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 Avena spp. (wild‐oats) in a field of seedling triticale (X Triticosecale , Wittmack). Images of the target field were acquired using a four‐camera airborne digital imaging system, recording in the infrared, red, green and blue wave‐bands. Spectral information derived from images of 0.5‐, 1.0‐, 1.5‐ and 2.0‐m spatial resolution were correlated with detailed on‐ground weed density measurements to investigate the effect of image resolution on mapping accuracy. Comparisons between normalized‐difference vegetation index (NDVI) or soil‐adjusted vegetation index (SAVI) images and weed data achieved correlations of 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 resolution, NDVI images could not reliably discriminate weed populations of less than 28 weeds m –2 from weed‐free regions, while SAVI images could not discriminate populations of less than 17 weeds m –2 . At 1.0‐, 1.5‐ and 2.0‐m resolution, SAVI images could not discriminate populations of less than 23 weeds m –2 , while NDVI images again demonstrated a higher discrimination threshold. Results suggest that airborne multispectral imaging could be used as part of a stratified weed sampling system.