Walter Scott, Jr. College of Engineering

Graduate Exam Abstract

Thaddeus Johnson
M.S. Final
Aug 29, 2014, 2:00 P.M.
Room 210, Computer Science
Abstract: Current satellite ocean altimeters include nadir-viewing, co-located 18-34 GHz microwave radiometers to measure wet-tropospheric path delay. Due to the large antenna footprint sizes at these frequencies, the accuracy of wet path retrievals is substantially degraded within 40 km of coastlines, and retrievals are not provided over land. A viable approach to improve their capability is to add high-frequency, wide-band millimeter-wave window channels in the 90-175 GHz frequency range, thereby achieving finer spatial resolution for a fixed antenna size. In this context, the upcoming Surface Water and Ocean Topography (SWOT) mission is being implemented by NASA and the French Space Agency (CNES) and is planned for launch in late 2020 to improve satellite altimetry to meet the science needs of both oceanography and hydrology and to transition satellite altimetry from the open ocean into the coastal zone and over inland water. To address wet-path delay in these regions, the addition of high-frequency (90-175 GHz) millimeter-wave window-channel radiometers to current Jason-class lower-frequency (18-34 GHz) microwave radiometers is expected to improve retrievals of wet-tropospheric delay in coastal areas and to enhance the potential for over-land retrievals.<br /><br />To this end, the High-frequency Airborne Microwave and Millimeter-wave Radiometer (HAMMR) has been designed, developed and demonstrated by a collaboration between Colorado State University and Caltech/NASA’s Jet Propulsion Laboratory. This airborne radiometer includes microwave channels at 18.7, 23.8, and 34.0 GHz at both H and V polarizations; millimeter-wave window channels at 90, 130, 168 GHz; and temperature and water vapor sounding channels adjacent to the 118 and 183 GHz absorption lines, respectively. Since one of the goals of this research is to demonstrate this technology for potential use in future Earth science missions, substantial effort has been put into ensuring that the radiometers have minimal mass and volume and are robust and well characterized.<br /><br />To this end, the alignment of the multiple reflectors and feed horns has been extensively tested and characterized, and a novel, wide-band blackbody calibration target has been designed and integrated into the system. All instrument sub-systems in support of the radiometers, such as power distribution and data acquisition, have been integrated into the chassis. The only external connections to the instrument are power, Ethernet and a GPS antenna, allowing a single operator to run the instrument aboard an aircraft using an external laptop. Engineering test flights have been performed for 15 hours aboard a Twin Otter aircraft over Colorado and Utah. These flights have demonstrated the reliability and robustness of this instrument as well as the improved special resolution of the high-frequency millimeter-wave window channels over those of lower-frequency microwave radiometers.
Adviser: Steven Reising
Co-Adviser: N/A
Non-ECE Member: Thomas H. Vonder Haar, Atmospheric Science
Member 3: Branislav M. Notaros, Electrical and Computer Engineering
Addional Members: Pekka Kangaslahti, Jet Propulsion Laboratory
Program of Study: