference baseline parameters. The estimation accuracy is not affected by the error in the length of the interference baseline. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the geometric relationship observed by the wide-angle altimeter; Figure 2 This is a flowchart of the method; Figure 3 This is a simulation example: the initial estimate and the corrected estimate of the interferometric baseline tilt angle. Detailed Implementation

[0016] To better understand the technical solution of the present invention, the principle of the present invention will first be explained in conjunction with the accompanying drawings.

[0017] Figure 1 The bilateral viewing geometry of the wide-angle altimeter is shown. The altitude of the satellite orbit. For the Earth's radius, The inclination angle of the interference baseline. The angle between the interferometric baseline and the line of sight. For altimeter perspective, h For the target height, The subscripts of the variables represent the distance from the altimeter antenna to the target. R Indicates right-side view, subscript L Indicates left-side view.

[0018] Target heights for right and left views and They can be represented as follows: (1) (2) in, (3) (4) The working principle of a wide-span altimeter is to calculate the path difference from the two antennas to the target based on the observed interferometric phase, and then combine this with the length of the interferometric baseline to obtain... Then by and Seeking Then, the target height is inverted according to equations (1) and (2). Assume the actual interferometric baseline tilt angle is... The tilt angle values ​​used in the inversion process contain errors. ,Right now ,So (5) (6) in and These represent the actual viewpoints of the left and right sides, respectively.

[0019] Substituting equations (5) and (6) into equations (1) and (2) respectively, we can... and Represented as: (7) (8) and To each Differentiation yields (9) (10) For wide-width height gauges, and It has a wide range of values, meaning there are multiple distance gates. We use the same distance gate position for both the right and left views ( To estimate the inclination angle of the interferometric baseline.

[0020] Ideally, when the sea surface height of the target is the same when viewed from both sides, the angle of view of a target equidistant from the altimeter is also equal. hour, .Depend on and From expressions (9) and (10), it can be seen that only when Only then will there be In other words, we only need to find what makes Established The value is the true value of the tilt angle. .

[0021] In reality, the target sea surface height is different when viewed from the left and right, even at the same distance. Down , then make Established The value is no longer 0. (By...) and From expressions (9) and (10), it can be seen that when At the time of its establishment, In other words, it makes Established Value and True Value The error between them is The relationship between this error and the sea surface height of the target viewed from the left and right is further calculated. The calculation process is as follows: Let the actual sea level height as seen from the right side be... The actual sea level height as seen from the left is The difference in sea level on both sides is ,Right now Put equal ones and Unified as r , and It can be represented as: (11) (12) Substituting equation (11) into equation (12), squaring both sides and simplifying, we can obtain... (13) By applying the sum-to-product formula to the left side of the equation and approximating both sides, we can derive the following: (14) Substitute equation (14) into From (15) Equation (15) represents the difference in sea level height between the left and right views. This results in an error in the tilt angle estimation. Correcting this error will yield an accurate estimate of the tilt angle of the interferometric baseline. In equation (15), It can be calculated from the publicly available mean sea level model. The estimation error caused by the difference between the actual sea level and the mean sea level model can be reduced in the following ways: (1) In the calculation and Previously, the sea level height will be inverted. and (2) Average along the azimuth direction; (3) Average the estimated tilt angle of each distance gate.

[0022] The specific embodiments of the present invention will be described in detail below based on the principles. Figure 2 A flowchart of this method is provided.

[0023] First, the settings The range of values ​​for this value. The satellite roll angle measured by the satellite attitude measurement instrument can be used as a reference initial value for the altimeter interferometric baseline tilt angle. .by Set a reasonable search range around the central point. Within the search range N Angle values ,i =1,2,… N , For each inclination angle, the corresponding sea level height is calculated according to equations (1) and (2), and the resulting two-dimensional sea level height matrix is ​​averaged along the azimuth direction to obtain... N The left-side sea level height vector and N Each vector contains a right-side sea level height vector. M The sea surface height value at the distance gate, i.e., the vector length is M For ease of subsequent operations, the sea surface height vectors can be arranged into a matrix according to the inclination angle values. The right-hand side view matrix is ​​denoted as... The left-side view matrix is ​​denoted as The size of each matrix is N × M .

[0024] Next, we perform a difference operation on the sea surface height matrix. In other words, in practical processing, the differentiation operation described in the principle is implemented by taking differences. Specifically, it is along... The direction of change, that is, the column direction of the matrix, is used to obtain the right-side view difference matrix by taking the difference between the right-side view matrix and the left-side view matrix respectively. and the left-side disparity matrix : (16) (17) in, This is the element in the (i+1)th row and jth column of the right-hand disparity matrix. This is the element in the (i+1)th row and jth column of the left-hand disparity matrix.

[0025] The equation described in the principle It also became accordingly (18) The next step is to find the equation (18) that makes it true. Value. For discrete data in practical processing, the specific implementation method is: within the search range N Among the tilt angle values, find The absolute minimum value corresponding to Value. Let (19) matrix Total M Column, corresponding M A distance door. We search. The minimum value corresponding to each column This value serves as a preliminary estimate of the tilt angle at each distance gate. This step yields... M A preliminary estimate, denoted as... The initial estimate needs error correction, the correction amount being... The correction amount for each initial estimate is different because of the different distances to the gate. r , , They are all different and can be recorded as , , A total of M The corrected estimate is denoted as . .

[0026] (20) in, The difference in average sea level model height at the j-th distance gate, For the j-th distance gate, The altitude of the satellite orbit. For the Earth's radius, Let be the altimeter viewpoint corresponding to the j-th distance gate.

[0027] Finally, M The final altimeter interferometer baseline tilt angle estimate is obtained by averaging the corrected estimates. (twenty one) The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0028] Example 1 Embodiment 1 of the present invention proposes a method for accurately estimating the inclination angle of the interferometric baseline of a wide-width altimeter, the method comprising: The satellite roll angle measured by the satellite attitude measurement instrument is used as the initial value of the altimeter interferometric baseline tilt angle, and a reasonable search range is set with the initial value as the center. Sea surface height inversion was performed on the right-side and left-side altimeter observation data. The two-dimensional sea surface height obtained by inversion was averaged along the azimuth direction to obtain a one-dimensional sea surface height vector. The sea surface height vectors obtained by inversion for each dip angle value within the search range were arranged into a matrix in order. Divide the right-side view matrix and the left-side view matrix along the column direction, and calculate the absolute value of the sum of the two difference matrices; The minimum value of each column of the absolute value matrix is ​​searched, and the corresponding tilt angle value is used as the preliminary estimate of each distance gate. Error correction is applied to the initial estimate of each distance gate to obtain the corrected estimate; The average of the corrected estimates is the estimated inclination angle of the altimeter's interferometric baseline.

[0029] The method specifically includes: Step 1) Use the satellite roll angle measured by the satellite attitude measurement instrument as the initial value of the altimeter interferometric baseline tilt angle. The search range for the tilt angle is set with the initial value as the center. Within the search range N Angle values , i =1,2,… N , .

[0030] Step 2) Invert the sea surface height from the right-side altimeter observation data, and average the inverted two-dimensional sea surface height along the azimuth direction to obtain a one-dimensional sea surface height vector. Arrange the sea surface height vectors obtained from each dip angle value within the search range into a matrix, denoted as . The same operation is performed on the left-side altimeter observation data to obtain the left-side view matrix, denoted as... .in For distance gate, j =1,2,… M , M This represents the total number of doors at a distance.

[0031] Step 3) Difference the right-side view matrix and the left-side view matrix along the column direction to obtain the right-side view difference matrix. and the left-side disparity matrix Calculate the absolute value of the sum of the two difference matrices, and denote the result as . :

[0032]

[0033]

[0034] Step 4) Search matrix The minimum value in each column, and its corresponding tilt angle value. This serves as an initial estimate for each distance gate.

[0035] Step 5) For the preliminary estimate Perform error correction to obtain the corrected estimate. The correction formula is as follows:

[0036] in, H The orbital altitude of the altimeter satellite. R For the Earth's radius, For altimeter perspective, To view the sea surface to the left and right in the first j The height difference of the average sea level model at the distance from the gate.

[0037] Step 6) Averaging the corrected estimates yields the final estimate of the altimeter's interferometric baseline tilt angle:

[0038] The following is a simulation result of estimating the inclination angle of the interferometric baseline of a wide-span altimeter using this method. The main simulation parameters are shown in Table 1.

[0039] Table 1 Main Simulation Parameters

[0040] Figure 3 Preliminary and corrected estimates are given for each range gate. Averaging the corrected estimates yields a final interferometric baseline tilt estimate of 3.6 × 10⁻⁶. -6 °, compared to the true value of 0° for the interference baseline tilt angle set in the simulation, the estimation error is only 0.013 arcseconds.

[0041] Example 2 Embodiment 2 of the present invention provides a system for accurately estimating the inclination angle of the interferometric baseline of a wide-span altimeter, based on the method of Embodiment 1. The system includes: The initial module is used to set the search range based on the satellite roll angle measured by the satellite attitude measurement instrument as the initial value of the interferometric baseline tilt angle, and select N tilt angles within the search range using this initial value as the center; The inversion and averaging modules are used to invert sea surface height from the right-side and left-side altimeter observation data, respectively. The inverted two-dimensional sea surface height is averaged along the azimuth direction to obtain a one-dimensional height vector from the right-side and left-side views. Each vector contains height values ​​corresponding to M range gates. The one-dimensional height vectors from the right-side views corresponding to N dip angles are arranged into a right-side view matrix of size N×M, and the one-dimensional height vectors from the left-side views corresponding to N dip angles are arranged into a left-side view matrix of size N×M. The difference and calculation module is used to perform difference operations along the column direction on the right view matrix and the left view matrix respectively to obtain the right view difference matrix and the left view difference matrix; and to calculate the absolute value of the sum of the right view difference matrix and the left view difference matrix to obtain the absolute value matrix. The estimation module is used to search for the minimum value in each column of the absolute value matrix and use the corresponding tilt angle value as the initial estimate of each distance gate. The correction module is used to correct the error of the initial estimate of each distance gate to obtain the corrected tilt angle estimate. The output module is used to average the corrected tilt angle estimates of all distance gates to obtain the final interferometric baseline tilt angle estimate.

[0042] It is worth noting that in the embodiments of the above system, the modules included are divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be achieved; in addition, the specific names of each functional module are only for easy differentiation and are not used to limit the scope of protection of the present invention.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for accurately estimating the inclination angle of the interferometric baseline of a wide-span altimeter, comprising: Step 1: Based on the satellite roll angle measured by the satellite attitude measurement instrument, the initial value of the interferometric baseline tilt angle is used as the center. The search range is set with this initial value as the center, and N tilt angles are selected within the search range. Step 2: Perform sea surface height inversion on the right-side and left-side altimeter observation data respectively. Average the obtained two-dimensional sea surface height along the azimuth direction to obtain a one-dimensional height vector for the right-side view and a one-dimensional height vector for the left-side view. Each vector contains height values ​​corresponding to M range gates. Arrange the one-dimensional height vectors for the right-side view corresponding to N dip angles into a right-side view matrix of size N×M. Arrange the one-dimensional height vectors for the left-side view corresponding to N dip angles into a left-side view matrix of size N×M. Step 3: Perform difference operations along the column direction on the right view matrix and the left view matrix respectively to obtain the right view difference matrix and the left view difference matrix; Calculate the absolute value of the sum of the right-side disparity matrix and the left-side disparity matrix to obtain the absolute value matrix; Step 4: Search for the minimum value in each column of the absolute value matrix, and use the corresponding tilt angle value as the preliminary estimate of each distance gate; Step 5: Perform error correction on the preliminary estimate of each distance gate to obtain the corrected tilt angle estimate; Step 6: Average the corrected tilt angle estimates for all distance gates to obtain the final interferometric baseline tilt angle estimate.

2. The method for accurately estimating the inclination angle of the interferometric baseline of a wide-width altimeter according to claim 1, wherein the initial value in step 1 is... The search scope is Select within the search range N Angle values , i =1,2,… N , .

3. The method for accurately estimating the inclination angle of the interferometric baseline of a wide-width altimeter according to claim 2, wherein the right-side view matrix obtained in step 2 is denoted as... The left-side view matrix is ​​denoted as ,in, This represents the j-th distance gate. j =1,2,…M.

4. The method for accurately estimating the inclination angle of the interferometric baseline of a wide-span altimeter according to claim 3, wherein the right-side parallax matrix in step 3... and the left-side disparity matrix They are respectively: ； ； in, This is the element in the (i+1)th row and jth column of the right-hand disparity matrix. This is the element in the (i+1)th row and jth column of the left-hand disparity matrix.

5. The method for accurately estimating the inclination angle of a wide-width altimeter interferometer according to claim 1, wherein step 5 yields a corrected inclination angle estimate. for: ； in, This is the preliminary estimate of the j-th distance gate obtained in step 4. The difference in average sea level model height at the j-th distance gate, For the j-th distance gate, The satellite's orbital altitude, For the Earth's radius, Let be the altimeter viewpoint corresponding to the j-th distance gate.

6. The method for accurately estimating the inclination angle of a wide-width altimeter interferometer according to claim 5, wherein step 6 yields the final estimated value of the inclination angle of the interferometer baseline. for: 。 7. A system for accurately estimating the inclination angle of the interferometric baseline of a wide-width altimeter, characterized in that, include: The initial module is used to set the search range based on the satellite roll angle measured by the satellite attitude measurement instrument as the initial value of the interferometric baseline tilt angle, and select N tilt angles within the search range using this initial value as the center; The inversion and averaging modules are used to invert sea surface height from the right-side and left-side altimeter observation data, respectively. The inverted two-dimensional sea surface height is averaged along the azimuth direction to obtain a one-dimensional height vector from the right-side and left-side views. Each vector contains height values ​​corresponding to M range gates. The one-dimensional height vectors from the right-side views corresponding to N dip angles are arranged into a right-side view matrix of size N×M, and the one-dimensional height vectors from the left-side views corresponding to N dip angles are arranged into a left-side view matrix of size N×M. The difference and calculation module is used to perform difference operations along the column direction on the right view matrix and the left view matrix respectively to obtain the right view difference matrix and the left view difference matrix; and to calculate the absolute value of the sum of the right view difference matrix and the left view difference matrix to obtain the absolute value matrix. The estimation module is used to search for the minimum value in each column of the absolute value matrix and use the corresponding tilt angle value as the initial estimate of each distance gate. The correction module is used to correct the error of the initial estimate of each distance gate to obtain the corrected tilt angle estimate. and The output module is used to average the corrected tilt angle estimates of all distance gates to obtain the final interferometric baseline tilt angle estimate.

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