CN118091566B - Automatic extraction and application method for interference SAR external calibration signal - Google Patents
Automatic extraction and application method for interference SAR external calibration signal Download PDFInfo
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Abstract
The invention provides an automatic extraction and application method of an interference SAR external calibration signal, which relates to the field of InSAR calibration and comprises the following steps: step 1, calculating sub-pixel image coordinates of a scaler based on imaging geometry and an up-sampling technology; step 2, estimating a slope distance error based on the error of the actual slope distance and the imaging slope distance of the scaler; the offset phase is estimated based on the sealer unwrapped phase. The invention provides an interference phase and skew calibration method based on external control point positioning information, which can be used as a general data product processing method.
Description
Technical Field
The invention belongs to the field of InSAR interference calibration, and particularly relates to an automatic extraction and application method of an interference SAR external calibration signal.
Background
In the face of increasingly heavy InSAR image scaling tasks, automatic acquisition of external scaling signals and estimation of scaling parameters are important requirements for interference scaling tasks. The reconstruction accuracy of a Digital Elevation Model (DEM) is affected by the accuracy of the bistatic SAR baseline, the standoff, and the interference phase, and in essence by the accuracy of the interference geometry. The satellite state vector changing along with SAR image imaging time can be calculated by inputting the time, position and speed information of the satellite into a high-precision orbit perturbation model. On the basis, the high-precision DEM reconstruction can be realized by only acquiring high-precision interference phase information and imaging geometry. However, errors introduced by the SAR system cannot be completely compensated through internal calibration, so that accurate compensation of the skew and the noise phase is realized by means of an external control point, namely a manually arranged scaler, and the reconstruction accuracy of the DEM is further improved.
Disclosure of Invention
In order to solve the technical problems, the invention provides an automatic extraction and application method of an interference SAR external calibration signal, which comprises the steps of calculating the sub-pixel image coordinates of a calibrator based on imaging geometry and an up-sampling technology, estimating a pitch error based on the error of the actual pitch of the calibrator and the imaging pitch, and estimating an offset phase based on the unwrapped phase of the calibrator.
In order to achieve the above purpose, the invention adopts the following technical scheme:
An automatic extraction and application method of an interference SAR external calibration signal comprises the following steps:
Step 1, calculating sub-pixel image coordinates of a scaler based on imaging geometry and an up-sampling method, wherein the calculating comprises calculating azimuth coordinates and calculating distance coordinates;
step 2, estimating a pitch error based on the error of the actual pitch of the scaler and the imaging pitch, and estimating an absolute offset phase based on the scaler unwrapping phase;
the estimating of the absolute offset phase includes:
taking the mean of the absolute interference phases of a plurality of scalers minus the unwrapping phase as the absolute offset phase Is the estimated value of (1), namely:
（11）
the superscript N denotes the sealer sequence number, N denotes the sealer total, Representing the absolute interference phase of the primary and secondary images of the nth scaler,Indicating the unwrapped phase of the nth sealer;
The estimation of the skew error includes:
Based on the scaler and the pitch of the radar sensor, acquiring the actual pitch of the range gate where the scaler and the radar sensor are positioned, and taking the average value of the pitch errors of each scaler as the estimated value of the pitch errors The method comprises the following steps:
（12）
Wherein, Indicating the actual skew of the range gate where the nth sealer is located,Representing a preset imaging skew of a range gate where the nth sealer is located.
The beneficial effects are that:
The invention provides a complete flow of interference phase and skew calibration based on external control point positioning information, can realize automatic extraction of calibration signals and estimation of interference errors, and can be used as a general data product processing flow.
Drawings
FIG. 1 is a flow chart of an automatic extraction and application method of an interferometric SAR external calibration signal;
fig. 2 is an unwrapped phase diagram.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
As shown in fig. 1, the method for automatically extracting and applying the interference SAR external calibration signal of the present invention comprises the following steps:
Step 1, calculating sub-pixel image coordinates of a scaler based on imaging geometry and an up-sampling technology;
and 2, estimating a pitch error based on the error of the actual pitch of the scaler and the imaging pitch, and estimating an offset phase based on the scaler unwrapping phase.
Specifically, the step 1 includes:
Calculating azimuth coordinates:
First, the scaler coordinate vector From coordinates in the geodetic coordinate systemIs converted into coordinates in a geocentric geodetic fixed coordinate systemWhere the E-axis represents earth longitude, the N-axis represents earth latitude, and the h-axis represents earth elevation. The origin O (0, 0) is the earth centroid, the z axis and the ground axis are parallel to point to the north pole, the x axis points to the intersection point of the original meridian and the equator, and the y axis is perpendicular to the xOz plane (namely, the intersection point of the east 90 degrees and the equator) to form a right-hand coordinate system.
Secondly, calculating Doppler frequency of radar echo of the scaler according to satellite orbit information and scaler position informationThe following formula is shown:
（1）
（2）
Wherein, Representing the distance of the radar from the sealer when the signal is transmitted,Representing the distance of the radar from the sealer at the time of receiving the signal,The echo delay is indicated as such,The azimuth time is indicated as such,Representing the radar wavelength. Under the geocentric and geodetic fixed coordinate system, the speed of the scaler is the autorotation speed of the earth assuming that the scaler is fixed on the surface of the earthIn the geocentric and geodetic coordinate system，Representing the modulus of the vector.A radar sensor velocity vector representing the transmitted signal,A radar sensor velocity vector representing the received signal,Representing a radar sensor position vector,Indicating the speed of light.A radar sensor position vector representing the transmitted signal,A radar sensor position vector representing the received signal. Main satellites and auxiliary satellites of the first satellite for land detection all adopt positive side view observation and Doppler central frequency. Phase delta methods based on echo data can be used for the estimation of the doppler center frequency when the radar cannot provide a sufficiently high accuracy attitude measurement or beam pointing for the geometrical calculation of the doppler center. From the echo azimuth signal chirp characteristics, the estimated Doppler center frequency can be obtained by using the phase angle of the mean value of the differential vector of the azimuth adjacent samplesThe method comprises the following steps:
（3）
Wherein, Representing echo signals, superscriptThe expression of the conjugate operation is given,The phase angle of the complex number is represented,Indicating the azimuth sampling time interval,Indicating the azimuthal sampling frequency,The distance-wise time is represented, and the difference vector between the distances is averaged to cause noise interference.
Estimated Doppler frequency obtained by the equation (3)Interpolation operation is carried out to obtain Doppler center momentI.e.
（4）
According to the Doppler central frequency momentCan obtain the azimuth coordinates of the scalerThe method comprises the following steps:
（5）
Wherein, Indicating the echo reception start time.
Calculating distance-direction coordinates:
the idea of equivalent single station is adopted, firstly, the Doppler central moment is calculated At this time, the pitch of the radar sensor to the scalerI.e.
（6）
Wherein,Indicating the Doppler shift center timeEcho signals at that time;
the distance coordinate of the scaler can be obtained The method comprises the following steps:
（7）
Wherein, Indicating the proximal slope distance, the distance between the two points,Representing the distance-to-sampling time interval,Representing the distance to the sampling frequency.
The method can obtain the rough coordinate of the scaler in the SAR imageAnd extracting slice data by taking the rough coordinates as the center to perform up-sampling operation, and obtaining sub-pixel level coordinate information corresponding to the amplitude peak point.
The automatic extraction of the external calibration signal is completed.
Specifically, the step 2 includes:
and carrying out InSAR height measurement, wherein the formula is as follows:
（8）
Wherein, Which is indicative of the altitude of the satellite,The height of the earth is indicated by the height of the earth,For the purpose of the slant distance of the object,Representing the angle of view of the radar in the down direction,For the base line tilt angle,Is the baseline length.Representing the skew difference of the main and auxiliary satellites, absolute interference phase of the main and auxiliary imagesInversion, namely:
（9）
and constructing a range Doppler equation between the main satellite and the auxiliary satellite and the target point through the fine orbit data, and solving the target elevation information by combining the equation (8).
Calculating a baseline error:
Baseline parameters The error of (c) may affect the high Cheng Chongjian accuracy. The actual base line is time-space changed under the influence of orbit control precision, and pixel-level base line estimation is realized by interpolating the base line estimated by fine orbit data so as to relieve the influence of base line errors.
Calculating offset phase:
due to the presence of winding and phase noise in absolute phase, i.e.:
（10）
Wherein, Indicating the phase of unwrapping,Representing the absolute offset phase of the signal,Is a constant of an integer which is a constant of the integer,Representing the phase error caused by the distortion of the SAR system,As phase noise, offset phase estimation based on a plurality of scalers is required to suppress interference of noise. Since the absolute phase of the scalers is known, the mean of the absolute phases of the scalers minus the unwrapped phase is taken as the absolute offset phaseIs the estimated value of (1), namely:
（11）
Wherein the superscript N denotes the sealer sequence number, N denotes the sealer total, Representing the absolute interference phase of the primary and secondary images of the nth scaler,Indicating the unwrapped phase of the nth sealer.
An unwrapped phase map is shown in fig. 2, where square-shaped callout points are sealer positions.
Calculating a skew error:
Because of the time sequence error of the receiving window, the actual inclined distance of each distance gate is not consistent with the preset inclined distance, and further deviation exists in elevation information reconstruction. Obtaining actual inclined distance of distance door where scaler and radar sensor are located based on inclined distance The mean value of the pitch error of each scaler is used as the estimated value of the pitch errorThe method comprises the following steps:
（12）
Wherein, Indicating the preset skew of the range gate where each sealer is located. In actual processing, the auxiliary image is geometrically registered to the main image to obtain an interference phase diagram, so that only the main image skew error is required to be calibrated.
In conclusion, the invention completes the automatic extraction and application of the InSAR external calibration signal.
Examples:
the interference error is analyzed and estimated by land detection of data acquired by the calibration field task number one. The results of the simulation experiment analysis are as follows.
The extraction result of the main image external calibration signal is shown in table 1.
TABLE 1
| Scaler numbering | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| Distance to coordinates | 9621.656 | 11883.531 | 14076.375 | 21234.344 | 17216.281 | 18608.344 | 20002.594 | 15743.406 |
| Azimuth coordinates | 14968.375 | 15183.500 | 15659.563 | 17116.656 | 16319.750 | 16598.594 | 16839.938 | 15997.719 |
| Amplitude/(dB) | 94.253 | 99.385 | 99.655 | 98.474 | 100.062 | 99.669 | 98.244 | 99.473 |
| Phase/(rad) | -1.249353 | 0.285858 | 3.126412 | -2.561855 | 1.468340 | 2.884696 | 0.296165 | 2.242702 |
The interferometric scaling results are shown in table 2.
TABLE 2
| Scaler numbering | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| Preset skew/(m) | 806903.325 | 810670.509 | 814322.720 | 826244.415 | 819552.277 | 821870.776 | 824192.918 | 817099.183 |
| Actual skew/(m) | 806865.926 | 810632.055 | 814283.964 | 826206.073 | 819513.856 | 821832.405 | 824154.390 | 817060.850 |
| Skew error/(m) | -37.3990 | -38.4532 | -38.7558 | -38.3411 | -38.4204 | -38.3708 | -38.5285 | -38.3327 |
| Phase error/(rad) | 14.7009 | 14.6279 | 14.7598 | 14.7386 | 14.7936 | 14.8800 | 14.7707 | 14.8297 |
The experimental results show that: the estimated skew error is-38.325 meters and the variance is 0.3729 meters. The estimated offset phase is 14.7626rad and the variance is 0.0773rad. The small variance indicates that the present invention can extract a stable error, i.e. the proposed scaling scheme is valid.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (1)
1. The automatic extraction and application method of the interference SAR external calibration signal is characterized by comprising the following steps:
Step 1, calculating sub-pixel image coordinates of a scaler based on imaging geometry and an up-sampling method, wherein the calculating comprises calculating azimuth coordinates and calculating distance coordinates;
The calculating azimuth coordinates includes:
First, the scaler coordinate vector From coordinates in the geodetic coordinate system/>Converted into the coordinates/>, under the geocentric and geodetic fixed coordinate systemThe geodetic coordinate system comprises an E axis, an N axis and an h axis, wherein the E axis represents geodetic longitude, the N axis represents geodetic latitude, and the h axis represents geodetic elevation;
Secondly, calculating Doppler frequency of radar echo of the scaler according to satellite orbit information and scaler position information The following formula is shown:
（1）
（2）
Wherein, Representing the distance between the radar and the scaler when transmitting signals,/>Representing the distance between the radar and the scaler when receiving the signal,/>Representing echo delay,/>Representing azimuth time,/>The radar wavelength is represented, and the speed of the scaler is the earth rotation speed/>There is/>, under the geocentric geodetic coordinate system，/>A module representing a vector; /(I)Radar sensor velocity vector representing the transmitted signal,/>Radar sensor velocity vector representing received signal,/>Representing a radar sensor position vector,/>Representing the speed of light; Radar sensor position vector representing transmitted signal,/> A radar sensor position vector representing a received signal;
Obtaining estimated Doppler center frequency from echo azimuth signal chirp characteristics using phase angle of mean value of differential vector of azimuth adjacent samples Doppler frequency/>, for sealer radar echoInterpolation operation is carried out to obtain Doppler center moment/>The method comprises the following steps:
（4）
according to Doppler central moment Obtain the azimuth coordinate/>, of the scalerThe method comprises the following steps:
（5）
Wherein, Indicating echo reception start time,/>Representing azimuth sampling time interval,/>Representing azimuth sampling frequency;
The calculating distance-to-coordinate includes:
First calculate Doppler center moment At this time, the pitch/>, of the radar sensor to the scalerObtaining the distance coordinate of the scalerThe method comprises the following steps:
（7）
Wherein, Representing proximal skew,/>Representing distance to sampling time interval,/>Representing distance-wise sampling frequency;
Scaler azimuth coordinates And scaler distance to coordinates/>Coarse coordinates in SAR image forming scalerAccording to rough coordinates/>, in SAR images, of the acquired scalerIn the rough coordinates/>Performing up-sampling operation on the extracted slice data of the center to obtain sub-pixel level coordinate information corresponding to the amplitude peak point;
step 2, estimating a pitch error based on the error of the actual pitch of the scaler and the imaging pitch, and estimating an absolute offset phase based on the scaler unwrapping phase;
the estimating of the absolute offset phase includes:
taking the mean of the absolute interference phases of a plurality of scalers minus the unwrapping phase as the absolute offset phase Is the estimated value of (1), namely:
（11）
the superscript N denotes the sealer sequence number, N denotes the sealer total, Representing absolute interference phases of the primary and secondary images of the nth scaler,/>Indicating the unwrapped phase of the nth sealer;
The estimation of the skew error includes:
Based on the scaler and the pitch of the radar sensor, acquiring the actual pitch of the range gate where the scaler and the radar sensor are positioned, and taking the average value of the pitch errors of each scaler as the estimated value of the pitch errors The method comprises the following steps:
（12）
Wherein, Representing the actual skew of the range gate where the nth sealer is located,/>Representing a preset imaging skew of a range gate where an nth scaler is located;
and carrying out InSAR height measurement, wherein the formula is as follows:
（8）
Wherein, Representing satellite altitude,/>Representing the elevation of the earth,/>For the target skew,/>Representing radar viewing angle,/>For the base line dip angle,/>Is the baseline length; /(I)Representing the difference of the pitch of the main and auxiliary satellites, and passing the absolute interference phase/>, of the main and auxiliary imagesInversion, namely:
（9）
constructing a range Doppler equation of a main star, an auxiliary star and a target point through fine orbit data, and solving target elevation information by combining with the equation (8);
Calculating a baseline error, comprising: the baseline estimation at the pixel level is achieved by interpolating the baseline of the fine orbit data estimation.
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