Image analysis study plot, NE apex by Chris Fastie

Nikkor P C 105mm f/2.5, Nikon...

I compared three methods of determining basal area (cross sectional area of trunks) in this stand of Alaskan birch at the Bonanza Creek LTER site near Fairbanks, Alaska. The diameter of each birch tree was measured in a 42 x 38 m plot surrounding this and two other sample/photo points. This provided a measurement of the actual basal area in the plot (30.0 m²/ha). A standard field method (referred to as plotless, prism, or Bitterlich sampling) was used to select trees which subtended at least a threshold angle (1.736°) from this viewpoint. This sample included 9 trees (124, 132, 58, 57, 56, 64, 63, 121, 120) and provided an estimate of basal area of 20.7 m²/ha. An equivalent method was performed on this 360° panoramic image using horizontal pixel counts to represent the subtending angle. Two additional trees (134, 116) were included in this sample for a basal area estimate of 25.3 m²/ha. The field- and image-based estimates were repeated at two replicate sample/photo points (see the south and NW points at gigapan.org/gigapans/54319/ and gigapan.org/gigapans/54293/).
This study was presented at the Fine International Conference on Gigapixel Imaging for Science (www.cmu.edu/events/gigapixel-science /). The proceedings paper is available here: fastie.net/wp-content/uploads/2010/11/Fastie-Fine-Conference-m-09-06-10.pdf . Video of the conference presentation is here: www.youtube.com/watch?v=gBQtVZfx9lc&playnext=1&list=PL6D6265673AAA1E78