Mapping Phragmites with PALSAR Radar Imagery

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The invasive wetland plant Phragmites australis forms very tall, monotypic, dense stands of reeds that cause massive habitat degradation and biological diversity reduction in Great Lakes wetlands. Early detection and treatment are key to controlling Phragmites.  A map of the current distribution and forecast of future expansion is needed to better target control strategies.  Previous research comparing hyperspectral and Synthetic Aperture Radar (SAR) imagery showed SAR to be more accurate over a pilot area in St. Clair, Michigan.  So Synthetic Aperture Radar (PALSAR) L-band imagery was used to produce the first basinwide distribution map showing the extent of large, dense invasive Phragmites-dominated wetlands and other coastal ecosystems along the U.S. shore of the Great Lakes through a Great Lakes Restoration Initiative funded project. 

PALSAR is a satellite imaging radar sensor that is very sensitive to differences in plant biomass, structure, and inundation patterns, allowing for the detection and delineation of these tall (up to 5 m), high density, high biomass invasive Phragmites stands.  Classification was based on multi-season PALSAR L-band (23 cm wavelength), HH, and HV polarization data.  Seasonal (spring, summer, and fall) datasets were used to improve discrimination of Phragmites by taking advantage of phenological changes in vegetation and inundation patterns over the seasons.  Extensive field collections of training and randomly selected validation data (over 300 per basin) were conducted in 2010–2011 to aid in mapping and for accuracy assessments. Overall basinwide map accuracy was 87% based on two classes of Phragmites and Other land cover types (primarily wetlands).

The invasive Phragmites maps are being used to identify major environmental drivers of this invader's distribution to assess areas vulnerable to new invasion and to provide information to regional stakeholders through a decision support tool.  Generation of these products was led by Dr. Laura Bourgeau-Chavez, Michigan Tech Research Institute, with funding support by the U.S. Fish & Wildlife Service and the U.S. Geological Survey via the Great Lakes Restoration Initiative.

Great Lakes distribution of the invasive Phragmites.

Great Lakes distribution of the invasive Phragmites.

Author Name
Brian Huberty
Author Email