Estimating stand basal area from forest panoramas

A common forest inventory technique involves making 360° visual scans within forests and selecting a sample of trees by assessing the horizontal angle subtended by their trunks. These samples allow quick and accurate estimates of forest stand basal area. All of the information required to complete such estimates can be obtained from high-resolution panoramic photographs of forest interiors. Stand basal area in an Alaskan birch forest was measured and the result compared to estimates of basal area made using a traditional Bitterlich visual scan in the field and an equivalent protocol performed on gigapixel images captured with a GigaPan imager. The image-based method has great precision and acceptable accuracy when tree trunks are not obscured by other trees or shrubs, when stitching is error free, and when adequate depth of field provides well focused images. This technique may have application using panoramas taken for other purposes, including historical photographs.