Long Term Interferometric Temporal Coherence and DInSAR Phase in Northern Peatlands

Tauri Tampuu,Ain Kull,Rivo Uiboupin,Jaan Praks

doi:10.3390/rs12101566

Tauri Tampuu, Ain Kull + Show 2 more

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https://doi.org/10.3390/rs12101566

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Abstract

Peatlands of northern temperate and cold climates are significant pools of stored carbon. Understanding seasonal dynamics of peatland surface height and volume, often referred to as mire breathing or oscillation, is the key to improve spatial models of material flow and gas exchange. The monitoring of this type of dynamics over large areas is only feasible by remote sensing instruments. The objective of this study is to examine the applicability of Sentinel-1 synthetic aperture radar interferometry (InSAR) to characterize seasonal dynamics of peatland surface height and water table (WT) over open raised bog areas in Endla mire complex in central Estonia, characteristic for northern temperate bogs. Our results show that InSAR temporal coherence, sufficient for differential InSAR (DInSAR), is preserved in the open bog over more than six months of temporal baseline. Moreover, the coherence which is lost in a dry summer, make a recovery in autumn correlate with WT dynamics. The relationship between the coherence from a single master image and the corresponding WT difference is described by the second degree polynomial regression model (Root Mean Squared Error RMSE = 0.041 for coherence magnitude). It is also demonstrated that DInSAR phase is connected to bog surface dynamics and reveals differences between bogs and for ecotopes within a bog. These findings suggest that InSAR long term temporal coherence could be used to describe seasonal bog WT dynamics and differentiate between mire types and ecotopes within a bog. Moreover, DInSAR analysis has the potential to characterize seasonal mire surface oscillation which may be important for assessing the capacity of water storage or restoration success in northern temperate bogs.

Highlights

Peatlands are an important storage buffer in the global carbon cycle
The objective of this study is to examine the applicability of Sentinel-1 synthetic aperture radar interferometry (InSAR) to characterize seasonal dynamics of peatland surface height and water table (WT) over open raised bog areas in Endla mire complex in central Estonia, characteristic for northern temperate bogs
Our results show that InSAR temporal coherence, sufficient for differential InSAR (DInSAR), is preserved in the open bog over more than six months of temporal baseline

Summary

Introduction

While covering only ∼3% of the world’s land area, they store about 20–30% of the global soil carbon [1,2,3,4]. This is equivalent to more than half of the carbon currently in the atmosphere [5], as much carbon as all terrestrial biomass, and twice the carbon stock of all forest biomass of the world [6]. Peatlands are known as pools of carbon but the balance between their ability to be net sequester or emitter of greenhouse gases (GHG) is delicate, depending on water regime which is highly vulnerable both to climatic changes and direct human impact [1,7,8,9]. SAR provides a large spatial coverage at a regular resampling interval which is weather-independent and cheap enough to be widely exploited [14,15]

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