1. Department of Agricultural Engineering; University of Peradeniya; Peradeniya KY 20400 Sri Lanka
2. Sensors and Software Inc.; Mississauga ON L4W 3R7 Canada
3. Dep. of Land Resource Science; University of Guelph; Guelph ON N1G 2W1 Canada
4. Dep. of Earth Science; University of Waterloo; Waterloo ON N2L 3G1 Canada