Use of hyperspectral reflectance for discrimination between grape varieties

Abstract

Visible-near infrared reflectance characteristics were examined for four varieties (Cabernet Sauvignon, Merlot, Semillon and Shiraz) of grape vine grape (Vitis vinifera) in a southern Australian vineyard. Reflectance measurements over the range 400-900 nm were acquired in the field under solar illumination using a Lastek VNIR spectroradiometer. Both reflectance and first derivative spectra were tested at 2 nm intervals for differences between the four varieties and pairs of varieties showing greatest significance were established using a Tukey post hoc test. The field reflectance spectra showed greatest difference at the red edge (~720 nm), followed by the green reflectance peak and its wings in the visible. Cabernet Sauvignon and Semillon were the most significantly different pair throughout the visible region, while the differences at the red edge were mainly attributed to Semillon. In the derivative spectra regions of significant difference were narrower and potentially attributable to chlorophyll content, leaf structure or water content. Cabernet Sauvignon differed most from the other varieties at approximately 512 nm and 580 nm. The wavelengths that showed the greatest potential for discrimination between all four varieties were 512 nm, 580 nm, 611 nm, 649 nm, 690 nm and 763 nm.