The use of shadows in high spatial resolution, remotely sensed, imagery to estimate the height of individual Eucalyptus trees on undulating land
Niva Kiran Verma A B and David W. Lamb A B C
+ Author Affiliations
- Author Affiliations
A Cooperative Research Centre for Spatial Information (CRCSI), University of New England, Armidale, NSW 2351, Australia.
B Precision Agriculture Research Group and School of Science and Technology, University of New England, Armidale, NSW 2351, Australia.
C Corresponding author. Email: dlamb@une.edu.au
The Rangeland Journal 37(5) 467-476 https://doi.org/10.1071/RJ15021
Submitted: 4 March 2015 Accepted: 19 August 2015 Published: 22 September 2015
Abstract
The shadows cast by 180 individual Eucalyptus trees, of varying canopy condition, on undulating land in south-eastern Australia were used to infer their heights from 50-cm spatial resolution, multispectral aerial imagery (blue = 0.4–0.5 μm; green = 0.5–0.6 μm; red = 0.6–0.7 μm; near infrared = 0.7–1 μm). A geometrical shadow model was developed incorporating the local slope and aspect of the ground from a digital elevation model at each tree location. A method of deriving ‘local tree time’ to infer the solar elevation angle, in situations where the image acquisition time is not available, was also developed. Based on a measurement of the shadow length from the geometric centre of the tree crowns, and ignoring the role of the crown periphery in distorting the shadow shape, the tree heights were estimated with a root mean square error of ±5.6 m (~±27%) with some overestimated by as much as 50%. A geometric correction for shadow distortion assuming spherical crown geometry provided an improved estimate with a root mean square error of ±4.8 m (~±23%).
Additional keywords: allometry, Eucalyptus, farm land, scattered trees, shadow, tree height.
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