Disputas: Kirsty Ann Langley

Prøveforelesning

Bedømmelseskomité

Prof. Dr. Per Holmlund, Inst. för naturgeografi och kvartärgeologi, Stockholms Universitet
Prof. Dr. Torbjørn Eltoft, Inst. for fysikk og teknologi, Universitetet i Tromsø
Prof. Dr. Andreas Kääb, Inst. for geofag, Universitetet i Oslo

Leder av disputas:  Nils Roar Sælthun

Veileder:  Svein-Erik Hamran (FFI), Jon Ove Hagen (UiO)

Sammendrag

Ground-based radar measurements help to understand satellite data of glaciers.

Observing the fluctuations of the world’s glaciers is crucial in predictions of future sea level changes and can tell us how the climate has and is changing.

Since the largest changes in climate are expected to be in the arctic areas, the Arctic glaciers are of key interest. This vast area has many challenges being remote and expensive to access. Satellites are really the only way to obtain a full overview of the area and offer a very effective means of viewing large portions of the surface in reasonable detail. Satellite borne radars operating in the microwave frequency range are considered best for Arctic operations where the long dark winters and often cloud covered skies hinder the use of many types of instruments.

The radar sends out a pulse of energy that is reflected back from the earth’s surface. Measuring the returned signal allows an image of the surface to be constructed. However it is not just the properties of the surface that determine the strength of the response. Depending on the type of surface the radar wave encounters (whether it is snow, ice, water etc) some of the energy may penetrate below the surface before it is reflected. Thus the satellite image also contains information about the subsurface.

How then can we interpret these images? How do we relate the satellite data to what is actually happening to the glacier? The answer is to start with what you know. A key feature of our work was the use of a ground based radar operating at the same frequency as the satellite radar. The results of the ground based radar matched very well with the satellite data and allowed us to determine which features within the glacier caused the energy to be reflected back to the satellite, for example, air bubbles in the ice, and melt water that had trickled down through the snow and refrozen as ice lenses. These results can help to interpret satellite data over the Arctic ice masses as well as the large ice sheets of Greenland and Antarctica.

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