Remote Sensing of Broom Snakeweed (Gutierrezia sarothrae) and Spiny Aster (Aster spinosus)

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Abstract
Field spectroradiometric plant canopy measurements showed that broom snakeweed [Gutierrezia sarothrae (Pursh.) Britt. and Rusby # GUESA] and spiny aster (Aster spinosus Benth. # ASTSN) had lower near-infrared (0.85-μm) reflectance than did other associated rangeland shrubs and herbaceous vegetation. The low near-infrared reflectances of both species were attributed to their erectophile (erect leaf/stem) canopy structures. These low near-infrared reflectance values caused broom snakeweed to have a dark-brown to black image on color-infrared aerial photos (0.50- to 0.90-μm), whereas spiny aster had a dark reddish-brown to black image. Other rangeland plant species had light-brown, red, or magenta images. Computer-based image analyses of color-infrared film positive transparencies showed that broom snakeweed and spiny aster infestations could be quantitatively differentiated from associated rangeland species. Computer analyses can permit “percent land area infested” estimates of broom snakeweed and spiny aster infestations on rangelands.