An ultra-wideband, microwave radar for measuring snow thickness on sea ice and mapping near-surface internal layers in polar firn

Abstract

ABSTRACT. Sea ice is generally covered with snow, which can vary in thickness from a few centimeters to >1 m. Snow cover acts as a thermal insulator modulating the heat exchange between the ocean and the atmosphere, and it impacts sea-ice growth rates and overall thickness, a key indicator of climate change in polar regions. Snow depth is required to estimate sea-ice thickness using freeboard measurements made with satellite altimeters. The snow cover also acts as a mechanical load that depresses ice freeboard (snow and ice above sea level). Freeboard depression can result in flooding of the snow/ice interface and the formation of a thick slush layer, particularly in the Antarctic sea-ice cover. The Center for Remote Sensing of Ice Sheets (CReSIS) has developed an ultra-wideband, microwave radar capable of operation on long-endurance aircraft to characterize the thickness of snow over sea ice. The low-power, 100 mW signal is swept from 2 to 8 GHz allowing the air/snow and snow/ ice interfaces to be mapped with 5 cm range resolution in snow; this is an improvement over the original system that worked from 2 to 6.5 GHz. From 2009 to 2012, CReSIS successfully operated the radar on the NASA P-3B and DC-8 aircraft to collect data on snow-covered sea ice in the Arctic and Antarctic for NASA Operation IceBridge. The radar was found capable of snow depth retrievals ranging from 10 cm to >1 m. We also demonstrated that this radar can be used to map near-surface internal layers in polar firn with fine range resolution. Here we describe the instrument design, characteristics and performance of the radar.

Changes in the firn structure of the western Greenland Ice Sheet caused by recent warming

“…We used remote sensing observations acquired by NASA's Operation IceBridge Snow Radar and the Airborne Topographic Mapper (ATM). The Snow Radar is a wideband radar that operates in the 2-6.5 GHz frequency range and can map polar firn internal layers with a range resolution of ∼ 5 cm (Panzer et al, 2013;Leuschen et al, 2014), and is used to trace the ice layers beneath the winter accumulation in 2011 by identifying internal radar reflections caused by melt layers. The ATM is a scanning laser altimeter used in this study to estimate annual elevation change between 2010 and 2013 along a frequently repeated transect in western Greenland (Fig.…”

Annual Greenland accumulation rates (2009–2012) from airborne snow radar

“…The snow radar operates over the frequency range from ∼ 2 to 6.5 GHz (Panzer et al, 2013;Rodriguez-Morales et al, 2014). The snow radar uses an FMCW design to provide a vertical-range resolution of ∼ 4 cm in snow/firn, capable of resolving annual layering, where preserved, to tens of meters in depth (Medley et al, 2013).…”

Sea ice thickness, freeboard, and snow depth products from Operation IceBridge airborne data

“…Snow depth was measured using a frequency-modulated, continuous-wave (FMCW) radar that utilizes dechirp on receive (Leuschen, 2009;Panzer et al, 2013). Mixing a delayed, attenuated receive signal with a copy of the transmit signal returns a beat frequency equal to the product of the chirp rate (bandwidth divided by pulse length) and the twoway delay time to the target.…”