Electromagnetic Modeling for Radar Remote Sensing of Snow-Covered Terrain

This thesis investigates the radar remote sensing of snow-covered terrain for estimation of snow equivalent water on global scale. The importance and impact of this research stems from the fact that water from snowmelt is the major source of water for inland cities and agriculture during summer. This effort is focused on developing a physics-based model for snow and a fully coherent polarimetric scattering model for snow above ground. Both the physical model and the forward polarimetric scattering model present a significant improvement compared to the existing models for snowpack. Computer-generated snow media are constructed using 3-D spatial exponential correlation functions, along with Lineal-Path functions that serve to preserve the connectivity of the snow particles. A fully-coherent model is presented through the use of the Statistical S-matrix Wave Propagation in Spectral-Domain (SSWaP-SD) technique. The SSWaP-SD depends on the discretization of the medium into thin slabs. Several realizations of a thin snow slab are solved numerically to form the statistics of the scattering matrix representing such a thin snow layer. For each thin slab of the snow-pack, a corresponding polarimetric N-port (representing different directions of scattering) S-matrix is generated. These S-matrices are cascaded using the SSWaP-SD method to calculate the total forward and backward bistatic scattered fields in a fully coherent way. The SSWaP-SD, in conjunction with a Method of Moments (MoM) code based on the Discrete-Dipole Approximation (DDA), is chosen to leverage both the time-efficient computations of the DDA and the full-coherency of the SSWaP-SD method, simultaneously. In addition to the MoM-DDA, a Finite Element Method (FEM) based on commercial software is used for cross-comparison and validation. The simulation results of the backscattering from an arbitrary thick snow layer are presented and validated with measurements. The underlying rough ground surface response is then estimated through both an analytical technique based on the Physical Optics (PO) method and a numerical solver based on MoM using a commercial full-wave solver. Finally, the complete response is then calculated by cascading the S-matrices representing the snow and the rough surface responses. The simulation results of the backscattering are presented using a Monte-Carlo process, which show very good agreement with measurements.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/167972/1/mzaky_1.pd

Radar Sub-surface Sensing for Mapping the Extent of Hydraulic Fractures and for Monitoring Lake Ice and Design of Some Novel Antennas.

Hydraulic fracturing, which is a fast-developing well-stimulation technique, has greatly expanded oil and natural gas production in the United States. As the use of hydraulic fracturing has grown, concerns about its environmental impacts have also increased. A sub-surface imaging radar that can detect the extent of hydraulic fractures is highly demanded, but existing radar designs cannot meet the requirement of penetration range on the order of kilometers due to the exorbitant propagation loss in the ground. In the thesis, a medium frequency (MF) band sub-surface radar sensing system is proposed to extend the detectable range to kilometers in rock layers. Algorithms for cross-hole and single-hole configurations are developed based on simulations using point targets and realistic fractured rock models. A super-miniaturized borehole antenna and its feeding network are also designed for this radar system. Also application of imaging radars for sub-surface sensing frozen lakes at Arctic regions is investigated. The scattering mechanism is the key point to understand the radar data and to extract useful information. To explore this topic, a full-wave simulation model to analyze lake ice scattering phenomenology that includes columnar air bubbles is presented. Based on this model, the scattering mechanism from the rough ice/water interface and columnar air bubbles in the ice at C band is addressed and concludes that the roughness at the interface between ice and water is the dominate contributor to backscatter and once the lake is completely frozen the backscatter diminishes significantly. Radar remote sensing systems often require high-performance antennas with special specifications. Besides the borehole antenna for MF band subsurface imaging system, several other antennas are also designed for potential radar systems. Surface-to-borehole setup is an alternative configuration for subsurface imaging system, which requires a miniaturized planar antenna placed on the surface. Such antenna is developed with using artificial electromagnetic materials for size reduction. Furthermore, circularly polarized (CP) waveform can be used for imaging system and omnidirectional CP antenna is needed. Thus, a low-profile planar azimuthal omnidirectional CP antenna with gain of 1dB and bandwidth of 40MHz is designed at 2.4GHz by combining a novel slot antenna and a PIFA antenna.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120674/1/wujf_1.pd