Studies of scintillation on earth-space paths

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Using the GPS to Improve Trajectory Position and Velocity Determination during Real-Time Ejection Seat Design, Test and Evaluation

Test and evaluation of the United States Air Force’s latest aircraft escape system technology requires accurate position and velocity profiles during each test to determine the relative positions between the aircraft, ejection seat, manikin and the ground. Current rocket sled testing relies on expensive ground based multiple camera systems to determine the position and velocity profiles. While these systems are satisfactory at determining seat and manikin trajectories for sled testing, their accuracy decreases when they are used for in-flight testing, especially at high altitudes. This research presents the design and test results from a new GPS-based system capable of monitoring all major ejection test components (including multiple ejection seat systems) during an entire escape system test run. This portable system can easily be integrated into the test manikin, within the flight equipment, or in the ejection seat. Small, low-power, lightweight Global Positioning System (GPS) GPS receivers, capable of handling high-accelerations, are mounted on the desired escape system component to maintain track during the escape system test sequence from initiation until the final landing. The GPS-based system will be used to augment the telemetry and photography systems currently being used at the Air Force (AF) and other Department of Defense’s (DoD) sled track test facilities to improve tracking accuracy and reduce testing costs

A Study of the Raindrop Size Distribution and its effect on Microwave Attenuation

Current frequency allocations below Ku- band are becoming increasingly congested. The problem continues to grow as the use of telecommunications becomes more pop- ular. In order to compensate for increased in demand, telecommunication operating frequencies have to be raised, yielding larger channel capacity. However, raising the operating frequency has the adverse result of intensifying the attenuation effects of the troposphere. At high frequencies, such as V-band, rain is known to cause the most severe attenuation. It has been shown that model data for numerical weather prediction, combined with propagation prediction models, can be used to forecast telecommunication link atten- uation. The forecast of attenuation can be used to improve the effectiveness of fade mitigation techniques. A key problem in determining rain attenuation from rainfall rate is the considerable variability of the raindrop size distribution (DSD). Based on the analysis of disdrometer and numerical weather prediction model data, the aim of this work is to constrain the parameters of the DSD and ultimately generate proba- bilistic forecasts of attenuation. Using disdrometer analysis, a relationship between mean raindrop size and rainfall rate is established, and a link between drop concentration and rainfall rate is also demon- strated. The DSD is shown to vary with season and shows some small relationships with meteorological parameters. It is concluded that, despite some relation of the DSD with rainfall rate and meteorological parameters, there are too many variables to conclusively recreate the DSD. Analysis of the attenuation-rainfall rate relationship illustrates that variability due to the DSD increases with frequency above 40GHz. At 30-40GHz the DSD is shown to have little impact on the attenuation-rainfall rate relationship. Finally, this thesis examines the horizontal structure of rain cells in the UK, demonstrating the suitability of the EXCELL model and illustrating that rain cells are more elliptical in the UK.EThOS - Electronic Theses Online ServiceGBUnited Kingdo