SPECTRAL INDICES SELECTION TO RETRIEVE WINTER WHEAT GROUND COVER

摘要

The ground cover of vegetation is an important parameter which indicates light interceptor of plant,plant productivity and so on. Vegetation indices have been usually employed to predict the ground coverage of crop, however vegetation indices were much affected by uncertain factors such as leaf color, crop cultivar and others. This paper compared the ability of retrievy winter wheat ground cover between near infrared and mid-infrared spectral indices, red and near-infrared vegetation indices. The digital photographs of wheat canopy were taken vertically 1.5 m aboveground and then wheat spectra were measured by an ASD Fieldspec FR2500 spectrometer. The ground cover was automatically extracted by a novel image processing procedure. 8 diagnostic bands in infrared and short-infrared region were selected to calculate 56 ratio indices and 28 normalized difference indices. The popular 7 red and near-infrared vegetation indices were calculated too.The general linear model (GLM) was applied to assess the relationship between ground coverage and spectral indices, and also to evaluate whether the spectral indices were sensitive to cultivar, fertilization, irrigation and leaf color. Results showed that red and near infrared vegetation indices that predict ground coverage were affected by at least one of the four factors mentioned above. However, it is promising that some infrared indices, such as RI690/R1450, R1450/R1690, R1450/R1690 can predict ground coverage very well and not sensitive to cultivar, fertilization, irrigation and leaf color.