Houra Rais

Conservative Polarimetric Scatterers and Their Role in Incorrect Extensions of the Cameron Decomposition

The properties of conservative symmetric polarimetric scatterer scattering matrices are examined. It is shown that the unambiguous rotation angle for conservative symmetric polarimetric scatterers is the interval (-pi/4,+pi/4] as compared with (-pi/2,+pi/2] for nonconservative symmetric scatterers. Errors relating to the Cameron decomposition, which are recently introduced into the literature, are discussed. It is demonstrated that these errors arise from a faulty symmetric scatterer scattering matrix distance measure. This, in turn, leads to an improper mapping of the symmetric scatterer unit disk to a hemisphere. The correct mapping of the symmetric scatterer unit disk to the symmetric scatterer unit sphere is described

Derivation of a Signed Cameron Decomposition Asymmetry Parameter and Relationship of Cameron to Huynen Decomposition Parameters

An alternate definition of the asymmetry parameter τ, appearing in the Cameron decomposition is presented. The new definition is signed as τs, but in absolute value, it is equivalent to the previous definition. The Cameron decomposition signed asymmetry parameter τs is given in terms of the Huynen decomposition parameters, including but not limited to the Huynen helicity (asymmetry) parameter. It is demonstrated that the Huynen decomposition asymmetry parameter is a poor indicator of scatterer symmetry. The relationship between the Cameron and Huynen decomposition parameters is examined for special cases.

Polarization Symmetric Scatterer Metric Space

The coherent polarization scattering matrix decomposition presented in Cameron et al. brought attention to the importance of Symmetric Scatterer Space, the space of scattering matrices corresponding to symmetric scatterers. Each symmetric scatterer scattering matrix can be associated with a complex number <i>z</i>, the scatterer-type parameter, where |<i>z</i>| les 1. A distance measure, <i>d</i>(<i>z</i> ₁, <i>z</i> ₂), was defined on Symmetric Scatterer Space providing a means of comparing scattering matrices. It will be demonstrated that Symmetric Scatterer Space is a metric space with metric <i>d</i>(<i>z</i> ₁, <i>z</i> ₂). A new mapping of the Unit Disc representation of Symmetric Scatterer Space to a sphere is also presented along with a metric on the sphere, <i>d</i> _s(thetas₁, phi₁; thetas₂, phi₂), that is equivalent to the metric <i>d</i>(<i>z</i> ₁, <i>z</i> ₂) on the Unit Disc.

Polarimetry and its use in automatic target detection with examples from Search and Rescue

The problem of automatically locating targets in synthetic aperture radar (SAR) imagery has traditionally been done in the image or intensity domain. A fully polarimetric SAR provides additional information that can be used in connection with SAR processing for speckle reduction, without any degradation of SAR resolution, and in automatic target detection for classifying the source of a particular scattering signature in an image. The polarimetric information can also aid in locating targets which lack a strong intensity return. This paper presents enhanced imagery and automatic target detection results using data collected under the NASA Search and Rescue Mission Office at Goddard Space Flight Center (GSFC) by the NASA/JPL AirSAR radar.

Polarimetric target detection techniques and results from the Goddard Space Flight Center Search and Rescue Synthetic Aperature Radar (SAR2) program

Over the SAR2 programs seven year history, a great deal of original research has been done in the area of automatic target detection for identifying aircraft crash site locations in synthetic aperture radar (SAR) imagery. The efforts have focused on using the polarimetric properties of the radar signal to both improve image quality and distinguish the crash sits from the natural background. A crash sites polarimetric signature is expected to be present even in the absence of a strong intensity return. Several of these advanced methods are summarized and a methodology for their application described. Several detection results are presented using data from the NASA/JPL AirSAR.

Synthetic aperture radar processing system for search and rescue

Synthetic aperture radar (SAR) is uniquely suited to help solve the search and rescue problem since it can be utilized either day or night and through both dense fog or thick cloud cover. This paper describes the search and rescue data processing system (SARDPS) developed at Goddard Space Flight Center. SARDPS was developed for the Search and Rescue Mission Office in order to conduct research, development, and technology demonstration of SAR to quickly locate small aircraft which have crashed in remote areas. In order to effectively apply SAR to the detection of crashed aircraft several technical challenges needed to be overcome. These include full resolution SAR image formation using low frequency radar appropriate for foliage penetration, the application of autofocusing for SAR motion compensation in the processing system, and the development of sophisticated candidate crash site detection algorithms. In addition, the need to dispatch rescue teams to specific locations requires precise SAR image georectification and map registration techniques. The final end-to-end processing system allows for raw SAR phase history data to be quickly converted to georeferenced map/image products with candidate crash site locations identified.

Polarization Scatterer Feature Metric Space

This paper extends prior work by Cameron and Rais to define new multidimensional representations of the reciprocal scatterer space and the general polarization scatterer space, including distance metric definitions for these representations. The relationship between the maximum symmetric scatterer type and the maximum value that can be attained by the asymmetry parameter is derived to determine the shape of the polarization reciprocal scatterer space. Moreover, a metric is derived for this space that reduces to the symmetric scatterer space metric when the asymmetry parameter is zero. These results are extended to the general polarization scatterer space by defining a metric on the polarization scatterer space that reduces to the polarization reciprocal scatterer metric when the reciprocity parameter θrec is zero.

SAR coherent change detection (CCD) for search and rescue

Recent advances in the areas of phase history processing, interferometry, and radargrammetric adjustment have made possible extremely accurate information extraction from synthetic aperture radar (SAR) image pairs by means of interferometric techniques. The potential gain in accuracy is significant since measurements can theoretically be determined to within a fraction of a wavelength (subcentimeter accuracy) as opposed to a fraction of pixel distance (meter accuracy). One promising application of interferometric SAR (IFSAR) is the use of coherent change detection (CCD) over large areas to locate downed aircraft. This application poses an additional challenge since IFSAR must be processed at longer wavelengths to achieve foliage penetration. In this paper a combination of advanced techniques is described for using airborne SAR imagery to carry out this mission. Performance parameters are derived, and some examples are given from actual data.

Polarimetric SAR Signature Detection Using the Cameron Decomposition

An approach to the detection of specific polarimetric SAR signatures is presented. The polarimetric response in a resolution cell can be viewed as a sample of the electromagnetic scattering matrix for that resolution cell. Through the use of multiple coherent apertures, multiple samples of the scattering matrix can be obtained. With the use of a suitable decomposition and a weighted log-likelihood formulation, it is possible to estimate the relative likelihoods that the observed scattering matrix responses match known electromagnetic signatures.

Wavenumber shift in search and rescue synthetic aperture radar

The wavenumber shift is an important tool in multiple pass synthetic aperture radar interferometry. In addition to overcoming baseline decorrelation, it has proven to have additional benefits. Chief among these is the ability to filter out much of the decorrelated signal, leaving the coherent portion. In the presence of foliage induced temporal decorrelation, this corresponds to filtering out much of the foliage return while strengthening any coherent ground return. We will examine this and other benefits of the wavenumber shift within the context of the Search and Rescue SAR program. An example based on ERS 1/2 data is provided.