A Yellowness Index for Oilseed Yield Estimation.

A new spectral index for multispectral sensors is presented that provides a means to estimate yield of Brassica oilseed crops. The ratio-based normalized difference yellowness index (NDYI) only requires wavebands in the visible region of the spectrum and can be applied to any satellite or aerial sensor that has blue and green channels. The derivation of the NDYI is based on the absorption feature of carotenoids present in the floral tissue of Brassica oilseeds such as canola. Empirical measurements and theoretical analyses suggest that NDYI is better correlated with final yield than other commonly used indices such as the normalized difference vegetation index (NDVI). In addition, NDYI may also be an effective tool for assessing within-field differences in relative yield potential and therefore provide a low cost alternative to yield monitors for delineating management zones.  Overall, NDYI is found to have a more linear relationship with final yield than NDVI, with NDVI saturating at high yield values. In addition, NDVI is confounded by variation in flowering whereas NDYI directly exploits variation in flowering. This highlights the benefit of using a spectral index that is sensitive to reproductive growth instead of vegetative growth for crops with spectrally conspicuous reproductive canopy elements.