Forestry professionals know the challenges of surveying dense woodlands. In stands with thick leaf canopies, collecting accurate ground and tree data is notoriously difficult. Traditional methods – from manual tree measurements to photogrammetry – often struggle under heavy foliage. Luckily, LiDAR (Light Detection and Ranging) is transforming forest data collection. By using laser scanners on drones and handheld units together, we can capture remarkably clean, robust data even in dense forests. Below, we explore how combining aerial and ground LiDAR yields the best results, and why it outshines old-school surveying.
Challenges of Dense Forest Canopies in Data Collection
Dense forests present a leafy obstacle course for any surveying method. Overhead tree canopies block views of the forest floor, making it hard to map terrain or count understory trees. Traditional ground surveys require crews to bushwhack through thickets, measuring tree by tree – a slow process prone to human error. It’s not uncommon to find that two surveyors come up with different tree counts for the same stand, or that a fatigued crew mis-measures tree diameters. These manual errors can force costly revisits to the field to remeasure plots (a practice foresters call “check cruising”).
Aerial imaging methods like satellite or drones with cameras also have limitations. Photogrammetry struggles to “see” the ground in closed-canopy forests – you often end up with missing data where the canopy occludes the view. In short, thick foliage leads to gaps and errors in conventional datasets, meaning forest consultants often must fill in the blanks later or resort to manual collection to verify details.
How LiDAR Sees Through Foliage
LiDAR offers a game-changing advantage: the ability to peer between the leaves by using laser pulses. A LiDAR sensor emits thousands of laser beams per second; many of these find their way through tiny gaps in the canopy and reflect off the ground or lower vegetation. By capturing multiple return echoes from each pulse, modern LiDAR can record different layers – from treetops to understory to ground. In effect, LiDAR paints a 3D picture of the forest structure.
Even in dense foliage, a fraction of laser shots will reach the forest floor, allowing the creation of detailed digital terrain models beneath the trees. For example, near-infrared LiDAR wavelengths can slip through foliage openings that would block normal light, yielding ground elevation points under canopy. As a result, LiDAR can map features like subtle terrain changes, streams, or understory clearings that were previously hidden.
It’s important to note LiDAR isn’t literally X-ray vision – it can’t go through solid wood – but by exploiting gaps and using many pulses from different angles, it effectively circumvents the canopy. As one remote sensing expert explains, an airborne LiDAR sensor moving over a forest will send out so many pulses at so many angles that sooner or later some hit the ground, “increasing the likelihood that some of the pulses will penetrate the canopy and return valuable information about the ground below”. This capability to capture the full vertical profile of the forest is what makes LiDAR invaluable for forestry.
Aerial LiDAR: Mapping Forests from Above
Mounting a LiDAR unit on a drone provides a powerful bird’s-eye view of the forest. From above, the sensor can blanket large areas quickly, raining laser pulses down through the canopy. The latest enterprise drones are making this easier than ever. For instance, DJI’s new Matrice 400 series drone boasts a 59-minute flight time and can carry up to a 6 kg payload. This heavy lift capacity means it can carry advanced LiDAR sensors (along with RGB cameras) to cover big forest tracts in one flight. The Matrice 400 (and its next-gen sibling, the Matrice 4D series) also features sophisticated obstacle sensing – including onboard rotating LiDAR for navigation – which helps it fly safely in complex terrain. Long endurance and safety features are crucial when flying over remote, forested areas.
Equally important is the LiDAR sensor itself. A prime example is the DJI Zenmuse L2 LiDAR module, designed for aerial surveying. The Zenmuse L2 integrates a high-precision IMU and a 4/3 CMOS camera alongside its laser, enabling precise georeferenced point clouds with color imagery. Critically for forests, the L2 can detect up to five returns per pulse, meaning each laser shot can register multiple reflection points (e.g. one from the canopy, another from a mid-story branch, and another from the ground). More returns translate to better canopy penetration and denser point clouds under the trees. In fact, the Zenmuse L2’s laser design yields smaller beam spots and denser point spacing, improving its ability to pick up fine details beneath foliage. With vertical accuracy on the order of 4 cm, a drone-mounted L2 can measure tree heights and ground elevations with exceptional precision. Even in dense forests, drone LiDAR can achieve accuracy within a tenth of a foot (a few centimeters), which is far beyond what most handheld GPS units or visual estimates could deliver.
Aerial LiDAR’s benefit is efficiency and coverage. A single drone flight can scan entire stands wall-to-wall, eliminating the sampling errors of plot-based surveys. By obtaining a “true census” of the terrain and vegetation, foresters get complete datasets rather than interpolating between sparse transects. Additionally, drone LiDAR greatly improves safety and speed – it can quickly map steep or hazardous terrain from above, areas that would be dangerous or time-consuming for crews on foot. The result is a high-resolution top-down view: a detailed canopy height model, a digital terrain model showing ground under canopy, and often the bulk structure of trees themselves.
However, even the best aerial LiDAR has limits under extreme canopy density. If the tree cover is truly closed (imagine an old-growth cedar stand in summer), there may be spots where few laser pulses reach the ground. Also, drone LiDAR usually scans from above downward, so it might miss features on the sides of tree trunks or under overhanging branches. This is where ground-based LiDAR comes in to fill the gaps.
Ground LiDAR: Scanning Under the Canopy
To capture what aerial scans might miss, foresters can complement them with ground-based LiDAR scanning. Terrestrial LiDAR – whether tripod-mounted laser scanners or newer handheld units – operates from the forest floor looking upward and around. These devices excel at mapping the understory, tree stems, and the lower portions of the canopy with incredible detail. In fact, terrestrial laser scanning can offer sub-centimeter accuracy on individual trees, picking up features like trunk diameters, fallen logs, and understory vegetation structure that may not be discernible from above.
Historically, terrestrial LiDAR was done with stationary scanners that you would set up at multiple locations in the woods. But carrying a heavy tripod through thick brush is not always practical. Enter modern handheld and mobile LiDAR. For example, GreenValley International’s LiGrip H300 is a rotating handheld LiDAR system that uses SLAM (simultaneous localization and mapping) to capture forests on the move. A forester can simply walk through the stand with the LiGrip H300, and its multi-sensor setup will continuously map the surroundings in 3D. Despite being compact, it’s very powerful – the unit scans at 640,000 points per second with a range up to 300 m, and achieves about ±1 cm accuracy. That means it can capture both dense undergrowth and tall trees from the ground with survey-grade precision.
Notably, many of these handheld LiDARs are multi-platform. The LiGrip H300, for instance, can be used in various modes: carried in the hand, worn as a backpack, mounted on a vehicle, or even attached to a drone as a lightweight aerial scanner. This flexibility blurs the line between “terrestrial” and “airborne” LiDAR. In a similar vein, GreenValley’s LiAir X4 system can operate as a drone payload and then be quickly converted to a handheld or backpack unit – allowing the same sensor to scan from above and below. Such hybrid LiDAR setups give field teams a lot of options: fly the drone to get the broad area and canopy heights, then walk the ground to enrich the data where the drone’s perspective was limited.
Combining Aerial and Ground Scans for Robust Data
Using aerial and ground LiDAR in tandem is often the key to truly clean data in dense forests. Each method compensates for the other’s blind spots. The drone’s top-down view ensures you map every square meter of ground (at least wherever a laser can find a gap), while the ground scan captures the understory detail and any occluded areas under the thickest canopy. When you merge the two point clouds, you get a far more complete 3D model of the forest than either alone could provide.
Consider what happens when you combine these datasets:
-
Complete Vertical Coverage: Airborne LiDAR nails the canopy top and terrain, whereas ground LiDAR fills in the tree trunks, understory shrubs, and low gaps. The merged data covers forest structure from the soil to the treetops.
-
Reduced Occlusion Shadows: If a dense clump of foliage blocked the drone’s lasers, the ground unit likely scanned it from below or the side. Conversely, features overshadowed from ground view (like very tall canopy crowns) were mapped from above. The result is minimal “shadow” zones.
-
Cross-Validation: Overlap regions can be used to cross-check accuracy. Ground scans can calibrate and validate the airborne data for things like understory density. If the drone data suggested an open gap but the ground scan shows vegetation, analysts can reconcile that discrepancy.
-
Rich Detail + Large Scale: Airborne LiDAR provides the big-picture layout (e.g. a continuous terrain model, overall canopy cover). Ground LiDAR provides granular details (individual tree architecture, downed logs). Together, you get both extents and details. This is extremely useful for forest management decisions – from calculating timber volume to assessing wildlife habitat structures.
In practical terms, a combined LiDAR approach might look like this: a forestry consultant first flies a DJI Matrice 400 with a Zenmuse L2 LiDAR over a woodlot to capture the broad area quickly. They obtain an initial point cloud showing terrain and canopy heights. Then, they take a GreenValley LiGrip H300 or LiAir X4 into denser sections of the forest, walking between the trees to scan spots the drone couldn’t “see” well (like under a thick cluster of hemlocks). Later, using software, they merge the handheld scan data with the aerial data. The final output is a high-resolution, gap-free point cloud of the entire forest stand. Foresters can slice and dice this data to extract tree counts, height measurements, canopy cover, understory volume, and more with confidence that nothing was missed.
From Manual Surveys to LiDAR: Efficiency and Accuracy Gains
Using LiDAR (drone, ground, or both) isn’t just about getting a prettier picture – it directly addresses the pain points of traditional forest surveys. One major pain point we identified was manual re-collection due to errors. With older methods, a simple mistake like a misread diameter tape or a mis-plotted transect could mean going back to the field. LiDAR dramatically reduces such do-overs. Because the sensors capture an entire scene digitally, you can review and correct measurements on the computer rather than remeasure in the woods. If you suspect an error in tree height, you simply re-check the point cloud (or even model the tree from combined LiDAR angles) instead of setting foot outside again.
LiDAR is also more consistent and objective. As one source notes, LiDAR’s tree height measurements are often more reliable than traditional ground-based methods. Humans might overlook a tall sapling in a thicket or differ in judgment on where the top of a tree is; a LiDAR point cloud objectively records it. Multiple studies have found that LiDAR-derived canopy heights can be as accurate as or better than field measurements, especially in tall, complex forests. In other words, the technology can out-measure the tape measure in many cases.
Compared to manual sampling, LiDAR also provides wall-to-wall coverage with no sampling error. Traditional cruising takes only a sample (maybe 5% of a stand) and then extrapolates, which introduces uncertainty and potential bias. LiDAR gives you every tree and every contour – effectively a 100% sample. This comprehensive data can then feed into models for timber volume, carbon stocks, or wildlife habitat without having to guess what’s between plots. And because the dataset is permanent, if you realize later you need an additional metric (say, the density of understory vegetation in a certain area), you can often extract it from the existing point cloud rather than commissioning a new survey.
Finally, let’s talk efficiency. Drones and portable LiDAR greatly speed up forest data collection. What might take a crew days or weeks bushwhacking with tapes and rangefinders can be done in hours with a drone flight followed by a quick ground scan. Plus, these tools improve safety by keeping foresters out of treacherous terrain – the drone can map a steep ravine or swampy section from above, and a handheld LiDAR can scan slash-covered or snake-infested ground in a fraction of the time it would take to traverse carefully. One industry source put it succinctly: LiDAR drones offer a cost-effective and superior alternative to the cumbersome and costly traditional surveying processes. Field professionals can spend less time slogging through plots and more time analyzing actionable data.
Conclusion
Collecting clean, reliable data in a dense forest no longer needs to be an uphill battle. By leveraging LiDAR both in the air and on the ground, forestry consultants and agencies can obtain a robust 3D map of even the leafiest canopy. Aerial LiDAR from long-endurance drones like the Matrice 400 provides broad coverage and penetrates many canopy gaps from above, while ground LiDAR units like the LiGrip H300 pick up the slack below the treetops. This one-two punch yields complete forest information – from precise terrain models to individual tree metrics – all with minimal human error.
Compared to traditional surveys, the LiDAR approach is faster, safer, and often more accurate. There’s less risk of having to redo measurements or of missing hidden features, since the combined dataset captures virtually everything visible and invisible (to the naked eye) under the canopy. For the forestry and environmental sector, this means better forest inventories, improved habitat assessments, and more informed management decisions. LiDAR’s ability to “see through” the leaf canopy truly empowers us to understand and manage dense forests in ways that simply weren’t possible before. In dense woods, laser beams beat tape measures – especially when you use them from both sky and soil.
