Walter Scott, Jr. College of Engineering

Graduate Exam Abstract

Abstract: This thesis describes the design, fabrication and testing of a miniaturized microwave radiometer as a prototype for satellite remote sensing of water vapor, called Microrad (“Micro” Radiometer). Microrad is a frequency-agile microwave radiometer that measures radiation from the atmosphere in the frequency range of 22-26 GHz. This is the frequency range near the water vapor absorption line at 22.235 GHz needed to provide vertical profile information on atmospheric humidity. The design includes a voltage controlled oscillator (VCO), enabling multi-frequency measurements to be performed sequentially as well as permitting avoidance or mitigation of potential radio frequency interference from transmitters in nearby bands or their out-of-band radiation, both of which are significant recent concerns in space-based passive microwave remote sensing.
Microrad evolved from the new and innovative design of the Compact Microwave Radiometer for Humidity profiling (CMR-H) developed at the Microwave Systems Laboratory in the Electrical and Computer Engineering Department. This design has enabled the deployment of a network of scanning ground-based radiometers to measure atmospheric water vapor with multiple observations of the same atmospheric volume from different perspectives. These first-time measurements allow the retrieval of 3D water vapor fields with fine spatial and temporal using 3D algebraic reconstruction tomography. CMR-H is a spectrometer radiometer with an RF/IF section based on monolithic microwave integrated circuit (MMIC) technology. A key improvement on the CMR-H design in Microrad is that all RF/IF components, except for an external IF filter and VCO, are packaged in a single MMIC multi-chip module (MCM). This provides a more compact design, allowing for greater modularity and flexibility in radiometer system design. The entire Microrad radiometer has a mass of 6 kg, a volume of 0.007 m3, and a maximum power consumption of 40W. For comparison, conventional radiometers are fabricated with waveguide- or coaxial connector-based RF/IF components and typically have a mass of 20-70 kg and a volume of 0.1-0.3 m3.
Water vapor is an important atmospheric gas. It has a strong role in climate change and severe storm formation. Observations of water vapor are used in weather prediction and climate change models. According to the Global Climate Observing System (GCOS), co-sponsored by the World Meteorological organization (WMO), the current observation of total column water vapor is adequate but water vapor profiles are not. The National Research Council (NRC) Committee on Earth Science Applications from Space’s decadal survey published in 2007 showed that the number of U.S. space-based Earth observation instruments is declining at a time when the WMO announced that “warming of the climate system is unequivocal”. In addition to beginning implementation of the first tier of NRC-recommended large missions, NASA has also created a “Venture Class” of small, cost-effective spacecraft to deploy light-weight, low-power instruments for environmental monitoring. This thesis describes a prototype light-weight, cost-effective, low-power microwave radiometer for observing water vapor profiles in the atmosphere from a space-based platform that also fits within the NASA Venture Class guidelines.
Adviser: Dr. Steven Reising
Co-Adviser: NA
Non-ECE Member: Dr. Christian Kummerow
Member 3: Dr. Branislav Notaros
Addional Members: NA
Program of Study: