RADAR STRATIGRAPHY OF THE GREENLAND ICE CAP: GROUNDTRUTH FOR SHARAD DATA

Ground penetrating radar measurements performed on the Greenland ice sheet show internal reflectors, possibly due to changes in ice chemical composition and physical properties. As discussed by several authors, ice includes many impurities, mainly due to wind deposition. Volcanic dusts related to major eruptions have been clearly detected and identified in ice cores. Varying concentration and composition of dust inclusions affects ice permittivity, most importantly causing changes in conductivity, as well as in Power Reflection Coefficient (PRC) value, thus causing radar reflections (i.e. radar layers).

The SHAllow RADar (SHARAD) is the subsurface radar on-board Mars Reconnaissance Orbiter (MRO). Radar profiles obtained on Mars Polar Layer Deposits (PLD) exhibit layering analogous to those found in the terrestrial ice sheets. As deep ground drilling is not currently feasible on Mars, we intend to use chemical and physical data coming from the Greenland ice core drilling campaigns to infer ice characteristics of the Mars ice caps. The first step is to integrate radar and core data taken from the same area in order to understand the causes of the radar reflections.

Greenland radar data were acquired by CReSIS teams using airborne radars. Chosen datasets for our analysis are from 2001-2002 campaigns. ICORDS2 radar emits a chirped signal with a center frequency of 150 MHz and a bandwidth of 17 MHz, reaching a vertical resolution (in ice) of about 7 m. On the other hand, SHARAD is a spaceborne, chirped radar operating at 20 MHz center frequency with a 10 MHz bandwidth (~15 m vertical resolution in ice).

Basing on a visual analysis of radargrams, we recognized four different stratigraphic units in the ice sheet beneath the Greenland Summit area, then we characterized them using data about macro- and microscopic properties coming from ice core records.

Our work aims to reproduce radar profiles acquired on terrestrial ice sheets with a direct inversion model obtained using dielectric properties data measured at Greenland ice cores. As the model demonstrates its robustness, we shall adapt the model to reproduce Sharad radar profiles acquired on Martian PLDs. Comparing with real data will give a stratigraphc interpretation to some of the observed features within PLDs.