MAPPING AQUATIC MACROPHYTES THROUGH DIGITAL IMAGE-ANALYSIS OF AERIAL PHOTOGRAPHS - AN ASSESSMENT

Distributional maps of aquatic vegetation are commonly produced from a erial photographs using visual interpretive techniques. Image analysis represents an alternative technique through which this process can be automated. The photographs are first digitized, and the system traine d to recognize a set of spectral patterns or 'signatures' which are un ique for particular macrophyte species or groups. All pixels which com prise the image are then classified on the basis of their conformance with these signature values; this results in a map or GIS overlay of a quatic plant distribution. We assessed the utility of the image analys is approach for mapping macrophytes of lakes of northwestern Ontario. The boundaries of plant beds could be defined with precision using thi s method, which contributed to a more accurate estimation of total pla nt cover and production. While submersed species proved difficult to c lassify, delineation to the species level was feasible for some floati ng-leafed and emergent forms, and the further partitioning into densit y classes may at times be possible. At this level of detail, however, spectral signatures are not transportable over space or time. Under th e tested conditions, it was possible to produce maps of emergent veget ation more accurately and efficiently with the image analysis techniqu e than with the visual interpretive method.