3 results
4 - Ground-penetrating radar
- Edited by C. Hauck, Université de Fribourg, Switzerland, C. Kneisel
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- Book:
- Applied Geophysics in Periglacial Environments
- Published online:
- 22 August 2009
- Print publication:
- 02 October 2008, pp 81-98
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Summary
Introduction
Ground-penetrating radar (GPR) is a geophysical method for subsurface investigation that utilises electromagnetic signals transmitted into the ground as pulses from an antenna. A receiver antenna picks up energy that is partially reflected as the signal passes through a dielectric boundary in the ground. Compared to other geophysical methods, GPR supplies data with very high vertical resolution, a potential high recording speed and real-time display of the acquired data. Commercial GPR systems have only been available since the mid 1970s and the first digitally controlled GPR system was introduced by Sensors & Software Inc. in the mid 1980s. Of early scientific applications of GPR, radar measurements in cold glacier ice are probably the most noteworthy and the technique became even more important within glaciology in the mid 1970s when technical development facilitated GPR applications also on temperate ice (see also Chapter 13). GPR was also applied early within permafrost studies (Annan and Davis 1976, Davis et al. 1976). GPR is today one of the standard methods for subsurface investigations, and the fundamentals of the method are provided in textbooks such as Daniels (1996) and Reynolds (1997).
The range and number of GPR applications have in general risen sharply during the past 4–5 years. This rise is also noticeable within the fields of permafrost and periglacial research. However, despite the early promising results from GPR profiling in cold environments, the absolute number of applications is still rather limited.
16 - Mapping frazil ice conditions in rivers using ground penetrating radar
- Edited by C. Hauck, Université de Fribourg, Switzerland, C. Kneisel
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- Book:
- Applied Geophysics in Periglacial Environments
- Published online:
- 22 August 2009
- Print publication:
- 02 October 2008, pp 217-224
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Summary
Introduction
In many high-latitude rivers, frazil ice production along open reaches sometimes causes blocking of the river course further downstream, beneath the seasonal ice cover, and may eventually lead to flooding and formation of extensive icing on the flood plain (Asvall 1998). When mitigation measures must be taken, rapid mapping of the ice conditions beneath the surface ice is advantageous. Therefore, the Norwegian Water Resources and Energy Directorate have tested the use of ground-penetrating radar (GPR) for this purpose.
The dielectric contrasts between ice and both water and wet sediments are large and clear reflections are expected (Table 16.1). Beneath the surface ice cover, a mixture of water and a variable amount of ice crystals (frazil ice) may be found. It is likely that this mixture of ice and water will cause clutter (chaotic returns from material inhomogeneity) and influence the velocity of a passing electromagnetic signal.
Airborne radar technology has been successfully applied to measure ice thickness on rivers and lakes (e.g. Arcone and Delaney 1987, Arcone 1991, Leconte and Klassen 1991, Arcone et al. 1997), and ground-based surveys of ice thickness have for instance been standardised by Sensors & Software Inc. through designated ‘ice picker’ software for use with their Noggin 500 MHz system. Other aspects of river ice, such as frazil ice and bottom ice, have received less attention, although there is a study by Dean (1977) and detection of frazil ice by airborne radar is also mentioned by Steven Arcone on the CRREL website (www.crrel.usace.army.mil/sid/gpr/Airborne_GPR.html).
12 - GPR soundings of rock glaciers on Svalbard
- Edited by C. Hauck, Université de Fribourg, Switzerland, C. Kneisel
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- Book:
- Applied Geophysics in Periglacial Environments
- Published online:
- 22 August 2009
- Print publication:
- 02 October 2008, pp 172-177
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Summary
Introduction
GPR has been used for rock glacier investigations on the following four sites on Svalbard: Hiorthfjellet rock glacier (78° 15′ N, 15° 47′ E) close to Longyearbyen; four rock glaciers on the northwestern part of Prins Karls Forland (Forlandet) (78° 50′ N, 10° 30′ E); Brøggerbreen rock glacier (78° 54′ N, 11° 53′ E) close to Ny Ålesund; and on Nordenskiöldkysten (77° 53′ N 13° 54′ E). The Hiorthfjellet rock glacier is a typical tongue-shaped, talus-derived rock glacier, which is confined by the large bowl in the Hiorthfjellet mountainside. The Brøggerbreen and Forlandet rock glaciers are lobe-shaped talus-derived rock glaciers situated at the break of slope between the backing rockwall/talus slope and the valley bottom (Brøggerbreen) or strandflat area (Forlandet). On Nordenskiöldkysten, a large, complex talus-derived rock glacier, with a similar setting as those on Forlandet, was investigated.
Methods
All GPR profiles were collected using antennae of 50 MHz centre frequency, aligned perpendicular to the profile direction. Data from the Hiorthfjellet rock glacier were obtained during the winter season in 1997 and followed the central flowline of the Hiorthfjellet rock glacier. The length of the profile was 303 m. The radar used was of the type pulseEKKO 100 (Sensors & Software Inc. Mississauga, Canada). The transmitter/receiver antenna spacing was 2 m. Topographic data from the rock glacier on Hiorthfjellet were obtained from a geodetic survey and a digital altimeter.