The energy balance of the Earth is regulated in part by ice clouds, which both reflect shortwave solar radiation and absorb infrared radiation from the Earth. These clouds appear frequently worldwide, with up to 70% coverage in tropical regions. The microphysics of ice clouds determines their radiative properties, and is important for accurately predicting the role of ice clouds in Earth’s energy balance. However, describing the microphysics of ice clouds remains a challenging problem, especially with regard to the shape of ice particles and the degree of ice particle surface roughening. In-situ studies have found evidence for ice surface roughness and have found many complex ice geometries; however, these studies are limited spatially and temporally. An approach which allows large-scale analysis is to retrieve these properties via theoretical modeling using satellite observations of polarized reflectance from ice clouds, since polarized reflectance is sensitive to the shape and roughness of ice particles. The theoretical model requires the scattering properties of simulated ice particles. These properties are obtained for 10 different ice shapes and 17 different levels of surface roughness. Simulations are performed for 3 different effective ice particle diameters: 30, 60 and 90 μm. Overall, the retrieved shape is dominated by the compact aggregate of columns. Although the exact composition of shapes varies from month to month, the compact aggregate of columns remains the most commonly retrieved shape. The retrieved roughness varies from moderately rough at σ = 0.1 to severely rough at σ = 0.5. Retrieved roughness varies more than shape, and smooth surfaced ice is most prominent in January. Tropical regions tend to have ice particles that are more roughened, while the midlatitudes and polar regions tend to have more smooth ice. In almost all cases, roughened ice represents > 60% of the total retrievals. The asymmetry parameter inferred from the retrieval of ice particle shape and roughness has a mean value near 0.77, with only small differences based on assumed ice effective diameter. The median value of the asymmetry parameter has a nearly constant value of approximately 0.75.

Graduate

This thesis presents a new dual circularly polarized antenna for ground penetrating radar applications. The new antenna design uses four crossed Resistive-Vee Dipoles (RVD) operating in bistatic mode to measure multiple polarizations. The antenna system is able to distinguish radially symmetric and linear targets with its ability to transmit right-hand circularly polarized (RHCP) fields and receive both left-hand circularly polarized (LHCP) and RHCP scattered fields. The type of target can be identified by comparing the relative amplitudes of the received LHCP fields and RHCP fields. For example, linear targets such as wires may be identified by equal amounts of scattered LHCP and RHCP fields. Numerical modeling was used to optimize the arrangement of the four RVDs in the RVD-based CP antenna to have low coupling and good circular polarization at close range. The resulting antenna design is shown to be very effective at finding buried wire targets without being costly. Additional modeling was performed to improve the circular polarization by changing the arm shape and resistive profile of the RVDs. Three methods are developed for estimating the spatial orientation angle of a detected wire target. The first method involves synthesizing transmission and reception of linear polarization at many angles to find the angle that matches the angle of the wire target. The second and third methods involve directly computing the angle of the wire target from the phase difference in the co-polarization and cross-polarization responses. All three methods provide accurate estimates. The RVD-based CP antenna enables strong detection of subsurface targets along with geometry-based classification of targets. The RVD-based CP antenna is well suited for finding buried wires and rejecting miscellaneous clutter that may be present in the ground.

Thesis (BSc. (Hons))--Australian National University, 2002. / Available via the Australian National University Library Electronic Pre and Post Print Repository. Title from title screen (viewed Mar. 28, 2003). "A thesis submitted for the degree of Bachelor of Science in Physics, The Australian National University" Bibliography: p. 77-80.

Thesis (Ph. D.)--University of Washington, 1915. / Autobiography. At head of title: The University of Washington. Department of chemistry. Bibliography: p. 37.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 175-178). Also available via the Internet.

Thesis (Ph. D.)--University of Michigan, 1934. / Cover title. "By A.L. Ferguson and George Dubpernell." "Reprinted from Trans. Electrochem. soc., vol. LXIV ... 1933."

Inaug.-diss.--Breslau. / Lebenslauf.

Thesis (Ph. D.)--University of Chicago, 1938. / Reproduced from type-written copy. "Private edition, distributed by the University of Chicago libraries, Chicago, Illinois." Includes bibliographical references.

Thesis (M.S.)--University of Michigan, 1984.