## 4 Discussion  
Our investigation revealed that seasonality analysis of C-band Sentinel-1 and L-band ALOS-2/PALSAR-2 allowed salar dynamics detection at different depths and salt pan-cover types. The results achieved in the current study suggest that the dynamics of the salar during the four years is the consequence of the development of temporal superficial saline crust affected by weather elements such as wind, snow, and rain. The meteorological information partially showed a relation between rain, snow events, and a decrease in the backscattered power. It is necessary to continue investigating the physical causes of the observed phenomenon. Sentinel-1 seasonality analysis showed three patterns in the backscatter power retrieved from the salt pan surfaces and better represented in VV polarization. The first one related to climate seasonalities starting with winters including sporadic snowfall conditions from 2014 to 2017 with the development of salt crust and backscattered power oscillating around 5 dB. Wet conditions given by La Nina from 2017 to 2018 led to snowfalls followed by floodings and a decrease of the backscattering power due to dilution of salts. Thus, VV-polarized \(\sigma^{0}\) reached variations up to 9 dB between dry and wet cycles. This is more evident on the Hard-pan crust 1, where VV-polarized backscattering coefficient had an 8.80-dB-increase between the flooded and the well-developed crust surfaces in a four-month period between 17 September 2017 and 15 January 2018, leading to a rate of 2.20 dB/month over the 120-day interval between the period mentioned. The annual seasonality seemed to depend on the humidity income given by either Altiplanic or southern winter through precipitations which resulted in decreasing the backscattered power by smoothening the salt crust roughness. Finally, episodic events occurred in a short time period and are principally triggered by wind blowing flooded areas increasing the backscattering power due to wind-induced roughness. Similar results were found at the Chott el Djerid Tunisia [6; 7; 8] in different climatic and geographic conditions, located near sea level (15 m.a.s.l) with precipitations events mainly in winter, dry and warm summer, and mean annual rainfall between 75-100 mm (almost the half of the amount for Salar de Aguas Calientes, Chile) without snowfalls. The authors show a relation in C-band monitoring changes over evaporitic surfaces and present that backscattering power increases where VV-polarized \(\sigma^{0}\) markedly raised during the evaporation phase in summer, being stable while humidity lacks, and either decreases rapidly due to precipitations in winter. In Figures 9 and 10, VV-polarized \(\sigma^{0}\) maps showed the vast superficial extensions over the salt flat affected either by flooding or snowfall events. In the case of flooding events, the areas are coincidental with previous studies for Salar de Aguas Calientes [2; 4]. Cross-polarized \(\sigma^{0}\) wet-and-dry cycles appeared not so marked in comparison to co-polarized ones. Sentinel 1 instrument noise floor reduced sensitivity for low \(\sigma^{0}\) such as those measured at VH polarization. Instrument performance for the IW mode has a marked dependence with the incidence angle [31]. In effect, the noise floor is about \(-25\) dB at \(35^{\circ}\) and marginally improves to about \(-27\) dB at angles between \(39^{\circ}\) and \(40^{\circ}\), which implied a precise VH-polarized returned power from the rougher crusts solely. ALOS-2/PALSAR-2 seasonality analysis showed subsurface scattering due to more extended penetration of the signal. Compare with Sentinel-1 the backscattering power seems to be less influenced by precipitations and more affected by flooding and wind blowing the water. Our analyses were limited here since its time series contained fewer images for the study area. A seasonal-trend analysis at L-band could, therefore, be useful in further studies when multiple years of ALOS-2/PALSAR-2 data will be available.