###### Abstract  
Seasonal changes control the development of salt crust over the Salar de Aguas Calientes Sur located in Andes Highlands, Chile. Precipitations throughout the Altiplanic winter (December to March) and austral winter (June to September) caused ponds to enlarge and surface salt crusts to dissolve driving roughness and dielectric features of the salar surface change over time. A four-year time series backscattering coefficient analysis, obtained by Sentinel 1 and ALOS-2/PALSAR-2 with 10 m of spatial resolution, demonstrated the capability of microwaves to discriminate seasonal patterns illustrated in this paper. Both sensors showed to be sensitive to changes in the surface crust due to weather conditions. Backscattered power gradually increased during the driest months as the rough salt crusts develop and decreased rapidly due to precipitations or flooding events, which lead to a smoothing appearance to radar. The high temporal frequency of acquisition in Sentinel 1 (5-13 scenes/month) allowed the discrimination among climate and annual seasonality and episodic events in the C-band backscatter coefficient. On the other hand, ALOS-2/PALSAR-2 showed subsurface changes at L-band since the salinity of the brine in the soil reduces the penetration depth of backscattered power for shorter wavelengths. Results might be useful to monitor salars with geographic and weather conditions similar to Salar de Aguas Calientes Sur. microwaves; evaporitic environment; Sentinel 1; ALOS-2/PALSAR-2; Chile 2020 February 2020202014 March 202031 December 201922 February to the presence of a surface or underground water. Surface water might appear in the form of rivers or ponds. Salar de Aguas Calientes Sur has a special climatic and geographical feature. Located 4000 m.a.s.l. at the Andes Highlands, it has an active tectonic influence together with extreme weather conditions given by high annual evaporations rates, snowfalls, and rainfall during austral winter (June to September) and Altiplanic winter in summer (December to March). Strong solar radiation and wind speeds that reach up to 70 km/h controls the evaporites minerals formation. Unlike rocks, evaporitic minerals in the salar are sensitive to changes by wind, ponds sedimentation and evaporation followed by chemical precipitation. Besides, evaporites are also sensitive to climatic changes because the salts are dissolved either by precipitation or the rise of groundwater. In the absence of these, the evaporation processes trigger changes in the salar surface, affecting its roughness and dielectric properties due to the crystallization of evaporite minerals [3]. A recent study with multispectral sensors on the Salar de Aguas Calientes Sur reports partially seasonal changes in its ponds. However, the cause of this phenomenon remains unknown [4]. The overall information points out evident dynamics within this detrtical and evaporitic sedimentary environment, where the salt crusts have a seasonal component not yet determined. Applying Synthetic Aperture Radar (SAR) data in the study of salars allows capturing information at different depths due to its ability to penetrate dry soil layers according to the wavelength of operation. Likewise, the backscattering coefficient (\(\sigma^{0}\)) is a function of the roughness of the surface (relative to the wavelength) and the dielectric constant, the latter influenced by soil moisture content and its salinity [5]. Furthermore, as long as the sensitivity of the SAR backscattered power to the physicochemical changes appears in salars, previous investigations demonstrate that the dielectric constant of saline soils plays a key role in the radar backscatter. In C-band, the approach is monitoring changes over evaporitic surfaces with ERS-1 SAR images on the Chott el Djerid (dry Salt Lake), Tunisia, at 20 m.a.s.l [6]. The authors present that backscattering power increases during dry seasons with precipitation of halite crystals.