Disclosure of Invention
The present invention addresses the shortcomings of the prior art described above by providing a method for phase unwrapping based on Rank Information Filtering (RIF) that can obtain more robust results from noise-wrapped interferograms.
The technical scheme for realizing the aim of the invention is as follows:
a phase unwrapping method based on rank information filtering comprises the following steps:
1) According to the existing nonlinear filtering phase unwrapping model, combining a local phase gradient estimation technology based on a correction matrix beam model (AMPM) with a rank information filter, establishing a phase unwrapping model based on rank information filtering, and converting an interferogram phase unwrapping problem into a state estimation problem under a rank information filtering frame;
2) According to the rank information filtering phase unwrapping model obtained in the step 1), a one-dimensional rank information filtering phase unwrapping algorithm is established;
3) And (3) according to the one-dimensional rank information filtering phase unwrapping algorithm obtained in the step (2), replacing the one-dimensional coordinates with the two-dimensional coordinates, and establishing the two-dimensional rank information filtering phase unwrapping algorithm.
Further, in step 1), using the relationship between the unwrapping phases of adjacent pixels of the interferogram, the interferogram phase unwrapping system equation can be expressed as follows:
wherein x is
k Representing the unwrapping phase of the k pixels of the interferogram as a state variable to be evaluated; mu (mu)
k-1 Representing the true phase gradient of the k-1 pixel of the interferogram, the estimated value can be obtained by using the local gradient estimation technology based on AMPM
w
k-1 Representing phase gradient estimation errors; zeta type toy
k Observation noise vector, ζ, for interference image k-element state variable
1,k And xi
2,k Measurement noise added to the imaginary and real parts of the complex interference signal, h x
k ]Noiseless observation vectors which are the state variables of k pixels of the interference image; z
k Is the observation vector of the state variable of the k pixel of the interference image.
Further, in step 2), the interference pattern k-1 pixel state estimation value and the estimation error variance are respectively set as
And->
The phase unwrapping based on the rank information filtering comprises the steps of:
2-1) generating rank information sampling points according to a rank sampling principle;
2-2) carrying out state prediction on the interference image k pixels to obtain one-step prediction values and one-step prediction error variances of the state variables of the interference image k pixels;
2-3) converting the state space of the interference image k pixels into the information space to obtain an information matrix Y of one-step prediction of the state variables of the interference image k pixels
k Sum information vector
2-4) carrying out state update on the interference image k pixels to obtain the unwrapped phase of the interference image k pixels and the variance of the phase estimation error.
Further, in step 2-1), the method includes the steps of generating rank information sampling points according to the rank sampling principle:
in the method, in the process of the invention,
for the initial estimation of the state variable of the k pixels of the interference image, χ
i,k Represents a rank information sample point generated according to the rank sampling principle, n represents the dimension of the state vector, n=1, u
1 And u
2 Represents a standard state offset, where u
1 =0.2,u
2 =0.5; i represents the number of sampling points; />
Representing an interference pattern k-1 pixel state estimation value; />
Representing an estimation error variance; />
Representing the value of the state variable of the k-1 picture element.
Further, in step 2-2), the one-step predicted value of the interferogram k pel state variable:
one-step prediction error variance of interferogram k pel state variables:
in the method, in the process of the invention,
as the weight coefficient, Q
k Process error variance caused by the local gradient estimation technology based on AMPM; />
Representing one-step predicted values of state variables of k pixels of the interference image; />
Representing one-step prediction error variance of the state variable of the k pixels of the interference image; t represents a transpose operation.
Further, in step 2-3), the information matrix Y of one-step prediction of the interferogram k-pel state variables
k Sum information vector
Information matrix Y using H-infinity operator k When the optimization is performed, the information matrix in the formula (5) becomes:
wherein, gamma
s As the attenuation factor, 0.8.ltoreq.gamma.is usually taken
s Less than or equal to 2, I is the same as
Identity matrix of the same dimension.
Further, the method comprises the steps of,in step 2-4), the cross covariance
Measurement prediction value +.>
The method comprises the following steps:
z i,k =h[χ i,k ] (8)
information status distribution i k And corresponding information matrix distribution I k The method comprises the following steps:
wherein eta is k Observing vector residual error for interference image k pixel state variable, R k Observing noise variance for the interferogram k pel state variable,
updated information matrix Y k And information vector y k The method comprises the following steps of:
the updated state estimation values and the state estimation error variances are respectively as follows:
wherein,,
representing the state estimation of the k pixels of the interference image, namely the unwrapping phase of the k pixels of the interference image; />
Representing the phase estimation error variance of the k pixels of the interference image; the one-dimensional RIF unwrapping algorithm can unwrap the interferogram wrapping phases in a row-by-row or column-by-column manner until all wrapping phases in the interferogram are unwrapped.
Further, in step 3), two-dimensional coordinates (m, n) are used to replace one-dimensional k, and if the interference image element (m, n) is the pixel to be unwound, the initial state predicted value of the pixel is obtained
And its prediction error variance->
The calculation can be as follows:
wherein the pixels of the interference pattern (a, s) are unwrapped pixels in 8 pixels adjacent to the pixel to be unwrapped,
and->
Representing state estimates of the pixels of the interferograms (a, s) and their estimated error variances; />
Phase gradient estimation values representing interference pixels (m, n) and (a, s) can be obtained by using an AMPM-based local gradient estimation technique; d, d
(a,s) Weights representing the state estimates of the pixels of the interferograms (a, s);
rank information sampling point χ of interferogram (m, n) pixel i,(m,n) The calculation can be as follows:
one-step predicted value of state variable
State variable one-step prediction error variance
Wherein Q is [(m,n)|(a,s)] For the variance of process errors caused by the local gradient estimation technology based on AMPM, a fast path tracking strategy based on heap ordering is utilized to guide a phase unwrapping path, and a RIF phase unwrapping program is guided to complete recursion estimation of interferogram wrapping pixels along a path from high-quality pixels to low-quality pixels.
The method applies a high-efficiency and steady rank information filter to interferogram phase unwrapping, and combines an AMPM-based local phase gradient estimation technology with a fast path tracking strategy based on heap ordering, so as to provide a phase unwrapping algorithm based on rank information filtering. The method comprises the steps of establishing a phase unwrapping program based on rank information filtering, and acquiring phase gradient information of the phase unwrapping program based on rank information filtering by using a local phase gradient estimation technology based on AMPM; and a fast path tracking strategy based on heap ordering is utilized to guide a phase unwrapping path, so that a phase unwrapping program based on rank information filtering is ensured to unwrap an interferogram along a path from a high-quality pixel to a low-quality pixel. The simulation data and the actual measurement data experimental results show that the effectiveness of the algorithm can obtain a more robust result from the noise winding interference diagram.
Detailed Description
The following description of the technical solutions according to the embodiments of the present invention will be provided fully with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Examples:
a phase unwrapping method based on rank information filtering comprises the following steps:
1) According to the existing nonlinear filtering phase unwrapping model, combining an AMPM-based local phase gradient estimation technology with a rank information filter, establishing a phase unwrapping model based on rank information filtering, and converting an interferogram phase unwrapping problem into a state estimation problem under a rank information filtering framework;
using the relationship between the unwrapped phases of adjacent pixels of the interferogram, the interferogram phase unwrapping system equation can be expressed as follows:
wherein x is
k Representing the unwrapping phase of the k pixels of the interferogram as a state variable to be evaluated; mu (mu)
k-1 Representing the true phase gradient of the k-1 pixel of the interferogram, the estimated value can be obtained by using the local gradient estimation technology based on AMPM
w
k-1 Representing phase gradient estimation errors; zeta type toy
k Observation noise vector, ζ, for interference image k-element state variable
1,k And xi
2,k Measurement noise added to the imaginary and real parts of the complex interference signal, h x
k ]Noiseless observation vectors which are the state variables of k pixels of the interference image; z
k An observation vector which is an interference image k pixel state variable;
2) According to the rank information filtering phase unwrapping model obtained in the step 1), a one-dimensional rank information filtering phase unwrapping algorithm is established;
let the state estimation value of the interference pattern k-1 pixel and the estimation error variance respectively be
And->
The phase unwrapping based on the rank information filtering comprises the steps of:
2-1) rank information sampling points generated according to the rank sampling principle:
in the method, in the process of the invention,
for the initial estimation of the state variable of the k pixels of the interference image, χ
i,k Represents a rank information sample point generated according to the rank sampling principle, n represents the dimension of the state vector, n=1, u
1 And u
2 Represents a standard state offset, where u
1 =0.2,u
2 =0.5; i represents the number of sampling points; />
And->
Respectively representing the state estimation value and the estimation error variance of the interference image k-1 pixel;
representing a k-1 pel state variable value;
2-2) carrying out state prediction on the interference image k pixels to obtain one-step prediction values and one-step prediction error variances of the state variables of the interference image k pixels;
one-step predicted value of state variable of k pixels of an interferogram:
one-step prediction error variance of interferogram k pel state variables:
in the method, in the process of the invention,
as the weight coefficient, Q
k Process error variance caused by the local gradient estimation technology based on AMPM; />
Representing one-step predicted values of state variables of k pixels of the interference image; />
Representing one-step prediction error variance of the state variable of the k pixels of the interference image; t represents a transpose operation;
2-3) converting the state space of the interference image k pixels into the information space to obtain an information matrix Y of one-step prediction of the state variables of the interference image k pixels
k Sum information vector
Information matrix Y for one-step prediction of interference image k pixel state variable
k And information vector->
Information matrix Y using H-infinity operator k When the optimization is performed, the information matrix in the formula (5) becomes:
wherein, gamma
s As the attenuation factor, 0.8.ltoreq.gamma.is usually taken
s Less than or equal to 2, I is the same as
A co-dimensional identity matrix;
2-4) carrying out state update on the interference image k pixels to obtain unwrapped phases of the interference image k pixels and a variance of phase estimation errors; cross covariance
Measurement prediction value +.>
The method comprises the following steps:
z i,k =h[χ i,k ] (8)
information status distribution i k And corresponding information matrix distribution I k The method comprises the following steps:
wherein eta is k Observing vector residual error for interference image k pixel state variable, R k Observing noise variance for the interferogram k pel state variable,
updated information matrix Y k And information vector y k The method comprises the following steps of:
the updated state estimation values and the state estimation error variances are respectively as follows:
wherein,,
representing the state estimation of the k pixels of the interference image, namely the unwrapping phase of the k pixels of the interference image; />
Representing the phase estimation error variance of the k pixels of the interference image; the one-dimensional RIF unwrapping algorithm can unwrap the interferogram wrapping phases in a row-by-row or column-by-column manner until all wrapping phases in the interferogram are unwrapped;
3) And (3) according to the one-dimensional rank information filtering phase unwrapping algorithm obtained in the step (2), replacing the one-dimensional coordinates with the two-dimensional coordinates, and establishing the two-dimensional rank information filtering phase unwrapping algorithm.
Using two-dimensional coordinates (m, n) to replace one-dimensional k, and setting an interference image element (m, n) as an element to be unwound, and predicting the initial state of the element
And its prediction error variance->
The calculation can be as follows:
wherein the pixels of the interference pattern (a, s) are unwrapped pixels in 8 pixels adjacent to the pixel to be unwrapped,
and->
Representing state estimates of the pixels of the interferograms (a, s) and their estimated error variances; />
Representing phase gradient estimates between interference pixels (m, n) and (a, s) can be obtained using AMPM-based local gradient estimation techniques [13 ]];d
(a,s) Weights representing the state estimates of the pixels of the interferograms (a, s);
rank information sampling point χ of interferogram (m, n) pixel i,(m,n) The calculation can be as follows:
one-step predicted value of state variable
State variable one-step prediction error variance
Wherein Q is [(m,n)|(a,s)] For the variance of process errors caused by the local gradient estimation technology based on AMPM, a fast path tracking strategy based on heap ordering is utilized to guide a phase unwrapping path, and a RIF phase unwrapping program is guided to complete recursion estimation of interferogram wrapping pixels along a path from high-quality pixels to low-quality pixels.
In order to verify the performance of each method, different algorithms comprise an iterative least squares method (ILS), a quality guide method (QGPU) and the method, the simulation and the actual measurement interferograms are unwrapped under the same MATLAB software environment (Intel i5-8265U@1.60G CPU+8GB RAM), and the unwrapped results of each algorithm are compared and analyzed.
Fig. 1 shows three different simulated interferograms of 256×256 pixels, wherein fig. 1 a-1 c show the real interference phases, fig. 1 d-1 f show the noisy winding phase diagrams, respectively, with signal to noise ratios of 7.44dB, 2.18dB, 0.73dB, and the three interferograms are unwrapped using a Rank Information Filter Phase Unwrapping (RIFPU) algorithm.
FIGS. 2 a-2 c are the results of unwrapping FIG. 1d with the method of the present invention, where FIG. 2a shows unwrapped phases, FIG. 2b shows phase unwrapped errors, and FIG. 2c shows phase unwrapped error histograms;
FIGS. 3 a-3 c are the results of unwrapping FIG. 1e with the method of the present invention, where FIG. 3a shows unwrapped phases, FIG. 3b shows phase unwrapped errors, and FIG. 3c shows phase unwrapped error histograms;
FIGS. 4 a-4 c are the results of unwrapping FIG. 1f with the method of the present invention, where FIG. 4a shows unwrapped phases, FIG. 4b shows phase unwrapped errors, and FIG. 4c shows phase unwrapped error histograms;
fig. 5 a-5 c show the results of unwrapping measured data using the method of the present invention, wherein fig. 5a shows a partial Etna volcanic interference pattern, fig. 5b shows unwrapping phase, and fig. 5c shows unwrapping phase re-wrapping results.
The result of unwrapping the noise-wrapped phase diagrams shown in fig. 1 d-1 f by the method is shown in fig. 2 a-4 c, and it can be seen that the unwrapping phase obtained by the method has better consistency with the real interference diagram, and the phase unwrapping error is smaller. The first list lists the root mean square error of Iterative Least Squares (ILS), quality guided methods (QGPU) and the method unwrapping different signal-to-noise interference patterns, it can be seen that the root mean square error of the method is much smaller than the QGPU and ILS methods.
Table one phase unwrapping error for each algorithm
In the experimental data, fig. 5a is a partial Etna volcanic interference diagram, the unwrapping phase of the method is shown in fig. 5b, and the unwrapping phase is shown in fig. 5 c. The unwrapping phase obtained by the method is continuous and consistent, and the rewinding phase diagram stripes are consistent with the original interference diagram stripes, which shows that the method obtains more effective unwrapping results.
The preferred embodiments of the invention disclosed above are merely to aid in the description of the invention and are not intended to limit the invention to the specific embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best understand and utilize the invention.