Electrical & Computer Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2765
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Item FREQUENCY DOMAIN CHARACTERIZATION OF OPTIC FLOW AND VISION-BASED OCELLAR SENSING FOR ROTATIONAL MOTION(2016) Gurel, Nil Zeynep; Horiuchi, Timothy K; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The structure of an animal’s eye is determined by the tasks it must perform. While vertebrates rely on their two eyes for all visual functions, insects have evolved a wide range of specialized visual organs to support behaviors such as prey capture, predator evasion, mate pursuit, flight stabilization, and navigation. Compound eyes and ocelli constitute the vision forming and sensing mechanisms of some flying insects. They provide signals useful for flight stabilization and navigation. In contrast to the well-studied compound eye, the ocelli, seen as the second visual system, sense fast luminance changes and allows for fast visual processing. Using a luminance-based sensor that mimics the insect ocelli and a camera-based motion detection system, a frequency-domain characterization of an ocellar sensor and optic flow (due to rotational motion) are analyzed. Inspired by the insect neurons that make use of signals from both vision sensing mechanisms, advantages, disadvantages and complementary properties of ocellar and optic flow estimates are discussed.Item VISION ALGORITHM FOR THE SOLAR ASPECT SYSTEM OF THE HIGH ENERGY REPLICATED OPTICS TO EXPLORE THE SUN MISSION(2014) Cramer, Alexander Krishnan; Chellappa, Rama; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work covers the design and test of a machine vision algorithm for generating high-accuracy pitch and yaw pointing solutions relative to the sun on a high altitude balloon. It describes how images were constructed by focusing an image of the sun onto a plate printed with a pattern of small cross-shaped fiducial markers. Images of this plate taken with an off-the-shelf camera were processed to determine relative position of the balloon payload to the sun. The algorithm is broken into four problems: circle detection, fiducial detection, fiducial identification, and image registration. Circle detection is handled by an "Average Intersection" method, fiducial detection by a matched filter approach, and identification with an ad-hoc method based on the spacing between fiducials. Performance is verified on real test data where possible, but otherwise uses artificially generated data. Pointing knowledge is ultimately verified to meet the 20 arcsecond requirement.Item A SUNLIGHT TO MICROWAVE POWER TRANSMISSION MODULE PROTOTYPE FOR SPACE SOLAR POWER(2013) Jaffe, Paul; Granatstein, Victor L; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The prospect of effectively limitless, continuous electricity from orbiting satellites for use on earth has captured many people's interest for decades. The proposed approach typically entails collection of solar energy, its conversion to microwave energy, and the wireless transmission of the microwaves to the earth. This offers the benefit of providing baseload power while avoiding diurnal cycle and atmospheric losses associated with terrestrial solar power. Proponents have contended that the implementation of such systems would offer energy security, environmental, and broad technological advantages to those who would undertake their development, while critics have pointed out economic, political, and logistical barriers. Niche applications, such as provision of power to remote military bases, might better tolerate the higher energy costs associated with early operational systems. Among recent implementations commonly proposed for solar power satellites, highly modular concepts have received considerable attention. Each employs an array of modules for performing conversion of sunlight into microwaves for transmission to earth. This work details results achieved in the design, development, integration, and testing of photovoltaic arrays, power electronics, microwave conversion electronics, and antennas for 2.45 GHz microwave-based "sandwich" module prototypes. Prototypes were fabricated and subjected to the challenging conditions inherent in the space environment, including solar concentration levels in which an array of modules might be required to operate. This testing of sandwich modules for solar power satellites in vacuum represents the first such effort. The effort culminated with two new sandwich module designs, "tile" and "step", each having respectively area-specific masses of 21.9 kg/m2 and 36.5 kg/m2, and mass-specific power figures of 4.5 W/kg at minimum one sun and 5.8 W/kg at minimum 2.2 suns (AM0) simulated solar illumination. The total combined sunlight to microwave efficiency of the modules was shown to be on the order of 8% and 7% for vacuum operation in the 10-6 torr regime. These represent the highest reported combined sandwich module efficiencies under either ambient or vacuum conditions, nearly quadrupling the previous efficiency record. The novel "step" concept was created to address thermal concerns and resulted in a patent publication. Results from module characterization are presented in context and compared with figures of merit, and practical thresholds are formulated and applied. The results and discussion presented provide an empirical basis for assessment of solar power satellite economic models, and point to several opportunities for improvements in area-specific mass, mass-specific power, and combined conversion efficiency of future prototypes.Item Identification of Air Traffic Flow Segments via Incremental Deterministic Annealing Clustering(2012) Nguyen, Alex T; Barras, John S; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Many of the traffic management decisions and initiatives in air traffic are based on "flows" of traffic in the National Airspace System (NAS), but the actual identification of the location and time of the flow segments are often left to interpretation based on observations of traffic data points over time. Having an automated method of identifying major flow segments can help to target traffic management initiatives, evaluate design of airspace, and enable actions to be taken on the collection of flights in a flow segment rather than on the flights individually. A novel approach is developed to identify the major flow segments of air traffic in the NAS that consists of a robust method for partitioning 4-dimensional traffic trajectories into a series of great circle segments, and clustering the segments using an Agglomerate Deterministic Annealing clustering algorithm. In addition, a very efficient algorithm to incrementally cluster the segments is developed that takes into account the spatial and temporal properties of the segments, and makes the method very suitable for real-time applications. Further, an enhancement to the algorithm is provided that requires only a small subset of the segments to be clustered, drastically reducing the run time. Results of the clustering technique are shown, highlighting various major traffic flow patterns in the NAS. In addition, organizing the traffic into the flow segments identified using the Incremental Clustering method is shown to have a potential reduction in the number of conflict points. An application of the flow information is presented in the form of a Decision Support Tool (DST) that aids traffic managers in establishing and managing Airspace Flow Programs. In addition, the flow segment information is applied to a low-level form of aggregated traffic management, showing that aggregating flights into the flow segments and rerouting the whole flow segment can be efficiently performed as compared to rerouting individual aircraft separately, and can reduce the number of conflict points. Considerations for implementing these techniques in real-time systems are also discussed.