Fig. 6

Empirical semivariograms and covariance models for the three RF-based groups of residuals; (a), (c) and (e) are the semivariogram models of the residuals for the ordinary kriging in RFOK model; and (b), (d) and (f) are the elevation-dependent covariance models of the residuals for the co-kriging in RFCK model; The vertical axis represents the 1/2 variance (γ) and covariance (C) of the two positions as the distance increases