A research on retrieval winter wheat ground cover by spectral indices in field

The ground cover of vegetation indicates light interceptor of plant, and plant productivity. The red and near-infrared vegetation indices have been employed to predict the ground coverage of crop, however these vegetation indices were much affected by uncertain factors such as leaf color, crop cultivar and others. This paper focused on the feasibility of predicting ground cover by near infrared and mid-infrared spectral indices, which were little sensitive to cultivar, fertilization, irrigation and leaf color. The digital photographs of wheat canopy were taken vertically 1.5 m aboveground and then 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. Also the popular 7 red and near-infrared vegetation indices were calculated. The general linear model (GLM) was applied to assess the relationship between ground coverage and spectral indices, and to evaluate whether they were sensitive to cultivar, fertilization, irrigation and leaf color. Results showed that red and near infrared vegetation indices to 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 R1690/R1450, R1450/R1690, R1450:R1690, predict ground coverage well and not sensitive to cultivar, fertilization, irrigation and leaf color