Ground-measured spectral signatures as indicators of ground cover and leafarea 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 i n the field using indirect techniques of digitized close-range vertical pho tography and Licor 2000 instrument readings, as well as direct destructive sampling. Simultaneously, field reflectance values were collected over spec ific spectral bandwidths using a handheld radiometer. Several vegetation in dices were derived from these spectral measurements and their predictive po wer (individually or in combination) with respect to field-measured ground cover and LAI quantified. The additional effects of plant chlorophyll conte nt, paddy depth, water sediment load, and bottom layer color were also inve stigated. None of these variables added significantly to the predictive pow er of the models. The models were refined for intra-seasonal variability an d a new growth-stage-dependent variable improved the models' predictive cap abilities. The results demonstrated that the monitoring of paddy rice crop status by m eans of its spectral signatures appears very promising. (C) 2001 Elsevier S cience B.V. All rights reserved.