Seasonality Analysis of Sentinel-1 and ALOS-2/PALSAR-2 Backscattered Power over Salar de Aguas Calientes Sur, Chile

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.

The definitive rediscovery of Telmatobius halli (Anura, Telmatobiidae) at its historic type locality and its synonymy with T. dankoi and T. vilamensis

“…The Loa River originates mainly from meltwater from throughout its upper drainage basin, where snow accumulates during austral winter. Several temporal ravines also gather the characteristic precipitations during the austral summer months (December to March), known as Altiplanic winter ( Berenguer and Cáceres 2008 ; Delsouc et al 2020 ). Lower down and descending from the east, there also are some important permanent affluents fed by aquifers.…”

Spaceborne Radars for Mapping Surface and Subsurface Salt Pan Configuration: A Case Study of the Pozuelos Salt Flat in Northern Argentina

“…Crust classification with a dense time series at the C-band was better suited with the co-polarized backscatter response (Figure 8) than that of the cross-polarized one (Figure 9), where differentiation between type II and type III crusts may be misleading. A potential radar characterization of crusts was first introduced by [26] as the monthly rate of increase of co-polarized backscattering coefficient at the C-band over large no-rainfall periods. For the type I crust analyzed in this work, the mentioned rate is around 0.2 dB/month, very different from the rates of 1-2 dB/month found in [26] corresponding to a soft pan crust with thrust polygons, possibly indicating different local features such as brine concentration, water availability, and/or solar radiation patterns.…”

“…A potential radar characterization of crusts was first introduced by [26] as the monthly rate of increase of co-polarized backscattering coefficient at the C-band over large no-rainfall periods. For the type I crust analyzed in this work, the mentioned rate is around 0.2 dB/month, very different from the rates of 1-2 dB/month found in [26] corresponding to a soft pan crust with thrust polygons, possibly indicating different local features such as brine concentration, water availability, and/or solar radiation patterns. An additional overall feature of crust dynamics might be the rate of variation around the summertime heavy rainfalls observed in the backscattering coefficient at the C-band, which seemed very uniform across the seasons for the halite crust.…”

“…On the other hand, multi-temporal studies make use of long-term, dense sets of radar acquisitions to monitor salt flat dynamics, usually with the only ancillary information provided by weather stations and visual information collected on a field visit. As soil moisture largely affects dielectric properties of soils, multi-temporal studies become important to analyze seasonal variations of the SAR response on salt pans, as was demonstrated in Chott El Djerid playa deposit in Tunisia using multi-temporal RADARSAT-2 C-band full polarimetric imagery [24,25] and in Salar de Aguas Calientes Sur in Chile using Sentinel-1 and ALOS-2/PALSAR-2 [26]. These investigations contributed to a better understanding of crust salt flat dynamics and related evaporitic processes.…”