Retrieval of Vegetation Indices Related to Leaf Water Content from a Single Index: A Case Study of Eucalyptus globulus (Labill.) and Pinus radiata (D. Don.)

Abstract

The vegetation indices derived from spectral reflectance have served as an indicator of vegetation's biophysical and biochemical parameters. Some of these indices are capable of characterizing more than one parameter at a time. This study examines the feasibility of retrieving several spectral vegetation indices from a single index under the assumption that all these indices are correlated with water content. The models used are based on a linear regression adjusted with least squares. The spectral signatures of Eucalyptus globulus and Pinus radiata, which constitute 97.5% of the forest plantation in Valparaiso region in Chile, have been used to test and validate the proposed approach. The linear models were fitted with an independent data set from which their performance was assessed. The results suggest that from the Leaf Water Index, other spectral indices can be recovered with a root mean square error up to 0.02, a bias of 1.12%, and a coefficient of determination of 0.77. The latter encourages using a sensor with discrete wavelengths instead of a continuum spectrum to estimate the forestry's essential parameters.

Keywords: Eucalyptus globulus; Pinus radiata; fuel moisture content; spectral reflectance; vegetation indices.

Figure A1

VIs variation as function of Fuel Moisture Content for Pinus radiata.

Figure A2

VIs variation as function of Fuel Moisture Content for Eucalyptus globulus.

Figure 1

General scheme of the measurement and modeling process of the vegetation indices.

Figure 2

Set of samples used for fitting and validating the models. In black line the average reflectance spectra and in grey the reflectance of the individual samples. Where: (a) Pinus radiata and (b) Eucalyptus globulus.

Figure 3

Evaluation of model performance for retrieval of vegetation indices. Where: (a) Pinus radiata and (b) Eucalyptus globulus.