Radar-Detected Layering in Ice: Experiments, Field Data, Modeling, and Application to Mars
Abstract
Here we report on lab experiments and analysis of field data to measure the effects of dust contamination and density variations on internal reflections in ground penetrating radar (GPR) profiles. This work was originally motivated by the presence of prominent radar-detected internal layering in the Northern Polar Layered Deposits (NPLD) on Mars, where the observed radar stratigraphy may indicate dust layers resulting from periodic climatic excursions causing variable rates of deposition or concentration via sublimation of the overlying ice. However, dust is not the sole source of intra-ice reflections: variations in ice density, for instance, can also give rise to these radar signatures. Moreover, these layers in Mars ice frequently occur in packets, and the correspondence between layer or packet spacing as a function of depth and the properties of the radar reflectors remains unclear.
On both Earth and Mars, a quantitative understanding of the causes of radar-detected ice layering is important for interpretation of underlying temporal variations in environmental conditions. To constrain the relationship between magnitude and vertical spacing of density variations and observed radar signatures, we constructed a tank, 6 m long x 4 m wide x 3 m deep, filled with layers of ice, snow, and snow / dust mixtures with known thicknesses and densities, at the US Army Corps of Engineers Cold Regions Research and Engineering Laboratory. We collected GPR profiles over this layered substrate using 200 MHz, 400 MHz, and 900 MHz GPR antennas. Here, we report on analysis of those lab data and on initial time-domain finite-difference modeling conducted to quantify the radar responses to variations in layer properties. We apply our modeling results to analysis of field data collected on the Langjökull Glacier in Iceland. Langjökull Glacier hosts a tourist tunnel bored into the ice that provided both a useful radar reflector and access to the interior of the glacier. In addition to GPR data (200 MHz, 350 MHz, and 900 MHz), we collected samples of ice and firn at various stratigraphic depths within the tunnel, and measured density variations, including those due to thin layers of volcanic ash. We use the combination of data analysis and modeling to quantify the sensitivity of the radar returns to the structure of measured density variations.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMNS14A..01G
- Keywords:
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- 0702 Permafrost;
- CRYOSPHERE;
- 0738 Ice;
- CRYOSPHERE;
- 0758 Remote sensing;
- CRYOSPHERE;
- 0794 Instruments and techniques;
- CRYOSPHERE