@article{923e319c9e23494a810ca2aecf61d7a7,
title = "Assessment of mitigation strategies for tropospheric phase contributions to InSAR time-series datasets over two Nicaraguan Volcanoes",
abstract = "Interferometric Synthetic Aperture Radar (InSAR) studies of ground displacement are often plagued by tropospheric artifacts, which are phase delays resulting from spatiotemporal variations in the refractivity of air within the troposphere. In this study, we focus on COSMO-SkyMed (X-band) InSAR products obtained over two different types of volcanoes in Nicaragua: the Telica stratovolcano and the Masaya caldera. We examine the applicability of an empirical linear correction method and three GlobalWeather Models (GWMs) with different spatial and temporal resolutions for removing the tropospheric phase component. We linearly invert the tropospheric-corrected interferograms using the Small BAseline Subset (SBAS) time-series technique to produce time-series of ground displacement. Statistical assessments were performed on the corrected interferograms to examine the significance of the applied corrections on the individual interferograms and time-series results. We find that the applicability of the correction methods is highly case-dependent and that in general, the temporal resolution of GWMs influences their ability to capture turbulent tropospheric phase delays. At the two target volcanoes, our study shows that none of the GWMs are able to accurately capture the tropospheric phase delays. Our study provides a guide for researchers using InSAR data in tropical regions who wish to use tropospheric model corrections to carefully assess the applicability of the different types of tropospheric correction methods.",
author = "Stephens, {Kirsten J.} and Christelle Wauthier and Bussard, {Rebecca C.} and Machel Higgins and LaFemina, {Peter C.}",
note = "Funding Information: Acknowledgments: All SAR COSMO-SkyMed data obtained over Masaya and Telica were provided through the Committee on Earth Observation Satellites (CEOS) Volcano Pilot and Demonstrator working group programs (http://ceos.org/ourwork/workinggroups/disasters/volcanoes/). TanDEM-X 12 m resolution data were obtained through the German Aerospace Center (DLR Proposal ID 1552). ERA5 ECMWF weather reanalysis datasets were obtained through the Copernicus Climate Change Service (C3S) online Data Store (https://cds.climate. copernicus.eu/cdsapp#!/home). HRES ECWMF zenith total delay maps were obtained through GACOS (http: //ceg-research.ncl.ac.uk/v2/gacos/) and provided MATLAB scripts for applying delay maps to interferograms were further modified to handle GAMMA interferograms and other functionalities by the authors. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus Information or Data contained in this manuscript. NARR NCEP Reanalysis data were provided online by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA (https://www.esrl.noaa.gov/psd/). MATLAB scripts for creating and applying NARR phase screens were kindly provided by Amy Parker (CSIRO Australia) and were also modified by the authors for creating and applying ERA5 phase screens to CSK data. Additionally, SBAS MATLAB original scripts were kindly provided by Susanna Ebmeier (Leeds University) and further modified to handle GAMMA interferograms and other functionalities by the authors. MATLAB code for computation of variograms was obtained and modified from “MATLAB{\textregistered} Recipes for Earth Sciences” (2015, 4 ed) by Martin H. Trauth. GMT6 was used to produce one figure [98]. Finally, this work was also conducted as part of the “Optimizing satellite resources for the global assessment and mitigation of volcanic hazards” Working Group supported by the John Wesley Powell Center for Analysis and Synthesis, funded by the U.S. Geological Survey. Authors would like to thank Romain Jolivet, Ang{\'e}lique Benoit, Kenneth Davis, Travis Tasker, Chuck Ammon, Raph{\"a}el Grandin, Francisco Delgado, Juliet Biggs, Fabien Albino, and Rowena Lohman for their helpful discussions and insight into weather models, time-series analysis and statistical assessment techniques, and Judit Gonzales-Santana and Sam Poppe for proof-reading later drafts of the manuscript. The authors would also like to thank five anonymous reviewers and the editor for their comments and suggestions which have helped to greatly improve this manuscript. Funding Information: This study was funded by National Aeronautics and Space Administration (NASA) Earth Surface and Interior (ESI) grants (NNX17AD70G) to P.C.L. and C.W., (ESI NNX16AK87G) to C.W., and NSF (EAR-0911546) to P.C.L. All SAR COSMO-SkyMed data obtained over Masaya and Telica were provided through the Committee on Earth Observation Satellites (CEOS) Volcano Pilot and Demonstrator working group programs (http://ceos.org/ourwork/workinggroups/disasters/volcanoes/). TanDEM-X 12 m resolution data were obtained through the German Aerospace Center (DLR Proposal ID 1552). ERA5 ECMWF weather reanalysis datasets were obtained through the Copernicus Climate Change Service (C3S) online Data Store (https://cds.climate.copernicus.eu/cdsapp#!/home). HRES ECWMF zenith total delay maps were obtained through GACOS (http://ceg-research.ncl.ac.uk/v2/gacos/) and provided MATLAB scripts for applying delay maps to interferograms were further modified to handle GAMMA interferograms and other functionalities by the authors. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus Information or Data contained in this manuscript. NARR NCEP Reanalysis data were provided online by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA (https://www.esrl.noaa.gov/psd/). MATLAB scripts for creating and applying NARR phase screens were kindly provided by Amy Parker (CSIRO Australia) and were also modified by the authors for creating and applying ERA5 phase screens to CSK data. Additionally, SBAS MATLAB original scripts were kindly provided by Susanna Ebmeier (Leeds University) and further modified to handle GAMMA interferograms and other functionalities by the authors. MATLAB code for computation of variograms was obtained and modified from {"}MATLAB? Recipes for Earth Sciences{"} (2015, 4 ed) by Martin H. Trauth. GMT6 was used to produce one figure [98]. Finally, this work was also conducted as part of the {"}Optimizing satellite resources for the global assessment and mitigation of volcanic hazards{"} Working Group supported by the John Wesley Powell Center for Analysis and Synthesis, funded by the U.S. Geological Survey. Authors would like to thank Romain Jolivet, Ang?lique Benoit, Kenneth Davis, Travis Tasker, Chuck Ammon, Raph?el Grandin, Francisco Delgado, Juliet Biggs, Fabien Albino, and Rowena Lohman for their helpful discussions and insight into weather models, time-series analysis and statistical assessment techniques, and Judit Gonzales-Santana and Sam Poppe for proof-reading later drafts of the manuscript. The authors would also like to thank five anonymous reviewers and the editor for their comments and suggestions which have helped to greatly improve this manuscript. Funding Information: Funding: This study was funded by National Aeronautics and Space Administration (NASA) Earth Surface and Interior (ESI) grants (NNX17AD70G) to P.C.L. and C.W., (ESI NNX16AK87G) to C.W., and NSF (EAR-0911546) to P.C.L. Publisher Copyright: {\textcopyright} 2020 by the author.",
year = "2020",
month = mar,
day = "1",
doi = "10.3390/rs12050782",
language = "English (US)",
volume = "12",
journal = "Remote Sensing",
issn = "2072-4292",
publisher = "Multidisciplinary Digital Publishing Institute (MDPI)",
number = "5",
}