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Abstract
This paper describes the spectral light reflectance characteristics of Eurasian watermilfoil (Myriophyllum spicatum L.) and the application of aerial colour-infrared (CIR) photography and videography for distinguishing infestations of this invasive, exotic, submersed aquatic weed in Texas waterways. Airborne videography was integrated with global positioning system (GPS) and geographic information system (GIS) technologies for mapping the distribution of Eurasian watermilfoil. Field reflectance measurements showed that Eurasian watermilfoil could be spectrally distinguished from other associated plant species in either the visible green, visible red or near-infrared regions of the electromagnetic spectrum. Eurasian watermilfoil submerged at depths greater than 5 cm below the water surface had similar visible reflectance to water. Surfaced Eurasian watermilfoil could be distinguished on CIR aerial photography and videography where it had a greyish-pink or faint pink image response. Integration of the GPS with the video imagery permitted latitude-longitude coordinates of Eurasian watermilfoil infestations to be recorded on each image. A stretch of the Rio Grande River in southwest Texas was flown with the photographic and video systems to detect Eurasian watermilfoil infestations. The GPS coordinates on the CIR video scenes depicting Eurasian watermilfoil infestations were entered into a GIS to map the distribution of this invasive weed in the Rio Grande.
Acknowledgements
Thanks are extended to Fred Gomez for his assistance in acquiring radiometric reflectance measurements and conducting ground truth, and Mario Alaniz for his help in analysing reflectance data and preparation of illustrations. We thank personnel at Coleto Creek Park and Reservoir for helping us locate study sites.