Applying geospatial technologies to weedmat monitoring and mapping: The Ythan Estuary, NE Scotland

Abstract

This paper examines the potential for using archival colour vertical aerial photography to map the spatial location, distribution, extent and changes over time in weedmat coverage for the Ythan estuary, North East Scotland, UK. Archival colour aerial photography scanned into a computer, and processed using image processing techniques resulted in a series of mosaiced images for visual interpretation of the location and extent of weedmats for each year of photography selected. Input of the imagery into a Geographical Information System enabled the derivation of maps showing change and quantitative estimates of the areal coverage of macro-algal weedmats for each year. It is concluded that macro-algal weedmats can easily be differentiated on colour aerial photography from background mud and sand deposits, but it is not possible to reliably separate individual macro-algal species from each other, or to distinguish weedmat densities without the availability of additional co-incident field data. In the future, large-scale colour aerial photography should be specially flown at times when the weedmat growth is at a maximum. It is also recommended that repeat photography should be acquired both at monthly intervals during the growing season and in successive years, combined with co-incident field-work. Other sources of map information and remotely sensed data and imagery should also be considered to aid in the interpretation process. This will help to improve calibration for purposes of interpretation and derivation of quantitative data to more conclusively establish the apparent changes in weedmat coverage and distribution that may be occurring over time. © 2005 Gebrüder Borntraeger.