Ludwig Hempel - Profile on Academia.edu (original) (raw)

Papers by Ludwig Hempel

Research paper thumbnail of Deep Radio Echo Soundings in the Vicinity of GRIP and GISP2 Drill Sites, Greenland

Surface based radio echo soundings with a specially designed burst system in'the areas around the... more Surface based radio echo soundings with a specially designed burst system in'the areas around the ice core drill sites GRIP and GISP2 in the central part of the Greenland ice sheet are presented. Digitally recorded and processed data sets show reflections from bedrock at ice thicknesses of more than 3 km and internal layerings in the ice sheet. The bedrock topography appears to be smoother in the close vicinity of the drill holes cornpared to more undulating bedrock in the south. The internallayerings show different behaviour above a bedrock trough between GRIP and GISP2 compared to most of the recorded dara, The maximum ice thickness of 3400 m ±26 m is found 80 km south of GRIP. Zusammenfassung: Boden-EMR-Messungen (Elektromagnetisches Reflexions-Verfahren) aus der Umgebung der Eiskernbohrungen GRIP und GISP2 im zentralen Teil Grönlands, die mit einer speziell entwickelten Burst-Apparatur durchgeführt wurden, werden vorgestellt. Digital aufgezeichnete und bearbeitete D;tensätze zeigen Reflexionen vom Felsuntergrund bei Eisdicken von mehr als 3 km und interne Schichtungen im Eisschild. Die Topographie des Felsuntergrundes erscheint glatter in der näheren Umgebung der Bohrlöcher verglichen mit stärker gewelltem Felsuntergrund im SÜden. Die internen Schichten zeigen unterschiedliches Verhalten Über einem Felstrog zwischen GRIP und GISP2 verglichen mit dem größten Teil der aufgezeichneten Daten. Die maximale Eisdicke von 3400 m ±26 rn wurde 80 km südlich von GRIP gefunden.

Research paper thumbnail of The newly developed airborne RES-System of the AWI as a glaciological tool

The newly developed airborne RES-System of the AWI as a glaciological tool

Research paper thumbnail of The newly developed airborne radio-echo sounding system of the AWI as a glaciological tool

Annals of Glaciology, 1999

Since 1994 the Alfred Wegener Institute (AWI) has operated an airborne radio-echo sounding system... more Since 1994 the Alfred Wegener Institute (AWI) has operated an airborne radio-echo sounding system for remote-sensing studies of the polar ice caps in Antarctica and in Greenland. It is used to map ice thicknesses and internal layernigs of glaciers, ice sheets and ice shelves, and is capable of penetrating ice thicknesses of up to 4 km. The system was designed and built by AWI in cooperation with Aerodata Flugmeßtechnik GmbH, Technische Umversitat Hamburg-Harburg and the Deutsches Zentrum fur Luft- und Raumfahrt e.V. The system uses state-of-the-art techniques, and results in high vertical (5 m) as well as along-track (3.25 m) resolution. The radar signal is a 150 MHz burst with a duration of 60 or 600 ns. The peak power is 1.6 kW, and the system sensitivity is 190 dB. The short backfire principle has been adopted and optimized for antennae used on Polar2, a Dormer 228-100 aircraft, resulting in an antenna gain of 14 dB each. Digital data recording allows further processing. The qual...

Research paper thumbnail of Schnelles Reverse Engineering für den Einsatz von Hibernate

Schnelles Reverse Engineering für den Einsatz von Hibernate

Hibernate ist der Defacto-Standard, wenn es darum geht, Daten aus einer relationalen Datenbank mi... more Hibernate ist der Defacto-Standard, wenn es darum geht, Daten aus einer relationalen Datenbank mit der objektorientierten Java-Welt zu verbinden. Dabei kann Hibernate seine volle Kraft entfalten, wenn neue Anwendungen von Grund auf zu entwickeln sind. Aber eine Neuentwicklung setzt nicht immer auf der grünen Wiese auf. Oft müssen bestehende Anwendungen integriert oder nachgebildet werden. Hier hilft das Reverse Engineering.

Research paper thumbnail of Glaeiologieal lnvestigations in the Grounding Line Area of the Foundation lee Stream, Antaretiea 1

Summary: During austral summer 1994/95, an extensive program of glaciological, geophysical and ge... more Summary: During austral summer 1994/95, an extensive program of glaciological, geophysical and geodetic measurements along a flow line of the Foundation lce Stream was carried out. The collected data are the basis for mass flux determinations in the entrainment area of the ice stream into the Ronne !ce Shelf. In this paper, the collected data and first results will be

Research paper thumbnail of Accumulation during the last 2000 years along the EGIG line and to GRIP drill site derived from radio-echo soundings

Accumulation during the last 2000 years along the EGIG line and to GRIP drill site derived from radio-echo soundings

Research paper thumbnail of Glaciological lnvestigations on the Foundation lce Stream

Glaciological lnvestigations on the Foundation lce Stream

Polarforschung

During austral summer 1994/95, an extensive program of glaciological, geophysical and geodetic me... more During austral summer 1994/95, an extensive program of glaciological, geophysical and geodetic measurements along a flow line of the Foundation lce Stream was carried out. The collected data are the basis for mass flux determinations in the entrainment area of the ice stream into the Ronne !ce Shelf. In this paper, the collected data and first results will be presented. Dur­ ing the expedition, 106 seismic soundings were performed to obtain informa­ tion about ice thickness, water column thickness and the uppermost layered sea bed in the grounding line area of the Foundation !ce Stream. In addition, air­ borne radio echo soundings (RES) took place over the southeastern part of the Ronne !ce Shelf gaining more widespread information about the icc thickness. The ice thickness data derived from these different methods agree weIl. At the base camp at 83°10.0' S, 59°34.45' W, the supposed position ofthe grounding line, a gravity meter measured the tide induced vertical movement o...

Research paper thumbnail of A comparison of radio-echo sounding data and electrical conductivity of the GRIP ice core

A comparison of radio-echo sounding data and electrical conductivity of the GRIP ice core

Journal of Glaciology, 2000

Research paper thumbnail of Deep Radio Echo Soundings in the vicinity of GRIP and GISP2 Drill Sites

Deep Radio Echo Soundings in the vicinity of GRIP and GISP2 Drill Sites

Research paper thumbnail of The 1994 North Greenland traverse

The 1994 North Greenland traverse

Research paper thumbnail of Glaciological investigations in the grounding line area of the Foundation Ice Stream, Antarctica

Glaciological investigations in the grounding line area of the Foundation Ice Stream, Antarctica

Research paper thumbnail of Modeling the radio echo reflections inside the ice sheet at Summit, Greenland

Journal of Geophysical Research, 2002

1] Radio echo surveys to determine the thickness of ice sheets often record reflections from insi... more 1] Radio echo surveys to determine the thickness of ice sheets often record reflections from inside the ice. To increase our understanding of these internal reflections, we have used synthetic seismogram techniques from early seismic modeling to construct two models. Both models were one-dimensional; the first considered only primary reflections, while the second included both primary and multiple reflections. The inputs to both models were a radio pulse and data from the Greenland Ice Core Project (GRIP) core of length 3028 m. The ice core data consisted of a profile of the high-frequency conductivity, calculated from dielectric profile (DEP) measurements, and a smooth profile of the real permittivity. The models produced synthetic radargrams which are the energy reflected from conductivity variations as a function of the two-way travel time. Both models gave similar results, indicating that multiples do not alter the travel time of the reflections, i.e., no O'Doherty-Anstey effect at our time resolution. One of the results was then processed to simulate the reflected energy passing through the receiver circuit of a radio echo system and then compared with a recorded trace. The processed result contained many of the larger reflections recorded below about 500 m, including nearly all the features from depths greater than 1500 m, in particular, several interstadial events in the Wisconsin age ice. Since high-frequency conductivity variations are dominated by chemical changes which are caused by deposition on the surface of the ice sheet, it is possible to conclude that the reflections deep inside the Greenland ice sheet can be treated as isochrons.

Research paper thumbnail of The newly developed airborne radio-echo sounding system of the AWI as a glaciological tool

The newly developed airborne radio-echo sounding system of the AWI as a glaciological tool

Annals of Glaciology, 1999

ABSTRACT Since 1994 the Alfred Wegener Institute (AWI) has operated an airborne radio-echo soundi... more ABSTRACT Since 1994 the Alfred Wegener Institute (AWI) has operated an airborne radio-echo sounding system for remote-sensing studies of the polar ice caps in Antarctica and in Greenland. It is used to map ice thicknesses and internal layerings of glaciers, ice sheets and ice shelves, and is capable of penetrating ice thicknesses of up to 4 km. The system was designed and built by AWI in cooperation with Aerodata Flugmeß-technik GmbH, Technische Universität Hamburg-Harburg and the Deutsches Zentrum fuür Luft- und Raumfahrt e.V. The system uses state-of-the-art techniques, and results in high vertical (5 m) as well as along-track (3.25 m) resolution. The radar signal is a 150 MHz burst with a duration of 60 or 600 ns. The peak power is 1.6 kW, and the system sensitivity is 190 dB. The short backfire principle has been adopted and optimized for antennae used on Polar2, a Dornier 228-100 aircraft, resulting in an antenna gain of 14 dB each. Digital data recording allows further processing. The quality of the recorded data can be monitored on screen and as online analogue plots during the flight.

Research paper thumbnail of Deep Radio Echo Soundings in the Vicinity of GRIP and GISP2 Drill Sites, Greenland

Surface based radio echo soundings with a specially designed burst system in'the areas around the... more Surface based radio echo soundings with a specially designed burst system in'the areas around the ice core drill sites GRIP and GISP2 in the central part of the Greenland ice sheet are presented. Digitally recorded and processed data sets show reflections from bedrock at ice thicknesses of more than 3 km and internal layerings in the ice sheet. The bedrock topography appears to be smoother in the close vicinity of the drill holes cornpared to more undulating bedrock in the south. The internallayerings show different behaviour above a bedrock trough between GRIP and GISP2 compared to most of the recorded dara, The maximum ice thickness of 3400 m ±26 m is found 80 km south of GRIP. Zusammenfassung: Boden-EMR-Messungen (Elektromagnetisches Reflexions-Verfahren) aus der Umgebung der Eiskernbohrungen GRIP und GISP2 im zentralen Teil Grönlands, die mit einer speziell entwickelten Burst-Apparatur durchgeführt wurden, werden vorgestellt. Digital aufgezeichnete und bearbeitete D;tensätze zeigen Reflexionen vom Felsuntergrund bei Eisdicken von mehr als 3 km und interne Schichtungen im Eisschild. Die Topographie des Felsuntergrundes erscheint glatter in der näheren Umgebung der Bohrlöcher verglichen mit stärker gewelltem Felsuntergrund im SÜden. Die internen Schichten zeigen unterschiedliches Verhalten Über einem Felstrog zwischen GRIP und GISP2 verglichen mit dem größten Teil der aufgezeichneten Daten. Die maximale Eisdicke von 3400 m ±26 rn wurde 80 km südlich von GRIP gefunden.

Research paper thumbnail of The newly developed airborne RES-System of the AWI as a glaciological tool

The newly developed airborne RES-System of the AWI as a glaciological tool

Research paper thumbnail of The newly developed airborne radio-echo sounding system of the AWI as a glaciological tool

Annals of Glaciology, 1999

Since 1994 the Alfred Wegener Institute (AWI) has operated an airborne radio-echo sounding system... more Since 1994 the Alfred Wegener Institute (AWI) has operated an airborne radio-echo sounding system for remote-sensing studies of the polar ice caps in Antarctica and in Greenland. It is used to map ice thicknesses and internal layernigs of glaciers, ice sheets and ice shelves, and is capable of penetrating ice thicknesses of up to 4 km. The system was designed and built by AWI in cooperation with Aerodata Flugmeßtechnik GmbH, Technische Umversitat Hamburg-Harburg and the Deutsches Zentrum fur Luft- und Raumfahrt e.V. The system uses state-of-the-art techniques, and results in high vertical (5 m) as well as along-track (3.25 m) resolution. The radar signal is a 150 MHz burst with a duration of 60 or 600 ns. The peak power is 1.6 kW, and the system sensitivity is 190 dB. The short backfire principle has been adopted and optimized for antennae used on Polar2, a Dormer 228-100 aircraft, resulting in an antenna gain of 14 dB each. Digital data recording allows further processing. The qual...

Research paper thumbnail of Schnelles Reverse Engineering für den Einsatz von Hibernate

Schnelles Reverse Engineering für den Einsatz von Hibernate

Hibernate ist der Defacto-Standard, wenn es darum geht, Daten aus einer relationalen Datenbank mi... more Hibernate ist der Defacto-Standard, wenn es darum geht, Daten aus einer relationalen Datenbank mit der objektorientierten Java-Welt zu verbinden. Dabei kann Hibernate seine volle Kraft entfalten, wenn neue Anwendungen von Grund auf zu entwickeln sind. Aber eine Neuentwicklung setzt nicht immer auf der grünen Wiese auf. Oft müssen bestehende Anwendungen integriert oder nachgebildet werden. Hier hilft das Reverse Engineering.

Research paper thumbnail of Glaeiologieal lnvestigations in the Grounding Line Area of the Foundation lee Stream, Antaretiea 1

Summary: During austral summer 1994/95, an extensive program of glaciological, geophysical and ge... more Summary: During austral summer 1994/95, an extensive program of glaciological, geophysical and geodetic measurements along a flow line of the Foundation lce Stream was carried out. The collected data are the basis for mass flux determinations in the entrainment area of the ice stream into the Ronne !ce Shelf. In this paper, the collected data and first results will be

Research paper thumbnail of Accumulation during the last 2000 years along the EGIG line and to GRIP drill site derived from radio-echo soundings

Accumulation during the last 2000 years along the EGIG line and to GRIP drill site derived from radio-echo soundings

Research paper thumbnail of Glaciological lnvestigations on the Foundation lce Stream

Glaciological lnvestigations on the Foundation lce Stream

Polarforschung

During austral summer 1994/95, an extensive program of glaciological, geophysical and geodetic me... more During austral summer 1994/95, an extensive program of glaciological, geophysical and geodetic measurements along a flow line of the Foundation lce Stream was carried out. The collected data are the basis for mass flux determinations in the entrainment area of the ice stream into the Ronne !ce Shelf. In this paper, the collected data and first results will be presented. Dur­ ing the expedition, 106 seismic soundings were performed to obtain informa­ tion about ice thickness, water column thickness and the uppermost layered sea bed in the grounding line area of the Foundation !ce Stream. In addition, air­ borne radio echo soundings (RES) took place over the southeastern part of the Ronne !ce Shelf gaining more widespread information about the icc thickness. The ice thickness data derived from these different methods agree weIl. At the base camp at 83°10.0' S, 59°34.45' W, the supposed position ofthe grounding line, a gravity meter measured the tide induced vertical movement o...

Research paper thumbnail of A comparison of radio-echo sounding data and electrical conductivity of the GRIP ice core

A comparison of radio-echo sounding data and electrical conductivity of the GRIP ice core

Journal of Glaciology, 2000

Research paper thumbnail of Deep Radio Echo Soundings in the vicinity of GRIP and GISP2 Drill Sites

Deep Radio Echo Soundings in the vicinity of GRIP and GISP2 Drill Sites

Research paper thumbnail of The 1994 North Greenland traverse

The 1994 North Greenland traverse

Research paper thumbnail of Glaciological investigations in the grounding line area of the Foundation Ice Stream, Antarctica

Glaciological investigations in the grounding line area of the Foundation Ice Stream, Antarctica

Research paper thumbnail of Modeling the radio echo reflections inside the ice sheet at Summit, Greenland

Journal of Geophysical Research, 2002

1] Radio echo surveys to determine the thickness of ice sheets often record reflections from insi... more 1] Radio echo surveys to determine the thickness of ice sheets often record reflections from inside the ice. To increase our understanding of these internal reflections, we have used synthetic seismogram techniques from early seismic modeling to construct two models. Both models were one-dimensional; the first considered only primary reflections, while the second included both primary and multiple reflections. The inputs to both models were a radio pulse and data from the Greenland Ice Core Project (GRIP) core of length 3028 m. The ice core data consisted of a profile of the high-frequency conductivity, calculated from dielectric profile (DEP) measurements, and a smooth profile of the real permittivity. The models produced synthetic radargrams which are the energy reflected from conductivity variations as a function of the two-way travel time. Both models gave similar results, indicating that multiples do not alter the travel time of the reflections, i.e., no O'Doherty-Anstey effect at our time resolution. One of the results was then processed to simulate the reflected energy passing through the receiver circuit of a radio echo system and then compared with a recorded trace. The processed result contained many of the larger reflections recorded below about 500 m, including nearly all the features from depths greater than 1500 m, in particular, several interstadial events in the Wisconsin age ice. Since high-frequency conductivity variations are dominated by chemical changes which are caused by deposition on the surface of the ice sheet, it is possible to conclude that the reflections deep inside the Greenland ice sheet can be treated as isochrons.

Research paper thumbnail of The newly developed airborne radio-echo sounding system of the AWI as a glaciological tool

The newly developed airborne radio-echo sounding system of the AWI as a glaciological tool

Annals of Glaciology, 1999

ABSTRACT Since 1994 the Alfred Wegener Institute (AWI) has operated an airborne radio-echo soundi... more ABSTRACT Since 1994 the Alfred Wegener Institute (AWI) has operated an airborne radio-echo sounding system for remote-sensing studies of the polar ice caps in Antarctica and in Greenland. It is used to map ice thicknesses and internal layerings of glaciers, ice sheets and ice shelves, and is capable of penetrating ice thicknesses of up to 4 km. The system was designed and built by AWI in cooperation with Aerodata Flugmeß-technik GmbH, Technische Universität Hamburg-Harburg and the Deutsches Zentrum fuür Luft- und Raumfahrt e.V. The system uses state-of-the-art techniques, and results in high vertical (5 m) as well as along-track (3.25 m) resolution. The radar signal is a 150 MHz burst with a duration of 60 or 600 ns. The peak power is 1.6 kW, and the system sensitivity is 190 dB. The short backfire principle has been adopted and optimized for antennae used on Polar2, a Dornier 228-100 aircraft, resulting in an antenna gain of 14 dB each. Digital data recording allows further processing. The quality of the recorded data can be monitored on screen and as online analogue plots during the flight.