Rail Embankment Investigation Using Remote Sensing for a Permafrost Region

Abstract

Remote sensing was used as a site investigative tool for the portion of the Hudson Bay railway embankment underlain with discontinuous permafrost in northern Manitoba, Canada. Imagery from Landsat 5’s Thematic Mapper were analyzed to observe changes in land surface temperatures, vegetation cover, and water content in vegetation canopies over the past three decades. The Landsat image analyses show evidence of the occurrences of significant wildfires near the railroad over the years. Temperature data indicate that land surfaces that have been burned are approximately 20˚F warmer on average than the surrounding unburned areas. The data also show that significant amounts of vegetation have been destroyed by these wildfires and that fire scars and temperature anomalies often persist for several years. Satellite imagery has also been used to map the severity of these wildfires by calculating normalized burn ratios before and after the fires and then solving for the differenced normalized burn ratio. Previous studies have shown that fire damage results in the removal of the insulating organic layer of the permafrost and exposing the mineral soil, which causes a decrease in thermal conductivity and thereby increases the active layer depth. Such increase in the depth of active layer typically results in ground subsidence and can be detrimental to engineered structures, such as rail embankments. However, ground subsidence is not exclusive to regions affected by fire and, therefore, more ground data, such as ground penetrating radar, maintenance records, and track geometry survey data are needed to validate this relationship.