Profiling Ice Depth and Stratigraphy with a 400-MHZ Time Domain Pulse

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2487 Wave Propagation (6934), 3672 Planetary Mineralogy And Petrology (5410), 5109 Magnetic And Electrical Properties, 5144 Wave Attenuation, 6969 Remote Sensing

Scientific paper

The only area on Mars where ground-penetrating radar, GPR, is sure to work is on the ice caps, which are stratified and appear to be as thick as 3 km. In Antarctica, surface-based GPR systems designed to profile bottom topography operate at 2--10 MHz and have antennas tens of meters long trailing behind the receiver. This is unacceptable for Mars because of the likelihood of snagging. Consequently, I look at the possibility and potential limitations of using UHF short-pulse radar to profile both stratigraphy, and ice bottom conditions which might contain water. In December, 2003 I used 400-MHz pulses to profile the McMurdo Ice Shelf, Antarctica, where the seawater at bottom provides a reflection coefficient of -1.0. I profiled along a section of the shelf that varied from about 100-160 m in depth, and used a time range of 1800 ns, 8192 16-bit samples/trace. Approximately one trace was recorded every second after a using a dynamic, running 8 stack during recording. The commercial transmitter had a maximum peak power output of about one Watt. The bottom ws profiled continuously, with a maximum approximate depth of 160 m with a signal to noise ratio as high as 17 dB. The bottom reflection waveform generally reproduced the transmitted wavelet. Given an approximate dielectric constant of 10 for either basalt or for sediments containing unfrozen and adsorbed water, this ratio would be reduced to about 6 dB, and thus afford another 160 m of penetration. 320 meters of ice would then require a 4000 ns time range, and 8192 samples/trace would then provide only 5 samples per cycle, which is barely adequate. Stratigraphic sensitivity would probably require dust layers because 400 MHz is too high to sense conductivity variations, and it is not clear if the upper tens of meters contain stratified firn or solid ice. It appears that a trace sampling rate of 16,384 coupled with a high rate of stacking to enhance the signal to noise ratio could possibly be used to profile 600 m of ice with a 400-MHz pulse.

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