A reflectance spectra model for copper-stressed leaves: advances in the PROSPECT model through addition of the specific absorption coefficients of the copper ion

Abstract

This study intended to investigate the reflectance model for a crop stressed by the heavy metal copper. Forty-six groups of copper-treated leaves were measured in a laboratory experiment. Through these measurements, we obtained leaf reflectance spectra from 400 to 2500 nm, information on the biochemical components of leaves, and their corresponding scanning electron microscopy images. We then developed a new reflectance spectral model based on the classic broadleaf radiative transfer model – PROSPECT. Compared with the PROSPECT model, the new model primarily considers the addition of the specific absorption coefficient of the copper ion. The scattering process is described by a refractive index (n) and a leaf structure parameter (N). The absorption is modelled with pigment concentration, water content, dry matter content, copper ion contamination, and the corresponding specific spectral absorption coefficients (, , , and ). Thus, reflectance spectral modelling is an inversion procedure to calculate the above six parameters accurately. For model validation, 16 leaves from the laboratory experiment were used. The validation showed that the inversion values for agree very well with the published absorption spectra of cupric chloride solutions. The linear regression analysis between the simulated and measured reflectance values provides a correlation coefficient of approximately 0.9441, and the root-mean-square error was less than 0.1 from 400 to 2500 nm.

Funding

This work was partly supported by the National Natural Science Foundation of China [41271348], the National Basic Research Programme of China [No. 2013CB733403]; and the National High Technology Research and Development Program [No. 2012AA12A303].