**5. Conclusions**

ΔΦ ΔΦ ΔΦ ΔΦ By comparing space-borne interferometric ground motion measurements with groundbased data for a well instrumented site at Chaingy (France), we provide evidence that Sentinel-1 InSAR data enables accurate measurement of small cyclic motions (in the order of a few millimeters) related to the shrink/swell process of expansive clays. A wavelet-based method has been applied to these MT-InSAR time series to better characterize the shrinking and swelling timeframes. Moreover, we show how coupling SMOS surface soil moisture and Sentinel-1 InSAR data may reveal apart from the presence of expansive clays additional information on their spatial characteristics. The relative phase differences between SMOS and InSAR time series are used for assessing the variations of the clay layer in terms of depth and thickness, as confirmed by an electrical resistivity tomography campaign. With regard to future works, the proposed methodology could be applied coupling different satellite observations to scale up over wide areas for tracking the presence of expansive clays, with the ultimate goal to better estimate the shrink-swell risk.

**Author Contributions:** Conceptualization, A.B.; Data curation, S.G. and J.D.; Funding acquisition, S.G. and D.R.; Methodology, M.F. and D.R.; Software, M.F.; Visualization, J.D.; Writing—original draft, A.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** The instrumentation of the new Chaingy experimental site was funded by the French Ministry of Environment (research program DGPR-BRGM 2016, Action C8).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Acquisitions of Sentinel-1 satellite were accessed and processed through GEP (https://geohazards-tep.eu, accessed on 23 September 2021) and SMOS satellite data via the French ground segment for the Level 3 data (CATDS, https://www.catds.fr/, accessed on 23 September 2021).

**Acknowledgments:** We would like to thank Céline Roux for her contribution to the graphical abstract.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

