Drone Used for 3D Measurement of Forestland (1)
For efficient development of mega solar plant
In the summer of 2017, 3D laser measurement using a drone (unmanned compact aircraft) was undertaken in a forest in Kanagawa Prefecture, Japan (Fig. 1).
The forest is a candidate site for the development of a mega (large-scale) solar power plant by Nippon Comsys Corp. The measurement was done to understand the shape of the ground hidden by trees to evaluate the feasibility of the project.
Conventionally, forests were measured manually. To create drawings, surveyors walked to every corner of the area to be measured carrying surveying instruments.
Exhaustive efforts are required if this method is applied to forests. Surveyors have to carry out measurements walking through trees and grass and climbing up and down slopes on land with very few trails. The operation takes time and effort and has safety issues including possible encounters with bees, snakes or bears.
In case a clear view cannot be achieved due to trees, they have to be cut down, requiring more time and cost. Measurement is one of the elements that lowers the feasibility of solar power plant development on forest land.
For efficiency improvement, aerial images were used in some cases instead of measuring by walking around. Even if this method is incorporated, however, a certain number of trees have to be cut down to estimate the distance from treetops to the land surface if the surface is densely covered with trees and cannot be seen. Furthermore, errors caused by the actual land surface occurred frequently, which was a problem.
If the errors are significant, the equipment cannot be installed according to the plans in the construction stage, resulting in a delay in the construction period and additional cost due to remeasurement and further land reclamation. If the quantity of solar panels installed has to be reduced following a change to the plans, the estimated income from the power sale will also be affected.
The 3D measurement using a drone, which Nippon Comsys utilized this time, eliminates these problems and can improve both the efficiency and accuracy of measurement. The measuring technology was provided by Terra Drone Corp based in Shibuya-ku, Tokyo.
An area of about 600m by 300m covering approximately 13ha of land area was measured. About 250 million survey points were measured by four drone and surveying engineers in two days.
If such area is measured by a conventional method, it will take about two months, according to the company. The operations up to presenting the measurement results in 3D land shape data were completed in about two weeks (Fig. 2).
An example of 3D laser measurement of a solar power plant candidate site in a forest in Kanagawa Prefecture. The top picture is an aerial image shot from above and the bottom picture shows an aerial image shot from the south (source: Terra Drone).
According to Terra Drone, the presence of multiple places that are comparatively flat and look like a terraced field was confirmed in the area halfway up the forest by the 3D measurement. It is estimated that the land development cost will be minimized if the area is used effectively in implementing the project.
The plan for a solar power plant in the area that was measured this time is in the initial stage of development, according to Nippon Comsys. The company will consider implementation of the plan in the future, using the data obtained by 3D measurement. The company says it is possible that the same method will be incorporated in the future in sites that are difficult to measure.