Estimation of number and diameter of apple fruits in an orchard during the growing season by thermal imaging

A new method for estimating the number of apple fruits and measuring their diameter in the orchard was developed and tested. A thermal camera captured images of apple trees five times during the vegetation period June-September 2001. Each time 120 images of twenty apple trees were recorded late in the afternoon to achieve a temperature gradient between fruits and their background. Recorded images were processed using several image processing algorithms. Correlation coefficients R-2 from 0.83 to 0.88 were established between the manually measured fruit number and the estimated number based on a fruit detection algorithm. According to fruit development and the established growing curve, the value of the correlation coefficient, R-2, increased during the ripening period. For measuring the fruit's diameter values of R-2 between 0.68 and 0.70 were established. These slightly increased according to the fruit's colour and size development during the ripening period. (C) 2003 Elsevier B.V. All rights reserved.