CN112050725A - Surface deformation monitoring method fusing InSAR and GPS - Google Patents
Surface deformation monitoring method fusing InSAR and GPS Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/16—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/004—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring coordinates of points
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/86—Combinations of radar systems with non-radar systems, e.g. sonar, direction finder
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/9021—SAR image post-processing techniques
- G01S13/9023—SAR image post-processing techniques combined with interferometric techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/9094—Theoretical aspects
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- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/14—Receivers specially adapted for specific applications
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- G—PHYSICS
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
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Abstract
The invention relates to a surface deformation monitoring technology based on mutual fusion of InSAR and GPS. The method comprises the following steps: arranging GPS characteristic points and monitoring points; collecting SAR images and GPS signals of corresponding time; resolving three-dimensional coordinate information of the GPS points; speckle noise suppression of the SAR image; searching SAR image characteristic points and calculating the conversion relation between the SAR image characteristic points and GPS characteristic points; track error correction of the SAR satellite; forming an InSAR differential interference pattern; inversion and correction of atmospheric delay; phase unwrapping of the differential interferogram; the unwrapping phase is converted into deformation information; geocoding; and fusing deformation information of the InSAR and the GPS to obtain a deformation monitoring result. The method disclosed by the invention utilizes the mutual combination of InSAR and GPS technologies, breaks through the traditional single monitoring technology, and makes full use of the advantages of the two technologies to make up each other, so that the accuracy of the deformation data is more accurate and reliable.
Description
Technical Field
The invention relates to a global positioning system and a synthetic aperture radar interferometry technique. In particular to a mode for improving insufficient monitoring information when the InSAR technology is used for monitoring surface deformation.
Background
The high time resolution and high precision earth surface three-dimensional monitoring is the advantage of the GPS technology, which can obtain high precision three-dimensional deformation information, however, the monitoring of the GPS technology is limited by the environment and cost, and the monitoring result is usually limited in spatial resolution and sparsely distributed, so the GPS technology can be ideally completed for small-range earth surface deformation monitoring, and for large-range monitoring, a large number of points need to be laid, which is not economically feasible.
The InSAR is an important space-to-ground monitoring technology at present, has all-weather all-day-long working capacity, and cannot be influenced by day and night and cloud layers, and meanwhile, the InSAR has the advantages of large coverage, convenience, rapidness, low cost and high spatial resolution, but is influenced by atmospheric delay, satellite orbit errors, surface coverage change and the like. The purpose of monitoring the ground surface deformation is to achieve a preventive effect, and in the InSAR technology, the problem of blurred vision direction exists, so the obtained result is one-dimensional deformation information of the vision direction, and in our life, many catastrophic deformations which occur in two-dimensional and three-dimensional are required to be monitored and prevented.
Disclosure of Invention
Combining the advantages and disadvantages of the two technologies, the invention solves the problems that: (1) correcting the orbit error of the InSAR technology by using GPS data; (2) correcting the atmospheric delay error of the InSAR technology by using GPS data; (3) correcting InSAR interference data by using a GPS; (4) InSAR and GPS fusion method.
(1) Track error of InSAR technology corrected by GPS data
In InSAR data processing, satellite orbit data affects important steps such as image registration and geocoding, so the accuracy of orbit data determines the accuracy of the result. In order to obtain high-precision orbit information, the invention utilizes InSAR visual line displacement to compare with GPS monitoring data, simulates an orbit error correction model and removes satellite orbit errors.
(2) Atmospheric delay error of InSAR technology corrected by GPS data
Deformation information can be obtained by carrying out differential processing on the interferogram, and the obtained deformation information can cause data errors due to relative atmospheric delay between two pixels on the SAR image and between the two SAR images. In order to eliminate such errors, the solution can be made by using the property of phase difference, and the difference of a certain fixed image element on the image reflects the phase difference and the surface deformation. Firstly, a random interpolation model is used for obtaining the estimation of a GPS troposphere, then an atmospheric delay error can be obtained through a double difference algorithm between time domains and stations, and an atmospheric delay error interpolation is obtained through an improved distance inverse ratio weighting interpolation method, so that the atmospheric delay error of InSAR data is removed.
(3) Correcting InSAR interferometric data using GPS
Nbc the unwrapping algorithm is a local unwrapping algorithm, the unwrapping precision is high, but the residual error points cannot be unwrapped; the Gud unwrapping algorithm is a global unwrapping algorithm, and unwrapping can be performed on each pixel, but unwrapping errors are propagated globally, so that unwrapping accuracy is low. In order to improve the unwrapping precision and the unwrapping range, the GPS characteristic point auxiliary InSAR phase unwrapping is carried out by combining Nbc unwrapping algorithm and Gud unwrapping algorithm.
(4) InSAR and GPS fusion method
Because the precision of the deformation field respectively established by the function model constraint and the random model constraint is not as high as that of the deformation field established by the dual-model constraint, the method adopts a mode of fusing InSAR and GPS data of the dual-constraint of the function model and the random model to establish the three-dimensional deformation field.
In order to solve the problems, the invention adopts the following technical scheme: an earth surface deformation monitoring method fusing an InSAR and a GPS is characterized by comprising the following steps:
step one, laying GPS characteristic points and monitoring points;
step two, collecting SAR images and GPS signals of corresponding time periods;
step three, resolving three-dimensional coordinate information of the GPS points;
step four, speckle noise suppression of the SAR image;
searching the SAR image feature points and calculating the conversion relation between the SAR image feature points and the GPS feature points;
sixthly, correcting the orbit error of the SAR satellite;
step seven, forming an InSAR differential interference pattern;
step eight, inverting and correcting atmospheric delay;
step nine, phase unwrapping of the differential interference pattern;
step ten, converting the unwrapping phase into deformation information;
step eleven, geocoding;
and step twelve, fusing deformation information of the InSAR and the GPS to obtain a deformation monitoring result.
Furthermore, in the first step, two types of GPS points are required to be distributed, and the two types of GPS points are divided into feature points and monitoring points; the characteristic points are used for unifying InSAR and GPS data to the same reference coordinate system and correcting a series of errors, so that the selected points have the characteristic of stability in a monitoring area; and the monitoring points are used for acquiring deformation information of the monitoring area.
Further, in the second step, in order to correct a series of errors of the InSAR data by using the GPS, a time period corresponding to the acquired GPS satellite signal needs to be synchronized with a time period of the SAR image.
Further, in the third step, the three-dimensional coordinate information of the distributed GPS characteristic points and the monitoring points is calculated according to the collected GPS satellite signals. Wherein the feature points require position information and elevation information; the monitoring points require position information and deformation information.
Furthermore, in the fourth step, in order to ensure the reliability of the result and need to suppress the speckle noise of the SAR image, the invention adopts wavelet transformation and fuzzy clustering to suppress the speckle noise of the image. The method mainly comprises the steps of firstly carrying out wavelet transform decomposition on an SAR image, dividing decomposed coefficients into two categories by utilizing fuzzy C-means clustering, wherein the first category is energy only containing speckle noise, the second category is energy containing signal energy, the first category is directly subjected to zero setting, and the second category is subjected to noise reduction, so that the purpose of inhibition is achieved.
Further, in the fifth step, according to the distributed GPS characteristic points, points corresponding to the GPS characteristic points on the SAR image are found, and a coordinate conversion relation between the points is established. At least three characteristic points are needed for achieving the purpose of coordinate conversion, and if the number of the characteristic points is more than three, the adjustment can be carried out by using a least square method.
Further, in the sixth step, the monitoring data of the GPS characteristic points and the sight direction data of the InSAR are used for comparative analysis, and a track error correction model is established, so that the track error in the InSAR data is removed. The specific operation is as follows:
converting the three-dimensional displacement of the GPS into the view direction of the InSAR by utilizing a coordinate conversion relation:
wherein d isGPSThe displacement of the GPS three-dimensional displacement in the sight line direction after coordinate conversion; n, E, U are components of the GPS three-dimensional displacement in the north-south, east-west and vertical directions respectively; a ishIs the flight direction of the flight platform; θ is the side view of the flight platform.
Assuming that n GPS feature points are distributed, the pixel positions of the n feature points in the image can be obtained through a coordinate conversion formula, which is denoted as I. Then the track error (d) of pixel iorbit(i) ) is:
dorbit(i)=dInSAR(i)-dGPS(i) (2)
the error of fitting the orbit by the quadric surface model is as follows:
where v is a correction number containing atmospheric delay, terrain error, etc.; the position of a pixel in the image is represented by (i, j); and a is0、a1、a2、a3、a4、a5Are parameters of the fitted model.
Can be expressed in the form of a matrix:
V=AX-l (6)
the weight matrix P can be expressed as:wherein gamma is the coherence value of the pixel, and satisfies that gamma is more than 0 and less than 1, and the larger gamma is, the larger the weight is; suppose σ0Is an error in the unit weight, thenPi=γi。
Solving the least square solution as:
X=(ATPA)-1APl (7)
the error estimate in the unit weight is:
and the allowable error is three times of the error in the unit weight, the value exceeding the allowable error is removed, and the removed value is iterated to obtain the final result, namely the pixel track error, so that the track error of the monitored area is obtained. Thus correcting InSAR data d after orbit errorcorrectionComprises the following steps:
dcorrection=dInSAR-dorbit (9)
further, in a seventh step, interference flow processing is performed on the SAR image data obtained after the sixth step is completed, so as to obtain an interferogram.
Further, in step eight, deformation information may be obtained by performing difference processing on the interferogram in the previous step, and the obtained deformation information may cause an error of data due to relative atmospheric delay between two pixels on the SAR image and between two SAR images. In order to eliminate such errors, the solution can be made by using the property of phase difference, and the difference of a certain fixed image element on the image reflects the phase difference and the surface deformation. Firstly, a random interpolation model is used for obtaining estimation of a GPS troposphere, and then an atmospheric delay error can be obtained through a double difference algorithm between time domains and stations. After the atmospheric delay error is obtained, the atmospheric delay needs to be corrected. The distributed GPS characteristic points are utilized, an inverse distance ratio weighting interpolation method is adopted, and because the correlation between the atmospheric delay and the elevation is strong, the atmospheric delay correction is reversed by adopting an improved inverse distance ratio weighting interpolation method, and the atmospheric delay is estimated; and correcting atmospheric delay correction of the InSAR differential interferogram using the estimated atmospheric delay. The specific operation is as follows:
obtaining an inverse distance weighted interpolation formula of the atmospheric delay from GPS observation data:
wherein the coordinate is eastNorth ChinaInterpolated atmospheric delay of points ofCoordinate is eastNorth ChinaGPS delay correction of points toWhereinRepresenting weights associated with delays of GPS acquisition. N represents the number of GPS points in the vicinity of the interpolated predicted point.
The weight of the inverse distance weighted interpolation method is:
wherein the distance from the characteristic point i to the point to be interpolated isModified inverse distance weighted interpolation:
the above principle makes the image proportion of horizontal distance and elevation interpolation identical, however, in practice, the proportion of the two is different, so an influence proportion is added:
the horizontal distance of a data point to a point to be interpolated is represented as:the elevation difference from the data point to the point to be interpolated is expressed as:thus, the improved inverse distance weighted interpolation method after improvement is:
further, in step nine, there are many ways to correct InSAR phase unwrapping using the GPS control point. Nbc the unwrapping algorithm is a local unwrapping algorithm, the unwrapping precision is high, but the residual error points cannot be unwrapped; the Gud unwrapping algorithm is a global unwrapping algorithm, and unwrapping can be performed on each pixel, but unwrapping errors are propagated globally, so that unwrapping accuracy is low. In order to improve the unwrapping precision and the unwrapping range, the GPS characteristic point auxiliary InSAR phase unwrapping is carried out by combining the Nbc unwrapping algorithm and the Gud unwrapping algorithm, and the method specifically comprises the following operations:
(1) firstly, phase unwrapping is carried out through an Nbc unwrapping algorithm, and initial values of the whole-cycle unknowns of the island pixels with the non-residual error points and the GPS characteristic points can be obtained.
(2) And removing decimal place of the initial value obtained in the last step to obtain an integer, and taking the integer as the starting value of Gub unwrapping algorithm to correct the unknown number of the whole week. And obtaining the unwrapping values of the non-residual points and the island pixels with the GPS characteristic points.
(3) And interpolating the winding result obtained in the last step, and supplementing residual points and unwrapping values of island pixels without GPS characteristic points.
(4) Marking the non-residual points with the final unwrapping values and the island pixels with the GPS characteristic points obtained in the second step as fixed domains, and marking the residual points with the initial wrapping values and the island pixels without the GPS characteristic points obtained in the third step as non-fixed domains. The winding values from the second and third steps are combined and taken as a starting value to Gub for phase unwrapping in the unwrapping algorithm. Thus yielding our final unwrapped value.
Further, in step ten, the phase of unwrapping in step nine is converted into intuitive deformation information. The specific operation is as follows:
wherein Δ RdFor the amount of deformation of the line of sight, phidFor unwrapping phase, λ is the radar wavelength.
Further, in the eleventh step, the deformation result in the SAR coordinate system is projected to the direction of the experimental setup, so as to obtain the deformation amount in the sight line direction. The specific operation is as follows:
distance equation:
doppler equation:
an earth model equation:
wherein R represents SAR satellite sensor and groundThe distance between the points; s represents the satellite sensor t represents a ground point;andrespectively representing the position vectors of the SAR satellite and the ground point;represents a doppler shift;representing the satellite velocity vector,Representing a ground speed vector;representing ground point location vectorsProjections on the x, y, z axes; a is the earth major semi-axis, b is the earth minor semi-axis, and h is the average normal height.
Further, in the twelfth step, a three-dimensional deformation field is established in a mode that a function model is fused with random model double-constrained InSAR and GPS data. The specific operation is as follows:
the amount of line-of-sight displacement of the synthetic aperture radar at a certain point P is denoted as LInSARAccording to the space position relation of InSAR technology imaging, the following observation equation can be obtained:
wherein, VInSARRepresents an observed value residual error; a. theInSAR=[Sx Sy Sz]Is a design matrix; for three-dimensional displacement of point PAnd (4) showing. And solving the three-dimensional deformation at the point P by using three or more than three line-of-sight observed values in the SAR interference pair.
Under the principle, the invention utilizes the GPS observation point as prior information to construct random model constraint. Recording the three-dimensional deformation monitoring value of the GPS characteristic point asWill be provided withAs a pseudo-observation vector, the pseudo-observation vector isCovariance matrix ofNote the bookIs a full matrix ofThe error equation for the additional stochastic model constraint is then:
wherein the content of the first and second substances, in the formula (I), the compound is shown in the specification,and representing the weight array corresponding to the observation value of the radar in the sight line direction.
In the InSAR technology, displacement information in the north-south direction is difficult to collect in the line of sight due to the influence of the flight mode of the flight platform. In order to make up for the defect, the invention utilizes the high-precision GPS characteristic point monitoring result to supplement the displacement information in the north-south direction. The error equation for the following additional functional model constraints can be listed:
where C is the coefficient matrix of the constraint equation and W is a constant term. The basic idea of least squares can be found:
In summary, the following error equation can be obtained by combining the stochastic model and the functional model dual constraint:
the basic idea of using least squares is:
wherein the content of the first and second substances,
in summary, there are:
through the analysis, the random model and the function model are more accurate than a single model by using double constraints. According to the basic principle, the three-dimensional deformation of the earth surface is further solved.
Drawings
FIG. 1: data processing flow diagram of the invention
FIG. 2: flow chart for correcting track error of InSAR data by using GPS monitoring point data
FIG. 3: schematic diagram for correcting atmospheric delay error by utilizing GPS (global positioning system) to invert atmospheric delay
FIG. 4: graph of cause of unwinding island formation
FIG. 5: GPS-assisted InSAR phase unwrapping flow chart
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
Example 1
As shown in fig. 1-5, the present invention adopts the following technical solutions: an earth surface deformation monitoring method fusing an InSAR and a GPS is characterized by comprising the following steps:
step one, laying GPS characteristic points and monitoring points;
step two, collecting SAR images and GPS signals of corresponding time periods;
step three, resolving three-dimensional coordinate information of the GPS points;
step four, speckle noise suppression of the SAR image;
searching the SAR image feature points and calculating the conversion relation between the SAR image feature points and the GPS feature points;
sixthly, correcting the orbit error of the SAR satellite;
step seven, forming an InSAR differential interference pattern;
step eight, inverting and correcting atmospheric delay;
step nine, phase unwrapping of the differential interference pattern;
step ten, converting the unwrapping phase into deformation information;
step eleven, geocoding;
and step twelve, fusing deformation information of the InSAR and the GPS to obtain a deformation monitoring result.
Furthermore, in the first step, two types of GPS points are required to be distributed, and the two types of GPS points are divided into feature points and monitoring points; the characteristic points are used for unifying InSAR and GPS data to the same reference coordinate system and correcting a series of errors, so that the selected points have the characteristic of stability in a monitoring area; and the monitoring points are used for acquiring deformation information of the monitoring area.
Further, in the second step, in order to correct a series of errors of the InSAR data by using the GPS, a time period corresponding to the acquired GPS satellite signal needs to be synchronized with a time period of the SAR image.
Further, in the third step, the three-dimensional coordinate information of the distributed GPS characteristic points and the monitoring points is calculated according to the collected GPS satellite signals. Wherein the feature points require position information and elevation information; the monitoring points require position information and deformation information.
Furthermore, in the fourth step, in order to ensure the reliability of the result and need to suppress the speckle noise of the SAR image, the invention adopts wavelet transformation and fuzzy clustering to suppress the speckle noise of the image. The method mainly comprises the steps of firstly carrying out wavelet transform decomposition on an SAR image, dividing decomposed coefficients into two categories by utilizing fuzzy C-means clustering, wherein the first category is energy only containing speckle noise, the second category is energy containing signal energy, the first category is directly subjected to zero setting, and the second category is subjected to noise reduction, so that the purpose of inhibition is achieved.
Further, in the fifth step, according to the distributed GPS characteristic points, points corresponding to the GPS characteristic points on the SAR image are found, and a coordinate conversion relation between the points is established. At least three characteristic points are needed for achieving the purpose of coordinate conversion, and if the number of the characteristic points is more than three, the adjustment can be carried out by using a least square method.
Further, in the sixth step, the monitoring data of the GPS characteristic points and the sight direction data of the InSAR are used for comparative analysis, and a track error correction model is established, so that the track error in the InSAR data is removed. The specific operation is as follows:
converting the three-dimensional displacement of the GPS into the view direction of the InSAR by utilizing a coordinate conversion relation:
wherein d isGPSThe displacement of the GPS three-dimensional displacement in the sight line direction after coordinate conversion; n, E, U are components of the GPS three-dimensional displacement in the north-south, east-west and vertical directions respectively; a ishIs the flight direction of the flight platform; θ is the side view of the flight platform.
Assuming that n GPS feature points are distributed, the pixel positions of the n feature points in the image can be obtained through a coordinate conversion formula, which is denoted as I. Then the track error (d) of pixel iorbit(i) ) is:
dorbit(i)=dInSAR(i)-dGPS(i) (2)
the error of fitting the orbit by the quadric surface model is as follows:
wherein v is a group containingCorrection numbers of atmospheric delay, terrain error, and the like; the position of a pixel in the image is represented by (i, j); and a is0、a1、a2、a3、a4、a5Are parameters of the fitted model.
Can be expressed in the form of a matrix:
V=AX-l (6)
wherein gamma is the coherence value of the pixel, and satisfies that gamma is more than 0 and less than 1, and the larger gamma is, the larger the weight is; suppose σ0Is an error in the unit weight, thenPi=γi。
Solving the least square solution as:
X=(ATPA)-1APl (7)
the error estimate in the unit weight is:
the tolerance error is three times of the error in the unit weight, the value exceeding the tolerance error is eliminated, and the eliminated value is iterated to obtain the final result, i.e. the pixel trackAnd error, thereby obtaining the track error of the monitoring area. Thus correcting InSAR data d after orbit errorcorrectionComprises the following steps:
dcorrection=dInSAR-dorbit (9)
further, in a seventh step, interference flow processing is performed on the SAR image data obtained after the sixth step is completed, so as to obtain an interferogram.
Further, in step eight, deformation information may be obtained by performing difference processing on the interferogram in the previous step, and the obtained deformation information may cause an error of data due to relative atmospheric delay between two pixels on the SAR image and between two SAR images. In order to eliminate such errors, the solution can be made by using the property of phase difference, and the difference of a certain fixed image element on the image reflects the phase difference and the surface deformation. Firstly, a random interpolation model is used for obtaining estimation of a GPS troposphere, and then an atmospheric delay error can be obtained through a double difference algorithm between time domains and stations. After the atmospheric delay error is obtained, the atmospheric delay needs to be corrected. The distributed GPS characteristic points are utilized, an inverse distance ratio weighting interpolation method is adopted, and because the correlation between the atmospheric delay and the elevation is strong, the atmospheric delay correction is reversed by adopting an improved inverse distance ratio weighting interpolation method, and the atmospheric delay is estimated; and correcting atmospheric delay correction of the InSAR differential interferogram using the estimated atmospheric delay. The specific operation is as follows:
obtaining an inverse distance weighted interpolation formula of the atmospheric delay from GPS observation data:
wherein the coordinate is eastNorth ChinaInterpolated atmospheric delay of points ofCoordinate is eastNorth ChinaGPS delay correction of points toWhereinRepresenting weights associated with delays of GPS acquisition. N represents the number of GPS points in the vicinity of the interpolated predicted point.
The weight of the inverse distance weighted interpolation method is:
wherein the distance from the characteristic point i to the point to be interpolated isModified inverse distance weighted interpolation:
the above principle makes the image proportion of horizontal distance and elevation interpolation identical, however, in practice, the proportion of the two is different, so an influence proportion is added:
thus, the improved inverse distance weighted interpolation method after improvement is:
further, in step nine, there are many ways to correct InSAR phase unwrapping using the GPS control point. Nbc the unwrapping algorithm is a local unwrapping algorithm, the unwrapping precision is high, but the residual error points cannot be unwrapped; the Gud unwrapping algorithm is a global unwrapping algorithm, and unwrapping can be performed on each pixel, but unwrapping errors are propagated globally, so that unwrapping accuracy is low. In order to improve the unwrapping precision and the unwrapping range, the GPS characteristic point auxiliary InSAR phase unwrapping is carried out by combining the Nbc unwrapping algorithm and the Gud unwrapping algorithm, and the method specifically comprises the following operations:
(1) firstly, phase unwrapping is carried out through an Nbc unwrapping algorithm, and initial values of the whole-cycle unknowns of the island pixels with the non-residual error points and the GPS characteristic points can be obtained.
(2) And removing decimal place of the initial value obtained in the last step to obtain an integer, and taking the integer as the starting value of Gub unwrapping algorithm to correct the unknown number of the whole week. And obtaining the unwrapping values of the non-residual points and the island pixels with the GPS characteristic points.
(3) And interpolating the winding result obtained in the last step, and supplementing residual points and unwrapping values of island pixels without GPS characteristic points.
(4) Marking the non-residual points with the final unwrapping values and the island pixels with the GPS characteristic points obtained in the second step as fixed domains, and marking the residual points with the initial wrapping values and the island pixels without the GPS characteristic points obtained in the third step as non-fixed domains. The winding values from the second and third steps are combined and taken as a starting value to Gub for phase unwrapping in the unwrapping algorithm. Thus yielding our final unwrapped value.
Further, in step ten, the phase of unwrapping in step nine is converted into intuitive deformation information. The specific operation is as follows:
wherein Δ RdFor the amount of deformation of the line of sight, phidFor unwrapping phase, λ is the radar wavelength.
Further, in the eleventh step, the deformation result in the SAR coordinate system is projected to the direction of the experimental setup, so as to obtain the deformation amount in the sight line direction. The specific operation is as follows:
distance equation:
doppler equation:
an earth model equation:
wherein R represents the distance between the SAR satellite sensor and a ground point; s represents the satellite sensor t represents a ground point;andrespectively representing the position vectors of the SAR satellite and the ground point;represents a doppler shift;representing the satellite velocity vector,Representing a ground speed vector;representing ground point location vectorsProjections on the x, y, z axes; a is the earth major semi-axis, b is the earth minor semi-axis, and h is the average normal height.
Further, in the twelfth step, a three-dimensional deformation field is established in a mode that a function model is fused with random model double-constrained InSAR and GPS data. The specific operation is as follows:
the amount of line-of-sight displacement of the synthetic aperture radar at a certain point P is denoted as LInSARAccording to the space position relation of InSAR technology imaging, the following observation equation can be obtained:
wherein, VInSARRepresents an observed value residual error; a. theInSAR=[Sx Sy Sz]Is a design matrix; for three-dimensional displacement of point PAnd (4) showing. To solve the three-dimensional deformation at point P is advantageousAnd solving the sight direction observation value in three or more SAR interference pairs.
Under the principle, the invention utilizes the GPS observation point as prior information to construct random model constraint. Recording the three-dimensional deformation monitoring value of the GPS characteristic point asWill be provided withAs a pseudo-observation vector, the pseudo-observation vector isCovariance matrix ofNote the bookIs a full matrix ofThe error equation for the additional stochastic model constraint is then:
wherein the content of the first and second substances, in the formula (I), the compound is shown in the specification,and representing the weight array corresponding to the observation value of the radar in the sight line direction.
In the InSAR technology, displacement information in the north-south direction is difficult to collect in the line of sight due to the influence of the flight mode of the flight platform. In order to make up for the defect, the invention utilizes the high-precision GPS characteristic point monitoring result to supplement the displacement information in the north-south direction. The error equation for the following additional functional model constraints can be listed:
where C is the coefficient matrix of the constraint equation and W is a constant term. The basic idea of least squares can be found:
In summary, the following error equation can be obtained by combining the stochastic model and the functional model dual constraint:
the basic idea of using least squares is:
wherein the content of the first and second substances,
in summary, there are:
example data
The InSAR sight line deformation and GPS point three-dimensional deformation data are shown in the following table 1:
TABLE 1
Algorithm scheme
For the simulation example, three schemes are adopted to carry out fusion of GPS and InSAR data to calculate the three-dimensional deformation.
According to the first scheme, a GPS monitoring value is used as a prior condition, an InSAR observation value is used as an observed quantity, and the GPS and InSAR data fusion is restrained by establishing a random model.
And secondly, establishing a function model to restrain the data fusion of the GPS and the InSAR by taking the observed value in the south-north direction of the GPS as a constraint condition
And thirdly, establishing a function model and a random model to perform double-constrained GPS and InSAR data fusion by taking the GPS monitoring value as a prior condition and the observation value in the north-south direction of the GPS as a constraint condition.
Algorithmic comparison
In the case of only InSAR data, the accuracy of the monitor values is estimated from the simulated InSAR data using a 5 x 5 square matrix, which is called direct decomposition. Under the condition of adding GPS data for fusion, the root mean square error of the three-dimensional deformation field established by the three schemes is obtained by using the basic principle of the step twelve, and the result is shown in the following table 2:
TABLE 2
It can be seen from the above data that the precision of the direct solution algorithm, the function model constraint, the random model constraint and the dual model constraint are consistent in the N direction. In the direction E, the accuracy of the function model constraint is lower than that of the direct method, because the accuracy of the direction E is greatly reduced by forcibly fixing the direction N under the algorithm. It can be seen from the table that the accuracy of the bi-model constraints, both in the whole and in all directions, is higher than that of the single model constraints and the direct solution. Under the double-model constraint, the precision of the E direction is improved by 18% compared with that of the direct InSAR solution, although the precision of the double-model constraint in the U direction is not greatly improved.
The method combines the advantages of InSAR and GPS technologies, breaks through the limitation of the traditional single surface deformation monitoring technology, and greatly improves the precision in the elevation direction.
Claims (9)
1. An earth surface deformation monitoring method fusing an InSAR and a GPS is characterized by comprising the following steps:
step one, laying GPS characteristic points and monitoring points;
step two, collecting SAR images and GPS signals of corresponding time periods;
step three, resolving three-dimensional coordinate information of the GPS points;
step four, speckle noise suppression of the SAR image;
searching the SAR image feature points and calculating the conversion relation between the SAR image feature points and the GPS feature points;
sixthly, correcting the orbit error of the SAR satellite;
step seven, forming an InSAR differential interference pattern;
step eight, inverting and correcting atmospheric delay;
step nine, phase unwrapping of the differential interference pattern;
step ten, converting the unwrapping phase into deformation information;
step eleven, geocoding;
and step twelve, fusing deformation information of the InSAR and the GPS to obtain a deformation monitoring result.
2. The earth surface deformation monitoring method fusing InSAR and GPS according to claim 1, characterized in that: in the step one, the characteristic points are used for unifying InSAR and GPS data to the same reference coordinate system and correcting a series of errors, so that the selected points have the characteristic of stability in a monitoring area; and the monitoring points are used for acquiring deformation information of the monitoring area.
3. The earth surface deformation monitoring method fusing InSAR and GPS according to claim 1, characterized in that: in the fourth step, in order to ensure the reliability of the result, the speckle noise of the SAR image needs to be suppressed, and the invention adopts wavelet transformation and fuzzy clustering to suppress the speckle noise of the image.
4. The earth surface deformation monitoring method fusing InSAR and GPS according to claim 1, characterized in that: and in the fifth step, according to the distributed GPS characteristic points, finding out points corresponding to the points on the SAR image, and establishing a conversion relation between the points.
5. The earth surface deformation monitoring method fusing InSAR and GPS according to claim 1, characterized in that: and in the sixth step, the monitoring data of the GPS characteristic points and the sight direction data of the InSAR are used for comparative analysis, and a track error correction model is established, so that the track error in the InSAR data is removed.
6. The earth surface deformation monitoring method fusing InSAR and GPS according to claim 1, characterized in that: in step eight, the estimation of the troposphere of the GPS is firstly obtained by using a random interpolation model, and then the atmospheric delay error is calculated by using the double difference between the sites and the time domain.
After the atmospheric delay error is obtained, the atmospheric delay needs to be corrected. The distributed GPS characteristic points are utilized, an inverse distance ratio weighted interpolation method is adopted, and because the correlation between the atmospheric delay and the elevation is strong, the atmospheric delay correction is reversed by adopting the improved inverse distance ratio weighted interpolation method, and the atmospheric delay is estimated; and correcting atmospheric delay correction of the InSAR differential interferogram using the estimated atmospheric delay. The specific operation is as follows:
obtaining an inverse distance weighted interpolation formula of the atmospheric delay from GPS observation data:
wherein the coordinate is eastNorth ChinaInterpolated atmospheric delay of points ofCoordinate is eastNorth ChinaGPS delay correction of points toWhereinRepresenting weights associated with delays of GPS acquisition. N represents the number of GPS points in the vicinity of the interpolated predicted point.
The weight of the inverse distance weighted interpolation method is:
Modified inverse distance weighted interpolation:
the above principle makes the image proportion of horizontal distance and elevation interpolation identical, however, in practice, the proportion of the two is different, so an influence proportion is added:
thus, the improved inverse distance weighted interpolation method after improvement is:
7. the earth surface deformation monitoring method fusing InSAR and GPS according to claim 1, characterized in that: in step nine, the GPS characteristic point auxiliary InSAR phase unwrapping is carried out by combining Nbc unwrapping algorithm and Gud unwrapping algorithm.
8. The earth surface deformation monitoring method fusing InSAR and GPS according to claim 1, characterized in that: in the eleventh step, the deformation result under the SAR coordinate system is projected to the direction set by the experiment to obtain the deformation amount in the sight line direction. The specific operation is as follows:
distance equation:
doppler equation:
an earth model equation:
wherein R represents the distance between the SAR satellite sensor and a ground point; s stands for satelliteSensor t represents a ground point;andrespectively representing the position vectors of the SAR satellite and the ground point;represents a doppler shift;representing the satellite velocity vector,Representing a ground speed vector;representing ground point location vectorsProjections on the x, y, z axes; a is the earth major semi-axis, b is the earth minor semi-axis, and h is the average normal height.
9. The earth surface deformation monitoring method fusing InSAR and GPS according to claim 1, characterized in that: in the step twelve, the precision of the three-dimensional deformation field established by adopting a mode of fusing the InSAR and GPS data of double constraints of the function model and the random model is higher than that of the deformation field established by single constraints of the function model and the random model. The specific operation is as follows:
the amount of line-of-sight displacement of the synthetic aperture radar at a certain point P is denoted as LInSARAccording to the space position relation of InSAR technology imaging, the following observation equation can be obtained:
wherein, VInSARRepresents an observed value residual error; a. theInSAR=[Sx Sy Sz]Is a design matrix; for three-dimensional displacement of point PAnd (4) showing. And solving the three-dimensional deformation at the point P by using three or more than three line-of-sight observed values in the SAR interference pair.
Under the principle, the invention utilizes the GPS observation point as prior information to construct random model constraint. Recording the three-dimensional deformation monitoring value of the GPS characteristic point asWill be provided withAs a pseudo-observation vector, the pseudo-observation vector isCovariance matrix ofNote the bookIs a full matrix ofThe error equation for the additional stochastic model constraint is then:
from the least squares it can be known that:
wherein the content of the first and second substances,in the formula (I), the compound is shown in the specification,and representing the weight array corresponding to the observation value of the radar in the sight line direction.
In the InSAR technology, displacement information in the north-south direction is difficult to collect in the line of sight due to the influence of the flight mode of the flight platform. In order to make up for the defect, the invention utilizes the high-precision GPS characteristic point monitoring result to supplement the displacement information in the north-south direction. The error equation for the following additional functional model constraints can be listed:
where C is the coefficient matrix of the constraint equation and W is a constant term. The basic idea of least squares can be found:
the co-factor matrix of (c) is:
In summary, the following error equation can be obtained by combining the stochastic model and the functional model dual constraint:
the basic idea of using least squares is:
wherein the content of the first and second substances,
in summary, there are:
through the analysis, the random model and the function model are more accurate than a single model by using double constraints. According to the basic principle, the three-dimensional deformation of the earth surface is further solved.
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