Ecohydrological Monitoring of Temperate Raised Bogs by Using Backscatter Intensity of Synthetic Aperture Radar

Peatland degradation promotes carbon emissions, biodiversity loss, water quality decline, and slope instability. Effective mitigation of these impacts depends on understanding and monitoring peatland ecohydrology across space and time. Synthetic Aperture Radar (SAR) satellites enable large-scale monitoring at moderate to high spatial resolution and, as SAR penetrates cloud, at consistent revisit times. However, exactly how SAR backscatter relates to peatland ecohydrology, in both space and time, is incompletely understood. We investigated spatio-temporal relationships between C-band SAR backscatter intensity and peatland ecohydrological characteristics at six temperate raised bogs in Ireland. The study sites range from near-intact raised bog to industrially-degraded bare peat; the near-natural sites have a well-characterized range of raised bog ecology. We assess Sentinel-1 C-band SAR backscatter intensity (radiometric terrain corrected) in both VV and VH polarization through time for the period 2015-2024. Time series of SAR backscatter intensity for all bogs show annual oscillations that are most pronounced in VV polarization. Intensity maxima occur in winter-spring; minima occur in summer-autumn. The amplitude of intensity oscillation and mean of VV intensity through time are consistently greater for bare peat than for near-intact bogs. The mean of VH intensity in time is lowest for areas of bare peat and areas of non-vascular vegetation (moss, Sphagnum), but it is highest for areas of vascular vegetation (Heather, Calluna). The annual oscillation in SAR intensity is attributed primarily to soil moisture variation, which is controlled by groundwater levels and seasonal precipitation. SAR intensity oscillation is greatest in drained bare peat because of more intense cycles of drying and wetting. The higher mean VV intensity in time of bare peat is attributed to the lack of attenuation of the SAR pulse by vegetation. The sensitivity of mean VH intensity in time to the nature of vegetation is explained by increased volumetric scattering of the radar waves in shrub-rich areas. Spatio-temporal shifts in SAR backscatter signatures can thus help identify and monitor the impacts of human activity on temperate raised bogs. For example, responses to early stages of restoration (rewetting) were detectable in the intensity time series as decreases in backscatter intensity and reduction, or loss of annual intensity oscillation. Consequently, this study provides an improved basis for incorporating SAR remote sensing into sustainable peatland management.