Monitoring The Dynamics Of Hyper-Saline Environments With Polarimetric SAR: Death Valley, California Example

Abstract : Soil salinization in arid and semi-arid regions still remains one of the most important threats not only for socio-economical issues when dealing with water ressources management, but also for ecological matters such as: desertification, climate changes, and biomass reduction. Then, monitoring and mapping of soil salinity distribution represent today a key challenge in our understanding of such environmental processes. Being highly dependent on the dielectric properties of soils, synthetic aperture radar (SAR) appears to be an efficient tool for the remote sensing of hyper-saline environments. More precisely, the influence of saline deposits on SAR imagery lies in the solubility and ionic properties of the minerals which strongly influence both real and imaginary parts of the complex permittivity of such deposits, and thus the radar backscattering coefficient. Based on temporal series acquired with spaceborne SAR systems (ALOS/PALSAR, SIR-C) over the Death Valley (CA), we show that the copolarized backscattering ratio and phase difference derived from SAR data can be used as suitable indicators to monitor the dynamics of hyper-saline deposits. In particular, we propose these copolar parameters to follow the variations in the dielectric properties of moistened and salt-affected soils on a seasonal time scale because of the close relationship between the salinity (governed by the soil moisture content) and the complex permittivity of the soils. We also highlight a strong temporal correlation between the copolar parameters and weather data since precipitation events control the soil moisture and salinity. In order to allow for a better interpretation of the saline deposits signatures observed on SAR data, we also perform analytical simulations of the radar backscattering associated with saline deposits by means of the IEM scattering model. Using laboratory and in~ situ dielectric measurements as input parameters, we simulate the copolar ratio and phase difference as function of the complex permittivity and surface roughness. Successfully reproducing the observed signature, our results indicate that the analysis of SAR data could also account for the monitoring and understanding of seasonal changes of evaporitic basins through a close correlation between the soil moisture and surface roughness related to the desiccation processes. Such results are of great interest for soil salinity monitoring and the detection of small amounts of subsurface water mixed with evaporites, not only for arid terrestrial surfaces but also for planetary missions, particularly the exploration of Mars. Both of the observation and simulation aspects of our methodology will be thouroughly described at time of the presentation as well as the sustaining measurement technique. We will also present preliminary results derived from the first high-resolution image acquired with the UAVSAR sensor operated by NASA/JPL/CalTech.
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Submitted on : Monday, July 20, 2009 - 2:09:46 PM
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Y. Lasne, K. Mcdonald, Philippe Paillou, A. Freeman, B. Chapman, et al.. Monitoring The Dynamics Of Hyper-Saline Environments With Polarimetric SAR: Death Valley, California Example. 2008AGUFM.H43G1101L -American Geophysical Union, Fall Meeting 2008, abstract #H43G-1101, 2008, France. ⟨hal-00405386⟩



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