Date of this Version
Published in Rundquist, Gitelson, Derry, Ramirez, Stark & Keydan in the Proceedings of the 3rd European Conference on Precision Agriculture, Montpelier, France, 2001. Grenier & Blackmore, editors.
The aim of the paper was to test two new techniques that make use of channels in the visible range of the spectrum only to estimate vegetation fraction in corn canopies. High spectral resolution radiometers were employed to measure spectral reflectance, and the information content of spectra was investigated. Radiances in spectral channels of MODIS and MERIS were used to calculate Visible Atmospherically Resistant Indices, VARIgreen=(Rgreen- Rred)/(Rgreen+Rred-Rblue) and VARI700=(R700-1.7*Rred+0.7*Rblue)/(R700+2.3*Rred-1.3*Rblue). The indices allowed for estimation of vegetation fraction with less than 10% error. One other technique was based on the well-documented approach for fully closed canopies involving the high degree of covariance for paired reflectances at 550 nm vs. 700 nm and at 500 nm vs. 670 nm. The coordinate location within the resulting spectral space was used as a measure of vegetation fraction.