CN106405545A - A dual-temporal phase-different-mode dual-polarization SAR-like Pauli false-color image synthesis method - Google Patents

Abstract

The invention discloses a synthetic method of a Pauli false color image of a double-time-phase different-mode dual-polarization SAR type, which aims at the problem that a double-polarization Synthetic Aperture Radar (SAR) image cannot adopt Pauli to decompose and synthesize a false color image like a full-polarization SAR image.

Description

A dual-temporal phase-different-mode dual-polarization SAR-like Pauli false-color image synthesis method

【Technical field】

The invention belongs to the field of remote sensing image processing, and in particular relates to a Pauli-like false-color image synthesis method of a dual-temporal, different-mode, dual-polarization synthetic aperture radar.

【Background technique】

Synthetic Aperture Radar (SAR) is not limited by factors such as weather, geography and time. It can perform high-resolution imaging of the ground and has certain penetrating power. Therefore, it is widely used in military reconnaissance, resource detection, and environmental protection. In ground remote sensing applications such as monitoring, surveying and mapping, and geographic national conditions monitoring, radar satellites currently in orbit generally have dual-polarization imaging modes, and a few satellites have full-polarization imaging modes. Since the full-polarization mode includes ground objects More information can be synthesized by Pauli decomposition and false color to obtain better interpretation effect, but dual-polarization SAR does not have the advantage of full polarization, and its interpretation effect is far inferior to that of full polarization data, which restricts the full-polarization data. The scope of application of polarimetric SAR data.

The current dual-polarization SAR satellites in orbit can generally obtain dual-polarization images in HH+VH and VV+HV modes. For double-track dual-polarization images with a short time interval between the two scenes, it is generally believed that the observed objects are basically unchanged. The traditional method is to process the two phases separately or only use the intensity information of the image to synthesize a false-color image. Since the phase information of the image is not used, the image interpretation effect is not good, and its visualization effect is far inferior to that of the Pauli SAR with full polarization SAR. False color image. If the correlation information between the two kinds of dual-polarization data can be used to obtain a Pauli false-color image similar to that of full-polarization SAR, the visualization effect of the image will be greatly improved, and the interpretation will be assisted, which will help to further expand the application of dual-polarization SAR. application range.

【Content of invention】

The technical problem to be solved by the present invention is to provide a dual-temporal, different-mode, dual-polarization SAR-like Pauli false-color image synthesis method that can obtain better interpretation effects. The polarization mode acquired in a shorter time interval is HH +VH and VV+HV dual polarization SAR images in two time phases solve the problem of Pauli false color image generation similar to full polarization SAR data.

The common SAR dual polarization modes are HH+VH and VV+HV. Dual-temporal different-mode dual-polarization means that the dual-polarization SAR modes obtained in the two phases are different, namely HH+VH and VV+HV. The processing object of the present invention is the satellite-borne dual-temporal different-mode dual-polarization SAR single-view complex image acquired by heavy orbit, the time interval of image acquisition is relatively short, the satellite attitude and incident angle are approximately equal, and there is a strong correlation between the images , respectively represent the bitemporal data with two-dimensional complex vectors:

In order to solve the above-mentioned technical problems, a kind of dual-temporal different-mode dual-polarization SAR Pauli false color image synthesis method of the present invention comprises the following steps:

Step 1: Use the polynomial registration method based on orbit information rough registration and coherence coefficient fine registration to perform high-precision image registration, and the registration accuracy should be higher than 0.1 pixel;

Step 2: Set the window size N×N for set average processing, where N is an odd number and N≥3, and the sliding window processes the pixels in the center of the window one by one according to steps 3 to 8;

Step 3: Calculate the respective covariance coefficients of the dual-polarization SAR images by means of set averaging:

Among them, <·> represents the set average processing, which is to calculate the average value in the N×N sliding window as the set average estimated value of the center pixel of the window, and the superscript ^* is the conjugate of the complex number;

Step 4: Estimate the phase difference between the different polarizations of the dual polarization data from the covariance coefficient and The relationship between the phase difference and the covariance coefficient is as follows:

The formula for estimating the phase difference is:

Where tan ^-1 is the arc tangent function;

Step 5: Estimate the third element of the full-polarization-like data constructed in the two dual-polarization modes respectively:

Step 5.1: Estimate the scattering intensity of VV and HH polarization under HH+VH and VV+HV dual polarization respectively as:

Step 5.2: According to the assumption that HV and VH are equal in full-polarization SAR data (the amplitude and phase of HV and VH are equal), estimate the phases of VV and HH polarization under HH+VH and VV+HV dual polarization respectively as :

Step 5.3: According to the intensity and phase obtained in steps 5.1 and 5.2, calculate the quasi-full polarization data constructed in two dual polarization modes. The third element is:

where i is a unit imaginary number, s _{hh, v} are the HH polarization scattering coefficients estimated using the HH+VH data in the VV+HV polarization mode, where s _vv,h are the HH+VH polarization estimated using the VV+HV data The HH polarization scattering coefficient in the mode.

Step 6: Composing two full-polarization-like complex scattering vectors through the third element of the quasi-full-polarization data constructed in two dual-polarization modes;

Step 7: Estimate the mean polarization covariance matrix for the two phases via the two fully polarimetric scattering vectors

in and The quasi-full-polarization scattering vectors constructed for two dual-different-mode dual-polarization data respectively:

Step 8: Polarization covariance matrix Convert to polarization coherence matrix:

where the superscript ^T denotes the transpose of the matrix,

Step 9: According to the diagonal elements T ₁₁ , T ₂₂ , T ₃₃ of the polarized coherence matrix obtained, the false color image is synthesized according to the Pauli decomposition method of RGB false color combination:

red=log(T ₂₂ )

green=log(T ₃₃ )

blue=log(T ₁₁ ),

where log(·) is the natural logarithm function;

Step 10: Stretch the RGB channel to the gray value of 0-255, and calculate the thresholds a and b used when quantizing to 0-255 for each RGB channel, so that log(T _xx )<a,x=1,2 , the probability of 3 is 1%, the probability of log(T _xx )>b, x=1, 2, 3 is 1%, and log(T _xx ) is discretized to 0-255 according to the following formula:

Compared with the prior art, a dual-temporal, different-mode, dual-polarization SAR-like Pauli false-color image synthesis method of the present invention has the following characteristics:

1. The generated Pauli-like false-color image is very similar to the Pauli false-color image synthesized from the full-polarization SAR image, in which the vegetation appears green, the buildings and urban areas appear red or white, and the water body appears black and bluish-purple;

2. The characteristics of the objects on the Pauli false-color image correspond to a specific physical scattering mechanism, and the interpretation effect has been greatly improved;

3. Without the algorithm processing in the present invention, the observation values of the two time phases are directly processed as full-polarization SAR data to carry out Pauli-based false-color image synthesis. Since the data is not full-polarization mode data, the synthetic images HH-VV and HH The ground feature regularity of odd and even times of scattering corresponding to +VV is not obvious;

4. For ground objects mainly based on volume scattering, due to the poor correlation between HH and VH, VV and HV, the reliability of the parameters obtained in the present invention is reduced, and the visualization effect will be deteriorated to a certain extent;

5. When the time interval is shorter, the effect is better. As the time interval increases, the coherence of the two sets of images will decrease, and the effect of the composite image will become worse.

【Description of drawings】

The specific embodiment of the present invention is described in further detail below in conjunction with accompanying drawing, wherein:

Fig. 1 is a schematic flow chart of the present invention.

【detailed description】

Embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings,

As shown in Figure 1, the data in this embodiment are two time-phase images acquired by the C-band radar of Sentinel 1 A star of the European Space Agency. The area is located near the Strait of Gibraltar at the western junction of Europe and Africa, and the acquisition dates are 2014. On November 3 and November 15, 2014, the polarization modes were HH+VH and VV+HV, and the product form of the image was single-view oblique-distance complex images, which included vegetation, urban areas, suburbs, water surfaces, etc. A part of a certain burst of object type is processed, and the image size is 1500*5000. Before processing, high-precision registration has been completed between different polarization modes in the same phase. Include the following processing steps:

Step 1: Use the polynomial registration method based on the rough registration of orbit information and the fine registration based on coherence coefficient to perform high-precision registration, and the registration accuracy is 0.083 pixels;

Step 2: Set the window size of set average processing to 5×5, and the sliding window processes the pixels in the center of the window one by one according to steps 3 to 8;

Step 3: Calculate the respective covariance coefficients of the dual-polarization SAR images by means of set averaging:

Among them, <·> is the set average processing, and the set average processing is to calculate the average value in the 5×5 sliding window as the set average estimated value of the center pixel of the window, and the superscript * is the conjugate of the complex number;

Step 4: Estimate the phase difference between the different polarizations of the dual polarization data from the covariance coefficient and The relationship between the phase difference and the covariance coefficient is as follows:

The formula for estimating the phase difference is:

Where tan ^-1 is the arc tangent function;

Step 5: Estimate the third element of the full-polarization-like data constructed in the two dual-polarization modes respectively:

Step 5.1: Estimate the scattering intensities of VV and HH polarizations under HH+VH and VV+HV dual polarizations, respectively, as:

Step 5.2: Set the amplitude and phase of HV and VH in the full-polarization SAR data to be equal, and estimate the phases of VV and HH polarizations under HH+VH and VV+HV dual polarizations, respectively:

Step 5.3: According to the intensity and phase obtained in steps 5.1 and 5.2, calculate the third element of the quasi-full polarization data constructed in the two dual polarization modes, which are:

where i is a unit imaginary number, s _hh,v is the HH polarization scattering coefficient estimated from the HH+VH data in the VV+HV polarization mode, and s _vv,h is the HH+VH polarization estimated from the VV+HV data The HH polarization scattering coefficient under the mode;

Step 6: Form two kinds of fully polarized complex scattering vectors, which are:

Step 7: Estimate the mean polarization covariance matrix for the two temporal phases

Step 8: The above mean polarization covariance matrix Convert to polarization coherence matrix

where the superscript ^T denotes the transpose of the matrix

Step 9: Coherence Matrix for Polarization The diagonal elements T ₁₁ , T ₂₂ , T ₃₃ perform logarithmic operations, and perform RGB combination in the way Pauli decomposes false color synthesis:

red=log(T ₂₂ )

green=log(T ₃₃ )

blue=log(T ₁₁ ),

where log(·) is the natural logarithm function;

Step 10: Stretch the RGB channel to the gray value of 0-255, and calculate the thresholds a and b used when quantizing to 0-255 for each RGB channel, so that log(T _xx )<a,x=1,2 , the probability of 3 is 1%, the probability of log(T _xx )>b, x=1, 2, 3 is 1%, and then the log(T _xx ) is discretized to the gray value of 0-255 according to the following formula:

The results of this embodiment are as follows: (1) the generated Pauli false color image has a strong similarity with the Pauli false color image synthesized by the full polarization SAR image, in which the vegetation etc. appear green, and the buildings and urban areas appear red or white. The water body appears black to blue-purple.

(2) Compared with the direct false-color image of Red=HH, Green=(HV+VH)/2, Blue=VV, since the characteristics of each object on the Pauli false-color image correspond to a specific physical scattering mechanism, the interpretation effect has been greatly improved.

(3) Without the algorithm processing in the present invention, the observation value of two time phases is directly processed as the full polarization SAR data processing and carries out the false color image of Pauli base synthesis, because the data is not full polarization SAR data, synthetic image HH-VV and There is no clear regularity for the ground objects with odd and even times of scattering corresponding to HH+VV.

(4) For ground objects dominated by volume scattering, due to the poor correlation between HH and VH, VV and HV, the reliability of the parameters obtained in the present invention is reduced, and the visualization effect will be worse to a certain extent.

(5) In this embodiment, the time interval is 12 days, and the assumption that the ground objects have not changed is generally valid. When the time interval is shorter, the effect will be better. As the time interval increases, the coherence of the two sets of images will decrease, and the effect of the composite image will deteriorate.

The above descriptions are only preferred embodiments of the present invention, and the present invention can be used for both spaceborne and airborne SAR data processing.

Claims (3)

1. a kind of pair of phase anomalous mode dual polarization SAR class Pauli pseudo color coding hologram image synthesis method is it is characterised in that include following walking Suddenly：

Step 1：Using based on orbit information rough registration and based on coherence factor essence registration multinomial method for registering carry out high-precision Degree Image registration, registration accuracy should be higher than that 0.1 pixel；

Step 2：Window size N × N that setting ensemble average is processed, wherein N is odd number, and N >=3, and sliding window arrives according to step 3 Step 8 is processed one by one to the pixel of window center；

Step 3：Processed by ensemble average and calculate the respective covariance coefficient of dual polarization SAR image：

Wherein<·>Represent that ensemble average is processed, ensemble average processes and averages in the sliding window of N × N as window center picture The ensemble average estimated value of element, subscript^*It is the conjugation of plural number；

Step 4：Estimate the phase contrast between dual polarization data not same polarization from covariance coefficientWithWherein phase contrast with The relation of covariance coefficient is as follows：

The estimation equation of phase contrast is：

Wherein tan^-1For arctan function；

Step 5：Estimate the 3rd element of class full polarimetric SAR data of construction under two dual polarization modes respectively；

Step 6：Dissipated by the elementary composition two class complete polarizations of class full polarimetric SAR data the 3rd of construction under two dual polarization modes Penetrate vector；

Step 7：Estimate the average polarization covariance matrix of two phases by two class Complete polarimetry vectors

Step 8：Polarization covariance matrixBe converted to polarization coherence matrix：

Wherein subscript^TThe transposition of representing matrix：

Step 9：Diagonal element T according to the polarization coherence matrix obtaining₁₁,T₂₂,T₃₃, decompose RGB pseudo color coding hologram group according to Pauli The mode closed synthesizes pseudo color coding hologram image：

Red=log (T₂₂)

Green=log (T₃₃)

Blue=log (T₁₁),

Wherein log () is natural logrithm function；

Step 10：RGB channel is stretched to the gray value of 0-255, each passage of RGB calculates quantization respectively and uses to during 0-255 Threshold value a and b so that log (T_xx)<A, x=1,2,3 probability is 1%, log (T_xx)>B, x=1,2,3 probability is 1%, And to log (T_xx) discretization is to 0-255 according to the following formula：

2. a kind of pair of phase anomalous mode dual polarization SAR class Pauli pseudo color coding hologram image synthesis method according to claim 1, its It is characterised by：Estimate in described step 5 that the 3rd element of class full polarimetric SAR data of construction under two dual polarization modes includes respectively Following steps：

Step 5.1：The scattering strength of the VV and HH polarization under estimation HH+VH and VV+HV dual polarization is respectively：

Step 5.2：According to the equal hypothesis of HV and VH in full-polarization SAR data (amplitude of HV and VH and phase place are all equal), point Gu Suan the phase place of VV and HH polarization under HH+VH and VV+HV dual polarization not be：

Step 5.3：The full pole of class of construction under the intensity being obtained according to step 5.1 and 5.2 and two dual polarization modes of phase calculation Changing the 3rd element of data is：

Wherein i is unit imaginary number, s_hh,vIt is using the HH Polarization scattering coefficient under the VV+HV polarization mode of HH+VH data estimation, Wherein s_vv,hIt is using the HH Polarization scattering coefficient under the HH+VH polarization mode of VV+HV data estimation.

3. a kind of pair of phase anomalous mode dual polarization SAR class Pauli pseudo color coding hologram image synthesis method according to claim 1, its It is characterised by：The average polarization covariance matrix of two phases is estimated in described step 7For：

$\hat{C}=\frac{1}{2}({\hat{C}}_h+{\hat{C}}_v)=\frac{1}{2}({\hat{S}}_h{\hat{S}}_h^{*}+{\hat{S}}_v{\hat{S}}_v^{*});$

WhereinWithIt is respectively the multiple Scattering of Vector of class complete polarization that two double anomalous mode dual polarization data configurations go out：