Noxious Weed Mapping: Hyperspectrally Detecting

Biological Desertification in a Purple Package

Purple loosestrife (lythrum salicaria) has a well-earned toxic reputation. This invasive wetland plant has spread to wetlands throughout 48 of 50 U.S. states as well as Canada, outcompeting native plant species. Purple loosestrife creates monotypic stands as it chokes off competitors, reducing the nutritional quality of wildlife forage. This process of "biological desertification" has economic impacts worth millions of dollars across North America.

Proof of Concept

The Kalamazoo Nature Center (KNC) contracted ITRES through Kieser and Associates to demonstrate the effectiveness of using high resolution hyperspectral CASI data to accurately detect and map occurrences of flowering purple loosestrife. In this project, 35 fl ight lines of imagery (80 cm resolution) were acquired over wetland areas, with the CASI programmed to provide 36 spectral bands across wavelengths of 380-1044nm.

Simple and Effective Analysis

Project constraints limited the analysis to a methodology based upon the use of four different spectral indicators with the acquired radiance data to distinguish purple loosestrife from other vegetation. Signatures & statistics generated from identified spectral endmembers were used to guide the analysis within the ENVI image analysis software. Spectral separability of this weed was further improved using principal components analysis. Thresholds defined through this analysis were then used to create purple loosestrife density maps.

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