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Feliciano, WalberDesign and Implementation of a Radiometer and Rain Data Collection System for a Ka-band LEO Ground Station
Master of Science, University of Akron, 2009, Electrical Engineering
The design and performance of broadband Ka-band satellite communication systems depends mostly on the radio propagation characteristics of the earth-to-space path. The goal of this project was to develop and deploy a low earth orbit (LEO) ground station terminal capable of collecting radiometric and beacon data at Ka-band frequencies; which ranges approximately from 20 to 30 GHz. LEO satellites will employ high data rates to transfer very large amounts of data. High data rates require large channel bandwidth; a motivation to utilized Ka-band frequencies. Many radio frequency (RF) propagation effects are more severe at Ka-band frequencies than at lower frequencies. Collected data can be statistically analyzed and used to study the Earth’s atmosphere RF propagation effects at Ka-band, applicable to LEO links; thus improving the system availability models currently used. Collection of propagation data and its analysis is important for the development of satellite link analysis and communication component design, capability and requirements. Currently no LEO attenuation prediction models are available at Ka-band. This project provides a starting point to understand the dynamic effects of the Earth’s atmosphere on rapidly changing Ka-band transmission from a LEO spacecraft. A LEO propagation model will enable communication system designers to improve their systems availability.

Committee:

Nathan Ida, PhD (Advisor)

Subjects:

Electrical Engineering

Keywords:

LEO;Ka-band;Propagation;Ground Station;Radiometer

Thrush, Samantha ElaineFact Checking LIGO's Radiometer Code with Simulated LIGO Data
Bachelor of Science (BS), Ohio University, 2015, Astrophysics
Gravitational waves are predicted by general relativity to be emitted from very massive and fast-moving objects, ranging from cosmological sources to astrophysical objects. Two examples of such objects that pertain to this project are a neutron star in a binary system, such as Scorpius X-1, or black holes in a binary system. A key set of instruments that are used to search for gravitational waves are the LIGO detectors, which utilize interferometry in order to observe gravitational wave signals. As the signal strength is expected to be small relative to the background noise from a single LIGO detector, data from two detectors are cross-correlated to increase sensitivity to any potential gravitational waves. In order to test the effectiveness of the cross-correlation 'radiometer' code in detecting point sources similar to Scorpius X-1 near frequency bin borders, the code was modified to have the capability to add multiple simulated pulsar signals. To check that the changes to the radiometer code did not adversely affect the results reached by the code, two trials were run. The first trial, the Troubleshooting Trial, read in real LIGO data through the traditional means and explored the effects of adding simulated data via the modified code. The graphs from this trial were then graded on three criteria to ascertain if the modified code worked as expected and did not introduce error. Once the modified code completed its vetting, a second trial, the Bin Shifting Trial, was used to ascertain how well injected signals can be recovered when they fall on the border between frequency bins. Through a series of seven tests, simulated signals were created with peak frequencies ranging from being on a bin border to half a bin border away, where the bin sizing was 0.25 Hz. Uniform attenuation was expected on the trial with frequencies on the bin border, and the trial with the signals located between two bin borders was expected to have the smallest attenuation. These tests revealed anomalous attenuation for three of the signals in all cases in the bin shift trial, with normal attenuation occurring in the rest of the simulated signals. Two of these anomalously attenuated signals seemed to be created by a peak masking routine found in stochastic.m, while the other anomalous peaks are currently unaccounted for. In addition, both trials experienced abnormal attenuation at times, which needs to be further investigated. In order to have a greater understanding of the data’s behavior, there needs to be further exploration of the codes at hand with more thorough testing with smaller frequency shifting of signals, as well as additional tests that test more signal frequencies around the strangely attenuated signals.

Committee:

Douglas Clowe (Advisor)

Subjects:

Astronomy; Astrophysics; Physics

Keywords:

LIGO; radiometer code; stochastic; gravitational waves

Pan, JinmeiApplication of Passive and Active Microwave Remote Sensing for Snow Water Equivalent Estimation
Doctor of Philosophy, The Ohio State University, 2017, Geodetic Science and Surveying
Snow accumulation on the ground changes the energy balance between the land and the atmosphere, and stores winter precipitation for water supplies in many parts of the world. In practice, the snow water equivalent (SWE), defined as the equivalent depth of liquid water when snow completely melts, is difficult to map in cold regions except via remote sensing techniques. The microwave remote sensing (MWRS) has been used for SWE estimation since the 1980s based on the interactions of microwave radiation with snow crystals. In this study, physically based radiative transfer (RT) models and the Bayesian-based Markov Chain Monte Carlo (MCMC) approach were applied to develop a high-accuracy SWE retrieval algorithm. The models and the algorithms were tested using ground-based snowpit and microwave measurements. Two widely-used snow RT models were fully-compared in the aspects of snow micro-structure assumptions, volume scattering theories and the RT equation resolution. The Microwave Emission Model of Layered Snowpacks (MEMLS) based on the Improved Born Approximation (IBA) was shown to be an adequate observation model to estimate SWE using the multi-frequency brightness temperature (TB) at 10.65 to 90 GHz. The prior information is from a set of globally-available datasets, and the performance is tested for local prior information derived from historical ground measurements. The retrieval algorithm was later adapted for active microwave SWE retrieval using the backscattering coefficient at 10.2 to 16.7 GHz. Results showed that MEMLS-IBA can simulate the measured microwave signals with a 10-K accuracy for TB and a 1-dB accuracy for the backscattering coefficient. The passive microwave retrieval algorithm achieved an accuracy of 30-mm for shallow snow, with two-layer snow properties estimated. However, the active microwave retrieval algorithm reproduced similar accuracy only in the synthetic experiment using 1-layer snow property estimates. Future improvement requires a better active microwave observation model.

Committee:

Michael Durand (Advisor); Che-Kwan Shum (Committee Member); Ian Howat (Committee Member); Joel Johnson (Committee Member); Barbara Wyslouzi (Committee Member)

Subjects:

Earth; Geography; Hydrologic Sciences

Keywords:

SWE, snow, microwave remote sensing, radiometer, scatterometer, Markov Chain Monte Carlo

Nessel, James AaronEstimation of Atmospheric Phase Scintillation Via Decorrelation of Water Vapor Radiometer Signals
Doctor of Philosophy, University of Akron, 2015, Electrical Engineering
The coherent arraying of antenna elements by widely distributed ground-based antenna systems has proven to be a valuable technological approach for high precision astrometric measurements and imaging via Very Long Baseline Interferometry (VLBI) and has been performed with considerable success by radio astronomers for several decades. The fundamental factor limiting the precision in which these measurements can be conducted, however, is due to the turbulence-induced refractivity changes of the atmospheric medium (troposphere) through which the propagating waves must traverse. For radio science applications, this problem can be significantly reduced via three well-demonstrated means: (1) proper choice of ground site location (i.e., dry, high altitude climates), (2) conducting observations during non-turbulent times (i.e., nights vs. days, winter vs. summer), and (3) employing relatively long integration time (on the order of minutes) compensation through the use of water vapor radiometers in data post-processing. For communications applications, however, this may not necessarily be the case, and a means to accurately estimate the water vapor variability of the troposphere at short time scales will be required to efficiently combine signals from ground-based antenna elements in an array environment, particularly for transmit arraying. It is thus the goal of this research effort to identify and validate a means in which phase fluctuations induced by the atmosphere can be accurately measured which could be employed to ultimately improve the coherent combining of several spatially separated signals transmitted from ground to space without the use of an active source (i.e., receive signal). The method in which this will be accomplished is through the use of a passive radiometric technique capable of accurately determining phase fluctuations on the necessary time scales to provide real-time phase compensation to realize transmit arraying at Ka-band frequencies and higher. To improve the accuracy over the state of the art in radiometric water vapor retrieval techniques, a novel blind source separation technique has been developed and demonstrated. Utilizing experimental data using a water vapor radiometer and a two-element interferometer, it is statistically shown that the approach described herein improves water vapor retrieval accuracy, particularly during cloudy conditions, over the state of the art.

Committee:

Nathan Ida, Dr. (Advisor); Igor Tsukerman, Dr. (Committee Member); Arjuna Madanayake, Dr. (Committee Member); Kevin Kreider, Dr. (Committee Member); Ernian Pan, Dr. (Committee Member)

Subjects:

Communication; Electrical Engineering; Electromagnetics

Keywords:

propagation; atmosphere; microwave; antenna array; Ka-band; water vapor radiometer; phase scintillation; interferometer; blind source separation