June 12, 2013
Completed in 1957, the Little Smoky river bridge and approach roads have been suffering ongoing valley-slope instability. These have affected the highway and west bridge abutment, resulting in ongoing and costly maintenance.
After the installation of the first slope indicators in Alberta, the University of Alberta carried out studies in the late 1960s to describe these movements. Detailed studies were undertaken more recently, focusing on a large, ongoing embankment failure on the northeast valley wall. This work was done by Alberta Transportation and its consultants to provide a viable, long-term solution to reduce the affects of the slope movement on the highway. Alberta Transportation considered options to stabilize the slide and to realign the highway away from the area of greatest instability. Not only were the proposed options costly, limited information is available to confirm the viability of each option due to the very deep slide plane.
In October 2006, staff from Alberta Geological Survey, Canada Centre for Remote Sensing, the University of Alberta and Alberta Transportation cleared the vegetation and installed 18 corner reflectors. The Canadian Space Agency provided partial funding for these installations. Each reflector, shaped like a four-sided pyramid, was aimed so its large open end was oriented directly perpendicular to the direction of radar pulses emitted from the orbiting Radarsat-1 satellite.
The reflectors provide an amplified signal when compared to the heavily vegetated surrounding areas, helping the satellite to obtain results over the site every 24 days. The corner reflectors provide point measurements with subcentimetre accuracy with a high level of confidence using InSAR (Interferometric Synthetic Aperture Radar) technology. The InSAR data were collected between the fall of 2006 and fall 2008, and the results were analyzed and compared to conventional monitoring information and GPS readings taken in fall 2006 and summer 2008.