Multi-sensor monitoring of soil moisture dynamics in subpolar environments using Sentinel-1 and Sentinel-2 data: A case study from the Falkland Islands

Monitoring soil moisture is critical for understanding Earth’s climate, hydrological variability, and vegetation dynamics, particularly in remote regions where ground observations are limited. We develop and validate a multi-sensor approach integrating Sentinel-1 radar (2016-2021) and Sentinel-2 optical data (2021-2025) within Google Earth Engine (GEE) to characterize surface soil moisture dynamics across the Falkland Islands. The aim was to evaluate temporal patterns, sensor consistency, and agreement with in-situ measurements. This will provide a continuous nine-year record of soil moisture dynamics to facilitate regional climate change adaptation and mitigation. We used Sentinel-1 synthetic aperture radar (SAR) backscatter to compute a 10-day interval time series of soil moisture index (SMI) through radar backscatter calibration, temporal compositing, and vegetation correction. While Sentinel-1 soil moisture estimates showed limited correlation with in-situ measurements at 20 cm depth (likely due to sensing depth differences) they exhibited moderate to strong correlations with rainfall, supporting the satellite’s ability to capture rainfall-driven hydrological variation. Due to data discontinuities in Sentinel-1 acquisitions after 2021, we used Sentinel-2 imagery to extend the analysis through September 2025. Both datasets were analysed for seasonal and interannual variability and validated against in-situ volumetric soil moisture (VSM) from Temperature Moisture Sensor (TMS) dataloggers installed across representative grassland and peatland habitats. Results reveal coherent seasonal cycles across all major regions of the Falklands, with recurring summer minima and winter maxima corresponding to drought and recharge periods. Overall, both sensors consistently detected the same hydrological patterns, including wet winters and dry summers with interannual variability linked to regional rainfall dynamics rather than spatially distinct behaviours between subregions. The integration of optical and radar observations provides a robust means of monitoring soil-moisture variability in remote environments. This multi-sensor framework supports future data assimilation, drought assessment, and climate-impact studies. Establishing long-term monitoring that integrates multi-sensor approaches is essential to understand the Falklands’ evolving hydrological and ecological trends.

Keywords: Soil moisture; Remote sensing; Sentinel-1; Sentinel-2; Google Earth Engine.