Potential of C and X Band SAR for Shrub Growth Monitoring in Sub-Arctic Environments

Yannick Duguay,Esther Lévesque,Monique Bernier,Benoit Tremblay

doi:10.3390/rs70709410

Abstract

The Arctic and sub-Arctic environments have seen a rapid growth of shrub vegetation at the expense of the Arctic tundra in recent decades. In order to develop better tools to assess and understand this phenomenon, the sensitivity of multi-polarized SAR backscattering at C and X band to shrub density and height is studied under various conditions. RADARSAT-2 and TerraSAR-X images were acquired from November 2011 to March 2012 over the Umiujaq community in northern Quebec (56.55°N, 76.55°W) and compared to in situ measurements of shrub vegetation density and height collected during the summer of 2009. The results show that σ0 is sensitive to changes in shrub coverage up to 20% and is sensitive to changes in shrub height up to around 1 m. The cross-polarized backscattering (σ0 HV ) displays the best sensitivity to both shrub height and density, and RADARSAT-2 is more sensitive to shrub height, as TerraSAR-X tends to saturate more rapidly with increasing volume scattering from the shrub branches. These results demonstrate that SAR data could provide essential information, not only on the spatial expansion of shrub vegetation, but also on its vertical growth, especially at early stages of colonization.

Highlights

The Arctic and sub-Arctic environments are undergoing rapid and dramatic changes due to the rise in air temperatures, which has been observed in the past few decades
The backscattering at θ = 27◦ incidence is consistently higher than at θ = 38◦ by around 1 dB to 2 dB, but the latter is more sensitive to shrub coverage, which is consistent with scattering theory [29], since higher incidence angles lead to higher sensitivity to volume scattering relative to surface scattering
Results for RADARSAT-2 can be viewed in Table 3, and those for TerraSAR-X can be viewed in November and December, ∆A1 A2 varies from 5.7 dB to 7.2 dB for cross-polarized backscattering, while

Summary

Introduction

The Arctic and sub-Arctic environments are undergoing rapid and dramatic changes due to the rise in air temperatures, which has been observed in the past few decades. Studies suggest that the presence of shrubs can trigger a feedback loop, where windblown snow is captured by shrub branches, favouring snow accumulation, which leads to warmer ground temperatures during the winter and accelerated onset of growth in the spring [2,5,6]. This can have an effect on the permafrost thawing processes, since ground temperatures will remain relatively warm during the winter.

Methods

Results

Conclusion