Type I: Snow Pit Analysis

Six experiments were conducted, all nearby the Australian Antarctic Station - Davis. Even within the close geophysical proximity of the experiments (no more than 1 km apart - although GPS coordinates were not recorded), a large variety of snow pack density and stratigraphy was observed. Figures 4.4, 4.5, 4.6, 4.7, 4.8, and 4.9 present a summary of thein-situmeasurements as well as the radar recorded signatures as a function of distance3_{, andin-situconditions recorded}

for the six snow pit studies. The air/snow and snow/ice interfaces were expected to correspond to the greatest changes in refractive index. Consequently, two strong peaks in the radar data are expected to indicate their presence, and the separation of the peaks to indicate the thickness of the snow layer.

Table 4.1 summarises the estimates of snow thickness measured in-situ and the snow thickness derived from data collected by the radar. The snow pack thickness estimated from the radar compares well with the in-situmeasurements. Considering that the vertical range resolution is theoretically 32.5 mm4_{, the agreement between the values is reasonable. The discrepancies, and}

observations regarding the relative amplitude are explained below on a case by case basis:

3_{The return from the metal plate occurs between 6 m and 7 m, which is much greater than the}

height of the antennas above the surface due to additional delay that the signal suffers from the cables connecting the antennas, and radar internal component delay.

4_{Provided with a 6 GHz bandwidth, as section 2.3.2 calculates, the vertical range resolution is}

25 mm. Consequently, when a Hamming window is applied to the data this increases by 1.3 to: 32.5 mm.

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Pit #: In-situdepth (mm) Radar derived depth (mm)

1 63.5 63.0 2 169.0 118.0 3 123.5 127.0 4 148.0 149.0 5 745.0 642.0 6 153.0 147.0

Table 4.1: Comparison between thein-situmeasured and radar estimated snow thickness pit measurements (theoretical radar range resolution of 32.5mm).

Pit #1 The radar performed well, reporting a snow thickness well within the range resolution limits. This was a result of a well-packed and dense snow cover, coupled with a dry and solid underlying ice surface. However, a comparison of the Fresnel coefcient term (R2), which captures the theoretical percentage power that should be reected at the air/snow and snow/ice interfaces, with the actual relative power levels of the two peaks identied as the relevant returns, indicates that the radar signal suffered a greater than anticipated power loss. This can be explained either by unaccounted scattering or, since the snow thickness is comparable to the wavelengths used (5 GHz is a 60 mm wavelength), by the inuence of thin-lm effects (Born and Wolf, 1965), and related phenomena requiring further study. Pit #2 The radar waveform does not display a peak that can be identied as the snow/ice layer.

Hence, a comparison is provided between the radar return from the untouched snow surface, and the radar return from the same surface, but with the snow cleared. The absence of reection can be explained by the fact that the surface layer was found to be wet, with large snow grains and hence likely to have absorbed all incident radiation.

Pit #3 Thein-situand radar measurements are within the range resolution. The minor discrepancy is explained by signal reection from an unobserved density change at the bottom of the snow layer before reaching the ice surface. The layering present in the snow pack was measured with a rule, but density samples were not taken due to time constraints during the experiment.

Pit #4 The in-situ and radar measurements are within the range resolution. An internal peak is seen at a distance of 58 mm away from the air/snow peak in the radar return, but this is not corroborated by visual evidence. This could be due to an unobserved density change.

Pit #5 The last visually recorded layer is not detected by the radar, and this is explained by the fact that the bottom was found to be wet and slushy and hence impenetrable to the radar signal. This likely resulted from the increasingly warmer weather conditions experienced later in the study.

Pit #6 The in-situ and radar measurements are within the range resolution; the relatively small difference is likely due to the presence of a slushy bottom layer.

In general it was observed that in-situmeasurements visually identied layers in the snow pits, which were frequently not detected by the radar. This is likely due to the fact that the thickness of the layers was comparable to the wavelengths used. However, with increasing frequency (smaller wavelength) such layering should be detected, as reported by Marshall et al.[2008b] and Koh et al.[1996].

In future work, enabling this radar with a capacity for detecting not only the thickness of the snow, but also layering within the snow pack would allow for increased understanding of the nature of snow accumulation. Potentially allowing for a judgement to be made on recent weather, and wind conditions.

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