Graduate Exam Abstract

Sharmila Padmanabhan

Ph.D. Final

November 17, 2008, 10:00 AM

ECE Conference Room

Three-Dimensional Water Vapor Retrieval Using a Scanning Network of Compact Microwave Radiometers

Abstract: Quantitative precipitation forecasting is currently limited by the paucity of observations on sufficiently fine temporal and spatial scales. In particular, convective storms have been observed to develop in regions of strong and rapidly evolving moisture gradients that vary spatially on sub-meso gamma scales (2 - 5 km). Therefore, measurements of water vapor aloft with high time resolution and sufficient spatial resolution have the potential to improve forecast skill for the initiation of convective storms. Such measurements may be used for assimilation into and validation of numerical weather prediction (NWP) models. Inversion of brightness temperatures measured by upward-looking, ground-based microwave radiometers allows the estimation of vertical profiles with high temporal resolution in both clear and cloudy conditions. Currently, water vapor density profiles are obtained using in-situ sensors on radiosondes and remotely using lidars, GPS ground-based networks, GPS radio occultation from satellites and a relatively small number of space-borne microwave radiometers. However, both the prediction of convective initiation and quantitative precipitation require knowledge of water vapor variations on sub-meso gamma scales (2-5 km) with update times on the order of a few tens of minutes. Due to the relatively high cost of both commercially-available microwave radiometers for network deployment and rapid radiosonde launches with close horizontal spacing, such measurements have not been available. Measurements using a network of multi-frequency microwave radiometers can provide information to retrieve the 3-D distribution of water vapor in the troposphere. An Observation System Simulation Experiment (OSSE) was performed in which synthetic examples of retrievals using a network of radiometers were compared with results from the Weather Research Forecasting (WRF) model at a grid scale of 500 m. These comparisons show that the 3-D water vapor field can be retrieved with an accuracy of better than 15%. Recently, field measurements at the DOE Atmospheric Radiation Measurement (ARM) Southern Great Plains site in Oklahoma have demonstrated the potential for coordinated, scanning microwave radiometers to provide 0.5-1 km resolution both vertically and horizontally with sampling times of 15 minutes or less. This work describes and demonstrates the use of algebraic reconstruction tomography to retrieve the 3-D water vapor field from simultaneous brightness temperatures using radiative transfer theory, optimal estimation and Kalman filtering.

Adviser: Dr. Steven C. Reising
Co-Adviser: n/a
Non-ECE Member: Dr. C. Kummerow
Member 3: Dr. V. N. Bringi
Addional Members: n/a


Program of Study: