Marine Geodesy, 32:284–302, 2009 Copyright © Taylor & Francis Group, LLC ISSN: 0149-0419 print / 1521-060X online DOI: 10.1080/01490410903094767 Louisiana Wetland Water Level Monitoring Using Retracked TOPEX/POSEIDON Altimetry HYONGKI LEE, 1 C. K. SHUM, 1 YUCHAN YI, 1 MOTOMU IBARAKI, 1 JIN-WOO KIM, 1 ALEXANDER BRAUN, 2 CHUNG-YEN KUO, 3 AND ZHONG LU 4 1 School of Earth Sciences, The Ohio State University, Columbus, Ohio, USA 2 Department of Geomatics Engineering, University of Calgary, Calgary, Canada 3 Department of Geomatics, National Cheng Kung University, Tainan, Taiwan 4 U.S. Geological Survey, Vancouver, Washington, USA Previous studies using satellite radar altimetry to observe inland river and wetland water level changes usually spatially average high-rate (10-Hz for TOPEX, 18-Hz for Envisat) measurements. Here we develop a technique to apply retracking of TOPEX waveforms by optimizing the estimated retracked gate positions using the Offset Center of Gravity retracker. This study, for the first time, utilizes stacking of retracked TOPEX data over Louisiana wetland and concludes that the water level observed by each of 10-Hz data with along-track sampling of ∼660 m exhibit variations, indicating detection of wetland dynamics. After further validations using nearby river gauges, we conclude that TOPEX is capable of measuring accurate water level changes beneath heavy- vegetation canopy region (swamp forest), and that it revealed wetland dynamic flow characteristics along track with spatial scale of 660 m or longer. Keywords Satellite radar altimetry, Louisiana wetlands, water level change, waveform retracking, stackfile 1. Introduction Coastal estuaries, which connect coastal ocean, wetlands, and land region, play an important role in ecology and environments in coastal regions. Wetlands typically occur in low-lying areas on the edges of lakes and rivers, or in coastal areas protected from waves. These wetlands are found in a variety of climates on every continent except Antarctica. Wetlands not only provide habitat for thousands of aquatic/terrestrial plant and animal species but also control floods by holding water like a sponge and reducing the velocity of storm water. Human activities have many negative impacts on wetlands and have become the main contributing factors to wetlands loss. Wetland loss is also caused by natural processes such as subsidence. Louisiana’s wetlands, one of the largest expanses of coastal wetland in the United States, have lost about 100–150 km 2 of its area per year, and the loss rate Received 29 December 2008; revised and accepted 4 June 2009. Address correspondence to Hyongki Lee, Division of Geodetic Sciences, School of Earth Sci- ences, The Ohio State University, 275 Mendenhall Laboratory, 125 South Oval Mall, Columbus, Ohio 43210. E-mail: lee.2444@osu.edu 284 Downloaded By: [Ohio State University Libraries] At: 13:50 12 August 2009