Remote sensing

Promising prospects for mobile ground-based laser scanning

Manual field measurements are time-consuming and provide limited information about individual trees. With mobile ground-based laser scanning, data collection is streamlined, and the 3D representation of the forest provides valuable new information, including timber quality. Various forms of mobile ground-based laser scanning are currently being tested to assess their potential for large-scale estimations.

Within Mistra Digital Forest, the possibility of combining mobile ground-based laser scanning with airborne laser scanning is being investigated to create detailed large-scale tree maps. In a study at SLU, a stationary laser scanner, scanning from one position at a time, has yielded excellent detailed results. However, challenges arise when laser scanners are mounted on moving platforms such as harvesters or handheld devices.

Johan Holmgren, SLU
Johan Holmgren, SLU. Photo: Johan Olsson

– In motion, the coordinates for positioning data become relative and difficult to correlate with other information, such as airborne laser data. It is also not possible to fully rely on GPS positioning because the signal is disrupted in dense forests, says Johan Holmgren, researcher at the Department of Forest Remote Sensing, SLU.

Unique tree patterns solve the problem

Now, the team at SLU has found a solution that involves creating a kind of tree pattern. In the ground-based laser data, a number of trees are identified, and their position and size serve as a fingerprint that is linked to the airborne data.

– In this way, we can position the laser data collected in motion and use it as reference data. We are not there yet, but in the long run, mobile laser data is likely to achieve the same high quality as data collected with stationary instruments, says Johan.

Efficient laser scanning with cars

In a project partially funded by Stora Enso, the possibility of scanning the forest using a car from forest roads is being studied.

Raul De Paula Pires
Raul De Paula Pires, PhD SLU

– Approximately 80 hectares of forest are scanned per day using a car, and the information about the thousands of trees has a high level of detail. Now, models are being developed to use this data as reference data for airborne laser scanning, enabling us to efficiently create tree maps over large areas, says Raul De Paula Pires, a PhD student at the Department of Forest Remote Sensing at SLU and the person working on the project.

But does scanning only along the roadside provide a representative picture of the forest?

– It is currently being studied, and so far, the results indicate that the data is representative of the entire stand. One explanation is that the instruments scan deep into the forest, says Raul.

Research makes the technology useful

Much of the technology that can be used in the digitization of forests already exists in other industries. The mobile scanners used on cars are employed in urban infrastructure projects, and a probable future scenario is that every mobile phone will have a scanner.

– We are researching methods to harness technological advancements and create better conditions for forest planning, says Johan.