Year of Award

2023

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Geosciences

Department or School/College

Department of Geosciences

Committee Chair

Nancy Hinman

Commitee Members

Michael Hofmann, Anna Klene

Keywords

SAR, salar, surface roughness, dielectric constant, moisture, remote sensing

Publisher

University of Montana

Subject Categories

Geochemistry | Geology | Hydrology

Abstract

Remotely sensed microwave radars provide the spatial and temporal coverage needed to improve our understanding of the relationship between moisture content and salt pan mineralogy and, ultimately, climate variability. Moisture content in the surface and near-surface crusts found in salt pan environments, such as salt pan, has a significant impact on the backscatter values recorded by synthetic aperture radar (SAR) systems. This is because moisture affects the dielectric constant and surface roughness of the saline surface, which in turn influences the amount of electromagnetic energy reflected back to the SAR sensor. Changes in backscatter values are attributed to seasonal and interannual variations in salar surface properties (dielectric constant and surface roughness) and correlate with variations in regional climate trends. To better understand the spatial and seasonal dynamics of a salt pan (also known as salar), this study interprets a series of Sentinel-1 SAR images collected over Salar de Pajonales, Chile between 01 January 2019 and 31 December 2021. A total of 171 images were collected at 6-day intervals and processed using the Alaska Satellite Facility’s Hyp3 pipeline. An image stack was compiled and a time series was explored with the open-source, cloud-based platform, OpenSARLab. The time series of a mixed evaporite-mineral surface (composite surface) revealed that seasonal changes in dielectric properties and surface roughness drive variations in backscatter values at Salar de Pajonales. Rougher surfaces had stronger backscatter values in areas with higher surface roughness, except in wet conditions when increased soil moisture led to higher dielectric properties and, consequently, increased backscatter values. Mean backscatter values varied across the salar, with greater variability for the composite surface. These results underscore the significance of both dielectric properties and surface roughness when interpreting SAR data in salt pan environments, such as Salar de Pajonales. Future field studies on different salar surfaces are needed. Those studies should include in situ surface and near-surface water samples, the composition of sediment samples, and the installation of climate stations. These surface data would enable precise dielectric constant and surface roughness models and subsequently, better remotely sensed soil moisture measurements.

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