CN110618409B - Multi-channel InSAR interferogram simulation method and system considering overlapping and shading - Google Patents

Multi-channel InSAR interferogram simulation method and system considering overlapping and shading Download PDF

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CN110618409B
CN110618409B CN201910849293.3A CN201910849293A CN110618409B CN 110618409 B CN110618409 B CN 110618409B CN 201910849293 A CN201910849293 A CN 201910849293A CN 110618409 B CN110618409 B CN 110618409B
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袁志辉
谷翼策
陈立福
邢学敏
俞晓莹
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Changsha University of Science and Technology
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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
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    • G01S13/9023—SAR image post-processing techniques combined with interferometric techniques
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Abstract

The invention discloses a method and a system for simulating a multichannel InSAR interferogram considering overlapping and shading, wherein the method comprises the steps of firstly calculating specific parameters of an existing DEM and a multichannel InSAR system to obtain the real interference phase of each interference channel; then generating corresponding phase noise according to the probability density function of the interference phase and adding the phase noise into the real interference phase; then, weighting and superposing interference phases of target points with the same slant distance in a superposition area by taking a coherence coefficient as a weight, and directly replacing Gaussian white noise in a shadow area; and finally, rearranging the interference phases according to the size of the skew distance, thereby obtaining a multi-channel InSAR interference phase diagram considering the overlapping and the shadow. Analysis and simulation results show that the method is simple and easy to implement, strictly considers the distribution function of the interference phase noise, and can provide proper simulation data for performance comparison and quantitative analysis of various multi-channel InSAR technologies.

Description

Multi-channel InSAR interferogram simulation method and system considering overlapping and shading
Technical Field
The invention belongs to the technical field of information processing, and particularly relates to a method and a system for simulating a multichannel InSAR interferogram considering overlapping and shadowing.
Background
At present, data in the aspect of real multi-channel InSAR which can be searched at home and abroad is rare, the cost of using an actual system is high, the data can not necessarily meet the requirement of people on theoretical research in the direction, and the method and the mode of InSAR data simulation for obtaining the required data are an economic and effective scheme. In addition, because the specific parameters of the system can be controlled and adjusted and the possible generated results can be predicted, the simulated InSAR data has important significance for various algorithms in the aspects of performance comparison, quantitative analysis and the like.
Disclosure of Invention
The invention provides a multi-channel InSAR interferogram simulation method and system under the condition that influence factors such as overlapping and shading exist in order to simplify the steps of multi-channel InSAR data simulation and provide parameter-controllable simulation data for the research of multi-channel InSAR technology.
A multi-channel InSAR interferogram simulation method considering overlapping and shading comprises the following steps:
generating a real interference phase and interference phase noise of each interference channel, and superposing the interference phase noise and the real interference phase to obtain a real interference phase with noise;
detecting a shadow area and an overlapping area in the SAR image, and extracting the shadow area and the overlapping area;
weighted superposition and replacement are respectively carried out on the noisy interference phases of the target points in the overlap area and the shadow area: in the overlap area, weighting and overlapping the noisy interference phases of the target points with the same slant range by taking the coherence coefficient as the weight to obtain the noisy interference phases considering overlap on the same slant range resolution unit; replacing the noisy interference phase of the target point in the shadow area with white Gaussian noise;
winding the latest interference phases of all the slant-range resolution units, and rearranging the interference phases according to the size of the slant range by taking the slant-range resolution units as units, thereby obtaining a multi-channel InSAR interference phase diagram considering overlapping and shading;
the method comprises the steps of obtaining a DEM of a real terrain or a simulated terrain, and system parameters and signal-to-noise ratios of a multi-channel InSAR system, and generating real interference phases of interference channels by using an interference phase simulation model of the multi-channel InSAR system;
the process of generating the interference phase noise is as follows: firstly, based on system parameters, signal-to-noise ratio and base line length, calculating a corresponding coherence coefficient of each target point in each interference channel by using a coherence coefficient calculation model; secondly, calculating a probability density function of interference phase noise corresponding to each target point in each interference channel based on the coherence coefficient; next, the interference phase noise of each target point in each interference channel is generated by using the interference phase noise probability density function.
Further, in the overlap area, weighted overlap is performed on the noisy interference phases of the target points with the same slant range by taking the coherence coefficient as a weight, and the noisy interference phases considering overlap on the same slant range resolution unit are obtained according to the following formula:
Figure RE-GDA0002281057650000021
wherein phi isi(r, z) is the noise-carrying interference phase of the ith interference channel on the slant range resolution unit with the slant range r and the azimuth distance z, which takes into account the overlap mask, gammai(km) Indicating the kth of a certain resolution cellmThe corresponding coherence coefficient of each target point in the ith interference channel; phi is ai(km) Indicating the kth position in a certain overlapping resolution cellmThe noise interference phase corresponding to the target point in the ith interference channel; e represents the base of the natural logarithm; j represents an imaginary unit; m denotes the number of overlapping target points of a certain resolution element.
Further, the specific process of generating the interference phase noise of each target point in each interference channel by using the probability density function of the interference phase noise and adopting a round-off method is as follows:
assuming that the size of the interferogram is row x col column target points, the phase noise of all target points is initialized to zero, and the following operations are performed from the first target point to the target point one by one:
1) let th equal 1/max (pdf (n)i(k)；γi(k)))，pdf(ni(k)；γi(k) A probability density function representing the phase noise corresponding to the k-th object point in the i-th interference channel,
Figure RE-GDA0002281057650000022
Figure RE-GDA0002281057650000023
and phii(k) Respectively representing the corresponding real interference phase and the interference phase with noise, gamma, of the k-th target point in the i-th interference channeli(k) Representing the corresponding coherence coefficient of the kth target point in the ith interference channel;
2) a constant beta is arbitrarily selected in the range of (0, th) so that beta is multiplied by pdf (n)i(k)；γi(k))<1, wherein ni(k)∈(-π,π)；
3) Generating two random numbers a uniformly distributed according to (0,1)1And a2Let y be-pi +2 pi-a1；
4) If a is2≤β·pdf(y；γi(k) Let n) theni(k) Otherwise, a is rejected1And a2And (4) returning to the step (3) until the condition is met.
And (4) repeatedly executing the steps (1) to (4) for each target point to generate phase noise corresponding to each target point in each interference channel.
Further, the generation process of the true interference phase of each interference channel is as follows:
firstly, inputting DEM information of real terrain or simulated terrain, system parameters of a multi-channel InSAR system, a signal-to-noise ratio and lengths of all base lines, and then calculating by an interference phase simulation model of the multi-channel InSAR system according to the DEM and the system parameters to obtain:
Figure RE-GDA0002281057650000024
wherein k is the kth target point in the DEM, h (k) is the elevation corresponding to the target point,
Figure RE-GDA0002281057650000031
for the corresponding true interference phase of the target point in the ith interference channel, BiFor the length of the base line corresponding to the ith interference channel, λ representing the carrier signalWavelength, H denotes the height of the SAR sensor, r0Denotes the center-of-view slope distance and α denotes the base line angle.
Further, the corresponding coherence coefficient γ of the k-th object point in the i-th interference channeli(k) The formula is as follows:
Figure RE-GDA0002281057650000032
wherein the SNR0(k)-1And SNRi(k)-1Respectively representing the signal-to-noise ratio corresponding to the main antenna and the ith auxiliary antenna; b is⊥iIs represented by BiCorresponding vertical base length, BiFor the base length, B, corresponding to the ith interference channel⊥CIs the critical vertical baseline length.
Further, the probability density function of the phase noise of the target point is calculated according to the following formula:
Figure RE-GDA0002281057650000033
wherein pdf (n)i(k)；γi(k) Means phase noise corresponding to the k-th object point in the i-th interference channel
Figure RE-GDA0002281057650000034
Is determined by the probability density function of (a),
Figure RE-GDA0002281057650000035
and phii(k) Respectively representing the corresponding real interference phase and the interference phase with noise, gamma, of the k-th target point in the i-th interference channeli(k) And representing the corresponding coherence coefficient of the k-th target point in the ith interference channel.
A multi-channel InSAR interferogram simulation system accounting for eclipse and shadow, comprising:
a true interference phase generation unit: generating real interference phases of all interference channels by acquiring DEMs of real terrains or simulated terrains and system parameters and signal-to-noise ratios of a multi-channel InSAR system and utilizing an interference phase simulation model of the multi-channel InSAR system;
interference phase noise generation unit: based on system parameters, signal-to-noise ratio and base line length, calculating the corresponding coherence coefficient of each target point in each interference channel by using a coherence coefficient calculation model; calculating probability density functions of interference phase noise corresponding to each target point in each interference channel based on the coherent coefficients, and generating the interference phase noise of each target point in each interference channel by using the probability density functions of the interference phase noise;
a noise superposition unit: superposing interference phase noise and a real interference phase to obtain a real interference phase with noise;
shadow region and overlap region extraction unit: extracting a shadow region and an overlap region by detecting the shadow region and the overlap region in the SAR image;
shadow region and overlap region noise processing unit: weighted superposition and replacement are respectively carried out on the noisy interference phases of the target points in the overlap area and the shadow area: in the overlap area, weighting and overlapping the noisy interference phases of the target points with the same slant range by taking the coherence coefficient as the weight to obtain the noisy interference phases considering overlap on the same slant range resolution unit; replacing the noisy interference phase of the target point in the shadow area with white Gaussian noise;
the multichannel InSAR interferogram simulation unit winds the latest interference phases of all the slant range resolution units, and arranges the interference phases again according to the size of the slant range by taking the slant range resolution units as units, so that the multichannel InSAR interferogram taking overlapping and shading into consideration is obtained.
Furthermore, the interference phase noise generating unit generates the interference phase noise of each target point in each interference channel by using an interference phase noise probability density function and adopting a round selection method.
Advantageous effects
The invention provides a method and a system for simulating a multichannel InSAR interferogram considering overlapping and shading, wherein the method comprises the steps of firstly calculating specific parameters of an existing DEM and a multichannel InSAR system to obtain the real interference phase of each interference channel; then generating corresponding phase noise according to the probability density function of the interference phase and adding the phase noise into the real interference phase; then, weighting and superposing interference phases of target points with the same slant distance in a superposition area by taking a coherence coefficient as a weight, and directly replacing Gaussian white noise in a shadow area; and finally, rearranging the interference phases according to the size of the skew distance, thereby obtaining a multi-channel InSAR interference phase diagram considering the overlapping and the shadow. Compared with the prior art that the phase unwrapping is carried out on the overlapping area, the phenomenon that the top and the bottom of the overlapping area are inverted after unwrapping positioning is caused, and height estimation errors are caused; in the radar echo signals in the shadow area, except for thermal noise or coherent speckle noise of nearby strong echoes, other signals do not exist, and the elevation information of the signals cannot be directly obtained by an InSAR technology; after the influence of the overlap mask and the shadow is considered, the generated simulation interference pattern is closer to a real interference pattern, and is more real and effective than the existing simulation method. Analysis and simulation results show that the method is simple and easy to implement, strictly considers the distribution function of the interference phase noise, and can provide proper simulation data for performance comparison and quantitative analysis of various multi-channel InSAR technologies.
Drawings
FIG. 1 is a schematic illustration of the formation of an overlap and shadow;
FIG. 2 is a schematic diagram of a multi-baseline interferometric synthetic aperture radar system;
FIG. 3 is a geometric schematic of a multi-baseline InSAR system;
FIG. 4 is a flow chart of a DEM-based multi-channel InSAR eclipse and shadow simulation method;
FIG. 5 is a simulated scene terrain map;
FIG. 6 is a simulated interferogram of the ground distance direction x the azimuth direction of different channels;
FIG. 7 is a simulated interferogram of various channel skew directions x azimuth directions, wherein (a) is a method according to an example of the present invention and (b) is a method according to the prior art;
FIG. 8 is an enlarged view of the overlap area of different channel pitches x azimuth wherein (a) is the method of applying the example of the present invention and (b) is the prior art method;
FIG. 9 is a simulated interferogram of different channels after skew direction x azimuth direction noise addition.
Detailed Description
The invention will be further described with reference to the following figures and examples.
Fig. 4 is a multi-channel InSAR eclipse and shadow simulation method based on DEM according to an embodiment of the present invention, which includes the following steps:
(1) firstly, inputting information such as DEM (ground distance direction multiplied by azimuth direction) of real terrain or simulated terrain, system parameters of a multi-channel InSAR system, signal-to-noise ratio, length of each base line (or working frequency of each interference channel) and the like, and according to the DEM and the system parameters, an interference phase simulation model, namely a formula, of the multi-channel InSAR system
Figure RE-GDA0002281057650000051
Or
Figure RE-GDA0002281057650000052
Generating real interference phases of all interference channels, wherein k is a k target point in the DEM, h (k) is an elevation corresponding to the target point,
Figure RE-GDA0002281057650000053
or
Figure RE-GDA0002281057650000054
For the corresponding true interference phase of the target point in the ith interference channel, BiFor the base length, B, corresponding to the ith interference channel⊥iIs BiThe corresponding base line length and the geometric meaning of other parameters are shown in the geometric schematic diagram of the multi-base line InSAR system of FIG. 3.
In this example, the parameters of the multichannel InSAR system take the following values:
TABLE 1 multichannel InSAR System parameters
Figure RE-GDA0002281057650000055
(2) Calculating a model or formula from the coherence coefficient according to the system parameters, the signal-to-noise ratio and the length (or working frequency) of the base line
Figure RE-GDA0002281057650000061
Calculating the corresponding coherence coefficient of the kth target point in the ith interference channel, B⊥CIs the critical vertical baseline length.
(3) Then according to the coherence coefficient and formula
Figure RE-GDA0002281057650000062
Calculating to obtain the corresponding phase noise of the k target point in the ith interference channel
Figure RE-GDA0002281057650000063
Of the probability density function pdf (n)i(k)；γi(k) Wherein phi isi(k) Is a noisy interference phase.
(4) Then, the probability density function pdf (n) of the interference phase noise is obtainedi(k)；γi(k) Using a truncation approach to generate phase noise.
The selection method comprises the following steps: for the k-th target point, the generation process of the corresponding phase noise in the i-th interference channel is as follows:
1) let th equal 1/max (pdf (n)i(k)；γi(k)))；
2) A constant beta is arbitrarily selected in the range of (0, th) so that beta is multiplied by pdf (n)i(k)；γi(k))<1, wherein ni(k)∈(-π,π)；
3) Generating two random numbers a uniformly distributed according to (0,1)1And a2Let y be-pi +2 pi-a1；
4) If a is2≤β·pdf(y；γi(k) Let n) theni(k) Otherwise, a is rejected1And a2And (5) returning to the step (3) until the condition is met.
Repeating steps (1) - (4) for each target point generates a phase noise corresponding to each target point in each interference channel.
(5) And adding the corresponding real interference phase of each target point in each interference channel with the phase noise to obtain the interference phase with noise.
(6) And determining the positions of the overlapping area and the shadow area according to the geometric relation of the figure 1, and finding the corresponding slant range.
(7) For target points of the overlapped area, weighted superposition is carried out on the noisy interference phases corresponding to the target points with the same slant distance by taking a coherence coefficient as a weight, and the weighted superposition is combined into effective interference phases corresponding to the same slant distance resolution unit; for the target point of the shadow area, the original noisy interference phase is directly replaced by Gaussian white noise.
In the overlap area, weighted overlap is carried out on the noisy interference phases corresponding to the target points with the same slant distance by taking a coherence coefficient as a weight, and M target points are supposed to overlap in a slant distance resolution unit with the slant distance of r and the azimuth distance of z and are respectively the kth corresponding to the original DEMmFor an object point (which is also the mth overlapped object point in the resolution unit), the phase of the interference with noise corresponding to the resolution unit is:
Figure RE-GDA0002281057650000071
wherein phi isi(r, z) is the corresponding noise interference phase, gamma, taking into account the overlap mask of the ith interference channel on the slant range resolution unit with the slant range r and the azimuth distance zi(km) Denotes the kthmThe corresponding coherence coefficient of each target point in the ith interference channel; phi is ai(km) Denotes the kthmThe noise interference phase corresponding to the target point in the ith interference channel; e represents the base of the natural logarithm; j represents an imaginary unit;
(8) finally all phi are measurediAnd (r, z) taking a principal value, transforming the principal value into a range of (-pi, pi) or (0,2 pi), and rearranging interference phases according to the size of the skew by taking the skew resolution unit as a unit, thereby obtaining a (skew direction multiplied by azimuth direction) multichannel InSAR interference phase diagram considering overlapping and shadow.
A multi-channel InSAR interferogram simulation system accounting for eclipse and shadow, comprising:
a true interference phase generation unit: generating real interference phases of all interference channels by acquiring DEMs of real terrains or simulated terrains and system parameters and signal-to-noise ratios of a multi-channel InSAR system and utilizing an interference phase simulation model of the multi-channel InSAR system;
interference phase noise generation unit: based on system parameters, signal-to-noise ratio and base line length, calculating the corresponding coherence coefficient of each target point in each interference channel by using a coherence coefficient calculation model; calculating probability density functions of interference phase noise corresponding to each target point in each interference channel based on the coherent coefficients, and generating the interference phase noise of each target point in each interference channel by using the probability density functions of the interference phase noise;
a noise superposition unit: superposing interference phase noise and a real interference phase to obtain a real interference phase with noise;
shadow region and overlap region extraction unit: extracting a shadow region and an overlap region by detecting the shadow region and the overlap region in the SAR image;
shadow region and overlap region noise processing unit: weighted superposition and replacement are respectively carried out on the noisy interference phases of the target points in the overlap area and the shadow area: in the overlap area, weighting and overlapping the noisy interference phases of the target points with the same slant range by taking the coherence coefficient as the weight to obtain the noisy interference phases considering overlap on the same slant range resolution unit; replacing the noisy interference phase of the target point in the shadow area with white Gaussian noise;
the multichannel InSAR interferogram simulation unit winds the latest interference phases of all the slant range resolution units, and arranges the interference phases again according to the size of the slant range by taking the slant range resolution units as units, so that the multichannel InSAR interferogram taking overlapping and shading into consideration is obtained.
The present embodiment is understood by referring to fig. 1 to 3, where S in fig. 1 refers to a satellite and θ to a radar down-view angle. The trapezoid angles alpha and beta represent the angle formed by the terrain and the ground. DotP1、P2And P3Are three different points of the ground target under the same slope distance. R1、R2And R3Are respectively their pitch, in this case R1＝R2＝R3. Thus, from A1、A2And A3The received interference phase signals will overlap and form a superposition mask. The B region represents a point which is occluded due to an excessively large slope of the back slope, and the portion thereof will form a shadow region in the SAR image.
In fig. 2, a plurality of antennas are provided in the cross-track line. Wherein D isi(i ═ 1,2, … M) denotes an antenna, DiAnd Di+1The distance between is d.
In FIG. 3, A0,A1,…,ANIs the antenna phase center distributed on the plane perpendicular to the course direction, and H is the ground and main antenna phase center A0Vertical distance therebetween, theta is the radar's downward angle of view, alpha is the horizontal base angle, r0,r1,…,rNRepresenting target points P and A0,A1,…,ANThe slant distance between the two sides of the steel pipe,yto ground distance, h is the height of the target point P, A1,…,ANAnd A0Forming an interference base line B1,…,BNAnd B is⊥1,…,B⊥NThen the corresponding vertical baseline.
If the interferogram under the (ground) distance direction x azimuth direction coordinate system is directly simulated, because pixels with the same slant distance are not overlapped and a shadow area is not detected, no matter the interferogram is simulated by the text method or the method in the prior art, the influence of overlapping and shadow cannot be seen on the obtained interferogram, the simulation results of the two methods are not different, as shown in fig. 6 (if no special description is provided, the winding phase threshold is assumed to be limited between (-pi, pi) in the embodiment of the invention), fig. 6 is the simulation result when no phase noise is added, and as can be seen from the simulation result of fig. 6, the interference phase fringes are dense when the base line is long, the interference phase fringes are sparse when the base line is short, and the influence of the base line length on the density degree of the interference phase fringes, namely the frequency height is reflected.
If the DEM shown in FIG. 5 is converted into an oblique direction X azimuth direction coordinate system, the interferogram corresponding to each channel is obtained by detecting the overlapping and masking region and the shadow region according to a multi-channel InSAR interferogram simulation model. The simulation result of the noise-free multi-channel InSAR interferometric phase diagram obtained at this time is shown in fig. 7 (a). The marked frame is overlapped, the overlapped area is 849.97km to 850.00km, and the shaded area is 850.03km to 850.09 km. In the overlap mask region, because the reflected signals are subjected to aliasing, the interference phase fringes in the region obviously become denser as can be seen from the figure; in the shadow region, the reflected radar echo signal cannot be received, and no effective phase exists, so that the zero phase is assumed.
Fig. 7(b) does not consider the effects of superposition and shadowing, so that phase loss occurs in the superposition area from 849.97km to 850.00km (only the interference phase of one pixel is reserved), and the corresponding simulated interference phase is still generated in the shadow area from 850.07km to 850.09 km. Obviously, the simulation result of the method of the embodiment of the invention is closer to the real situation than the simulation result.
FIG. 8 is a magnified contrast image of interference fringes of overlapping mask regions in different channels under two methods. Fig. 8(a) is a simulation result of the method according to the embodiment of the present invention, and it can be seen that, in the overlap region, since the interference phases of different coordinate points within the same slant range are overlapped, the interference phase of the region is significantly changed, which shows the relevant characteristics of overlap. Fig. 8(b) is a simulation result of the prior art method, and it can be seen from comparison with fig. 8(a) that in the overlap area, since the interference phases thereof are not overlapped, the interference phase of one point is taken as a simulation result at different points of the same slant distance, and the interference phases of other pixels are lost, so that the corresponding interference phase thereof is obviously different from the interference phase of the overlap area shown in fig. 8 (a). Thereby verifying the superiority of the method described in the examples of the present invention.
Fig. 9 is the result after adding noise only, and the difference between the overlap and shadow areas is detailed in fig. 8.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.

Claims (8)

1. A multi-channel InSAR interferogram simulation method considering overlapping and shadowing is characterized by comprising the following steps:
generating a real interference phase and interference phase noise of each interference channel, and superposing the interference phase noise and the real interference phase to obtain a real interference phase with noise;
detecting a shadow area and an overlapping area in the SAR image, and extracting the shadow area and the overlapping area;
respectively carrying out weighted superposition and replacement on the noisy real interference phases of the target points in the overlap area and the shadow area: in the overlap area, weighting and overlapping the noise real interference phases of target points with the same slant range by taking a coherence coefficient as a weight to obtain the noise interference phases which consider overlap on the same slant range resolution unit; replacing the noisy interference phase of the target point in the shadow area with white Gaussian noise;
winding the latest interference phases of all the slant-range resolution units, and rearranging the interference phases according to the size of the slant range by taking the slant-range resolution units as units, thereby obtaining a multi-channel InSAR interference phase diagram considering overlapping and shading;
the method comprises the steps of obtaining a DEM of a real terrain or a simulated terrain, and system parameters and signal-to-noise ratios of a multi-channel InSAR system, and generating real interference phases of interference channels by using an interference phase simulation model of the multi-channel InSAR system;
the process of generating the interference phase noise is as follows: firstly, based on system parameters, signal-to-noise ratio and base line length, calculating a corresponding coherence coefficient of each target point in each interference channel by using a coherence coefficient calculation model; secondly, calculating a probability density function of interference phase noise corresponding to each target point in each interference channel based on the coherence coefficient; next, the interference phase noise of each target point in each interference channel is generated by using the interference phase noise probability density function.
2. The method according to claim 1, wherein in the overlap area, the noise-bearing real simulated interference phases of the target points with the same slant range are weighted and overlapped by taking the coherence coefficient as a weight, and the overlap-bearing noise-bearing interference phases of the same slant range resolution unit are obtained according to the following formula:
Figure FDA0002969639570000011
wherein phi isi(r, z) is the noise-carrying interference phase of the ith interference channel on the slant range resolution unit with the slant range r and the azimuth distance z, which takes into account the overlap mask, gammai(km) Indicating the kth of a certain resolution cellmThe corresponding coherence coefficient of each target point in the ith interference channel; phi is ai(km) Indicating the kth position in a certain overlapping resolution cellmThe noise interference phase corresponding to the target point in the ith interference channel; e represents the base of the natural logarithm; j represents an imaginary unit; m denotes the number of overlapping target points of a certain resolution element.
3. The method according to claim 1, wherein the interference phase noise of each target point in each interference channel is generated by using the probability density function of the interference phase noise in the following specific process:
assuming that the size of the interferogram is row x col column target points, the phase noise of all target points is initialized to zero by using a rounding method, and the following operations are performed from the first target point one by one:
1) let th equal 1/max (pdf (n)i(k)；γi(k)))，pdf(ni(k)；γi(k) A probability density function representing the phase noise corresponding to the k-th object point in the i-th interference channel,
Figure FDA0002969639570000024
Figure FDA0002969639570000025
and phii(k) Respectively representing the corresponding real interference phase and the interference phase with noise, gamma, of the k-th target point in the i-th interference channeli(k) Representing the corresponding coherence coefficient of the kth target point in the ith interference channel;
2) a constant beta is arbitrarily selected in the range of (0, th) so that beta is multiplied by pdf (n)i(k)；γi(k))<1, wherein ni(k)∈(-π,π)；
3) Generating two random numbers a uniformly distributed according to (0,1)1And a2Let y be-pi +2 pi-a1；
4) If a is2≤β·pdf(y；γi(k) Let n) theni(k) Otherwise, a is rejected1And a2And (4) returning to the step (3) until the condition is met.
4. A method according to any one of claims 1 to 3, wherein the true interference phase for each interference channel is generated as follows:
firstly, inputting DEM information of real terrain or simulated terrain, system parameters of a multi-channel InSAR system, a signal-to-noise ratio and lengths of all base lines, and then calculating by an interference phase simulation model of the multi-channel InSAR system according to the DEM and the system parameters to obtain:
Figure FDA0002969639570000021
wherein k is the kth target point in the DEM, h (k) is the elevation corresponding to the target point,
Figure FDA0002969639570000022
for the corresponding true interference phase of the target point in the ith interference channel, BiFor the ith interference channelThe length of the base line, λ represents the wavelength of the carrier signal, H represents the height of the SAR sensor, r0Denotes the center-of-view slope distance and α denotes the base line angle.
5. A method according to any one of claims 1 to 3, wherein the k-th object point has a corresponding coherence coefficient γ in the i-th interference channeli(k) The formula is as follows:
Figure FDA0002969639570000023
wherein the SNR0(k)-1And SNRi(k)-1Respectively representing the signal-to-noise ratio corresponding to the main antenna and the auxiliary antenna; b is⊥iIs represented by BiCorresponding vertical base length, BiFor the base length, B, corresponding to the ith interference channel⊥CIs the critical vertical baseline length.
6. A method according to any one of claims 1-3, characterized in that the probability density function of the phase noise of the target point is calculated according to the following formula:
Figure FDA0002969639570000031
wherein pdf (n)i(k)；γi(k) Means phase noise corresponding to the k-th object point in the i-th interference channel
Figure FDA0002969639570000032
Is determined by the probability density function of (a),
Figure FDA0002969639570000033
and phii(k) Respectively representing the corresponding real interference phase and the interference phase with noise, gamma, of the k-th target point in the i-th interference channeli(k) Indicating the corresponding coherence of the k-th object point in the i-th interference channelAnd (4) the coefficient.
7. A multi-channel InSAR interferogram simulation system accounting for eclipse and shadow, comprising:
a true interference phase generation unit: generating real interference phases of all interference channels by acquiring DEMs of real terrains or simulated terrains and system parameters and signal-to-noise ratios of a multi-channel InSAR system and utilizing an interference phase simulation model of the multi-channel InSAR system;
interference phase noise generation unit: based on system parameters, signal-to-noise ratio and base line length, calculating the corresponding coherence coefficient of each target point in each interference channel by using a coherence coefficient calculation model; calculating probability density functions of interference phase noise corresponding to each target point in each interference channel based on the coherent coefficients, and generating the interference phase noise of each target point in each interference channel by using the probability density functions of the interference phase noise;
a noise superposition unit: superposing interference phase noise and a real interference phase to obtain a real interference phase with noise;
shadow region and overlap region extraction unit: extracting a shadow region and an overlap region by detecting the shadow region and the overlap region in the SAR image;
shadow region and overlap region noise processing unit: weighted superposition and replacement are respectively carried out on the noisy interference phases of the target points in the overlap area and the shadow area: in the overlap area, weighting and overlapping the noisy interference phases of the target points with the same slant range by taking the coherence coefficient as the weight to obtain the noisy interference phases considering overlap on the same slant range resolution unit; replacing the noisy interference phase of the target point in the shadow area with white Gaussian noise;
the multichannel InSAR interferogram simulation unit winds the latest interference phases of all the slant range resolution units, and arranges the interference phases again according to the size of the slant range by taking the slant range resolution units as units, so that the multichannel InSAR interferogram taking overlapping and shading into consideration is obtained.
8. The system of claim 7, wherein the interference phase noise generation unit generates the interference phase noise of each target point in each interference channel by using a probability density function of the interference phase noise using a round-off method.
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