ASSESSING TEMPORAL VARIATION IN THE EXTENT OF KELP BEDS IN THE NORTHERNGULF OF ST. LAWRENCE USING ANALOG AND DIGITAL AERIAL PHOTOGRAPHY AND GIS*

摘要

We used conventional scanned aerial photography, Landsat TM, image processingsystems, and geographic information system (GIS) technologies to study changes in theextent of shallow kelp beds over a 20-year period and an 85-kmkm2 area in the northernGulf of St. Lawrence, Eastern Canada. The position of the lower limit of the beds wasdetermined in situ at random locations across the study area and compared with imageryto validate our fully supervised kelp habitat classification method and insure properderivation of spatial and temporal patterns in kelp distribution. Preliminary analysis ofone image subset (?le à Firmin) showed good data interpretability (based on imagecontrasts) to a depth of ~5 m. The spatially explicit quantification of the presence andabsence of kelp using a fixed, virtual sampling grid applied over the imagery served asthe basis for the implementation of synoptic, geographic maps of annual kelpdistribution and of overall temporal stability in community states.