CN113702972A - Airborne multi-channel radar amplitude-phase error estimation method based on terrain prior - Google Patents

Airborne multi-channel radar amplitude-phase error estimation method based on terrain prior Download PDF

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CN113702972A
CN113702972A CN202111008103.9A CN202111008103A CN113702972A CN 113702972 A CN113702972 A CN 113702972A CN 202111008103 A CN202111008103 A CN 202111008103A CN 113702972 A CN113702972 A CN 113702972A
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amplitude
channel
phase error
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焦泽坤
仇晓兰
周良将
韩冬
丁赤飚
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Aerospace Information Research Institute of CAS
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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
    • G01S13/9021—SAR image post-processing techniques
    • 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
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    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section

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Abstract

The invention provides a terrain prior-based airborne multi-channel radar amplitude-phase error estimation method, which comprises the following steps: carrying out image registration operation on the acquired multi-channel two-dimensional SAR image; for the SAR image after registration, selecting strong scattering points in a non-overlap building area aiming at an urban scene, and calculating actual phase difference and amplitude among channels; calculating ideal phase difference and amplitude between channels by using POS data of an airborne platform and radar imaging parameters, and calculating an initial value of channel amplitude-phase error by combining the actual phase difference and amplitude; compensating the multi-channel image by using an initial result of amplitude-phase error estimation, performing chromatography SAR three-dimensional reconstruction, and updating the height information of the selected strong scattering point in combination with the prior of the urban building target structure; and iterating the two steps of operations by using the updated height information of the scattering points until the difference between two adjacent reconstruction steps is smaller than a preset threshold value, and outputting a final multi-channel amplitude-phase error estimation result.

Description

Airborne multi-channel radar amplitude-phase error estimation method based on terrain prior
Technical Field
The disclosure relates to the field of radar signal processing, in particular to an airborne multi-channel radar amplitude and phase error estimation method based on terrain prior.
Background
The array radar utilizes the space gain brought by array element space diversity, and has stronger detection capability compared with the traditional single-station radar. The tomography SAR three-dimensional imaging is a typical application of a multi-channel radar, and can utilize a plurality of observation channels in the elevation direction to construct an elevation-direction synthetic aperture. However, due to the influence of factors such as channel hardware and equipment thermal noise, the amplitudes and phases of different channels of the array antenna are difficult to be completely consistent, and if the amplitude and phase errors among the channels are not estimated and compensated, the tomography SAR three-dimensional imaging effect is rapidly reduced, and ghosting (false target) occurs in the high-direction reconstruction. Therefore, the method for estimating the amplitude and phase errors of the multi-channel radar suitable for the application requirements is researched by combining the application background of the tomography SAR three-dimensional imaging, and the method has important research significance.
Aiming at the application requirements, a large number of research on amplitude and phase error estimation methods of multi-channel radars are developed at home and abroad. For the estimation of the amplitude error, the better effect can be achieved by using the techniques such as channel equalization and the like at the present stage, however, the estimation of the phase error between channels still is a difficult problem. At present, a typical radar multi-channel amplitude and phase error estimation method is an airborne multi-channel amplitude and phase error estimation method proposed by Liu of the university of electronic technology of Western's Security. The Korean industry of the electronic institute of Chinese academy of sciences and the like provides a multi-channel amplitude and phase error correction three-dimensional imaging algorithm for carrying out amplitude and phase correction based on echo data, and can process multi-channel radar original echo data with amplitude and phase errors. The trade sample et al propose a multi-channel scaling method based on orthogonal subspaces. In general, most of the methods are developed based on echo data, are not suitable for SAR image users, and often require calibration points to perform accurate amplitude and phase error calibration.
For SAR image users, how to utilize array radar multi-channel SAR image data to realize high-precision inter-channel amplitude and phase error estimation and compensation in urban scene areas which are not suitable for arrangement of scalers has important significance. Therefore, for the requirement of multi-channel SAR three-dimensional imaging, a systematic development of an urban scene multi-channel amplitude and phase error estimation technology research based on SAR image data without a scaler is required. The research content has important significance for improving the SAR three-dimensional imaging effect.
Disclosure of Invention
In view of the above, a primary object of the present disclosure is to provide a terrain prior-based method for estimating magnitude-phase error of an airborne multi-channel radar, so as to partially solve at least one of the above technical problems.
In order to achieve the purpose, the invention provides a terrain prior-based airborne multi-channel radar amplitude and phase error estimation method, which is based on a multi-channel data two-dimensional imaging result, selects strong scattering points in a scene, iteratively estimates the amplitude and phase errors among channels by using town scene terrain prior knowledge, and can realize accurate estimation of the radar multi-channel amplitude and phase errors under the condition of no scaler, and comprises the following steps:
carrying out image registration operation on the acquired multi-channel two-dimensional SAR image;
for the SAR image after registration, selecting strong scattering points in a non-overlap building area aiming at an urban scene, and calculating actual phase difference and amplitude among channels;
calculating ideal phase difference and amplitude between channels by using POS data of an airborne platform and radar imaging parameters, and calculating an initial value of channel amplitude-phase error by combining the actual phase difference and amplitude;
compensating the multi-channel image by using an initial result of amplitude-phase error estimation, performing chromatography SAR three-dimensional reconstruction, and updating the height information of the selected strong scattering point in combination with the prior of the urban building target structure;
and iterating the two steps of operations by using the updated height information of the scattering points until the difference between two adjacent reconstruction steps is smaller than a preset threshold value, and outputting a final multi-channel amplitude-phase error estimation result.
According to the embodiment of the disclosure, in the step of selecting the strong scattering points of the non-overlapping building region for the registered SAR image aiming at the urban scene and calculating the actual phase difference and amplitude between the channels, the method is suitable for the urban scene containing the building target region, and the strong scattering points A of the non-overlapping building region are selected by using the criteria of amplitude dispersion and the like.
According to the embodiment of the disclosure, the step of selecting the strong scattering points of the non-overlap building region and calculating the actual phase difference and amplitude between the channels for the registered SAR image according to the urban scene further includes:
for the registered multi-channel image, assuming that N channels are total, and recording as N as 1, 2.., N; for the nth channel, the pixel value of the pixel point A' corresponding to the strong scattering point A is recorded as
Figure BDA0003236087780000021
And respectively carrying out conjugate multiplication by taking the first channel as a reference phase:
Figure BDA0003236087780000022
according to the formula, the actual phase difference between the channels can be obtained for the pixel point a', and is recorded as:
Δp1＝0；
Δpn＝angle(In)，n＝2，3，...，N；
wherein, angle (#) represents the phase value of the complex number;
with the channel-echo amplitude as a reference, a normalized inter-channel amplitude imbalance factor can be obtained:
a1＝1；
Figure BDA0003236087780000031
according to the embodiment of the disclosure, the steps of calculating the ideal phase difference and amplitude between channels by using the POS data of the airborne platform and the radar imaging parameters, and calculating the initial value of the amplitude-phase error of the channel by combining the actual phase difference and amplitude comprise:
for the pixel point A', according to the radar observation geometry, the two-dimensional longitude and latitude coordinates can be obtained, and according to the imaging processing, the altitude is assumed to be hiniObtaining the three-dimensional coordinate (lat) of the pixel point AA，lngA，hini) Further, the distance R from the pixel point A' to the nth equivalent phase center can be calculatedn：
Figure BDA0003236087780000032
Wherein elevation (x) is a function for calculating the distance between two points according to longitude and latitude coordinates of the two points; in the nth channel image, the ideal phase value of the pixel point A' is
Figure BDA0003236087780000033
Similarly, according to the radar equation, the amplitude of the echo signal is inversely proportional to the fourth power of the distance, and under the condition that amplitude inconsistency does not exist among the channels, the amplitude value of the pixel point a' pixel satisfies the following conditions:
Figure BDA0003236087780000034
in combination with the above analysis, with the echo of the first channel as a reference, the ideal phase difference between the channels can be obtained as follows:
Figure BDA0003236087780000035
the ideal magnitude imbalance factor between channels is:
Figure BDA0003236087780000041
combining inter-channel phase differences Δ p extracted from echo data according to embodiments of the present disclosurenAnd an amplitude imbalance factor anAnd an inter-channel ideal phase difference Delta theta extracted based on the distance from the equivalent phase center of the radar to the scattering pointnAnd amplitude imbalance factor alphanObtaining the amplitude and phase error initial values of each channelThe estimation is as follows:
φn (0)＝Δpn-Δθn
Figure BDA0003236087780000042
the superscript of the left variable of the above expression represents the 0 th iteration, i.e., the initial value of the magnitude-phase error correction factor.
According to the embodiment of the disclosure, the step of compensating the multi-channel image by using the initial result of the amplitude-phase error estimation, performing the chromatography SAR three-dimensional reconstruction, and updating the height information of the selected strong scattering point in combination with the prior of the urban building target structure comprises the following steps:
using the obtained inter-channel amplitude and phase error correction factors, assuming that for the k-th iteration, the inter-channel amplitude and phase correction factors are χn (k)，φn (k)And then, performing amplitude-phase error correction on the multi-channel SAR image by using an amplitude-phase correction factor:
for i＝1：1：N
In＝In·exp(-j·φn (k))·χn (k)
end。
according to the embodiment of the disclosure, the height information of the scattering point A is updated by combining with the terrain prior knowledge of the urban scene; specifically, after chromatography SAR three-dimensional reconstruction is carried out based on urban building terrain prior knowledge, the elevation of a previously selected strong scattering point is calculated according to multi-channel radar imaging geometry, and after the kth iteration, the elevation of an A point is updated to h(k)。
According to the embodiment of the disclosure, the step of iterating the two steps of operations by using the updated height information of the scattering point until the difference between two adjacent reconstructed times is smaller than a preset threshold value and outputting the final multi-channel amplitude-phase error estimation result comprises the following steps:
according to the three-dimensional reconstruction result obtained by two adjacent iterations, the amplitude and phase information of scattering points is contained; and calculating the variable quantity of the three-dimensional reconstruction results of two adjacent times.
According to the embodiment of the disclosure, the relative variation of the three-dimensional reconstruction of two adjacent iterations is judged, and if the variation is smaller than a preset threshold, a final amplitude-phase error estimation result is output; otherwise, the method jumps to the step, ideal phase difference and amplitude between channels are calculated by using the POS data of the airborne platform and radar imaging parameters, the initial value of the amplitude-phase error of the channels is calculated by combining the actual phase difference and amplitude, and the updated height of the scattering point A is used for calculation.
Based on the technical scheme, compared with the prior art, the terrain prior-based airborne multi-channel radar amplitude-phase error estimation method at least has one of the following beneficial effects:
aiming at the problems that the existing multi-channel amplitude and phase error estimation method is mostly developed based on echo data and accurate amplitude and phase error calibration is often required to be carried out on calibration points, the method is based on a multi-channel data two-dimensional imaging result, strong scattering points in a scene are selected, town scene terrain priori knowledge is utilized, inter-channel amplitude and phase errors and actual heights of the scattering points are iteratively estimated, accurate estimation of the radar multi-channel amplitude and phase errors under the condition of no calibrator can be achieved, and effectiveness of the method is verified through actually measured data.
Drawings
Fig. 1 is a flowchart of an airborne multi-channel radar amplitude-phase error estimation method based on terrain priors according to an embodiment of the present disclosure;
fig. 2 is a schematic diagram of selecting strong scattering points of an SAR image according to an embodiment of the present disclosure;
FIG. 3a is an optical image of an imaged scene shown in an embodiment of the present disclosure; fig. 3b is a SAR image of an imaging scene presented by an embodiment of the present disclosure; FIG. 3c is a schematic diagram illustrating comparison results of inter-channel amplitude errors of different methods shown in the embodiments of the present disclosure; FIG. 3d is a diagram illustrating phase error comparison results between channels according to various methods disclosed in this disclosure; fig. 3e is a schematic diagram of a three-dimensional reconstruction result before amplitude and phase error correction shown in the embodiment of the present disclosure; fig. 3f is a schematic diagram of a three-dimensional reconstruction result after amplitude and phase error correction shown in the embodiment of the present disclosure.
FIG. 4a is an optical image of an imaged scene shown in an embodiment of the present disclosure; fig. 4b is a SAR image of an imaging scene presented by an embodiment of the present disclosure; FIG. 4c is a schematic diagram illustrating an amplitude correction factor according to an embodiment of the present disclosure; 4d is a schematic diagram of a phase correction factor shown in the embodiments of the present disclosure; 4e is a schematic diagram of a three-dimensional reconstruction result before amplitude and phase error correction shown in the embodiment of the disclosure; and 4f is a schematic diagram of a three-dimensional reconstruction result after amplitude and phase error correction shown in the embodiment of the disclosure.
Detailed Description
For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.
The method comprises the steps of selecting strong scattering points in a scene, iteratively estimating inter-channel amplitude-phase errors and actual heights of the scattering points by using town scene terrain priori knowledge, and accurately estimating the multi-channel amplitude-phase errors of the radar under the condition of no calibrator. As shown in fig. 1, the main operations include:
s1: selecting non-strong scattering points, and calculating actual phase difference and amplitude among channels;
specifically, a strong scattering point A of the non-overlapping area is selected by using the criteria of amplitude dispersion and the like, the distance direction and azimuth direction coordinates of the corresponding pixel are (i, j), and the corresponding azimuth time is tj. As shown in fig. 2, the selected strong scattering points are marked with a star.
For the registered multi-channel images, a total of N channels, denoted as N1, 2. For the nth channel, the pixel value of the pixel point A' corresponding to the strong scattering point A is recorded as
Figure BDA0003236087780000061
And respectively carrying out conjugate multiplication by taking the first channel as a reference phase:
Figure BDA0003236087780000062
according to the formula (1), the actual phase difference between the channels for the pixel point a' can be obtained and recorded as:
Δp1＝0；
Δpn＝angle(In)，n＝2，3，...，N (2)
the expression indicates the value of the complex phase. With the amplitude of the first channel echo as a reference, a normalized inter-channel amplitude imbalance factor can be obtained:
a1＝1；
Figure BDA0003236087780000063
s2: calculating an initial value of the channel amplitude-phase error by using POS data;
and calculating the ideal phase difference and amplitude between channels by using the POS data of the airborne platform and the radar imaging parameters, and calculating the initial value of the amplitude-phase error of the channels by combining the actual measurement phase difference obtained in the second step.
Suppose that in the SAR two-dimensional imaging process, the reference altitude of the imaging scene is selected as hrefThen, then
The initial altitude of scattering point A is hini＝href. According to the POS data of the carrier platform, a total of N channels are assumed, which is denoted as N ═ 1, 2. For the nth channel, the azimuth time tjThe equivalent phase center coordinate is obtained from the POS data reading
Figure BDA0003236087780000071
It should be noted that the equivalent phase center coordinate is an airplane coordinate system, and after coordinate transformation, the equivalent phase center coordinate can be transformed into longitude and latitude coordinates
Figure BDA0003236087780000072
For the point A, according to the radar observation geometry, the two-dimensional longitude and latitude coordinates can be obtained, and according to the imaging processing, the altitude is assumed to be hiniObtaining the three-dimensional coordinate of the scattering point A as (lat)A，lngA，hini) Further, the distance R from the point A to the nth equivalent phase center can be calculatedn：
Figure BDA0003236087780000073
In the above expression, elevation (×) is a function for calculating the distance between two points according to longitude and latitude coordinates of the two points. In the nth channel image, the ideal phase value of the point A is
Figure BDA0003236087780000074
Similarly, according to the radar equation, the amplitude of the echo signal is inversely proportional to the fourth power of the distance, and the amplitude value of the pixel at the point a satisfies the following condition that amplitude inconsistency does not exist among the channels:
Figure BDA0003236087780000075
in combination with the above analysis, with the echo of the first channel as a reference, the ideal phase difference between the channels can be obtained as follows:
Figure BDA0003236087780000076
the ideal magnitude imbalance factor between channels is:
Figure BDA0003236087780000077
combining inter-channel phase differences Δ p extracted from echo datanAnd an amplitude imbalance factor anAnd an inter-channel ideal phase difference Delta theta extracted based on the distance from the equivalent phase center of the radar to the scattering pointnAnd amplitude imbalance factor alphanThe initial estimates of the amplitude and phase errors for each channel can be obtained as follows:
φn (0)＝Δpn-Δθn
Figure BDA0003236087780000078
the superscript of the left variable of the above expression represents the 0 th iteration, i.e., the initial value of the magnitude-phase error correction factor.
S3: compensating the inter-channel amplitude-phase error, performing three-dimensional reconstruction, and updating the height information of the strong scattering point;
using the inter-channel amplitude and phase error correction factors obtained in the previous steps, assuming that for the kth iteration, the inter-channel amplitude and phase correction factors are χn (k)，φn (k)And then, performing amplitude-phase error correction on the multi-channel SAR image by using the amplitude-phase correction factor:
for i＝1：1：N
In＝In·exp(-j·φn (k))·χn (k)
end (9)
based on the foregoing operations, amplitude-phase error compensation of the N channel images can be achieved. On the basis, the height information of the scattering point A is updated by combining with the terrain prior knowledge of the urban scene. Specifically, based on urban building terrain prior knowledge, the building target outer vertical surface is vertical to the ground, so that chromatography SAR three-dimensional reconstruction is carried out. The implementation of the three-dimensional imaging method of the chromatographic SAR is mature, and the disclosure is not expanded.
It should be noted that after tomographic SAR three-dimensional imaging reconstruction, the oblique altitude position of the scattering point perpendicular to the radar line-of-sight direction is obtained, and the altitude needs to be obtained after a series of coordinate transformations, which is not described in detail herein.
The elevation of the selected strong scattering point can be calculated according to the multi-channel radar imaging geometry, and after the k-th iteration, the elevation of the A point is updated to h(k)。
S4: and iterating S2 and S3 until the difference of the reconstruction is smaller than a threshold value, and outputting an error estimation result.
Three from two adjacent iterations (kth and k + 1)Dimensional reconstruction result, denoted as σ(k)，σ(k+1)The amplitude and phase information of the scattering points is included. And calculating the variable quantity of the three-dimensional reconstruction results of two adjacent times.
Judging the relative variation of the two adjacent iterations of three-dimensional reconstruction, and outputting a final amplitude-phase error estimation result if the variation is smaller than a preset threshold; otherwise, the step S2 is skipped to, and iterative calculation is performed using the updated a-point height.
Figure BDA0003236087780000091
output：χn (k)，φn (k)
else
update：h(k+1)
go to Step3
end (10)
Example one
Airborne multi-channel radar amplitude and phase error estimation test (X wave band) based on terrain prior
In the embodiment, an X-band multi-channel SAR image is adopted, the carrier frequency is 10GHz, and the signal bandwidth is 1 GHz. And estimating the amplitude-phase error of the channel by adopting an airborne multi-channel radar amplitude-phase error estimation method based on terrain prior. In order to more visually display the effect of the method provided by the disclosure, the effectiveness of the method is displayed by displaying three-dimensional reconstruction results before and after amplitude and phase error estimation and compensation.
Fig. 3 a-3 f illustrate the imaging results based on the area image. Wherein fig. 3a shows an optical image of an imaged scene and fig. 3b shows a SAR image of an imaged scene. As shown in fig. 3c, the solid curve in the graph represents the estimation result of the amplitude error of the method provided by the present disclosure, and the dashed curve is the estimation result of the amplitude error estimation method based on the calibration point, and the consistency of the amplitude error between the two channels is good. As shown in fig. 3d, the curve with a x represents the final phase error estimation result of the method of the present disclosure, and the curve with a Δ is the estimation result of the phase error estimation method based on the calibration point, and the two are consistent. FIG. 3e is a schematic diagram of a three-dimensional reconstruction result before amplitude and phase error correction; fig. 3f is a schematic diagram of a three-dimensional reconstruction result after amplitude and phase error correction. As shown in fig. 3e, before correction, the reconstruction result has more ghosts (as indicated by 1, 2 and 3 in the figure) due to the existence of more serious amplitude and phase errors, and the target is difficult to distinguish, and after correction as shown in fig. 3f, the false target disappears, which confirms the effectiveness of the amplitude and phase error estimation method provided by the present disclosure.
Example two
Airborne multi-channel radar amplitude and phase error estimation test (Ku wave band) based on terrain prior
In this embodiment, a Ku-band multi-channel SAR image is used, and the carrier frequency is 15GHz, and the test results obtained by using the amplitude-phase error estimation method disclosed herein are shown in fig. 4a to 4 f. FIG. 4a is an optical image of an imaged scene; FIG. 4b is a SAR image of an imaged scene; FIG. 4c is a schematic diagram of an amplitude correction factor; 4d is a schematic diagram of the phase correction factor; 4e is a schematic diagram of a three-dimensional reconstruction result before amplitude and phase error correction; and 4f is a schematic diagram of the three-dimensional reconstruction result after amplitude and phase error correction. As shown in the figure, the experimental results confirm the feasibility and effectiveness of the disclosed method.
The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.

Claims (9)

1. The method for estimating the amplitude-phase error of the airborne multi-channel radar based on terrain prior is characterized in that strong scattering points in a scene are selected based on a multi-channel data two-dimensional imaging result, the amplitude-phase error between channels is iteratively estimated by using town scene terrain prior knowledge, and the accurate estimation of the multi-channel amplitude-phase error of the radar can be realized under the condition of no scaler, and the method comprises the following steps:
carrying out image registration operation on the acquired multi-channel two-dimensional SAR image;
for the SAR image after registration, selecting strong scattering points in a non-overlap building area aiming at an urban scene, and calculating actual phase difference and amplitude among channels;
calculating ideal phase difference and amplitude between channels by using POS data of an airborne platform and radar imaging parameters, and calculating an initial value of channel amplitude-phase error by combining the actual phase difference and amplitude;
compensating the multi-channel image by using an initial result of amplitude-phase error estimation, performing chromatography SAR three-dimensional reconstruction, and updating the height information of the selected strong scattering point in combination with the prior of the urban building target structure;
and iterating the two steps of operations by using the updated height information of the scattering points until the difference between two adjacent reconstruction steps is smaller than a preset threshold value, and outputting a final multi-channel amplitude-phase error estimation result.
2. The method according to claim 1, wherein in the step of selecting, for the SAR image after registration, strong scattering points in the non-overlapping building region for the urban scene, and calculating the actual phase difference and amplitude between each channel, the method is applicable to the urban scene including the building target region, and the strong scattering points A in the non-overlapping building region are selected by using an amplitude dispersion criterion and the like.
3. The method according to claim 2, wherein the step of selecting, for the registered SAR image and for an urban scene, a strong scattering point in a non-overlap building area, and calculating an actual phase difference and amplitude between each channel further comprises:
for the registered multi-channel image, assuming that N channels are total, and recording as N as 1, 2.., N; for the nth channel, the pixel value of the pixel point A' corresponding to the strong scattering point A is recorded as
Figure FDA0003236087770000011
And respectively carrying out conjugate multiplication by taking the first channel as a reference phase:
Figure FDA0003236087770000012
according to the formula, the actual phase difference between the channels can be obtained for the pixel point a', and is recorded as:
Δp1＝0；
Δpn＝angle(In)，n＝2，3，...，；
wherein, angle (#) represents the phase value of the complex number;
with the channel-echo amplitude as a reference, a normalized inter-channel amplitude imbalance factor can be obtained:
a1＝1；
Figure FDA0003236087770000021
4. the method of claim 3, wherein the step of calculating the channel amplitude and phase error initial value by using the onboard platform POS data and the radar imaging parameters and combining the actual phase difference and amplitude comprises:
for the pixel point A', according to the radar observation geometry, the two-dimensional longitude and latitude coordinates can be obtained, and according to the imaging processing, the altitude is assumed to be hiniObtaining the three-dimensional coordinate (lat) of the pixel point AA，lngA，hini) Further, the distance R from the pixel point A' to the nth equivalent phase center can be calculatedn：
Figure FDA0003236087770000022
Wherein elevation (x) is a function for calculating the distance between two points according to longitude and latitude coordinates of the two points; in the nth channel image, the ideal phase value of the pixel point A' is
Figure FDA0003236087770000023
Similarly, according to the radar equation, the amplitude of the echo signal is inversely proportional to the fourth power of the distance, and under the condition that amplitude inconsistency does not exist among the channels, the amplitude value of the pixel point a' pixel satisfies the following conditions:
Figure FDA0003236087770000024
in combination with the above analysis, with the echo of the first channel as a reference, the ideal phase difference between the channels can be obtained as follows:
Figure FDA0003236087770000025
the ideal magnitude imbalance factor between channels is:
Figure FDA0003236087770000026
5. method according to claim 4, characterized in that the inter-channel phase difference Δ ρ extracted from the echo data is combinednAnd an amplitude imbalance factor anAnd an inter-channel ideal phase difference Delta theta extracted based on the distance from the equivalent phase center of the radar to the scattering pointnAnd amplitude imbalance factor alphanThe initial estimates of the amplitude and phase errors for each channel are obtained as follows:
φΦ (0)＝Δpn-Δθn
Figure FDA0003236087770000031
the superscript of the left variable of the above expression represents the 0 th iteration, i.e., the initial value of the magnitude-phase error correction factor.
6. The method of claim 5, wherein the step of compensating the multi-channel image by using the initial result of the amplitude-phase error estimation, performing the chromatography SAR three-dimensional reconstruction, and updating the height information of the selected strong scattering point in combination with the urban building target structure a priori comprises:
using the obtained inter-channel amplitude and phase error correction factors, assuming that for the k-th iteration, the inter-channel amplitude and phase correction factors are χn (k)，φn (k)And then, performing amplitude-phase error correction on the multi-channel SAR image by using an amplitude-phase correction factor:
for i＝1∶1∶N
In＝In·exp(-j·φn (k))·χn (k)
end。
7. the method according to claim 6, characterized in that the height information of scattering point A is updated in combination with the prior knowledge of urban scene terrain; specifically, after chromatography SAR three-dimensional reconstruction is carried out based on urban building terrain prior knowledge, the elevation of a previously selected strong scattering point is calculated according to multi-channel radar imaging geometry, and after the kth iteration, the elevation of an A point is updated to h(k)。
8. The method according to claim 7, wherein the step of iterating the two steps of operations using the updated scattering point height information until the difference between two adjacent reconstructed differences is smaller than a predetermined threshold value, and the step of outputting the final multi-channel amplitude-phase error estimation result comprises:
according to the three-dimensional reconstruction result obtained by two adjacent iterations, the amplitude and phase information of scattering points is contained; and calculating the variable quantity of the three-dimensional reconstruction results of two adjacent times.
9. The method according to claim 8, characterized in that the relative variation of the three-dimensional reconstruction of two adjacent iterations is judged, and if the variation is smaller than a preset threshold value, the final amplitude-phase error estimation result is output; otherwise, the method jumps to the step, ideal phase difference and amplitude between channels are calculated by using the POS data of the airborne platform and radar imaging parameters, the initial value of the amplitude-phase error of the channels is calculated by combining the actual phase difference and amplitude, and the updated height of the scattering point A is used for calculation.
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