The impact of calibration on the accuracy of harvester measurement of total harvest volume and assortment volume for Sitka spruce clearfells in Ireland.

Abstract

Almost all timber in Ireland is felled using harvesters; the objective of the work reported here was to assess the impact of calibration on the accuracy of harvester wood volume measurement systems. The harvester used was a Timberjack 1270D with a 762C harvester head and a Timbermatic 300 control and measurement system. Harvester measurement was compared to weighbridge measurement (weight was converted into volume using volume-weight conversion factors) and to log volume, measured using standard calliper-and-tape log measurement. The first part of the study dealt with the accuracy of the harvester system in measuring total and assortment volumes for whole stands, when compared to weighbridge results. Regular calibration resulted in a significant improvement in accuracy, reducing differences between the two estimates, from 12% to around 6%. However, this compares with accuracy levels of ± 2% of total site volume, which have been achieved in Finland on an annual basis. The second part of the work comprised a more detailed analysis of the accuracy of the harvester system in measuring assortment volumes. Length measurement of four assortment categories was accurate after calibration, while the volume measurement was satisfactory for 5.50, 4.90 and 3.10 m lengths, but not for the 2.90 m category. Statistically significant differences in volume estimation were found for three assortment categories (4.90, 3.10 and 2.90 m). However, the differences between the harvester head and calliper-and-tape values were small (less than 30 mm and 0.007 m3 in all cases), so the operational significance of these findings might be limited.