Sentinel-1 time-series SAR interferometry for understanding tropical peat surface oscillation

Rapid degradation of tropical peatlands in Southeast Asia, driven by land conversion and drainage, has led to severe subsidence, forest fires, and carbon emissions, prompting restoration efforts to raise groundwater levels (GWL). Monitoring peatland surface displacement, including irreversible long-term subsidence and reversible oscillations, is crucial for assessing peat conditions and hydrology. Studies have shown peat surface oscillation (PSO) dynamics vary with peat degradation, highlighting their potential as indicators of restoration progress. This study explores the feasibility of large-scale PSO analysis in tropical peatlands in Kalimantan using a series of spaceborne synthetic aperture radar (SAR) data. We applied time-series interferometric SAR (TInSAR) analysis to three years of Sentinel-1 C-band SAR data to derive displacement time-series across the study area. The displacement data were further decomposed into long-term and short-term components using Seasonal-Trend decomposition based on Loess (STL) to estimate PSO. The estimated PSO was then compared with in-situ GWL data to analyze their relationship and reveal the oscillation coefficient, defined as the slope of this relationship. Our results revealed a statistically significant linear relationship between PSO and GWL dynamics, with correlation coefficients ranging from 0.23 to 0.8. The derived oscillation coefficients at in-situ locations indicated that peat elevation change accounted for 2.8 %–8.3 % of GWL variation. Additionally, the PSO amplitude was found to be greater in degraded peatlands than in less degraded ones. These findings highlight the potential of spaceborne SAR data to enhance understanding of PSO mechanisms and support effective evaluations of peatland restoration efforts.