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Monitoring Water Level Change and Seasonal Vegetation Change in the Coastal Wetlands of Louisiana Using L-Band Time-Series

Liao, Tien-Hao and Simard, Marc and Denbina, Michael and Lamb, Michael P. (2020) Monitoring Water Level Change and Seasonal Vegetation Change in the Coastal Wetlands of Louisiana Using L-Band Time-Series. Remote Sensing, 12 (15). Art. No. 2351. ISSN 2072-4292. https://resolver.caltech.edu/CaltechAUTHORS:20200722-122153414

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Abstract

Coastal wetlands are productive ecosystems driven by highly dynamic hydrological processes such as tides and river discharge, which operate at daily to seasonal timescales, respectively. The scientific community has been calling for landscape-scale measurements of hydrological variables that could help understand the flow of water and transport of sediment across coastal wetlands. While in situ water level gauge data have enabled significant advances, they are limited in coverage and largely unavailable in many parts of the world. In preparation for the NISAR mission, we investigate the use of spaceborne Interferometric Synthetic Aperture Radar (InSAR) observations of phase and coherence at L-band for landscape-scale monitoring of water level change and vegetation cover in coastal wetlands across seasons. We use L-band SAR images acquired by ALOS/PALSAR from 2007 to 2011 to study the impact of seasonal changes in vegetation cover on InSAR sensitivity to water level change in the wetlands of the Atchafalaya basin located in coastal Louisiana, USA. Seasonal variations are observed in the interferometric coherence (γ) time-series over wetlands, with higher coherence during the winter and lower coherence during the summer. We show with InSAR time-series that coherence is inversely correlated with Normalized Difference Vegetation Index (NDVI). Our analysis of polarimetric scattering mechanisms demonstrates that double-bounce is the dominant mechanism in swamps while its weakness in marshes hinders estimation of water level changes. In swamps, water level change maps derived from InSAR are highly correlated (r2 = 0.83) with in situ data from the Coastwide Reference Monitoring System (CRMS). From October to December, we observed that the water level may be below wetland elevation and thus not inundating wetlands significantly. Our analysis shows that water level can only be retrieved when both images used for InSAR are acquired when wetlands are inundated. The L-band derived-maps of water level change show large scale gradients originating from the Gulf Intracoastal Waterway rather than the main delta trunk channel, confirming its significant role as a source of hydrologic connectivity across these coastal wetlands. These results indicate that NISAR, with its InSAR observations every 12 days, will provide the measurements necessary to reveal large scale hydrodynamic processes that occur in swamps across seasons.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3390/rs12152351DOIArticle
https://www.mdpi.com/2072-4292/12/15/2351PublisherArticle
ORCID:
AuthorORCID
Lamb, Michael P.0000-0002-5701-0504
Additional Information:© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Received: 15 April 2020; Revised: 18 July 2020; Accepted: 20 July 2020; Published: 22 July 2020. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA), and supported by NASA’s Terrestrial Ecology Program. Authors acknowledge the help from, National Aeronautics and Space Administration (NASA), Jet Propulsion Laboratory (JPL), the Japan Aerospace Exploration Agency (JAXA), the Alaska Satellite Facility (ASF) and the U.S. Geological Survey (USGS) including providing access to the satellite images, wetlands gauge station information, and suggestion for data processing. The leading author would like to thank Charlie, Daniel, Tom, Jessica, and Talib for useful discussions, as well as the anonymous reviewers for their constructive comments. The research was supported by the Terrestrial Ecology Program at National Aeronautics and Space Administration (NASA). Author Contributions: All four authors devised the study. The SAR processing was done by T.-H.L. The data processing, the generation and analysis of results were performed by T.-H.L., M.S., and M.D. The hydrologic connection to the results was analyzed and interpreted by T.-H.L., M.S. and M.L. T.-H.L. generated the figures and all four authors contributed nearly equally in writing the manuscript. All authors have read and agreed to the published version of the manuscript. The authors declare no conflict of interest.
Funders:
Funding AgencyGrant Number
NASAUNSPECIFIED
Subject Keywords:InSAR, wetlands, water level change, ISCE
Issue or Number:15
Record Number:CaltechAUTHORS:20200722-122153414
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200722-122153414
Official Citation:Liao, T.-H.; Simard, M.; Denbina, M.; Lamb, M.P. Monitoring Water Level Change and Seasonal Vegetation Change in the Coastal Wetlands of Louisiana Using L-Band Time-Series. Remote Sens. 2020, 12, 2351
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104511
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:22 Jul 2020 19:31
Last Modified:22 Jul 2020 19:31

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