INTRODUCTION

Perspectives on modern geodesy research

For the past few decades the old science of geodesy hasbeen tremendously impacted by developments in space tech-nology. Dedicated satellite missions for positioning and navi-gation, measuring sea level and deformations of Earthsurface, as well as for measuring the Earth’s gravity field(both static and time-varying components) have beenlaunched. They provided the opportunity not only tostrengthen traditional applications of geodesy but also to cre-ate new ones. Never before has geodesy been used so muchin the earth and atmospheric sciences.

This special issue of the Canadian Journal of Earth Scien-ces is composed of five papers, all originally presented ingeodesy-related sessions during the 34th Annual Meeting ofthe Canadian Geophysical Union, held in Banff, Alberta, 11–14 May 2008. These papers provide a glimpse of current re-search in geodetic sciences in Canada.

The first paper, by Kingdon et al. deals with the traditionalapplication of geodesy in the determination of the geoid. Thatdetermination requires the knowledge of the topographicaldensity distribution around the computation point. The authorsdiscuss the use of a 3-dimensional model instead of the con-ventional 2-dimensional model and present an example to val-idate their results.

In the second paper, van der Wal et al. use a glacial iso-static adjustment (GIA) model to calculate elevation and slopechanges in regions affected by GIA in North America. GIA isthe leading process that produces vertical motion in Canada.The model is validated with global positioning system (GPS)observations.

GPS is just one among several of the global navigation sat-

ellite systems, but GPS was the system that allowed the de-velopment of novel applications of space positioning. One ofthose applications is the investigation of neutral atmosphereand ionosphere by looking at the bending that GPS signalssuffer while crossing these two atmospheric layers. Vergadosand Pagiatakis present a new bending algorithm, comparingtheir results with those from the dedicated COSMIC (Constel-lation Observing System for Meterology, Ionosphere & Cli-mate) constellation.

Another application of GPS has been the retrieval of thecontent of water vapour in the neutral atmosphere. This isone of the novel applications that flourished as a conse-quence of GPS and represents an application of space geod-esy to meteorology. Tao and Gao developed a procedure thatpredicts the precipitable water vapour (PWV) content of theatmosphere using a precise point positioning (PPP) technique.

The last contribution to this special issue comes from El-Ghazouly et al. and deals with one of the remaining accuracylimits of GPS: multipath. Multipath is a site dependent errorcaused by reflection of the incoming signal on nearby struc-tures and restricts the final accuracy of the position determina-tion. Several mitigation algorithms have been suggested andused in an attempt to reduce the effect of multipath. The au-thors describe their own algorithm based on wavelets.

The diversity of the subjects covered by these papers givessome perspective on the promise for continued major advan-ces in this broad area of research.

Special acknowledgement goes to the industrious work ofD.F. Cook and J.-C. Mareschal, Associate Editors of theCanadian Journal of Earth Sciences.

Marcelo C. Santos

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Published by NRC Research Press