The directional dependence of the Ground Penetrating Radar response on the accumulation zones of temperate Alpine glaciers

Nobes, David C.

doi:10.1046/j.1365-2397.1999.00028.x

Cited by 19 publications

(10 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A more clear bottom reflection is observed in (b), particularly in its central part, because the diffraction hyperbolae are clearly enhanced in (a) and, consequently, the smaller amount of energy transmitted to the lower levels results in a reduced contrast of the ice-bed interface. The enhancement of the energy from the diffraction hyperbolae can be attributed to: (1) the directionality of the radar antennae with respect to the flow direction and the crevasse orientation (Nobes, 1999), as the antennae are collinear with the flow direction and cross the crevasses perpendicularly in (b), and (2) water content in the glacier, consistent with meteorological data available. In Nobes experiments, the internal reflectivity is significantly less and the basal ice-rock reflection is clearer for the axially orientated radar antennae, in agreement with our results.…”

Section: Radar Datasupporting

confidence: 74%

Application of radar and seismic methods for the investigation of temperate glaciers

Navarro

Macheret

Benjumea

2005

Journal of Applied Geophysics

View full text Add to dashboard Cite

Section: Radar Datasupporting

confidence: 74%

Application of radar and seismic methods for the investigation of temperate glaciers

Navarro

Macheret

Benjumea

2005

Journal of Applied Geophysics

View full text Add to dashboard Cite

“…The same effect appears to be true for Bas Glacier d' Arolla. Again, as found by Nobes (1999), transversely orientated antennae pick out more internal reflectivity than axially orientated antennae. Nobes (1999) accounted for increased internal reflectivity with transversely orientated antennae as the product of reflections from crevasses and``crevasse remains extending to great depths'', which are orientated transverse to flow.…”

Section: Interpretation Of Gpr Data Differences Between Antennae Oriesupporting

confidence: 69%

“…Again, as found by Nobes (1999), transversely orientated antennae pick out more internal reflectivity than axially orientated antennae. Nobes (1999) accounted for increased internal reflectivity with transversely orientated antennae as the product of reflections from crevasses and``crevasse remains extending to great depths'', which are orientated transverse to flow. A comparable structure on Bas Glacier d' Arolla would be the multiple foliation planes, many originating from crevasse traces, which are also perpendicular to glacier flow.…”

Section: Interpretation Of Gpr Data Differences Between Antennae Oriesupporting

confidence: 69%

“…10, profile B) has enhanced the quality of data at depth. In addition, the near-surface``reflection-poor'' areas appear deeper and``cleaner'' during inline data collection.The differences in data are related to the preferential orientation of structural features within the ice relative to the polarization of the radar signal (Nobes, 1999). Nobes (1999) found that the basal ice/rock reflection at Franz Josef Glacier, New Zealand, is clearer when antennae are axially orientated with respect to the direction of glacier flow, but obscured by internal reflections when antennae are transversely orientated to flow.…”

Section: Interpretation Of Gpr Data Differences Between Antennae Oriementioning

confidence: 99%

See 1 more Smart Citation

Formation of band ogives and associated structures at Bas Glacier d’Arolla, Valais, Switzerland

2002

View full text Add to dashboard Cite

ABSTRACT. Structural glaciological, sedimentological and geophysical techniques are used to provide new insight concerning the formation of band ogives and associated structures at Bas Glacier d' Arolla, Switzerland. Sedimentary stratification, crevasse traces and transverse foliation are identified as planar structures in the lower icefall and glacier tongue. Stratification and crevasse traces are progressively deformed into, and enhance, the transverse foliation found in the glacier tongue. Three-dimensional geometry has been defined using ground-penetrating radar, which portrays four main characteristics: (i) deep reflectors interpreted as the ice/bed interface, (ii) alternating reflection-rich and reflection-poor zones interpreted as ogives, (iii) up-glacier-dipping reflectors, interpreted as planar structures, and (iv) down-glacier-dipping reflectors of uncertain origin. At the glacier surface, each band ogive consists of a light and dark band. The dark bands contain more intense foliation which, on differential weathering, traps fine debris. Clasts and clear ice of basal character within dark ogive bands suggest that basal ice has been raised to the glacier surface.The most applicable model for the formation of band ogives at Bas Glacier d' Arolla is a refinement of Posamentier's (1978)``reverse faulting'' hypothesis. In this context, multiple shear zones are formed, through which basal ice is uplifted to the glacier surface to produce the dark, foliated ogive bands. This model fits observations reported from other glaciers with band ogives.

show abstract

“…For example, Nobes (1999) found that the response on temperate glaciers depends on the orientation of the antennas relative to the glacier flow direction; van Overmeeren (1994) noted that the response from sedimentary sequences varies depending on the orientation of the antennas relative to the dip of the beds; and Tillard (1994) observed that the response for radar experiments in granite and schist depends on the orientation of the antennas relative to the schistosity. Such observations are consistent with the character of the signal transmitted from a GPR antenna into the ground under different conditions (Annan et al, 1975 and Figure 1).…”

mentioning

confidence: 99%

<title>"Broadside" versus "end-fire" radar response: some simple illustrative examples</title>

Nobes

Annan²

2000

SPIE Proceedings

View full text Add to dashboard Cite

A few field studies have noted a directional dependence in the ground-penetrating radar response. Such observations are consistent with the character of the signal transmitted from a GPR antenna into the ground under different conditions. However, the antenna orientation relative to the target geometry is seldom given much consideration in GPR survey design and execution. We use simple models to illustrate the influence of antenna orientation relative to dipping reflectors. The two fundamental responses are presented: The "broadside" response arises when the transmitting and receiving antenna axes are parallel to the strike of the dipping feature. The "end-fire" response is obtained when the antennas are perpendicular to the strike. Both the reflector dip and host velocity are varied. Antenna orientation relative to the target is important because of the lobate nature of the transmitted GPR signal. The signal strength is zero or almost zero at "null points" , where the energy available for reflection is small, and any reflected energy is almost non-existent. The broadside and end-fire signals have different forms, and yield different responses to dipping features. Thus, if the angle at which a null occurs is complementary to the angle of the dip, then little or no reflection occurs.

show abstract

The directional dependence of the Ground Penetrating Radar response on the accumulation zones of temperate Alpine glaciers

Cited by 19 publications

References 15 publications

Application of radar and seismic methods for the investigation of temperate glaciers

Application of radar and seismic methods for the investigation of temperate glaciers

Formation of band ogives and associated structures at Bas Glacier d’Arolla, Valais, Switzerland

<title>"Broadside" versus "end-fire" radar response: some simple illustrative examples</title>

Contact Info

Product

Resources

About