Detection of individual trees remains a challenge for forest inventory efforts especially in homogeneous, even-aged plantation scenarios. Airborne imagery has mainly been used for detection of individual trees using local maxima filtering, as point spread function and signal-to-noise
ratio are smaller than with satellite-borne imagery. This led to the development of a novel approach to local maxima filtering for tree detection in plantation forests in KwaZulu-Natal, South Africa, using satellite remote sensing imagery. Our approach is based on Gaussian smoothing for noise
elimination and image classification, that is, natural break classification to determine the threshold for removing pixels of extremely bright and dark areas in the imagery. These pixels are assumed to belong to the background and hinder the search for tree peaks. A semivariogram technique
was applied to determine variable window sizes for local maxima filtering within a plantation stand. A fixed window size for local maxima filtering was also applied using pre-determined tree spacing. Evaluation of the various approaches was based on aggregated assessment methods. The overall
accuracy using a variable window size was 85%, root mean square error (RMSE) = 189 trees, whereas a fixed window size resulted in an accuracy of 80%, RMSE = 258 trees. The approach worked remarkably well in mature forest stands as compared to young forest stands.
These results are encouraging for temperate–warm climate plantation forest companies, who deal with even-aged, broadleaf plantations and forest inventory practices that require assessment 1 year before harvesting.
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Document Type: Research Article
Malaria Research Programme, Medical Research Council, 491 Ridge Road, OverportDurban4091, South Africa
University of KwaZulu Natal, School of Environmental Sciences, King George V Avenue, GlenwoodDurban4041, South Africa
Rochester Institute of Technology, Center for Imaging Science–Laboratory for Imaging Algorithms and Systems, 54 Lomb Memorial DriveRochesterNY14623, USA
Council for Scientific and Industrial Research, Natural Resources and the Environment, Ecosystems, Earth Observation, PO Box 395Pretoria0001, South Africa
August 10, 2011
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