Calibration of the Wedge Prism

Abstract

Since the introduction of plotless cruising in this country by Grosenbaugh and the later suggestion of using a wedge prism as an angle gauge by Bruce this method of determining basal area has been widely adopted in the South. One of the factors contributing to the occasionally unsatisfactory results obtained is failure to calibrate the prism used. As noted by Bruce the inexpensive prisms commonly used require the computation of a basal area factor for each prism. This is done by setting up a target of convenient width (w), sighting on it through the prism, then moving the prism forward or backward at a right angle to the target until one side of the refracted portion of the target exactly coincides with the other side of the unrefracted portion. Measure the distance (d) from the center of the prism to the face of the target.

Citation

Briscoe, Charles B. 1957. Calibration of the Wedge Prism. LSU Forestry Note AESRR-FN-14. Baton Rouge, LA: Louisiana State University & A & M College, School of Forestry. 2 p.