InSAR Coherence Linked to Soil Moisture, Water Level and Precipitation on a Blanket Peatland in Scotland

Abstract

Highlights: What are the main findings? Sentinel-1 InSAR coherence is strongly and seasonally related to peatland soil moisture, with the highest linear relationships in spring and summer, and strongest at intact bogs. Water level–InSAR coherence relationships are weaker and often out-of-phase, while precipitation timing is strongly cross-correlated with InSAR coherence but not linearly related. What are the implications of the main findings? InSAR coherence provides a useful remotely sensed indicator of peatland soil moisture and hydrological seasonality, especially when between peatlands of different condition. Combining InSAR coherence with ground data can enhance peatland monitoring and support restoration assessment in blanket bog ecosystems. Hydrological changes in peatland are directly related to peat condition. Restoration projects typically aim to raise the water table to enhance peat development, support ecology and increase carbon storage. Remote monitoring of peatland hydrology is challenging but advantageous for assessing condition and restoration effectiveness. This study explores how temporal Sentinel-1-derived InSAR coherence relates to ground-based measurements of soil moisture, water level and local precipitation at two sites, near-natural (Munsary) and degraded (Knockfin Heights), in the Flow Country, Scotland, alongside regional Wick weather station precipitation data (2015–2024). Stronger seasonal linear relationships were observed between soil moisture and InSAR coherence in spring/summer (R2 reaching 0.83 at Munsary subsite C, p < 0.001), with in-phase cross correlation throughout the year. In contrast, the relationship between water level and InSAR coherence was more complex with an out-of-phase relationship for much of the year and a weaker linear correlation. These relationships varied with peatland condition, strongest at the more intact bog (Munsary). InSAR coherence and precipitation were in-phase, but not linearly correlated, and land use/cover had no significant effect. Outcomes suggest that InSAR coherence could, when combined with other data, assist in mapping soil moisture/water level dynamics in blanket peatlands, and identify the timing of precipitation events in areas with non-frontal rainfall.