Percentage vegetation cover of a degrading rangeland from SPOT

Abstract
Multispectral SPOT imagery is used to map percentage vegetation cover in the Mackenzie Basin of the South Island, New Zealand. Twenty ground measurements of quadrats 60 by 60 m2 relate percentage vegetation cover to normalized vegetation index. The non-linear calibration curve is C = 50 tanh (6·1(NV1-0·22))+ 50 (1) where C is percentage vegetation cover and NVI is normalized vegetation index. The vertical spread of quadrat points about the calibration curve gives the accuracy of a percentage cover prediction from NVI. In the linear part of the calibration curve the upper and lower prediction limits (80 per cent confidence interval) are plus or minus 15 per cent cover.