## 3 Results
### Annual Seasonality  
Humidity increase and water availability over the wet months are the main drivers to an annual-basis dynamic of the crust development and therefore of the corresponding backscattering coefficients. Changes in the backscattered power due to annual temporality showed different patterns depending on the salt pan spatial distribution and composition. For type 2 (S6) and type 1 (S10) hard crusts, Figure 8b,c, respectively, \(\sigma^{0}\) increase and decrease pattern accounted for inter-annual wet and dry periods. 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. On the other hand, for the Soft pan crust in S1, Figure 8a, annual seasonality had little impact on \(\sigma^{0}\). Note that backscattering coefficients differences in S6 between descending (incidence angle at 31\({}^{\circ}\)) and ascending (40\({}^{\circ}\)) pass demonstrated spatial heterogeneities in the crusts in the period from January to July 2018. Due to its lower sensitivity to surface changes, cross-polarized \(\sigma^{0}\) wet-and-dry cycles appeared not so marked in comparison to co-polarized ones. The two major snowfall events caused the backscattering coefficient to decrease, as shown in Figures 8c and 10a from March to August 2017 and from June to September 2018. Snow crystals have a dielectric constant around 4 with a negligible imaginary part [29], therefore reducing the dielectric contrast in comparison to a brine-dry soil mixture. Moreover, the effect of a snow cover on the backscattered power is to decrease co-polarized \(\sigma^{0}\) by smoothing the surface roughness as seen in Figure 1a. As snow accumulated over the surface, volume scattering increased in September 2017. Over the following dry period, VH increased in the hard crusts possibly due to the rise of underground water that filled pore space within the crust. By the end of the time series, VH-polarized \(\sigma^{0}\) remained more or less constant showing low sensitivity to weather conditions. When the snow melted, flooded areas over the salar, as shown in Figure 1c, are subjected to episodic events such as wind and freezing as shown in Figure 1b. Figure 9: **(a)** Sentinel 1A, VV polarization, descending orbit (9 March 2015). High backscattering coefficient accounted for well-developed salt crusts formed by capillarity over dry periods before La Nira, **(b)** Sentinel 1A, VV polarization, ascending orbit (13 April 2015). Extreme rainfall event left vast areas with a smoothened surface after salts dissolved. Intense southeast winds caused standing water to depart from flooded areas to dry areas. The opposite also occurred with loose soil particles from dry areas to flooded ones. Other \(\sigma^{0}\) variations are summarized in Table 3 for those sites with monthly rates greater than 1.00 dB. Rates are computed as the ratio of the interval to month on a 30-day month basis. For sites 1, 10 and 6 a large growth rate is found over the dry period after the snowfall at the beginning of the time series. When the water input is in the form of rainfall, as in February 2018, the halite growth rate that followed drops by about one half on sites 1 and 10. On site 11 and 4, the influence of precipitation type on the rate seemed not so marked. Thus, the effect of water droplets dissolving previously grown salt aggregates has different impacts on \(\sigma^{0}\). Figure 10: (**a**) Sentinel 1-B, VV polarization, descending orbit (27 May 2017). The salar surface is fully covered by snow, (**b**) Sentinel 1-B, VV polarization, ascending orbit (11 September 2017). Flooding event following the snow melting with wind-generated roughness over the water beds. (**c**) Sentinel 1-B, VV polarization, descending orbit (7 September 2018).