Gitelson et al. (2002) and Merzlyak et al. (2003) proposed that to measure carotenoid content, reciprocal reflectance (1/reflectance) related to chlorophyll content should be subtracted from the reciprocal of reflectance on this spectral region combining chlorophyll and carotenoids absorption, and then divided by a reference (Reflectance at 800 nm) for normalization.