ALBERT

Description: Ekströmisen is a small catchment area in coastal Dronning Maud Land, Antarctica,terminating in the Ekström ice shelf, which is bounded by a narrow embaymentformed by two ice ridges. A seismic survey has been performed alonga flow line on Ekströmisen over about 22 km, crossing the grounding line betweenicesheet and shelf approximately midway of the profile. The measurementswere performed with explosives in shallow firn holes as seismic sources and a60 channel 1.5 km snow streamer for data recording. The data has been resortedto form a virtual 120 channel 3 km streamer, consisting of 150 shots. Themaximumshot-receiver offset is thus about three times larger then the ice thickness,yielding wide angle information for intra-ice and bedrock reflections. Standardseismic data processing yields 862 common depth points in total, with an incrementof 25 m. This provides a 20-fold coverage of each commondepth point. Inaddition to yielding the distribution of seismic velocity within the firn, ice andsediment, the data clearly images ice and sedimentary layers. Within the bottompart of the ice, a number of continuous internal layers are visible upstream of thegrounding line. Currently, our favorite explanation is abrupt changes in the crystalorientation fabric caused by a combination of laterally compressional flow andvertical shear, as observed with radio-echo sounding at other places in Antarctica.Upstream of and at the grounding line, structures are visible within the bedrock,which we interpret as sedimentary deposits related to glacial activity. The dataprovide the base for interpretations of the ice-dynamic and sedimentary processesoccurring in the basal ice layer and at the ice-bedrock boundary, of relevance forfurther understanding details of the ice sheet-to-shelf transition area.

Description: The cold alpine saddle Colle Gnifetti, Monte Rosa, Swiss-Italian Alps resembles very much polar and subpolar ice masses in terms of glaciological conditions.It has been the site for several ice-core drilling campaigns over more than 20 years to determine paleoclimatological and glaciological conditions.To investigate the feasibility of geophysical methods for improved characterization of ice masses surrounding borehole and ice-core sites, a combined active reflection seismic and ground-penetrating radar pilot study has been carried out in summer 2008.Aims are the characterization of density, internal layering, seismic and radar wave speed and attenuation, identification of anisotropic features (like crystal orientation or bubble content and shape).Here we present the overall setup and first results. Seismic and GPR profiles were centered on an existing borehole location covering the full ice thickness of 62 m.Active seismics was carried out with 24-channel 3-m spacing recording, using a Seismic Impulse Source System (SISSY) along two profiles parallel and perpendicular to the ice-flow direction.The same profiles were complemented with GPR measurements utilizing 250, 500 MHz frequencies.Additionally, circular profiles with 250, 500 and 800 MHz were carried out circumferencing the borehole to detect anisotropic features.

Description: The cold alpine saddle Colle Gnifetti, Monte Rosa, Swiss-Italian Alps resembles very much polar and subpolar ice masses in terms of glaciological conditions.It has been the site for several ice-core drilling campaigns over more than 20 years to determine paleoclimatological and glaciological conditions.To investigate the feasibility of geophysical methods for improved characterization of ice masses surrounding borehole and ice-core sites, a combined active reflection seismic and ground-penetrating radar pilot study has been carried out in summer 2008.Aims are the characterization of density, internal layering, seismic and radar wave speed and attenuation, identification of anisotropic features (like crystal orientation or bubble content and shape).Here we present the overall setup and first results. Seismic and GPR profiles were centered on an existing borehole location covering the full ice thickness of 62 m.Active seismics was carried out with 24-channel 3-m spacing recording, using a Seismic Impulse Source System (SISSY) along two profiles parallel and perpendicular to the ice-flow direction.The same profiles were complemented with GPR measurements utilizing 250, 500 MHz frequencies.Additionally, circular profiles with 250, 500 and 800 MHz were carried out circumferencing the borehole to detect anisotropic features.

Description: When investigated by radio echo sounding (RES) polar ice sheets exhibit internal reflection horizons which stem from variations in the dielectric properties of the ice. These are caused by enhanced conductivity, density fluctuation and changes in crystal orientation fabric. The envisaged application of an inverse method to the RES data as to reconstruct profiles of physical properties, e.g. conductivity, independently of ice cores is hampered by insufficient knowledge of the frequency dependence of the complex dielectric permittivity of ice in the MHz-range, where RES typcially operates. The well established method of dielectrical profiling (DEP) is usually deployed up to 1 MHz only.Here we present an adapted device for dielectric measurements, originally developed for measuring soil samples between between 1 MHz and 3 GHz with a coaxial cell. This includes the preparation of the laboratory ice to fit the coaxial geometry as well as the acquisition of the scattering parameters with a network analyser. The dielectric permittivity is infered by a genetic optimisation algorithm adjusting a debye model to fit the scattering data. Furthermore we outline the potential of the setup to process natural ice and to provide results for the complex dielectric permittivity in the MHz-range.

Description: Ground-penetrating radar systems (GPR) offer a wide field of applications.Especially in cryospheric implementations GPR proved to be an adequate toolto determine fast and non-destructively media transitions. In this study, weanalyse the feasibility of impulse radar in recording internal snowpack transitions of density or moisture content. The utilized impulse radar systems for this research purpose are commercially available and the gathered data needs no calibration measurement for interpretation, which is a distinct advantage in comparison to frequency modulated continuous wave (FMCW) systems. Currently available methods monitoring seasonal snowpacks are either destructive as snow profiling or insufficient for measuring in slope areas or to determine snow stratigraphy as ultra-sonic sensors. Additionally, the risk exposure for the profiling teams is often a limiting factor for the data acquisition, especially in avalanche paths and ridge areas. In such regions an all-season monitoring system must be secured against being destroyed by avalanches. Thus, the implemented system operates from beneath the snowpack measuring in upward direction. The GPR system was tested in several varying snow conditions as cold dry snow and wet snowpacks. Furthermore, different frequencies, polarisations and two different radar systems were analyzed on their applicability for the snowpack monitoring from beneath and the system was utilized in periods with various meteorological parameter. The results of these preliminary tests showed, that with a moved antenna it is possible to record snow layers in dry snow with adequate density steps and layer thickness, supplementary to the snow depth. A one meter-thick wet snowpack was penetrateable although the signal was very much attenuated. GPR systems with frequencies above 1GHz provided insufficient pentration depth in late season snowpacks. Analysis of reflection phases allowed interpretation of their physical origin in terms of permittivity. The system set-up used is capable of improving information of spatial and temporal snow-pack characteristics especially in stratigraphy and snow depth and has the potential to be remotely operated.

Description: Currently available methods monitoring seasonal snowpacks are either destructive as snow profiling or insufficient for measuring in slope areas or todetermine snow stratigraphy as ultra-sonic sensors. Internal snowpack information is indispensably necessary for the prediction of the current avalanche danger. Furthermore, in mountain regions the spatial distribution of snow accumulations by wind is extremely inhomogeneous. Even single measurements of at least the varying snow depth at ridge areas or in avalanche paths can significantly improve the predictability of avalanches. In such areas, the risk exposure for the profiling teams is often a limiting factor for the data acquisition. An observation of the snowpack development with time enables real-time information about accumulation rates and settlement speed. However, a temporal observation of the snow depth and of internal layering is only possible with sensor systems which are able to penetrate the snowpack as well as adequately resolve internal layers. Thus, in this study, the feasibility of groundpenetrating radar (GPR) systems in recording snow depth as well as internal snowpack transitions of density or moisture content was analyzed. Especially in cryospheric implementations GPR proved to be an adequate tool to determine fast and non-destructively media transitions. The utilized impulse radar systems for this research purpose are commercially available and the gathered data needs no calibration measurement for interpretation, which is a distinct advantage in comparison to frequency modulated continuous wave (FMCW) systems. In regions with a predominant avalanche danger, an all-season monitoring system must be secured against being destroyed by avalanches. Thus, the implemented system operates from beneath the snowpack measuring in upward direction. The GPR system was tested in several varying snow conditions as cold dry snow and wet snowpacks. Furthermore, different frequencies, polarizationsand two different radar systems were analyzed on their applicability for the snowpack monitoring from beneath and the system was utilized in periodswith various meteorological parameter. The results of these preliminary tests showed, that with a moved antenna it is possible to record snow layers in dry snow with adequate density steps and layer thickness, supplementary to the snow depth. A one meter-thick wet snowpack was penetrateable although the signal was very much attenuated. GPR systems with frequencies above 1 GHz provided insufficient pentration depth in late season snowpacks. Analysisof reflection phases allowed interpretation of their physical origin in terms ofpermittivity. The system set-up used is capable of improving information ofspatial and temporal snow-pack characteristics especially in stratigraphy andsnow depth and has the potential to be remotely operated.