The bigger peat picture: Spatio-temporal modelling of peatland water table depth using Sentinel-1, Sentinel-2, DSM, and field collected data.

High water table depths (WTD) and water-saturated soil are important elements for peatlands to remain healthy and are crucial targets in peatland restoration projects. Recent studies have suggested that Earth Observation data might be applicable for this task, but proposed models often lack either the spatial extension or the temporal dimension. This study has been developing a spatio-temporal model of peatland water table depth by combining time series of satellite data, namely Sentinel-1, Sentinel-2; aerial data, namely Getmapping Digital Surface Model (DSM); and field collected water table depth measurements to provide the ability to evaluate WTD changes both spatially and over time. 

Water table depth measurements were collected from 59 loggers between February and September of 2018, with loggers covering peatlands in various condition clustered around four research sites in the North of Scotland. NDVI, NDWI and OPTRAM indices were derived from reconstructed cloud-free imagery of Sentinel-2 at 5-day intervals. Similarly, VV, VH, and incidence angle values were obtained from Sentinel-1 imagery at the same time interval. Finally, a Topographic Wetness Index (TWI) was calculated using GetMapping DSM data. A Generalised Additive Model (GAM) was then fitted using all above mentioned inputs with 70% training and 30% testing split method. The model showed a good overall fit (R²=0.59 for training data; R²=0.49 for testing data), with optical covariates outperforming the radar covariates. The model was then applied spatially using the R terra package, providing raster imagery of predicted WTD for 24 unique dates with clear distinction in wetness both over different seasons, and spatially in the landscape.

Following this successful application, work is in progress to test the model on additional sites across Scotland and on European level to further test the applicability of the model to a wider range of northern peatlands.