Three-Dimensional Interferometric ISAR Imaging Algorithm Based on Cross Coherence Processing

Interferometric inverse synthetic aperture radar (InISAR) has received significant attention in three-dimensional (3D) imaging due to its applications in target classification and recognition. The traditional two-dimensional (2D) ISAR image can be interpreted as a filtered projection of a 3D target’s reflectivity function onto an image plane. Such a plane usually depends on unknown radar-target geometry and dynamics, which results in difficulty interpreting an ISAR image. Using the L-shape InISAR imaging system, this paper proposes a novel 3D target reconstruction algorithm based on Dechirp processing and 2D interferometric ISAR imaging, which can jointly estimate the effective rotation vector and the height of scattering center. In order to consider only the areas of the target with meaningful interferometric phase and mitigate the effects of noise and sidelobes, a special cross-channel coherence-based detector (C3D) is introduced. Compared to the multichannel CLEAN technique, advantages of the C3D include the following: (1) the computational cost is lower without complex iteration and (2) the proposed method, which can avoid propagating errors, is more suitable for a target with multi-scattering points. Moreover, misregistration and its influence on target reconstruction are quantitatively discussed. Theoretical analysis and numerical simulations confirm the suitability of the algorithm for 3D imaging of multi-scattering point targets with high efficiency and demonstrate the reliability and effectiveness of the proposed method in the presence of noise.

SEISMIC SIGNAL ANALYSIS USING MINIMUM PHASE AND SINGULAR VALUE DECOMPOSITION METHODS. APPLICATION TO GROUNDROLL ATTENUATION

ABSTRACT. A challenge in land seismic data processing is the coherent noise groundroll. This noise is related to the propagation of surface waves of the Rayleigh type, this undesired event has as characteristics: low frequencies, high amplitudes and strong dispersion, which masks the events of interest in the stacked seismic section. The seismic data from the Tacutu Basin, besides having a low signal-to-noise ratio, are also strongly contaminated by groundroll noise, which makes it a challenge to obtain stacked seismic section with high resolution of this sedimentary basin. The 1D and 2D frequency filters are widely used for groundroll attenuation, but these methods besides attenuating the noisy also eliminate part of the signal by rejecting part of the frequency band of the seismic signal. Therefore, we are introduce a new filter to groundroll attenuation that uses two powerful tools for decomposition of the seismic signal together, minimum phase decomposition and singular value decomposition. The proposed method aims to estimate the reflectivity function for each seismic trace and then perform a decomposition of this reflectivity function. Since the low frequency noise is confined in the first portion of the decomposed signal it is possible to make a separation between the noise and the signal. The filtering method was included in the 2D seismic processing flow chart of the Tacutu Basin. The results showed that the proposed method was capable of attenuate the groundroll noise and generated at the end a stacked seismic section with a good resolution. Keywords: minimum phase decomposition, singular value decomposition, groundroll attenuation.RESUMO. Um desafio no processamento de dados sísmicos terrestres é o ruído coerente groundroll. Este ruído está relacionado à propagação de ondas de superfície do tipo Rayleigh, este evento indesejado tem como características: baixas frequências, altas amplitudes e forte dispersão, o que mascara os eventos de interesse na seção sísmica empilhada. Os dados sísmicos da Bacia do Tacutu, além de apresentar uma baixa relação sinal-ruído, também estão fortemente contaminados pelo ruído do solo, o que dificulta a obtenção de seções sísmicas empilhadas com alta resolução desta bacia sedimentar. Os filtros de frequência 1D e 2D são amplamente utilizados para a atenuação do groundroll, mas esses métodos além de atenuar o ruído também eliminam parte do sinal rejeitando parte da banda de frequência do sinal sísmico. Portanto, estamos introduzindo um novo filtro para a atenuação de groundroll que usa duas ferramentas poderosas para a decomposição do sinal sísmico, decomposição em fase mínima e decomposição em valor singular. O método proposto tem como objetivo estimar a função de refletividade para cada traço sísmico e então realizar a decomposição dessa função refletividade. Uma vez que o ruído de baixa frequência é confinado na primeira porção do sinal decomposto, é possível fazer uma separação entre o ruído e o sinal. O método de filtragem foi incluído no fluxograma de processamento sísmico 2D da Bacia do Tacutu. Os resultados mostraram que o método proposto foi capaz de atenuar o ruído groundroll e gerar ao final uma seção sísmica empilhada com boa resolução.Palavras-chave: decomposição em fase mínima, decomposição em valores singulares, atenuação do groundroll.

Ab Initio Calculations on the Structural, Mechanical, Electronic, Dynamic, and Optical Properties of Semiconductor Half-Heusler Compound ZrPdSn

The structural, mechanical, electronic, dynamic, and optical properties of the ZrPdSn compound crystallising into the MgAgAs structure are investigated by the ab initio calculations based on the density functional theory. The lattice constant, bulk modulus, and first derivative of bulk modulus were obtained by fitting the calculated total energy-atomic volume results to the Murnaghan equation of state. These results were compared to the previous data. The band structure and corresponding density of states (DOS) were also calculated and discussed. The elastic properties were calculated by using the stress-strain method, which shows that the MgAgAs phase of this compound is mechanically stable. The presented phonon dispersion curves and one-phonon DOS confirms that this compound is dynamically stable. In addition, the heat capacity, entropy, and free energy of ZrPdSn were calculated by using the phonon frequencies. Finally, the optical properties, such as dielectric function, reflectivity function, extinction coefficient, refractive index, and energy loss spectrum, were obtained under different pressures.

Seismic data deconvolution using Kalman filter based on a new system model

Seismic resolution plays an important role in geologic interpretation and reservoir prediction. To improve the vertical resolution of a seismic image, we have developed a new Kalman filter system model for seismic deconvolution. Similar to the conventional Kalman filter model for seismic deconvolution, our new Kalman model is also based on the common viewpoint that a reflected seismic record can be regarded as a convolution of a seismic wavelet with a reflection coefficient series. The new model uses a reversed seismic wavelet to slide across a reflectivity function to achieve the convolution result, instead of using a reversed reflectivity function to slide across a seismic wavelet in the conventional Kalman filter model. A simpler state equation for the new model is achieved, and the number of parameters to select is fewer than the conventional. Furthermore, the number of parameters can be reduced to only one by a theoretical demonstration for stationary noisy signals, which decreases the requirement for multiple parameters selection in the conventional model. The practical selection for this parameter should be a compromise between resolution improvement and noise amplification. Experimental results in the time and frequency domains on synthetic and field seismic records revealed that the Kalman filter based on the new model has the advantages of a higher resolution and peak signal-to-noise ratio (PS/N) than the conventional Kalman filter for stationary and nonstationary signals, and it works similarly to the Wiener filter for stationary signals, and it is superior to the Wiener filter in resolution and PS/N for nonstationary signals. The Kalman filter based on the new model can be applied to seismic resolution improvement.

Approximate Image Reconstruction in Landscape Reflection Imaging

Simple reflection imaging of landscape (scenery or extended objects) poses the inverse problem of reconstructing the landscape reflectivity function from its integrals on some particular family of spheres. Such data acquisition is encoded in the framework of a Radon transform on this family of spheres. In spite of the existence of an exact inversion formula, the numerical landscape reflectivity function reconstitution is best obtained with an approximate but judiciously chosen reconstruction kernel. We describe the working of this reflection imaging modality and its theoretical handling, introduce an efficient and stable image reconstruction algorithm, and present simulation results to prove the validity of this choice as well as to demonstrate the feasibility of this imaging process.