2 Current Research in Coastal and Marine Processes

Sunday, 14 March 2021
8:00 AM - 12:00 PM
Windsor

GEOCLUTTER ON THE BACKSHORE: EXPERIMENTAL HIGH-FREQUENCY GEORADAR IMAGING OF DYNAMIC SEDIMENT DEFORMATION

Paper number: 2-6
Program: Theme Sessions
Time: 9:25 AM – 9:45 AM

Authors

Abstract

Supratidal settings along sandy coastlines, which include upper berm/foredune area and their ancient counterparts in ridge-swale strandplains, contain a diversity of 3D features, such as small channels, heavy-mineral lenses, biogenic structures (nests, burrows, tracks, tramplegrounds), buried vegetation, and anthropogenic objects (engineering structures, unexploded ordnance, hydrocarbon-impregnated sands, artifacts, and debris). Ground-penetrating radar (GPR) imaging has been used to identify some of these features above the fresh-saltwater interface, however, discrimination between the targets, which can contribute to geoclutter, remains a challenge. This study focuses on decimeter-scale laboratory GPR experiments using both traditional odometer wheel-triggered mode (OTM) and a time-triggered mode (TTM), with air- and liquid-filled balloons simulating a buried target (e.g., small animal). The substrate consisted of dry, well-mixed, moderately sorted, medium sand common for upper beach (berm/foredune) and aeolian settings. Targets were placed on a basal layer (L1) buried by ~20-cm-thick cover horizon (L2), both with near identical mean grain size (1.69 and 1.65 ϕ, respectively). A slightly less positive near-symmetrical skewness of the upper layer (0.056 vs 0.061 for L1) likely resulted from a loss of minor silt fraction during manual excavation and burial phases. High-frequency (2,300 MHz) surveys were captured in TTM while manually extracting the target (time interval: 20 seconds), as well as before and after extraction in OTM. Due to higher dielectric contrast, the air-filled target showed a stronger signature in all three survey phases. The flat antenna base (plexiglass cover) eliminated topographic effects, however minor post-emergence disruption of sediment surface has to be rectified during post-processing or avoided through surface planation prior to OTM re-survey. Our study demonstrates promise in non-invasive in situ identification of small targets (e.g., sea turtle egg chamber) in areas with signal-noise ratio, as well as potential for real-time monitoring of dynamic changes in sediment properties on very short time scales (e.g., hatchling emergence), with implications to geological, archaeological, ichnological, and conservation research along sandy coasts.

Geological Society of America Abstracts with Programs. Vol. 53, No. 1

doi: 10.1130/abs/2021NE-361462

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