Abstract

Satellites provide long time series of measurements to support scientific and operational studies of polar regions. The sensors on these satellites have revealed the speed-up and retreat of glaciers, the break-up of ice shelves, and the reduction of sea ice thickness and extent in the Arctic. However, satellite observations alone are not sufficient to understand the processes causing glacier speed-up and retreat and sea ice retreat. Airborne and in-situ measurements are also required to interpret satellite data sets and to understand the processes causing the observed changes. For example, we need deeper knowledge of bed topography and basal conditions to obtain both an improved understanding of the processes causing glacier retreat and speed-up and incorporate this knowledge into next-generation ice-sheet models. Sea ice thickness is a key variable in modeling ice-ocean-atmosphere interactions, and it is one of the most difficult variables to measure over large areas. Additional information on snow thickness is required to convert satellite altimeter-measured free-board measurements of snow and ice into sea-ice thickness.

We developed radar instrumentation for polar research that is being operated on both long-range and short-range aircraft in conjunction with other sensors. The instrumentation include radars operating over a frequency range of about 14 MHz to 18 GHz. These are: (1) a radar depth sounder/imager that operates at a center frequency of 195 MHz to sound ice and image the ice-bed interface; (2) an ultra-wideband radar that operates over a frequency range of 600 -900 MHz to map near-surface internal layers in polar firn and ice; (3) an ultra-wideband microwave radar that operates over a frequency range of 2-8 GHz to measure the thickness of snow cover over sea ice and map near-surface internal layers in polar firn with fine range resolution of about 3 cm; and (4) a radar altimeter that operates over a frequency range of 12-18 GHz for high-precision surface elevation measurements. These radars are being used to collect data as a part of NASA Operation Ice Bridge (OIB) and CReSIS field activities over the Antarctic and Greenland ice sheets, as well as over Arctic and Antarctic sea ice.

In this talk, I will discuss the scientific and technical requirements for radar sounding and imaging of the ice sheets, mapping near-surface internal layers, and measuring snow thickness over sea ice. I will also discuss the technical challenges associated with sounding fast-flowing glaciers and ice-sheet margins, as well as our solutions to these challenges. I will present the way in which ice-core measurements and radar data can be combined to generate unambiguous determinations of basal conditions, and I will show sample results obtained with advanced signal processing techniques to identify undisturbed internal layers for selecting optimum drill sites for future ice core collection. Finally, I will discuss the recent technical advances in radar, antenna and signal-processing technologies and the potential development of ultra-wideband radars that can be operated from aircraft for sounding sea ice and sounding and imaging ice sheets and mapping internal layers from the surface to the bed with fine resolution.