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Research article - Peer-reviewed, 2020

Satellite Determination of Peatland Water Table Temporal Dynamics by Localizing Representative Pixels of A SWIR-Based Moisture Index

Burdun, Iuliia; Bechtold, Michel; Sagris, Valentina; Lohila, Annalea; Humphreys, Elyn; Desai, Ankur R.; Nilsson, Mats B.; De Lannoy, Gabrielle; Mander, Ulo


The OPtical TRApezoid Model (OPTRAM) is a physically-based approach for remote soil moisture estimation. OPTRAM is based on the response of short-wave infrared (SWIR) reflectance to vegetation water status, which in turn responds to changes of root-zone soil moisture. In peatlands, the latter is tightly coupled to water table depth (WTD). Therefore, in theory, the OPTRAM index might be a useful tool to monitor WTD dynamics in peatlands, although the sensitivity of OPTRAM index to WTD changes will likely depend on vegetation cover and related rooting depth. In this study, we aim at identifying those locations (further called 'best pixels') where the OPTRAM index is most representative of overall peatland WTD dynamics. In peatlands, the high saturated hydraulic conductivity of the upper layer largely synchronizes the temporal WTD fluctuations over several kilometers, i.e., even though the mean and amplitude of the WTD dynamics may vary in space. Therefore, it can be assumed that the WTD time series, either measured at a single location or simulated for a grid cell with the PEATland-specific adaptation of the NASA Catchment Land Surface Model (PEATCLSM), are representative of the overall peatland WTD dynamics. We took advantage of this concept to identify the 'best pixel' of all spatially distributed OPTRAM pixels within a peatland, as that pixel with the highest time series Pearson correlation (R) with WTD data accounting for temporal autocorrelation. The OPTRAM index was calculated based on various remotely sensed images, namely, Landsat, MODIS, and aggregated Landsat images at MODIS resolution for five northern peatlands with long-term WTD records, including both bogs and fens. The 'best pixels' were dominantly covered with mosses and graminoids with little or no shrub or trees. However, the performance of OPTRAM highly depended on the spatial resolution of the remotely sensed data. The Landsat-based OPTRAM index yielded the highest R values (mean of 0.7 across the 'best pixels' in five peatlands). Our study further indicates that, in the absence of historical in situ data, PEATCLSM can be used as an alternative to localize 'best pixels'. This finding enables the future applicability of OPTRAM to monitor WTD changes in peatlands on a global scale.


Landsat; MODIS; bogs; fens; sphagnum; soil moisture; wetland; shortwave infrared transformed reflectance

Published in

Remote Sensing
2020, volume: 12, number: 18, article number: 2936
Publisher: MDPI

Authors' information

Burdun, Iuliia
University of Tartu
Bechtold, Michel
KU Leuven
Sagris, Valentina
University of Tartu
Lohila, Annalea
Finnish Meteorological Institute
Humphreys, Elyn
Carleton University
Desai, Ankur R.
University of Wisconsin Madison
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management
De Lannoy, Gabrielle
KU Leuven
Mander, Ulo
University of Tartu

UKÄ Subject classification

Remote Sensing

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