STRESS DETECTION OF CITRUS TREES WITH COLOR AND COLOR INFRARED OBLIQUE AERIAL-PHOTOGRAPHY

Oblique aerial photographs were taken with a 23-cm camera, using natural color and color infrared films from altitudes of 30.5-271 m to determine the effect of health, size, stress, and shadows on the images of citrus trees. Photographs taken with natural color film had less contrast than color infrared film between tree color and shadows. Densitometric measurements of natural color photographs produced transmittance peaks at 500-520 nm and 600-620 nm with a significant correlation between the spectral ratio of the transmittance (r = -0.61; p < 0.01), integrals (r = - 0.72; p < 0.01), and visual grades. Measurements of color infrared film also produced two peaks at the same wavelengths. Ratios of the color infrared transmittances (SRT) (r = 0.85; p < 0.01) and integrals (r = 0.57; p < 0.05) correlated significantly with visual grades. The best results with both films were obtained in the 12:30 p.m. flights, as color was improved and tree shadows were less evident.