Ground-measured spectral signatures as indicators of ground cover and leaf area index: the case of paddy rice

A methodology is described to use spectral signatures as indicators of the vegetative status in rice paddy cultures. Ground cover and leaf area index(LAI), considered as indicators of above-ground biomass, and were measured in the field using indirect techniques of digitized close-range vertical photography and Licor 2000 instrument readings, as well as direct destructive sampling. Simultaneously, field reflectance values were collected over specific spectral bandwidths using a handheld radiometer. Several vegetation indices were derived from these spectral measurements and their predictive power (individually or in combination) with respect to field-measured ground cover and LAI quantified. The additional effects of plant chlorophyll content, paddy depth, water sediment load, and bottom layer color were also investigated. None of these variables added significantly to the predictive power of the models. The models were refined for intra-seasonal variability and a new growth-stage-dependent variable improved the models' predictive capabilities. The results demonstrated that the monitoring of paddy rice crop status by means of its spectral signatures appears very promising. (C) 2001 Elsevier Science B.V. All rights reserved.