Development of a large-scale, aerial photography technique to assess the severity of upper mid-crown yellowing (UMCY) in Pinus radiata trees

Authors: J.G. Firth, R.K. Brownlie, S.T. Olykan
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 1997, Issue N.Z.J.For. 42(1) 1997, pp 19-26, May 1997
Publisher: New Zealand Institute of Forestry

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Abstract: A number of photographic variables were evaluated for assessing Upper Mid-Crown Yellowing in Pinus radiata D. Don trees. These included comparing: vertical and oblique photography, several image scales, different camera look-angles, two film types, various light conditions, mono versus stereo imagery and fixed wing versus helicopter camera platforms.

As a result of this work, a technique has been developed and used operationally for surveying the extent and severity of UMCY in several forests. The method is based upon colour, oblique stereo photography taken from a helicopter flying at approximately 100 m above the canopy. A Global Positioning System (GPS) is used to navigate to the photo-site and a radar altimeter for determining the required flying height.

A methodology was also developed to quantify the severity of UMCY, when viewed on the stereo-photographs. This involves assessing approximately 30 trees per stereopair using a four-point classification. The results obtained are converted to a compound value for each photo-site which can be used to map the distribution of UMCY throughout a compartment or forest.

The methodologies described could have application for assessing other disorders in tree crowns.

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