Correlation of Densitometric Measurements of Aerial Color Infrared Photography with Visual Grades of Citrus Groves. C. H. Blazquez, Associate Professor, Citrus Research and Education Center, University of Florida, Institute of Food and Agricultural Sciences, 700 Experiment Station Road, Lake Alfred 33850. . Plant Dis. 77:477-479. Accepted for publication 13 January 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0477.

Aerial color infrared photographs taken in April 1986 and April 1989 were used to select three blocks of a citrus grove for image analysis. In ground surveys, trees were counted and classified according to percent stress and canopy growth. Measurements, made on the positive color infrared transparencies with a scanning densitometer over the 500- to 520-nm and 600- to 620-nm spectral ranges, correlated with visual grades assigned in surveys. Ratios of the spectral range integrals and the peak transmittances of the two spectral curves showed significant correlations with the visual grades. In the 1989 photographs, significant correlations were found between visual grades and the integral and transmittance of the first peak. Visual grades assigned through photointerpretation were comparable with densitometric measurements of both years, suggesting that the scanning densitometer may be a good tool for interpretation because it was not affected by the different color balance or the hue found in the 1986 and 1989 aerial color infrared photographs while measuring stress and growth.