Changes in the first derivatives of leaf reflectance spectra of various plants induced by variations of chlorophyll content.

Reflectance spectra of leaves of winter wheat, maize, sugar beet and wild vine have been measured. Chlorophyll variations induce changes in the first derivatives of the reflectance spectra. A correlation of various derivative indices such as D(725)/D(702), D(lw)/D(sw), D(lw)/D(702), D(725)/D(sw,)D(715)/D(702), D(m)/D(sw), D(m)/D(702) and D(715)/D(sw) with chlorophyll content was tested, when D is the relative height of the first derivative, the subscript numbers give the wavelength in nm for fixed determination and lw, m and sw are the determination in the long-, medium- and short-wavelength maximum, respectively. The short- and long-wavelength maxima are in the range of 690-730 nm, the medium peak is within the other two, in the range of 710-715 nm. Regression models have been obtained for all types of indices and for all studied plant species. The most promising regression model has been selected. This type of model has been similar for maize, sugar beet and wild vine; therefore, a unified regression model is shown to be applicable for chlorophyll estimation in leaves of these species. The regression model for winter wheat was essentially distinct from both individual and unified models for other studied plants. Reasons for the difference in regression models for various species are discussed.