scholarly journals Beach-ridge architecture constrained by beach topography and ground-penetrating radar, Itilleq (Laksebugt), south-west Disko, Greenland – implications for sea-level reconstructions.

2018 ◽  
Vol 66 ◽  
pp. 167-179
Author(s):  
Priscila E. Souza ◽  
Aart Kroon ◽  
Lars Nielsen
Keyword(s):  
Ground Penetrating Radar ◽  
Abrupt Change ◽  
Beach Ridge ◽  
Sediment Grain Size ◽  
Beach Ridges ◽  
Reflection Data ◽  
South West ◽  
Tide Level ◽  
Ground Penetrating ◽  
Reflection Characteristics

Detailed topographic data and high-resolution ground-penetrating radar (GPR) reflection data are presented from the present-day beach and across successive raised beach ridges at Itilleq, south-west Disko, West Greenland. In the western part of the study area, the present low-tide level is well defined by an abrupt change in sediment grain size between the sandy foreshore and the upper shoreface that is characterised by frequently occurring large clasts. The main parts of both fine and large clasts appear to be locally derived. Seaward-dipping reflections form downlap points, which are clearly identified in all beach-ridge GPR profiles. Most of them are located at the boundary between a unit with reflection characteristics representing palaeo-foreshore deposits and a deeper and more complex radar unit characterised by diffractions; the deeper unit is not penetrated to large depths by the GPR signals. Based on observations of the active shoreface regime, large clasts are interpreted to give rise to scattering observed near the top of the deeper radar unit. We regard the downlap points located at this radar boundary as markers of palaeo-low-tide levels. In some places, scattering hyperbolas are more pronounced and frequent than in others, suggesting differences in the occurrence of large boulders.

scholarly journals Ground Penetrating Radar Investigation of Late Pleistocene Shorelines of Pluvial Lake Clover, Elko County, Nevada, USA

Quaternary ◽  
2020 ◽  
Vol 3 (1) ◽  
pp. 9
Author(s):  
Jeffrey S. Munroe
Keyword(s):  
Late Pleistocene ◽  
Ground Penetrating Radar ◽  
Land Surface ◽  
Primary Objective ◽  
Water Levels ◽  
Beach Ridge ◽  
Beach Ridges ◽  
Sand And Gravel ◽  
Ground Penetrating ◽  
Topographic Surveys

Beach ridges constructed by pluvial Lake Clover in Elko County, Nevada during the Late Pleistocene were investigated with ground-penetrating radar (GPR). The primary objective was to document the internal architecture of these shorelines and to evaluate whether they were constructed during lake rise or fall. GPR data were collected with a ground-coupled 400-Mhz antenna and SIR-3000 controller. To constrain the morphology of the ridges, detailed topographic surveys were collected with a Topcon GTS-235W total station referenced to a second class 0 vertical survey point. GPR transects crossed the beach ridge built by Lake Clover at its highstand of 1725 m, along with seven other ridges down to the lowest beach at 1712 m. An average dielectric permittivity of 5.0, typical for dry sand and gravel, was calculated from GPR surveys in the vicinity of hand-excavations that encountered prominent stratigraphic discontinuities at known depths. Assuming this value, consistent radar signals were returned to a depth of ~3 m. Beach ridges are resolvable as ~90 to 150-cm thick stratified packages of gravelly sand overlying a prominent lakeward-dipping reflector, interpreted as the pre-lake land surface. Many ridges contain a package of sediment resembling a buried berm at their core, typically offset in a landward direction from the geomorphic crest of the beach ridge. Sequences of lakeward-dipping reflectors are resolvable beneath the beach face of all ridges. No evidence was observed to indicate that beach ridges were submerged by higher water levels after their formation. Instead, the GPR data are consistent with a model of sequential ridge formation during a monotonic lake regression.

scholarly journals Sea-level proxies in Holocene raised beach ridge deposits (Greenland) revealed by ground-penetrating radar

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Lars Nielsen ◽  
Mette Bendixen ◽  
Aart Kroon ◽  
Mikkel Ulfeldt Hede ◽  
Lars B. Clemmensen ◽  
...  
Keyword(s):  
Sea Level ◽  
Ground Penetrating Radar ◽  
Beach Ridge ◽  
Ground Penetrating

scholarly journals Frequency-dependent attenuation analysis of ground-penetrating radar data

Geophysics ◽  
2007 ◽  
Vol 72 (3) ◽  
pp. J7-J16 ◽  
Author(s):  
John H. Bradford
Keyword(s):  
Attenuation Coefficient ◽  
Ground Penetrating Radar ◽  
A Priori ◽  
Radar Data ◽  
Frequency Dependent ◽  
First Order ◽  
Reflection Data ◽  
Frequency Independent ◽  
Band Limited ◽  
Ground Penetrating

In the early 1990s, it was established empirically that, in many materials, ground-penetrating radar (GPR) attenuation is approximately linear with frequency over the bandwidth of a typical pulse. Further, a frequency-independent [Formula: see text] parameter characterizes the slope of the band-limited attenuation versus frequency curve. Here, I derive the band-limited [Formula: see text] function from a first-order Taylor expansion of the attenuation coefficient. This approach provides a basis for computing [Formula: see text] from any arbitrary dielectric permittivity model. For Cole-Cole relaxation, I find good correlation between the first-order [Formula: see text] approximation and [Formula: see text] computed from linear fits to the attenuation coefficient curve over two-octave bands. The correlation holds over the primary relaxation frequency. For some materials, this relaxation occurs between 10 and [Formula: see text], a typical frequency range for many GPR applications. Frequency-dependent losses caused by scattering and by the commonly overlooked problem of frequency-dependent reflection make it difficult or impossible to measure [Formula: see text] from reflection data without a priori understanding of the materials. Despite these complications, frequency-dependent attenuation analysis of reflection data can provide valuable subsurface information. At two field sites, I find well-defined frequency-dependent attenuation anomalies associated with nonaqueous-phase liquid contaminants.

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