Ground-penetrating Radar Transects Research Articles

GPR, VES and refraction seismic surveys in the karstic area “Spedicaturo” near Nociglia (Lecce, Italy)

ABSTRACTThe present work shows some results of an early ground‐penetrating radar (GPR) study performed in a hazardous karstic area near the village of Nociglia in the central part of the Salento peninsula (Apulia, southern Italy), after a sudden subsidence event occurred on March 13th, 1996. The geophysical study, also involving vertical electric sounding (VES) and refraction seismics, is part of a multidisciplinary research project, aimed at determining the climatic, geological, morphological and hydrogeological conditions of the area in order to assess geological hazards and to prevent groundwater pollution due to agricultural activities. GPR transects led to the identification of some shallow subsurface structures including a known cave and probable karstified bedding joints, weakened shallow layers, fractures, fault zones, and burrows. The VES and seismic surveys resulted in a better understanding of the geology of the area and supported the interpretation of the GPR data.

Foraminiferal and Sedimentary Record of Late Holocene Barrier Island Evolution, Pea Island, North Carolina: The Role of Storm Overwash, Inlet Processes, and Anthropogenic Modification

Abstract Foraminiferal and sedimentary data, supplemented with geochemical dating and ground-penetrating radar transects, show that the barrier island at Pea Island National Wildlife Refuge just north of Rodanthe, North Carolina, has been dominated by a combination of inlet and overwash processes for at least 1000 years. The stratigraphic record of several vibracores does not preserve every, or even many, overwash events but, instead, is characterized by three to four fining-upward sequences. The last three commence with overwash sand or gravel that is overlain by a variety of finer-grained estuarine, inlet, and marsh deposits. The dynamic nature of this segment of the Outer Banks was muted in the late 1930s by construction of artificial barrier dune ridges, extensive planting of grass and shrubs, and construction of Highway 12 in 1953. Subsequently, the road and barrier dune ridge were rebuilt and relocated several times following storm events.

Estimating the Fine Soil Fraction of Desert Pavements Using Ground Penetrating Radar

A reconnaissance tool that can estimate the clay content and saturated hydraulic conductivity (Ks) of well‐developed desert pavements has immediate applications for researchers and practitioners who work in arid environments. We examined the use of surface‐based ground penetrating radar (GPR) to rapidly approximate these properties on six, 100‐m‐long transects for two different aged (∼100 000 vs. 4000 yr) desert pavement surfaces. We determined early‐time amplitudes from GPR transects, ground electrical conductivity, hydraulic properties, clay content, water content, and soil salinity at regular intervals along each transect. Both surfaces were low in water content and salinity; however, the older pavement contained substantial amounts of silt and clay in the surficial soil horizon. Using multivariate linear regression, which included GPR amplitude and a nominal measure of soil structure ascertained by visual field inspection, we show significant correlations between measured and predicted values of both silt plus clay content (r = 0.84, P < 0.0001) and Ks (r = 0.73, P < 0.0001) for the older surface. No significant correlations were found on the younger surface. This is probably due to the low concentrations of clays in the young soil. Including the metric of soil structure improved the predictive capabilities on the older surface. The GPR method provides higher spatial resolution than electromagnetic measurements. The results suggest that, at this location, the approach is not influenced by heterogeneities in lower soil horizons. The method can be used for reconnaissance surveys as a means of estimating the clay content, and in some cases Ks, of surficial soils on certain well‐developed desert pavements.

Investigation of large-scale washover of a small barrier system on the southeast Australian coast using ground penetrating radar

Prehistoric depositional signatures for large-scale washover involving marine inundation events such as storms and tsunami have been the subject of considerable research over the last 15 years. Much of this research has focused on the identification of sandsheets in back-barrier environments as depositional records for extreme washover events. All these deposits must have a sediment source and, by their nature, the most likely source of sediment for washover into back-barrier environments is the barrier itself. This study identifies an erosional signature for large-scale washover from a small coastal barrier on the southeast Australian coast. A distinct lens of marine sand, up to 90 cm thick, confined vertically by peat, is found in the upper fill of a closed freshwater back-barrier lagoon sequence. This sand lens is attributed to a large-scale washover event during the last 800 years, and was possibly deposited by a tsunami. The hypothesis for this study was that any event that breached the dune system must have caused considerable geomorphic change to the dunes and hence may have left an erosional signature. Ground penetrating radar transects of the system show an erosional contact between a series of truncated pre-event dunes and several small overlying post-event dunes. This study outlines a relatively simple non-invasive method for the identification of an erosional signature for prehistoric large-scale washovers caused by storm surge, exceptionally large waves, or tsunami.

Recent Developments in the Geomorphic Investigation of Engineered Tidal Inlets

In recent years, numerous technological advances have made field studies and laboratory analyses of tidal inlets more time efficient while also substantially improved data quality. Mapping channel bathymetry was once a labor-intensive task that was accomplished by measuring water depths along a detailed network of channel profiles. Now aircraft-operated LIight Detection and Ranging (LIDAR) can accurately map the bathymetry of most tidal inlets in a few hours' time. If greater detail of the channel bottom is required, then a multibeam acoustic system is utilized, although this technique is deployed from a boat and is less time efficient. The topographic version of LIDAR enables the construction of inlet shoreline maps and determination of volumes associated with shoreline gains and losses. In another advancement, side scan sonar mosaics now provide a picture of the bottom indicating different sediment types, bedrock outcrops, and bedform distributions. These surveys have also become essential for identifying scour holes next to rock jetties and assessing the susceptibility of these structures to collapse. The accretionary history and/or migrational trend of a tidal inlet can be determined from ground-penetrating radar transects on land and from shallow seismic surveys in water. These records provide a representation of the layers of sediment left behind as the inlet shifted positions. The hydraulic regime of a tidal inlet can be much more accurately determined using the Acoustic Doppler Current Profiler (ADCP). This instrument produces velocity profiles for an entire inlet cross section and provides almost instantaneous discharges for small and moderately sized inlets. In a slightly different mode, ADCP technology has been used for directional wave measurements. Finally, significant upgrades in the manipulation of information, including Geographic Information System (GIS) and image analysis methods, have greatly facilitated the analyses and interpretation of the field data. These advancements have provided scientists with more effective means of gathering data, testing numerical models, and finding solutions to coastal engineering problems.

Using ground-penetrating radar to detect layers in a sandy field soil

Pollutant transport in sandy soils can be very complex due to the presence of coarse sand lenses. Water flows laterally over the coarse material and, subsequently, breakthrough occurs in concentrated pathways, called fingers. This (funneled) flow process is a form of preferential flow reducing solute travel time and degradation of organic chemicals. In this paper, we test ground-penetrating radar (GPR) as a tool for detecting layers in the soil. Several GPR transects were established on a fine sandy loam soil throughout the growing season and subsequent fall period to find the best time to reveal layer structures. The effect of the spatially varying moisture content on the radar velocity was determined from actual measurements with soil samples and by using the Common Mid-Point (CMP) technique. The optimal time to find coarse layers with GPR in this soil was at the end of the fall season when the soil was wetted and evaporation had decreased. The depth of layers, as indicated by GPR, was highly sensitive to the soil moisture content and could be in error by as much as ±0.4 m on a depth scale of 1.5 to 2 m if an average propagation velocity was used. A satisfactory depth prediction of textural interfaces was obtained non-destructively by collecting data in both reflection and CMP mode.

Ground-penetrating radar used to assess aggregate in catastrophic flood deposits, northeast Alberta, Canada

Coarse-grained aggregate deposited by a catastrophic flood located north of Fort McMurray, Alberta, was examined using ground-penetrating radar (GPR) and lithostratigraphic logging techniques. GPR transects were acquired from an upper scoured zone of flood deposits. Sedimentary structures (cross-beds and plane-beds) within the coarse sand and gravel and determinations of depth to bedrock (sediment thickness of the aggregate) were recognized in the GPR profiles by their varying dielectric properties. Fine-grained, conductive underlying oil-sand, till, or glaciolacustrine sediment (silt and clay) attenuated the radar signal. The sedimentary structures mapped from the GPR transects were confirmed in adjacent trench exposures. We suggest that GPR is an efficient methodology for determining volumes of aggregate reserves, thicknesses of aggregate deposits, and mapping sedimentary structures of high-energy fluvial sediments. Key words : aggregate, ground-penetrating radar, Alberta, spillway.

Design of Soil Map Units on a Karst Area in West Central Florida

AbstractThe objectives of this research were to identify soil taxa and to evaluate soil‐landscape relationships in order to design map units that accurately describe soil distribution on the Chiefland Limestone Plain (CLP) in west central Florida. A conceptual soil‐landscape model for mapping the CLP was derived based on information from similar karst areas in adjacent counties. Preliminary field observations using the model along with analysis of initial ground‐penetrating radar (GPR) data indicated intricate soil patterns and little relationship between soil occurrence and landscape position. Flexgrid surveys were conducted and 61 GPR transects were performed to design map units and to facilitate placement of map‐unit boundaries. Confidence levels of 95 and 80% were used to establish confidence intervals for named and similar soils in each map unit. A new kind of map unit termed “intriplex” was defined to bridge the gap between complexes and undifferentiated groups.