HF/VHF Radar Sounding of Ice from Manned and Unmanned Airborne Platforms

Emily Arnold,Carl Leuschen,Shawn Keshmiri,Akhilesh Mishra,Fernando Rodriguez-Morales,Bailey Miller,Aaron Blevins,Mark Ewing,Teja Karidi,John Sonntag,Stephen Yan,John Paden,Rick Hale,Ali Mahmood

doi:10.3390/geosciences8050182

Abstract

Ice thickness and bed topography of fast-flowing outlet glaciers are large sources of uncertainty for the current ice sheet models used to predict future contributions to sea-level rise. Due to a lack of coverage and difficulty in sounding and imaging with ice-penetrating radars, these regions remain poorly constrained in models. Increases in off-nadir scattering due to the highly crevassed surfaces, volumetric scattering (due to debris and/or pockets of liquid water), and signal attenuation (due to warmer ice near the bottom) are all impediments in detecting bed-echoes. A set of high-frequency (HF)/very high-frequency (VHF) radars operating at 14 MHz and 30–35 MHz were developed at the University of Kansas to sound temperate ice and outlet glaciers. We have deployed these radars on a small unmanned aircraft system (UAS) and a DHC-6 Twin Otter. For both installations, the system utilized a dipole antenna oriented in the cross-track direction, providing some performance advantages over other temperate ice sounders operating at lower frequencies. In this paper, we describe the platform-sensor systems, field operations, data-processing techniques, and preliminary results. We also compare our results with data from other ice-sounding radars that operate at frequencies both above (Center for Remote Sensing of Ice Sheets (CReSIS) Multichannel Coherent Depth Sounder (MCoRDS)) and below (Jet Propulsion Laboratory (JPL) Warm Ice Sounding Explorer (WISE)) our HF/VHF system. During field campaigns, both unmanned and manned platforms flew closely spaced parallel and repeat flight lines. We examine these data sets to determine image coherency between flight lines and discuss the feasibility of forming 2D synthetic apertures by using such a mission approach.

Highlights

Glaciers in both Greenland and Antarctica are undergoing significant changes due to a changing climate
The lower frequency band operating around 14 MHz (Band 1) was identified based on the favorable results demonstrated by Arcone (2000) with a 12 MHz radar in Alaska where scattering from volumetric debris is high [53]
(14 MHz)/low very high-frequency (VHF) (30–35 MHz) for sounding temperate glaciers. This is clear in areas like the Russell Glacier, where surface clutter is low enough that improved HF penetration allowed the ice bottom to be detected with even a single antenna system

Summary

Introduction

Glaciers in both Greenland and Antarctica are undergoing significant changes due to a changing climate. While it is well-established that mass losses from these polar ice sheets contribute to global sea-level rise (SLR) [1], there remains great uncertainty about how these contributions will change in Geosciences 2018, 8, 182; doi:10.3390/geosciences8050182 www.mdpi.com/journal/geosciences. Ice sheet models are our primary tool for integrating observations in predictions of polar ice contributions to future SLR. These models predict future trends in mass balance through ice thickness, snow accumulation, and ice velocities derived from satellite measurements. Jacobs et al [7] and Larour et al [8] suggest that ice thickness and bed elevation are the most important model parameters in reducing model uncertainties; even small uncertainties in ice thickness can lead to large biases in discharge estimates

Methods

Results

Conclusion