Beata M. Csatho

Greenland Ice Sheet: Increased coastal thinning

Repeated laser-altimeter surveys and modelled snowfall/summer melt show average ice loss from Greenland between 1997 and 2003 was 80 ± 12 km3 yr-1, compared to about 60 km3 yr -1 for 1993/4-1998/9. Half of the increase was from higher summer melting, with the rest caused by velocities of some glaciers exceeding those needed to balance upstream snow accumulation. Velocities of one large glacier almost doubled between 1997 and 2003, resulting in net loss from its drainage basin by about 20 km3 of ice between 2002 and 2003. Copyright 2004 by the American Geophysical Union.

Substantial thinning of a major east Greenland outlet glacier

Aircraft laser-altimeter surveys in 1993 and 1998 over Kangerdlugssuaq Glacier in east Greenland reveal thinning, over the 5-year interim, of several meters for all surveyed areas within 70 km of the seaward ice front, rising to 50 meters in the final 5 km. Such rapid thinning is best explained by increased discharge velocities and associated creep thinning, most probably caused by enhanced lubrication of the glacier bed. The calving ice front over the past decade has occupied approximately the same location as in 1966. Velocity estimates for 1995/96 are about the same as those for 1966 and 1988, but significantly less than for 1999, suggesting that major thinning began after 1995.

Mass balance of higher‐elevation parts of the Greenland ice sheet

Satellite radar and aircraft laser altimeter data and a volume budget comparison of total snow accumulation with total ice discharge give three independent estimates of the recent mass balance of parts of the Greenland ice sheet above ∼2000 m elevation. Results show the entire region, on average, to be in balance to within 10 mm yr−1, with very low rates of regional thickness change (dH/dt) in the northeast but high rates with large spatial variability in the south. Only the volume budget estimates show significant thinning in the northwest, but thinning in this area is also inferred from local measurements of ice vertical velocities down boreholes. South of latitude 68°N, there has been rapid thickening west of the ice divide, with equally rapid thinning in the southeast, but with large differences between the three estimates of dH/dt throughout this region. The radar data apply to the period 1978–1988, the laser data are for 1993/1994–1998/1999, and the volume budget calculations represent conditions over at least the last few decades. Consequently, many of the differences between results could be caused by temporal changes, particularly in snow accumulation rates, that occurred since the 1970s. However, taken with other information, our results suggest long-term thickening in the southwest and possibly quite recent onset of rapid thinning in the southeast.

Fusing Imagery and 3D Point Clouds for Reconstructing Visible Surfaces of Urban Scenes

The automatic reconstruction of urban scenes from sensory input data is a daunting task. By and large the task remains unresolved, although a considerable amount of research has been devoted to its solution. Many of the proposed methods are either too application dependent, or address only some aspects of the general problem. Moreover it appears that solutions based on a single sensor source, for example intensity images or laser point clouds, lead to partial solutions. In this paper we propose the reconstruction of visible surfaces from multi-sensor data, embedded in a fusion framework. We postulate that the reconstructed surface is an intermediate and application independent representation of the scene, similar to the 2.5 D sketch proposed by Marr in his vision paradigm. In contrast to the viewer based 2.5 D sketch, our reconstructed surface is represented in a suitable 3D Cartesian reference system. It contains explicit surface information, including shape and surface discontinuities. We argue that such an explicit description greatly benefits applications, such as object recognition, populating or updating GIS, change detection, city modeling, and true orthophoto generation. This is because the 3D object space enables more powerful reasoning methods to aid object recognition and image understanding as opposed to the traditional approach of reasoning in the 2D image space. Another strong motivation for the proposed application independent surface reconstruction scheme is the multi-source scenario with imaging and laser point data, and possibly hyperspectral data. These widely disparate data sets contain common (redundant), complementary and occasionally conflicting information about the surface. The paper discusses the notion of different surfaces and their relationships. Major emphasis is placed on the development of a general, true 3D surface representation scheme that copes with the problem of multi layer surfaces (e.g. multiple overpass).

Spectral interpretation based on multisensor fusion for urban mapping

This paper is concerned with fusing aerial imagery, LIDAR point clouds, and hyperspectral imagery for the purpose of automated urban mapping. Instead of performing traditional supervised and unsupervised classification of hyperspectral data we propose a region growing approach from seed pixels that originate from fusing LIDAR and aerial imagery. This requires a thorough alignment of all sensors involved - a problem that is solved with sensor invariant features. The common system is the geodetic reference frame in which the LIDAR points are computed. The alignment results in transformations from sensor space to object space and back, avoiding resampling the sensor data. After describing the major aspects, an example demonstrates the feasibility of the proposed fusion approach.