Graduate Exam Abstract

Kyle Gilliam

M.S. Final

November 30, 2012, 10:00 AM

ECE Conference Room

A New Algorithm For Retrieval of Tropospheric Wet Path Delay Over Inland Water Bodies and Coastal Zones Using Brightness Temperature Deflection Ratios

Abstract: As part of former and current sea-surface altimetry missions, brightness temperatures measured by nadir-viewing 18-34 GHz microwave radiometers are used to determine apparent path delay due to variations in index of refraction caused by changes in the humidity of the troposphere. This tropospheric wet-path delay can be retrieved from these measurements with sufficient accuracy over open oceans. However, in coastal zones and over inland water the highly variable radiometric emission from land surfaces at microwave frequencies has prevented accurate retrieval of wet-path delay using conventional algorithms. To extend wet path delay corrections into the coastal zone (within 25 km of land) and to inland water bodies, a new method is proposed to correct for tropospheric wet-path delay by using higher-frequency radiometer channels from approximately 50-170 GHz to provide sufficiently small fields of view on the surface. A new approach is introduced based on the observation of small spatial scale variability in surface emissivity in contrast to the larger-scale variability in atmospheric absorption at several millimeter-wave channels. The new technique is based on the measurement of deflection ratios among several radiometric bands to estimate the transmissivity of the atmosphere due to water vapor. To this end, the Brightness Temperature Deflection Ratio (BTDR) method is developed starting from a radiative transfer model for a downward-looking microwave radiometer, and is extended to pairs of frequency channels to retrieve the wet path delay. Then a mapping between the wet transmissivity and wet-path delay is performed using absorption models. A frequency selection study is presented to determine the suitability of frequency triplets for accurate retrieval of tropospheric wet-path delay, and comparisons are made to frequency triplets based on currently-available microwave radiometers. Statistical noise analysis results are presented for a number of frequency triplets. Additionally, this thesis demonstrates a method of extracting contrasting surface pixels by use of edge detection algorithms to identify contrasting scenes in brightness temperature images for retrieval with the BTDR method. Finally, retrievals are demonstrated using measured brightness temperatures measured by several Special Sensor Microwave Imager/Sounder (SSMIS) for coastal and inland water scenes. For validation, these retrievals are qualitatively compared to independently-derived total precipitable water products from SSMIS, the Tropical Rainfall Measurement Mission (TRMM) Microwave Imager (TMI) and the Advanced Microwave Sounding Radiometer for Earth Observing System (EOS) (AMSR-E). Finally, a quantitative method for analyzing the data consistency of the retrieval is presented as an estimate of the error in the retrieved wet path delay. From these comparisons, one can see that the BTDR method shows promise for retrieving wet path delays over inland water and coastal regions and several future uses for the algorithm are described.

Adviser: Steven Reising
Co-Adviser: N/A
Non-ECE Member: Christian Kummerow
Member 3: Branislav Notaros
Addional Members: N/A

K. L. Gilliam, X. Bosch-Lluis, S. C. Reising, A. B. Tanner and S. T. Brown, "An Inland Water Wet Path Delay Retrieval Algorithm for Nadir-Viewing Microwave Radiometers," in USNC-URSI National Radio Science Meeting, Boulder, CO, Jan. 2012.

K. L. Gilliam, X. Bosch-Lluis, S. C. Reising, A. B. Tanner and S. T. Brown, "An Inland Water and Coastal Wet Path Delay Retreival Algorithm for Microwave Radiometers," in International Geoscience and Remote Sensing Symposium 2012, Munich, Germany, Jul. 2012.

K. L. Gilliam, X. Bosch-Lluis, S. C. Reising, A. B. Tanner, S. T. Brown and P. Kangaslahti, "Retrieval of Wet Path Delay From SSMIS Observations Over Coastal and Inland Water Regions Using the Brightness Temperature Deflection Ratio Method," in USNC-URSI National Radio Science Meeting, Boulder, CO, Jan. 2013, Under Review.

K. L. Gilliam, X. Bosch-Lluis, S. C. Reising, A. B. Tanner, S. T. Brown and P. Kangaslahti, "Retrieval of Tropospheric Wet-Path Delay in Coastal Zones and over Inland Water Using Microwave Brightness Temperature Deflection Ratios," IEEE Trans. Geosci. Remote Sens., Oct. 2012, Under Review.

Program of Study: