Technology of multiple concentric circles for surveying forest volume with electronic angle gauge

In order to realize the precision and real-time measurement of the forest volume, the paper took the partial plots of the Jiufeng Forest Farm as the case to propose the principle and method of the forest volume measurement by the multiple concentric circles with the electronic angle gauge. The study showed that the forest volume of the spots measured by five concentric circles with the electronic angle gauge decreased gradually. The change tended to be stable when reaching the fourth concentric circle, with reliable results. On the contrary, there was no regularity in measurement by using the multiple observation points based on the conventional angle gauge, with insignificant changing trend. There was low changing rate of the angle gauge calculation, but the volume changing was relatively large. As for the spots with inconsistent forest forms and uneven spatial distribution, the forest volume was with the low precision. The relative errors of the forest volume by using the multiple observation points based on the conventional angle gauge could reach 40%. The electronic angle gauge took the telescope and charge-coupled device (CCD) system, which largely reduced the probability of the misreading. Meanwhile, the automatic calculation was made by PDA to realize the automation and precision of the forest volume measurement.