Image

Remote height measurement of seedlings

1 June 2021

New, accurate lower limits for measuring tree height have been established using unmanned aerial vehicles.

Height is a good indication of how productive (and healthy) a tree is. Height can be measured from the ground, but this can be expensive and time consuming, especially over large areas. An alternative method is to use laser scanners mounted on aircraft or unmanned aerial vehicles (UAVs) to predict height and other metrics.

The height of trees around 5.5 m and taller have been accurately predicted using laser scanning. The question is: how low can we go? Is it possible to use UAV-mounted scanners to estimate the heights of recently planted trees (with small crowns)?

Scion scientists have recently flown UAV-mounted laser scanners and cameras over six plantation radiata pine trials in the central North Island. The trees in the different trial plots ranged in height from 0.4 to 6.1 m. “We found we could predict tree heights very precisely and accurately,” reports Robin Hartley, lead author of a paper describing the work.

“The correlation between field measurements and our laser scanning predictions had an R2 of 0.99, with a very slight bias towards underestimation of less than 10 cm. However, when trees were shorter than one metre, laser scanning was much less precise and underestimated tree height.”

The research team also considered a more cost-effective way to gather data to predict tree height. Laser scanners are often too expensive to use on a day-to-day basis. An alternative is to use cameras to capture overlapping images that can be assembled into a 3D representation of the area being scanned (structure from motion photogrammetry). The photogrammetry data was captured by a DJI Phantom 4 Pro UAV, a UAV commonly used by foresters in New Zealand.

“Using photogrammetry, we were able to predict heights accurately (R2=0.94) but less precisely,” reports Robin. “Like laser scanning, the accuracy of photogrammetric measurements dropped off dramatically below one metre and tended to underestimate tree heights but to a greater extent. However, it is a cost-effective remote sensing option for estimating the height of trees that are over one metre tall, although height could be underestimated by up to half a metre.

“Now that we have explored the accuracies that we can expect and the limits associated with these technologies, we hope that this this work will give foresters and researchers such as tree breeders the confidence to start introducing this technology for monitoring trials and as part of routine forest management.”

Source: Scion

Read More
Image

New tool to manage forestry slash

Better management of forest felling waste has gained new impetus in Cyclone Gabrielle’s wake, with the sector firmly in the spotlight for the impact such waste has had on communities, ecosystems, and farmland downstream from harvest areas. Rotorua-based forest management ...
Read more
Image

New multi-species carbon calculator available

A new multi-species carbon calculator developed by Mark Kimberley and Michael Watt to support grower decision-making is freely available on the Forest Growers Research website ( Multi-Species Carbon Calculator (fgr.nz)). The calculator predicts growth metrics for eleven species that include ...
Read more
Image

JOUAV unveils advanced airborne Lidar sensor

JOUAV has released the JoLiDAR-1000 Lidar sensor designed specifically for uncrewed aerial vehicles (UAVs or ‘drones’) as the latest addition to its array of high-performance Lidar sensors for use in UAV applications such as GIS, surveying and precision powerline inspections. ...
Read more
Image

Wingtra debuts pioneering Lidar drone solution

Wingtra has unveiled its innovative Lidar-drone solution. The new Lidar payload is designed to seamlessly integrate the efficiency, ease of operation, and high accuracy of the WingtraOne GEN II drones with an advanced Wingtra-engineered Lidar sensor, offering notable advancements in ...
Read more
Image

Trimble and DroneDeploy improved UAV mapping

Trimble has unveiled the integration of the Trimble Applanix POSPac Cloud post-processed kinematic (PPK) GNSS positioning service, featuring CenterPoint RTX, with the UAV-based mapping and data collection capabilities of DroneDeploy’s reality capture platform. With the Trimble cloud positioning service, DroneDeploy ...
Read more
Image

Blue gum expansion & mechanised planting planned

Australia’s dwindling timber reserves could be exhausted in less than a decade, but industry experts are hoping a new native nursery in Western Australia could help ease the pressure. In the coastal city of Albany, 450 kilometres south of Perth, ...
Read more