Graduate Exam Abstract

Swaroop Sahoo

M.S. Final

November 22, 2010, 12:00 noon

Engineering B101

Increasing Vertical Resolution of Three-Dimensional Atmospheric Water Vapor Retrievals using a Network of Scanning Compact Microwave Radiometers

Abstract: Thermodynamic properties of the troposphere, particularly water vapor content and temperature, change in response to physical mechanisms, including frictional drag, evaporation, transpiration, heat transfer and flow modification due to terrain. The planetary boundary layer (PBL) is characterized by a very high rate of change in its thermodynamic state on time scales of typically less than one hour. Large horizontal gradients in vertical wind speed and steep vertical gradients in water vapor and temperature in the PBL are associated with high-impact weather. Observation of these gradients in the PBL with high vertical resolution and accuracy is important for improvement of weather prediction. Satellite remote sensing in the visible, infrared and microwave has the capability of qualitative and quantitative measurements of many atmospheric properties, including cloud cover, precipitation, liquid water content and precipitable water vapor in the upper troposphere. However, the ability to characterize thermodynamic properties of the PBL is limited by the confounding factors of ground emission in microwave channels and of cloud cover in visible and IR channels. Ground-based microwave radiometers are routinely used in estimating thermodynamic profiles. The vertical resolution of profiles retrieved from radiometric brightness temperatures depends on the number and choice of frequency channels, the scanning strategy and the accuracy of brightness temperature measurements. In the standard technique, which uses vertically pointing brightness temperature measurements, the spatial resolution of retrieved water vapor is comparable to or larger than the altitude at which retrievals are estimated. This study focuses on the improvement of the vertical resolution of water vapor retrievals by including scanning measurements at a variety of elevation angles. In a vertically stratified atmosphere, observations at elevation angles less than 90 degrees contain water vapor profile information. An observation system simulation experiment (OSSE) was performed using local analysis and prediction system (LAPS) data to verify the validity of the resolution of the retrieved profile. Results of the OSSE will be presented and discussed. This thesis also discusses the European Space Agency?s project “Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water Vapor Effects” (METAWAVE) conducted in the fall of 2008. CSU deployed a ground-based network of three Compact Microwave Radiometers for Humidity profiling (CMR-Hs) in Rome to measure atmospheric brightness temperatures. These measurements were used to retrieve high-resolution 3-D atmospheric water vapor and its variation with time. High-resolution information about water vapor can be crucial for the mitigation of wet tropospheric path delay variations that limit the quality of Interferometric Synthetic Aperture Radar (InSAR) satellite interferograms. 3-D water vapor retrieval makes use of radiative transfer theory, algebraic tomographic reconstruction and Bayesian optimal estimation coupled with Kalman filtering. In addition, spatial interpolation (kriging) is used to retrieve water vapor density at unsampled locations. 3-D humidity retrievals from Rome data with vertical and horizontal resolution of 0.5 km are presented. The water vapor retrieved from CMR-H measurements is compared with MM5 Mesoscale Model output, as well as measurements from the Medium Resolution Imaging Spectrometer (MERIS) and the Moderate Resolution Imaging Spectroradiometer (MODIS).

Adviser: Dr. Steven C. Reising
Co-Adviser: N/A
Non-ECE Member: Dr. David A. Krueger (Physics)
Member 3: Dr. V. N. Bringi,(Electrical and Computer Engineering)
Addional Members: N/A,N/A

Accepted publication: Sahoo, S., S. C. Reising, S. Padmanabhan, J. Vivekanandan, F. Iturbide-Sanchez, N. Pierdicca, E. Pichelli and D. Cimini, "3-D Humidity Retrieval using a Network of Compact Microwave Radiometers to Correct for Variations in Wet Tropospheric Path Delay in Spaceborne Interferometric SAR Imagery," accepted for publication in the MicroRad 2010 Special Issue, IEEE Trans. Geosci. Remote Sensing, Oct. 2010.

Program of Study:
ATS 650
ATS 622
ECE 451
ECE 534
ECE 699
ECE 536
ECE 548
ECE 554