Dependence of C-Band Backscatter on Ground Temperature, Air Temperature and Snow Depth in Arctic Permafrost Regions

Helena Bergstedt,Marina Leibman,Annett Bartsch,Simon Zwieback

doi:10.3390/rs10010142

Abstract

Microwave remote sensing has found numerous applications in areas affected by permafrost and seasonally frozen ground. In this study, we focused on data obtained by the Advanced Scatterometer (ASCAT, C-band) during winter periods when the ground is assumed to be frozen. This paper discusses the relationships of ASCAT backscatter with snow depth, air and ground temperature through correlations and the analysis of covariance (ANCOVA) to quantify influences on backscatter values during situations of frozen ground. We studied sites in Alaska, Northern Canada, Scandinavia and Siberia. Air temperature and snow depth data were obtained from 19 World Meteorological Organization (WMO) and 4 Snow Telemetry (SNOTEL) stations. Ground temperature data were obtained from 36 boreholes through the Global Terrestrial Network for Permafrost Database (GTN-P) and additional records from central Yamal. Results suggest distinct differences between sites with and without underlying continuous permafrost. Sites characterized by high freezing indices (>4000 degree-days) have consistently stronger median correlations of ASCAT backscatter with ground temperature for all measurement depths. We show that the dynamics in winter-time backscatter cannot be solely explained through snow processes, but are also highly correlated with ground temperature up to a considerable depth (60 cm). These findings have important implications for both freeze/thaw and snow water equivalent retrieval algorithms based on C-band radar measurements.

Highlights

The usage of microwave remote sensing in cold environments is a well established practice in a variety of research fields
The results reveal no apparent differences between median correlations of backscatter and ground temperature of different depths
While analysis of covariance (ANCOVA) has been shown to be relatively robust to the violation of the assumption of normality of the residuals [84,85,86], the parameter of dependence of backscatter on air temperature, snow depth and ground temperature has to be seen together with the results reported in Table 4; p–values of the estimated parameters might not be reliable in some cases

Summary

Introduction

The usage of microwave remote sensing in cold environments is a well established practice in a variety of research fields. Microwave remote sensing allows obtaining additional information not available from optical data such as surface structure and parameters related to dielectric properties [7]. During transitional periods in spring and autumn a sudden change in backscatter values can be observed [13,14]. This phenomenon is caused by the sensitivity of the microwave signal to the change of the dielectric constant of the ground that is in turn caused by the state change of the water contained in the ground [15,16]. To detect the timing of freeze and thaw events, algorithms sensitive to the abrupt increase and decrease in backscatter values have been developed [8,13,17,21,22,23]

Methods

Results

Discussion

Conclusion