In Eqs. (8) and (9), , , and are unknown terms, and the known terms include and (training samples). The training samples in Eqs. (8) and (9) are obtained from a vegetated and a nonvegetated region, respectively. Both classifications (vegetated and nonvegetated) are selected as training samples to constrain the values of RVI (vegetated: 4, nonvegetated: 1.5). The training-sample spectra are processed by a least-squares (LS) approach with Eqs. (8) and (9), and the system parameters , , and are obtained. These parameters only represent the relationship between the band pairs [Eqs. (6) and (7)], so we declare , , and as the relative additional factors (relative gain and offset).