Multi-Temporal Remotely Sensed Data For Monitoring Environmental Change In Northern Ontario (Canada)

摘要

Over the last 100 years, the city of Sudbury (Ontario, Canada) had undergone through significant ecological changes due to the industrial mining activities. The impact from the mining activities ranged widely from disturbance to the local forest cover, land disturbance due to the mine developments, airborne pollution due to the smelting activities to the the acid-generating mine tailings. The forest cover was by far the one that was seriously affected, leading to the ioss of large areas of green cover and soil erosion. Towards the end of the 70s, the city of Sudbury started an ambitious program for the re-vegetating of the seriously affected areas. Barren areas with significant vegetation cover loss, were first limed to reduce soil acidity. This process was later followed by the planting of mixed grasses, trees and shrubs. Pines (Pinus resinosa, P. strobus, P. banksinana), birch (Betula papyrifera) and trembling aspen (Populus tremuloides) were the major tree type planted in the area. The primary objectives of this study is to provide an assessment for the cological restoration program and provide an extensive geospatial database about the re-vegetated areas using multi-temporal remotely sensed data. In this study a Landsat TM dataset spanning a period of almost 20 years over the study area was used to evaluate the success of the restoration program. A set of environmental indicators was developed to provide a measure for each re-vegetated site, and hence, provide an assessment for the health of the vegetation, and its growth status. The study makes use of indicators as the normalized vegetation index (NDVI), crown closure, and tree density as primary factors for characterizing a restoration site. Preliminary results indicate that with the improvement of the atmospheric conditions and soil many of the revegetated sites showed significant improvements and expansion of the tree and grass cover. Some sites are displaying weak or no growth, however, the overall re-greening of the area is evident. The results obtained from the satellite data analysis, thus far, are in agreement of with the field observation conducted over the area in August 2004. Multi-temporal satellite data have proven useful in providing key information for monitoring the ecological restoration.