*Article* **Monitoring of Expansive Clays over Drought-Rewetting Cycles Using Satellite Remote Sensing**

**André Burnol 1,\*, Michael Foumelis 1,2,\*, Sébastien Gourdier 1, Jacques Deparis <sup>1</sup> and Daniel Raucoules <sup>1</sup>**


**Abstract:** New capabilities for measuring and monitoring are needed to prevent the shrink-swell risk caused by drought-rewetting cycles. A clayey soil in the Loire Valley at Chaingy (France) has been instrumented with two extensometers and several soil moisture sensors. Here we show by direct comparison between remote and in situ data that the vertical ground displacements due to clay expansion are well-captured by the Multi-Temporal Synthetic Aperture Radar Interferometry (MT-InSAR) technique. In addition to the one-year period, two sub-annual periods that reflect both average ground shrinking and swelling timeframes are unraveled by a wavelet-based analysis. Moreover, the relative phase difference between the vertical displacement and surface soil moisture show local variations that are interpreted in terms of depth and thickness of the clay layer, as visualized by an electrical resistivity tomography. With regard to future works, a similar treatment relying fully on remote sensing observations may be scaled up to map larger areas in order to better assess the shrink-swell risk.

**Keywords:** Copernicus Sentinel-1; electrical resistivity tomography; expansive clay; InSAR; shrinkswell risk; SMOS surface soil moisture; wavelet analysis
