Snow Thickness Estimation on First-Year Sea Ice from Late Winter Spaceborne Scatterometer Backscatter Variance

John Yackel,Randall Scharien,Torsten Geldsetzer,Vishnu Nandan,Mallik Mahmud,Stephen Howell,Hoi Lam

doi:10.3390/rs11040417

John Yackel, Randall Scharien + Show 5 more

Open Access

https://doi.org/10.3390/rs11040417

Copy DOI

Abstract

Ku- and C-band spaceborne scatterometer sigma nought (σ°) backscatter data of snow covered landfast first-year sea ice from the Canadian Arctic Archipelago are acquired during the winter season with coincident in situ snow-thickness observations. Our objective is to describe a methodological framework for estimating relative snow thickness on first-year sea ice based on the variance in σ° from daily time series ASCAT and QuikSCAT scatterometer measurements during the late winter season prior to melt onset. We first describe our theoretical basis for this approach, including assumptions and conditions under which the method is ideally suited and then present observational evidence from four independent case studies to support our hypothesis. Results suggest that the approach can provide a relative measure of snow thickness prior to σ° detected melt onset at both Ku- and C-band frequencies. We observe that, during the late winter season, a thinner snow cover displays a larger variance in daily σ° compared to a thicker snow cover on first-year sea ice. This is because for a given increase in air temperature, a thinner snow cover manifests a larger increase in basal snow layer brine volume owing to its higher thermal conductivity, a larger increase in the dielectric constant and a larger increase in σ° at both Ku- and C bands. The approach does not apply when snow thickness distributions on first-year sea ice being compared are statistically similar, indicating that similar late winter σ° variances likely indicate regions of similar snow thickness.

Highlights

Past and state-of-the-art climate models indicate that under a warming Arctic we should expect an increase in sea ice melt during the summer months leading to a reduction in extent and thickness [1,2]
The objectives of this paper were to present a simple empirically-derived approach for estimating relative snow thickness on smooth, landfast FYI, based on the variance in daily measured spaceborne Ku- and C-band microwave σ◦ during the late winter season prior to melt onset (MO). We investigate both Kuand C-band frequencies for their ability to do so primarily because of spaceborne scatterometer data availability
We investigate only the FYI type because we are interested in exploiting the thermodynamic-brine-dielectric effect within the snow cover and its effect on microwave σ◦

Summary

Introduction

Past and state-of-the-art climate models indicate that under a warming Arctic we should expect an increase in sea ice melt during the summer months leading to a reduction in extent and thickness [1,2]. Some studies suggest that the snow thickness on western Arctic sea ice has declined in recent years [10,11], largely a result of later fall freeze-up If such trends and increased variability persist it is possible that we could expect enhanced variability or pronounced increases/decreases in wintertime snow accumulation in certain sectors of the Arctic Ocean [12,13,14], thereby influencing atmosphere-sea ice-ocean exchanges and sea ice growth and decay rates. Model-based projections of summer sea ice loss in these regions may be problematic due to unrepresentative parameterizations

Objectives

Methods

Results

Discussion

Conclusion