Doing Big BAF with Cruise Angle iCMT
November 25, 2013 Leave a comment
Two major concerns in sampling trees for estimating quantity of wood are accuracy and cost. Previously we talked about the Point Sampling method, which employs an angle gauge for selecting the sample trees.
With Simple Point Sampling, the selected trees at all points are tallied for computing the basal area per acre (BAPA) and the same trees are measured for volume computation. With Double Point Sampling, the sample trees at all the points are tallied, while tree measurements are only taken on some proportion of the points. This reduces the effort and cost for measuring the trees, but the sample trees are clustered at the selected volume points.
For more even distribution of sample trees, the “Big BAF method” selects sample trees at all points for computing BAPA and VBAR (Volume to Basal Area Ratio). However, a larger BAF is used for selecting the volume trees, resulting in fewer trees being measured. This method is described in “Using a large-angle gauge to select trees for measurement in variable plot sampling”, David D. Marshall, Kim Iles, and John F. Bell, Can. J. For. Res. 34: 840-845 (2004).
The “Big BAF method” is an efficient method that is statistically sound and easy to implement. Using the Cruise Angle iCMT, you can easily select the regular BAF for tallying the trees and then switch to the larger BAF to do a second sweep of each point to select the volume trees.
The Cruise Angle functionality is built into the Forester GPS GIS app. The Forester GPS GIS app will let you save the BAPA value for each point into the Sheet View. You could add a VBAR Attribute field and a Volume per Acre field for the Point Topic. For the Volume per Acre field you could define a formula to compute the product of BAPA and VBAR. Once you enter the VBAR value, the Volume per Acre will be automatically computed for each point.
Cruise Angle iCMT will run on the iPhone, the iPod touch or the iPad. Being relatively small and lightweight, the iPad mini with Retina Display is quite suited for outdoor use. At this link is a discussion on iPad battery care.