Monitoring of Belvedere Glacier using a wide angle GBSAR interferometer
Linhsia Noferini(1), guido luzi(1), giovanni macaluso(1), daniele mecatti(1), massimiliano pieraccini(1) and carlo atzeni(1)
(1) Università di Firenze, Via C. Lombroso, 6/b/11, 50134 Firenze, Italy
Nowadays GBSAR interferometers are generally used to monitor landslides by gathering images at adjustable time rates and from the same viewing position. Based on the same principles as satellite SAR interferometry, they can also produce digital elevation models (DEMs) by looking at the same scene from different angles. These features can be exploited in glacier monitoring applications as well: ice flow velocity evolution with time and ice mass geometry can be retrieved.
In this paper the case study of the Belvedere Glacier, east face of Monte Rosa, during summer 2007 is reported. The Belvedere Glacier experienced a large surge-type movement since 2001, resulting in astonishing changes in ice flow velocity, volume growth and morphology. Due to this extraordinary activity, it has been object of many researches over the recent years and it still under surveillance by the local authorities.
Because it is a debris-cover glacier and the most of the backscattered radar signal comes from the surface of the glacier, only the movements and the shape of the ice mass surface affect the GBSAR sensor. Accurate superficial deformation maps can be produced at a rate of about two per hour. Obviously only the ice velocity along the range direction can be actually measured, anyway by choosing the GBSAR location properly, the most part of the wanted motion could be retrieved for the most of the radar image. In order to widen the illuminated area to nearly all the valley occupied by the glacier, the GBSAR antenna, which has a pattern limited to about 30° around the looking direction, gathered images at two different looking angles about 30° apart.
The radar system worked almost continuously gathering wide images all August long. Data were available for analyzing flow velocity changes during this observation period.
Finally a DEM of the all illuminated area was generated. In order to achieve a different viewing angle the antenna was lift along a vertical bar fixed to the slide supporting it. Wide images from different quotes above the horizontal rail, ranging from 0 cm up to 25 cm, were collected over a period of 6 hours. Here the main problem was that while images were collected the illuminated scene was changing because of the motion of the glacier. A phase model was used for taking into account at the same time the range movements, the atmospheric contribution and the acquisition geometry. In the model the glacier motion is supposed at a constant speed and the atmospheric contribution is described as a ramp. Final results from this processing are both the range velocity map and the elevation map. The most of the noise on the final maps depends on the atmospheric contribution that seriously compromised the interferograms before unwrapping and whose pattern is not well described in the model.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,