Abstract
A modified multiple-component scattering power decomposition for analyzing polarimetric synthetic aperture radar (PolSAR) data is proposed. The modified decomposition involves two distinct steps. Firstly, eigenvectors of the coherency matrix are used to modify the scattering models. Secondly, the entropy and anisotropy of targets are used to improve the volume scattering power. With the guarantee of high double-bounce scattering power in the urban areas, the proposed algorithm effectively improves the volume scattering power of vegetation areas. The efficacy of the modified multiple-component scattering power decomposition is validated using actual AIRSAR PolSAR data. The scattering power obtained through decomposing the original coherency matrix and the coherency matrix after orientation angle compensation is compared with three algorithms. Results from the experiment demonstrate that the proposed decomposition yields more effective scattering power for different PolSAR data sets.
Because of all-time, all-weather, and multi-band imaging characteristics, polarimetric synthetic aperture radar (PolSAR) has been widely used in various application areas. In recent years, various new PolSAR sensors have been launched and various PolSAR missions have been carried out, resulting in an increase in the amount of data requiring interpretation and processing. Target decomposition has emerged as the primary approach for interpretation and preprocessing due to its ease of implementation and strong physical meaning. For PolSAR images, target decomposition methods can be categorized into two groups: model-based decompositio
In 1998, Freeman and Durden introduced the Freeman-Durden decomposition (FDD
There are three primary methods for enhancing FDD. The first technique involves performing orientation angle compensation (OAC) on the coherency matrix or the covariance matrix of the PolSAR data prior to decompositio
In this letter, authors present an improved version of multiple component scattering decomposition for PolSAR data. Seven scattering models are use
This letter is organized as follows. The method is presented in Section I, including the proposed scattering model and the improved multiple-component scattering power decomposition. Experimental results on real PolSAR data are compared with several decomposition methods in Section 2, and followed by the conclusions in Section 3.
The multi-look data received in PolSAR systems using the {H, V} basis can be represented as a 3x3 complex matrix, which is also referred to as the coherency matrix. This matrix provides information about the polarization properties of the radar signal, including the phase and amplitude relationships between different polarization components. The coherency matrix of PolSAR image is presented as
. | (1) |
In the PolSAR systems, is a Pauli vector representing single-look data. The angle brackets denote the mean of several observations from the objects within a resolution cell. As a result, is a positive semidefinite Hermitian matrix.
Freeman and Durden developed the technique for PolSAR systems to break down the covariance matrix or the coherency matrix into three separate components. These three components consist of the surface scattering component, double-bounce scattering component, and volume scattering componen
, | (2) |
where , , , , , and denote surface scattering model, double-bounce scattering model, volume scattering model, helix scattering model, oriented dipole scattering model, compound dipole scattering model, and mixed dipole scattering model respectively. Correspondingly, , , , , , , and represent the corresponding scattering power of the seven scattering models.
, , , , , and are shown as follow
, | (3) |
, | (4) |
, | (5a) |
, | (5b) |
, | (5c) |
, | (5d) |
, | (6) |
, | (7) |
, | (8) |
, | (9) |
where coefficient in
This part presents an improved multiple component scattering decomposition for PolSAR data based on entropy and anisotropy . These two parameters are used to enhance the volume scattering power in vegetation areas with high-entropy. PolSAR data are divided into two categories: vegetation areas with high-entropy and other areas. Different decomposition techniques are adopted to obtain better scattering power. The volume scattering power in vegetation areas has been improved while ensuring good performance in other areas.
According to the decomposition formula in
, | (10) |
, | (11) |
, | (12) |
, | (13) |
where in Eqs. (
After removing the four scattering power mentioned above from the coherency matrix, the residual part contains surface scattering power, double-bounce scattering power, and volume scattering power as shown in
, | (14) |
. | (15) |
Each element in is represented as follows:
, | (16) |
, | (17) |
, | (18) |
, | (19) |
, | (20) |
. | (21) |
To ensure that the three scattering power, i.e., , and from is positive, it is necessary to ensure that , and are all positive. However, there may be certain pixels where these values are less than zero. In these instances, , , , and must be modified appropriately to ensure that , and remain non-negative. If <0, gradually reduce , , , and at the same time until >=0 is satisfied. Then, if is still less than 0, set and . Similarly, if is still less than 0, set and .
After obtaining the values of , , , and through the above solution, in order to calculate the value of , and , and which are not equal to 0 in some pixels are ignored, and the residual matrix is set to the following form as Eqs. (
, | (22) |
. | (23) |
To determine the volume scattering power , it is first necessary to determine whether the volume scattering is from the dihedral structure or the dipole structure. Set , such that if , the volume scattering model is shown as
, | (24) |
. | (25) |
After subtracting the volume scattering part from denoted by as shown in
, | (26) |
. | (27) |
The volume scattering power is represented as
, | (28) |
, | (29) |
where and are the eigenvalues, and and are the corresponding eigenvectors as shown in
. | (30) |
In cases where or of is less than zero, the volume scattering power can be gradually reduced until and conditions are met. Subsequently, surface scattering power and double-bounce scattering power can be calculated using
To ensure non-negative eigenvalues and , the volume scattering power is typically reduced, often leading to an underestimation of , especially in high-entropy regions. To address this issue, adjustments are made to the calculation method for volume scattering power in high-entropy regions. It is considered that of high-entropy regions comprises the double-bounce scattering and the volume scattering, with the surface scattering excluded.
Entropy of the coherency matrix is calculated as
, | (31) |
, | (32) |
. | (33) |
Anisotropy in
. | (34) |
The flowchart of the modified multiple-component scattering power decomposition for the original coherency matrix of the PolSAR data is depicted in

Fig. 1 Flowchart of modified multiple-component scattering power decomposition
图1 改进的多元散射能量分解方法流程图
In this letter, the orientation angle compensation (OAC) can be applied to the modified decomposition method. The rotation matrices are presented in Eqs. (
, | (35) |
, | (36) |
, | (37) |
, | (38) |
, | (39) |
. | (40) |
After the first OAC by , , as per
To demonstrate the effectiveness of the proposed multiple-component scattering power decomposition for PolSAR data based on eigenspace of coherency matrix, various experiments were conducted using fully PolSAR data. An L-band 4-look AIRSAR dataset covering San Francisco is utilized. It has a resolution of 10 m×10 m, with the radar incidence angles ranging from 5° to 60°, and the selected image size is 700×600 pixels. The data is in the {H, V} base, and the diagonal elements of the coherency matrix form a color image with representing blue, representing red, and representing green, as shown in

Fig. 2 Original image
图2 原图
Three decomposition algorithms are selected to compare and demonstrate the results of the proposed decomposition (PD) in this letter, including the Freeman-Durden scattering power decomposition (FDD

(a) FDD

(b) Y4D

(c) 7SD

(d) PD
Fig. 3 Decomposition results for the coherency matrix
图3 相干矩阵的分解结果

(a) FDD

(b) Y4D

(c) 7SD

(d) PD
Fig. 4 Decomposition results for the coherency matrix with OAC by
图4 R(θ)方位角补偿后相干矩阵的分解结果

(a) FDD

(b) Y4D

(c) 7SD

(d) PD
Fig. 5 Decomposition results for the coherency matrix with OAC by and
图5 R(θ)和U(φ)方位角补偿后相干矩阵的分解结果
As shown in Figs.

(a) FDD

(b) Y4D

(c) 7SD

(d) PD
Fig. 6 Surface scattering power of the coherency matrix
图6 相干矩阵的表面散射能量

(a) FDD

(b) Y4D

(c) 7SD

(d) PD
Fig. 7 Double-bounce scattering power of the coherency matrix
图7 相干矩阵的二次散射能量
To visually demonstrate the effectiveness of the proposed algorithm in scattering power, the scattering power of the original coherency matrix of the AIRSAR data without OAC are represented in Figs.

(a) FDD

(b) Y4D

(c) 7SD

(d) PD
Fig. 8 Volume scattering power of the coherency matrix
图8 相干矩阵的体散射能量
Quantitative comparison is made using the three zones in
From Tables 1-3, it can be observed that, compared with the other three algorithms, the proportion of surface scattering power of PD algorithm in zone1 is as high as 93.64%, only slightly inferior to Y4D. In zone2, PD algorithm has the highest proportion of double-bounce scattering power, while 7SD algorithm focuses its power on double-bounce scattering, mixed dipole scattering and surface scattering. PD algorithm concentrates its power on double-bounce scattering, surface scattering, and mixed dipole scattering sequentially. This phenomenon is consistent with the possible scattering types that may occur in urban areas. In zone3, PD algorithm obtains the highest volume scattering power, accounting for as much as 90.41%. Because the PD algorithm has been improved using entropy to decompose the coherency matrix. If entropy H is high and anisotropy A is low, i.e., , it considers that surface scattering does not exist, and the scattering power with scattering angle less than is classified as volume scattering, which increases the volume scattering power.
Method Powers | FDD | Y4D | 7SD | PD |
---|---|---|---|---|
91.62 | 94.21 | 91.85 | 93.64 | |
0.01 | 0.18 | 0.25 | 0.95 | |
8.36 | 3.02 | 7.91 | 2.60 | |
—— | 2.59 | 0 | 0.28 | |
—— | —— | 0 | 0.10 | |
—— | —— | 0 | 1.16 | |
—— | —— | 0 | 1.26 |
Method Powers | FDD | Y4D | 7SD | PD |
---|---|---|---|---|
13.21 | 30.41 | 25.81 | 32.90 | |
35.41 | 37.82 | 32.75 | 40.51 | |
51.38 | 26.50 | 6.51 | 7.03 | |
—— | 5.27 | 3.59 | 1.95 | |
—— | —— | 18.36 | 8.98 | |
—— | —— | 9.98 | 5.78 | |
—— | —— | 3.02 | 2.85 |
The scattering power from these decomposition algorithms for the coherency matrices with OAC by using in zone1, zone2, and zone3 is displayed in Tables 4-6, respectively. Because after OAC , , so PD and 7SD both have six scattering power. In zone1 (shown in
Method Powers | FDD | Y4D | 7SD | PD |
---|---|---|---|---|
92.07 | 94.67 | 92.26 | 93.96 | |
0.07 | 0.15 | 0.29 | 1.00 | |
7.91 | 2.61 | 7.44 | 2.34 | |
—— | 2.57 | 0 | 0.34 | |
—— | —— | 0 | 0.64 | |
—— | —— | 0 | 1.73 |
Method Powers | FDD | Y4D | 7SD | PD |
---|---|---|---|---|
19.58 | 34.61 | 28.45 | 31.04 | |
43.35 | 43.37 | 47.51 | 50.06 | |
37.08 | 17.03 | 3.39 | 4.89 | |
—— | 4.99 | 4.80 | 2.80 | |
—— | —— | 10.14 | 7.27 | |
—— | —— | 5.71 | 3.94 |
Method Powers | FDD | Y4D | 7SD | PD |
---|---|---|---|---|
3.79 | 9.06 | 13.58 | 4.49 | |
10.14 | 12.60 | 19.46 | 6.84 | |
86.07 | 73.69 | 48.26 | 88.58 | |
—— | 4.65 | 4.59 | 0.02 | |
—— | —— | 7.83 | 0.02 | |
—— | —— | 6.29 | 0.05 |
The scattering power from these decomposition algorithms for the coherency matrices with two types of OAC by using and successively in zone1, zone2, and zone3 is displayed in Tables 7-9, respectively. Because after OAC by and , and , PD and 7SD both have five scattering power. In zone1 (shown in
Method Powers | FDD | Y4D | 7SD | PD |
---|---|---|---|---|
94.08 | 93.95 | 94.52 | 95.17 | |
0.19 | 0.67 | 1.01 | 1.33 | |
5.74 | 5.38 | 3.45 | 1.34 | |
—— | —— | 0.62 | 1.33 | |
—— | —— | 0.41 | 0.82 |
Method Powers | FDD | Y4D | 7SD | PD |
---|---|---|---|---|
20.15 | 32.73 | 29.26 | 30.04 | |
43.93 | 45.83 | 50.19 | 51.77 | |
35.92 | 21.44 | 4.62 | 5.23 | |
—— | —— | 10.11 | 8.36 | |
—— | —— | 5.81 | 4.60 |
Method Powers | FDD | Y4D | 7SD | PD |
---|---|---|---|---|
4.34 | 8.05 | 10.55 | 5.31 | |
12.13 | 14.86 | 21.01 | 7.31 | |
83.53 | 77.09 | 54.86 | 87.30 | |
—— | —— | 7.29 | 0.02 | |
—— | —— | 6.29 | 0.05 |
Method Powers | FDD | Y4D | 7SD | PD |
---|---|---|---|---|
3.15 | 7.09 | 15.97 | 2.96 | |
7.07 | 9.14 | 15.17 | 6.53 | |
89.77 | 79.12 | 44.92 | 90.41 | |
—— | 4.65 | 4.46 | 0.02 | |
—— | —— | 5.38 | 0.02 | |
—— | —— | 7.11 | 0.02 | |
—— | —— | 6.99 | 0.04 |
This letter proposes a modified multiple-component scattering power decomposition. This proposed algorithm combines eigenvalue decomposition with model decomposition. Referring to 7S
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