| As one basic feature of electromagnetic wave, the utilization of radar polarization has the advantages of improving radar detection and recognition ability. Thanks to advances in POLSAR systems and information technology over the past decade,radar polarimetry has become a subject of recurring and globally intensifying interest all around world. However, the basic theories of radar polarimetry are still not perfect, which blocks its applicactions. With such a researching background, this thesis comprehensively investigates multi basic theories of radar polarimetry, namely target characteristic polarization theory and target scattering modeling. Some new theories and techniques are proposed, and their joint applications in improving terrain classification of polarimetric SAR(POLSAR) image are also systematically studied by theoretic analysis and experimental validation with lots of real high-resolution POLSAR data.Our research follows the ordinary process: first, existing work is thoroughly reviewed; second, based on related research and problems, researching points of this thesis are determined and further research is carried out. The work of this thesis can be concluded as follows.1) Target characteristic polarization theory for the coherent case is studied in greater detail, which develop target characteristic polarization theory ulteriorly. Power extrema and their conditions are derived firstly. And then the behavior of target characteristic polarization states as functions of target parameters are discussed for the first time and important conlusions are gived, which can be used to decrease computational complexity of target characteristic polarization states and anticipat their positions on the power density plot. Some of this studies have been published in some Chinese journals such as Signal Processing, cience in China Series E: Technological Science, etc.2) An improven Lagrange multiplier method is proposed to find the optimal polarizations for the co-polarized incoherent case. The traditional Lagrange multiplier method requires solving a sixth-order polynomial equation of the Lagrange multiplier. However, since it is unknown which of the roots corresponds to the maximum received power and which corresponds to the minimum, all the real roots need to be found, which will cause heavy computational burden. Thus two aspects are studied in thesis. First, We have proved for the first time that the largest and smallest roots of the Lagrange multiplier equation correspond to the maximum and minimum received powers, respectively. Second, the minimum search intervals of these two roots are also given by some theoretical analysises. Based on these researches, the flow of the proposed procedure is presented, which takes at least one to three times less computational time than the original procedure. The achievement of this aspect has been accepted to publish by"Signal Processing"and IEEE Transactions on Geoscience and Remote Sensing Letter.3) A fast algorithm is proposed to find the optimal polarizations for arbitrary polarized channel. Firstly, the function of received power in arbitrary channel is unified as the form of copolar power. Then based on the change of polarimetric basis, the copolar power is analyzed theoretically to obtain the minimum interval of target optimal polarization state, which provides theoretic support for simpling the process of obtaining optimal polarization states or anticipating their positions. Finally, the interval dichotomy is used to search in the minimum interval of target optimal polarization state. The experiment results have demonstrated the validity of the proposed algorithm. The achievement of this aspect has been accepted to publish by"acta geodaetica et cartographica sinica".4) A three step procedure is proposed to find the optimal polarizations of random targets for the case of no restriction between receiving and transimitting antenna. Considering that the scattering waves of random targets are partially polarized, the optimal receiving is firstly discussed for partially polarized wave, and the mismatched/matched receiving conditions and their corresponding receiving powers are obtained. Then the flow of the proposed three procedure is given: a) the optimal transmitted polarization states is obtained by optimizing mismatched/matched receiving power; b) the optimal scattering wave can be derived by substituting the optimal transmitted polarization states into the scattering equation; c) the optimal received polarization states can be obtained by the mismatched/matched receiving conditions for the incoherent case. The experiment results have demonstrated the practicability of the proposed procedure. The achievement of this aspect has been accepted to publish by"Signal Processing".5) after thoroughly reviewing existing works, we conclude that the scattering model based H/Alpha is the most integrated one of target scattering now. But through some theoretical analysis of polarimetric scattering entropy, we find that this scattering model is not reasonable for some cases because it sets out with the assumption that there is always a dominant"average"scattering mechanism, which doesn't always come into existence. And the more reasonable model is to represent target scattering with different scattering mechanism according to target scattering randomness. That is to say, the main scattering mechanism is used for low scattering randomness; the main and minor scattering mechanism are adopted together for median scattering randomness. The achievement of this aspect has been submitted to IEEE Transactions on Geoscience and Remote Sensing.6) Aiming at the deficiency of the similarity parameter to measure the degree of scattering similarity between distributed targets and canonical targets, a new parameter, namely polarimetric scattering similarity, is proposed based on the Pauli vector of a canonical target and the coherency matrix of a distributed target firstly. And the existing similarity parameter is just a special case of the proposed parameter. As an application, the parameters to several canonical targets, eg. metal sphere are derived and their physical meanings or properties are discussed. Finally, the relationship between the surface scattering similarity and average apha angle or polarimetry scattering entropy is also analysized. The achievement of this aspect has been accepted to publish by"Signal Processing","Acta Electronica Ainica"and IEEE Transactions on Geoscience and Remote Sensing Letter.7) Aiming at the deficiency of the present parameters to measure target scattering randomness, a novel parameter is defined based on the degree of polarization of target scattering wave. Firstly, after the analysis of the relationship between the degree of polarization of target scattering wave and target scattering randomness, the novel parameter is constructed with the degree of polarization of target scattering wave. And then the feasibility of the novel parameter to measure target scattering randomness is clarified by the analysis of the behavior of the novel parameter as a function of the scattering order in volume backscatter or target anisotropy. As the new parameter involves simple operation, it overcomes the time-consuming operation of the present parameters. The achievement of this aspect has been accepted to publish by"Signal Processing".8) A fast algorithm based on the automatic censoring is proposed to filter the speckle in POLSAR image. Firstly, a rectangle widow is sliding through each pixel of POLSAR imagery. For each current pixel, a global threshold is used to determine whether the current pixel is a point target. If not, then the homogeneous pixels of the same main scattering mechanism with this current pixel are censored automatically in the current sliding-window. Finally, the locally linear minimum mean-squared error (LLMMSE) estimator is used to filter this pixel with the selected pixels. The selection of homogeneous pixels based on the ML texture reduces the effect of speckle; the selection of the same main scattering mechanism pixels based on scattering similarity preserves the main scattering mechanism. The experiment results show that the proposed algorithm has the well theoretical and actual performance in speckle filtering, texture preservation and target main scattering preservation. The achievement of this aspect has been accepted to publish by"Signal Processing".9) Aiming at the deficiencies of the H/Alpha based classification, an alternative to H/Alpha based classification is proposed by replacing alpha angle with surface scattering similarity. But it still has the deficiency of arbitrarily fixed linear decision boundaries. Thus, a new scheme of unsupervised terrain classification is proposed based on multi scattering similarities. This new scheme divides terrain scattering into three classes with target scattering randomness firstly; and subdivides three classes into ten classes with surface scattering similarity, double scattering similarity and volume scattering similarity ulteriorly. As terrain scattering class is determined by target scattering similarities automatically, the deficiency of the arbitrarily fixed linear decision boundaries of Alpha angle is overcomed. Surface scattering, double scattering and volume scattering are the inherent characteristics of terrain physical scattering mechanisms, the classification result of the new method is consistent with the real terrain scattering. The achievement of this aspect has been accepted to publish by"Signal Processing"and"Acta Electronica Ainica".10) Aiming at the deficiencies of wishart classifier, a new parameter is proposed to measure target scattering difference first, and then applied to refine the result of the above proposed scattering classification. And good performance is avcheived for POLSAR image terrain classification. The achievement of this aspect has been accepted to publish by"Acta Electronica Ainica".
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