Compass insar atmospheric error compensation method based on region division

Abstract

The application discloses a Beidou InSAR atmospheric error compensation method based on region division, and divides the propagation path from a receiver to a PS point target into a propagation region and an estimation region. For the atmospheric error phase of the propagation region, it is regarded as a constant; and for the estimation region, the atmospheric refractive index is estimated by combining the imaging of different satellites, phase results and PS point selection results. The atmospheric refractive index of each PS point in the scene is estimated, the connectivity of the atmospheric refractive index of the scene is judged by using the median absolute deviation method, the atmospheric refractive index of the points which do not satisfy the connectivity, i.e. outliers, is corrected. Finally, the phases in the propagation region and the estimation region are added, so that the atmospheric phase of each target is obtained, the atmospheric phase compensation is realized, and the precision of deformation inversion and the effective early warning of disasters are improved.

Description

Technical Field

[0001] This invention belongs to the field of bistatic synthetic aperture radar technology, specifically relating to a method for compensating atmospheric phase errors in a BeiDou satellite bistatic InSAR system. Background Technology

[0002] The BeiDou-InSAR (BeiDou based Interferometric Synthetic Aperture Radar System) system can be used to monitor scene deformation. This system utilizes in-orbit BeiDou satellites as transmitters and deploys ground-based geostationary receivers to form a bistatic SAR system. Deformation monitoring is then achieved using heavy-orbit SAR imagery. This system inherits the advantages of both the BeiDou positioning system and radar systems, enabling three-dimensional deformation measurement of an opposite scene using a single device. Compared to traditional deformation detection methods, this system offers advantages such as low cost and shorter monitoring cycle.

[0003] Achieving 3D deformation inversion requires interferometric processing of echoes. However, at different data acquisition times, variations in scene parameters such as temperature, humidity, atmospheric pressure, wind speed, and rainfall can alter the atmospheric refractive index, affecting signal propagation and causing echo delays. For two echoes of the same target at different times, a phase error, known as atmospheric error, is introduced, impacting the accuracy of deformation inversion. Therefore, to achieve high-precision deformation inversion, an algorithm is needed to compensate for the atmospheric phase error in the BeiDou InSAR system. Summary of the Invention

[0004] In view of this, the present invention provides a BeiDou InSAR atmospheric error compensation method based on region division. The propagation path from the receiver to the target PS point is divided into a propagation zone and an estimation zone. The atmospheric error phase in the propagation zone is treated as a constant; while for the estimation zone, the atmospheric refractive index is estimated by combining the imaging and phase results of different satellites and the PS point selection results. The atmospheric refractive index of each PS point in the scene is estimated separately. The median absolute deviation method is used to determine the connectivity of the atmospheric refractive index of the scene. Points that do not meet the connectivity requirement, i.e., outliers, are corrected for atmospheric refractive index. Finally, the phases in the propagation zone and the estimation zone are added together to obtain the atmospheric phase of each target, achieving atmospheric phase compensation, thereby improving the accuracy of deformation inversion and effective disaster early warning.

[0005] The specific solution of the present invention is as follows:

[0006] The BeiDou InSAR atmospheric error compensation method based on region division includes:

[0007] Step 1: Obtain the PS point set by combining data from multiple satellites;

[0008] Step 2: Division of the propagation zone;

[0009] Step 3: Estimate the division of the region;

[0010] Step 4: Estimate the atmospheric refractive index within the estimation area;

[0011] Step 5: Determine the connectivity of atmospheric refractive index.

[0012] Furthermore, in step five, the method for determining atmospheric refractive index connectivity is the median absolute deviation method. The median absolute deviation of the atmospheric refractive index within the support region of the target point is calculated. When the difference between the atmospheric refractive index at that point and the median is greater than three times the median absolute deviation, that point is considered an outlier. The method for compensating for outliers is to perform a linear fit using the two nearest non-outlier points, and the resulting atmospheric refractive index is used as the new atmospheric refractive index for the outlier.

[0013] The present invention has the following beneficial effects:

[0014] This invention solves the problem of low accuracy in three-dimensional deformation inversion caused by atmospheric phase error during interferometric processing in the BeiDou satellite bistatic InSAR system, compensates for atmospheric phase error, and improves the accuracy of deformation inversion. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the atmospheric phase according to an embodiment of the present invention.

[0016] Figure 2 This is a schematic diagram of the estimation region division in an embodiment of the present invention.

[0017] Figure 3 This is a schematic diagram showing the locations of two exemplary points in an embodiment of the present invention.

[0018] Figure 4 The accuracy of example point 1 in the embodiment of the present invention before compensation.

[0019] Figure 5 The accuracy of example point 2 in the embodiment of the present invention before compensation.

[0020] Figure 6 This is the accuracy of example point 1 in the embodiment of the present invention after compensating for atmospheric phase error.

[0021] Figure 7 This is the accuracy of example point 2 in the embodiment of the present invention after compensating for atmospheric phase error. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] The BeiDou InSAR atmospheric error compensation method based on region division specifically includes the following steps:

[0024] Step 1: Obtain PS point set by combining multi-satellite data

[0025] Specifically:

[0026] For K satellites The corresponding PS point selection result is The point set used for atmospheric phase compensation is:

[0027] (1)

[0028] Calculate the bistatic distance difference for each point on each day, based on their respective system configurations:

[0029] (2)

[0030] Step Two: Division of Propagation Zones

[0031] Specifically:

[0032] In the BeiDou InSAR system, the atmospheric phase of the target is:

[0033] (3)

[0034] in, This represents the atmospheric refractive index at the current time and location. This indicates the distance difference between the two base stations.

[0035] In the interference phase, the introduction of atmospheric error is due to the change in atmospheric refractive index, which can be expressed as:

[0036] (4)

[0037] In actual data processing, we can assume that within a small range, It is a constant. Therefore, equation (4) can be expressed as a summation:

[0038] (5)

[0039] In equation (5), it is assumed that the distance changes upwards. The atmospheric refractive index within a certain range is constant. Dividing the total transmission path into multiple segments and transforming the integral over the path into a discrete summation form, it is only necessary to estimate the refractive index of each segment. This allows for compensation for atmospheric errors.

[0040] However, in reality, there is often a targetless region between the receiver and the monitoring scene. For example, when monitoring the deformation of the opposite bank of a river, there is no target above the river to estimate the atmospheric phase, making it impossible to obtain every detail. corresponding Therefore, the propagation zone from the receiver to the target is divided into two segments: the propagation zone and the estimation zone. The path from the receiver to the left boundary of the estimation zone is the propagation zone, as illustrated in the diagram below. Figure 1 As shown, the atmospheric error within the propagation zone is considered to be a constant.

[0041] Step 3: Estimating the division of the region

[0042] Specifically:

[0043] A schematic diagram of the estimated region division is shown below. Figure 2 As shown: For each target in the scene, its estimated region is calculated independently.

[0044] Taking any point Q of PS as an example, such as Figure 2 As shown: Centered on the target point, first divide the area to the left and right along the distance direction. The distance, such as Figure 2 As shown by the red line. Then, using the target point as the center, Drawing a circle with a radius means limiting the absolute distance; the corresponding region is as follows: Figure 2 The area shown is a light blue circle. The region formed by this circle and the two arcs is the estimation area, as shown below. Figure 2 As shown in yellow in the middle, by limiting the system's range and the absolute distance between targets, the estimated range for the target point can be obtained.

[0045] In the process of atmospheric compensation for point Q, it is necessary to eliminate the influence of Q itself on the estimation results. Since the phase calculation incorporates imaging results from different satellites, the focusing position of the same target point will deviate at different angles. These points need to be eliminated during the estimation of atmospheric refractive index. Therefore, the concept of a protected area is proposed, assuming point Q as the center and a radius of... The circular area is a protected area, such as Figure 2 As shown in the green circle. In estimating the atmospheric refractive index, points in the green region and their corresponding phases need to be removed.

[0046] Step 4: Estimation of Atmospheric Refractive Index in the Estimation Area

[0047] Specifically:

[0048] In the BeiDou InSAR system, the atmospheric error within the propagation zone is considered to be a constant, and the atmospheric refractive index is constant within the estimation zone at the target point. Within the estimation region, any point The atmospheric phase can be expressed as:

[0049] (6)

[0050] in, express The constant atmospheric phase within the estimation region, express The shortest bibase path difference within the estimated region can be expressed as: . express The atmospheric refractive index within the estimated region is determined using a point set. The data in the middle can be used to achieve... and The estimate.

[0051] (7)

[0052] in, Indicates all The average of the bibase path difference, Indicates all The average atmospheric phase is calculated using points. Since accurate atmospheric phases are not readily available in practice, the phase extracted from PS points is used as a substitute.

[0053] (8)

[0054] Here, Includes deformed phase However, the deformation phase only occurs locally, and the area affected is smaller than the estimation region, therefore it does not affect the parameter estimation results within the estimation region. Even if the deformation area is large, atmospheric parameters can still be estimated through subsequent connectivity determinations. Corrections are made to eliminate the influence of the deformation phase. Therefore, It can be used as an input value for estimating atmospheric errors.

[0055] Step 5: Determining Atmospheric Refractive Index Connectivity

[0056] Specifically:

[0057] In the process of atmospheric refractive index estimation, the deformation phase can affect the estimation results, causing outliers and impacting atmospheric error compensation. Therefore, it is necessary to compensate for these outliers. Here, the median absolute deviation method is used to determine the connectivity of the atmospheric refractive index and correct points that do not meet the connectivity requirements. The median absolute deviation method has advantages such as strong outlier detection capability, simple calculation, and high computational efficiency. It is a simple and elegant outlier detection method, and its main steps can be expressed as follows:

[0058] For the target value Its support area is defined as:

[0059] (9)

[0060] The median is defined as:

[0061] (10)

[0062] The absolute deviation of the median is defined as:

[0063] (11)

[0064] in, A point is considered an outlier if its difference from the median is greater than three times the absolute deviation of the median. Based on this, the atmospheric refractive index can be corrected as follows:

[0065] (12)

[0066] in, This represents the linear fit between the two non-outlier points that are closest to the outlier.

[0067] At this point, regarding Point at The atmospheric error estimation results for the day are as follows:

[0068] (13)

[0069] For all PS points of all satellites in all days, i.e., the point set For each point, its estimation region is calculated, and then atmospheric refractive index estimation and connectivity determination are performed to obtain the atmospheric error estimation results for all points. The final differential phase is the phase caused by deformation.

[0070] (14)

[0071] In this embodiment, a 1200m × 1200m deformation scene is selected, the transmitter is Beidou2IGSO3, and the two PS points are located at [157, 218] and [304, 266], as shown in the figure. Figure 3 The red dots in the diagram indicate the interference phase accuracy of the two demonstration points before compensation. Figure 4 , Figure 5 As shown, the average accuracy of the two PS points is 17.4168 mm and 9.4958 mm. The results after atmospheric error compensation are as follows... Figure 6 , Figure 7 As shown, the precision of the two PS points is 7.5528 mm and 3.0722 mm.

[0072] Table 1 Accuracy Comparison

[0073]

[0074] As can be seen from the results in Table 1, the deformation inversion accuracy after processing by the BeiDou InSAR atmospheric phase error compensation method based on regional division proposed in this paper is improved compared with that before processing, which proves the effectiveness of the present invention.

[0075] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A BeiDou InSAR atmospheric phase error compensation method based on region division, characterized in that, The method includes: Step 1: Obtain the PS point set by combining data from multiple satellites; Step 2, Propagation Zone Delineation; In the BeiDou InSAR system, the atmospheric phase of the target is: ； in, This represents the atmospheric refractive index at the current moment and location. Indicates the difference in distance between two base stations; In the interference phase, atmospheric error is introduced due to changes in the atmospheric refractive index, expressed as: ； In actual data processing, assuming a small range, It is a constant; therefore, it can be represented as an accumulation: ； in Indicates the upward change in distance; In reality, there will be a targetless area between the receiver and the monitoring scene, making it impossible to obtain data for every individual target. corresponding Therefore, the propagation zone from the receiver to the target is divided into two segments: the propagation zone and the estimation zone. The path from the receiver to the left boundary of the estimation zone is the propagation zone, and the atmospheric error within the propagation zone is considered to be a constant. Step 3: Estimation Region Division; For each target in the scene, calculate its estimation region independently; Taking any PS point Q as an example, with the target point as the center, first divide the region to the left and right along the distance direction. The distance, then, with the target point as the center, Draw a circle with a radius, that is, restrict the absolute distance to obtain the estimated range of the target point; In the process of atmospheric compensation for point Q, it is necessary to eliminate the influence of Q itself on the estimation results. Since the phase calculation incorporates imaging results from different satellites, the focusing position of the same target point will deviate at different angles; these points need to be eliminated during atmospheric refractive index estimation. Therefore, the concept of a protected area is proposed, assuming point Q as the center and a radius of... The circular area is a protected area; Step 4: Estimate the atmospheric refractive index within the estimation area; Step 5: Atmospheric Refractive Index Connectivity Determination; During the atmospheric refractive index estimation process, the deformation phase can affect the estimation results, causing outliers and impacting atmospheric error compensation. Therefore, it is necessary to compensate for outliers. Here, the median absolute deviation method is used to determine the connectivity of the atmospheric refractive index, correcting points that do not meet the connectivity requirements. The median absolute deviation method has the advantages of strong outlier detection capability, simple calculation, and high computational efficiency. It is a simple and elegant outlier detection method, and its steps can be expressed as follows: For the target value Its support area is defined as: ； The median value of the refractive index variation in this region is defined as: ； The absolute deviation of the median is defined as: ； in, A point is considered an outlier if the difference between it and the median is greater than three times the absolute deviation of the median. Based on this, the atmospheric refractive index can be corrected as follows: ； in, This represents a linear fit between the two non-outliers that are closest to the outlier. At this point, regarding Point at The atmospheric error estimation results for the day are as follows: ； For all PS points of all satellites in all days, i.e., the point set For each point, its estimated region is calculated, and then atmospheric refractive index estimation and connectivity determination are performed to achieve atmospheric error compensation for all points.

2. The method as described in claim 1, characterized in that, In step one, for K satellites The corresponding PS point selection result is The point set used for atmospheric phase compensation is: ； Calculate the bistatic distance difference for each point on each day, based on their respective system configurations: 。 3. The method as described in claim 2, characterized in that, In step four, the BeiDou InSAR system assumes that the atmospheric error within the propagation zone is a constant, the atmospheric refractive index is constant within the estimation zone, and the target point... Within the estimation region, any point Atmospheric phase ； in, express The constant atmospheric phase within the estimation region, express The shortest bibase path difference within the estimated area, ; express The atmospheric refractive index within the estimated region; using point sets The data in the middle can enable the following: and The estimate; ； in, Indicates all The average of the bibase path difference, Indicates all The average atmospheric phase is calculated using points; since accurate atmospheric phase cannot be obtained in practice, the phase extracted from PS points is used instead. ； Here, It includes a deformation phase; however, the deformation phase only occurs locally, and the area where it occurs is smaller than the estimation region, so it will not affect the parameter estimation results within the estimation region; even if the deformation area is large, the atmospheric parameters can still be estimated through subsequent connectivity determination. Corrections are made to eliminate the influence of the deformation phase; therefore... It can be used as an input value for estimating atmospheric errors.

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