Evaluating the accuracy of mapping weeds in seedling crops using airborne digital imaging: Avena spp. in seedling triticale

Airborne multispectral imaging has been used to map patches of A venn spp. (wild-oats) in a field of seedling triticale (X Triticosecale, Wittmack). I mages of the target field were acquired using a four-camera airborne digita l imaging system, recording in the infrared, red, green and blue wavebands. Spectral information derived from images of 0.5-, 1.0-, 1.5- and 2.0-m spa tial resolution were correlated with detailed on-ground weed density measur ements to investigate the effect of image resolution on mapping accuracy. C omparisons between normalized-difference vegetation index (NDVI) or soil-ad justed vegetation index (SAVI) images and weed data achieved correlations o f up to 71%. The highest correlation was achieved with the 0.5-m-resolution images and the lowest with the 2.0-m-resolution images. At 0.5-m resolutio n, NDVI images could not reliably discriminate weed populations of less tha n 28 weeds m(-2) from weed-free regions, while SAVI images could not discri minate populations of less than 17 weeds m(-2) At 1.0-, 1.5- and 2.0-m reso lution, SAVI images could not discriminate populations of less than 23 weed s m(-2) while NDVI images again demonstrated a higher discrimination thresh old. Results suggest that airborne multispectral imaging could be used as p art of a stratified weed sampling system.