In areas with difficult terrain, thick bush, coastal scrub, mature tree cover and dense undergrowth can make a conventional ground survey slower and restrict what can be captured from aerial photographs.
This is where drone LiDAR is often considered. But can LiDAR really see through trees and vegetation? Read on to find out.
Key Points
- Drone LiDAR does not see through solid vegetation. Laser pulses reach the ground through gaps between leaves, branches and understorey.
- Multiple returns can capture different surface levels, including the tree canopy, lower vegetation, and the underlying terrain.
- Dense canopy and thick undergrowth can reduce ground coverage, leaving fewer reliable points for the bare-earth model.
- LiDAR is often more effective than photogrammetry on vegetated sites because photogrammetry generally requires the ground to be visible in aerial photographs.
- Survey control, point classification and professional validation remain essential before the terrain data is used for design, planning or quantities.
How Does Drone LiDAR Map Ground Beneath Vegetation?
LiDAR stands for Light Detection and Ranging. A LiDAR sensor mounted to a drone sends laser pulses towards the site and measures how long each pulse takes to return.
The pulses may reflect from several surfaces, including:
- The upper tree canopy
- Branches and lower vegetation
- Buildings and other structures
- Rocks and exposed surfaces
- The ground
These measurements create a three-dimensional collection of points known as a point cloud.
A raw point cloud may contain millions of points representing everything the sensor has detected. During processing, the points can be classified into groups such as ground, vegetation and structures.
The ground-classified points are then used to generate a bare-earth terrain model, contours, cross-sections or other project deliverables.
The United States Geological Survey explains that LiDAR point clouds may contain returns from terrain, vegetation and buildings. The relevant points are classified before a bare-earth elevation model is produced. USGS provides a useful explanation of this process.
Does LiDAR Actually See Through Trees?
No. LiDAR cannot see through solid trees in the same way that an X-ray passes through an object.
It works by recording laser pulses that reach the ground through gaps between leaves, branches and other vegetation.
A single emitted pulse may produce several returns. The first return could come from the upper canopy, while later returns may come from lower branches, shrubs or the ground.
According to the National Oceanic and Atmospheric Administration, dense vegetation with limited canopy openings can result in poor ground representation because fewer pulses reach the terrain.
What Affects LiDAR Performance in Vegetated Areas?
The success of a drone LiDAR survey beneath tree canopy depends on several factors.
1. Canopy density
An open woodland may provide many clear paths between branches and leaves. A dense, continuous canopy may provide far fewer.
When fewer laser pulses reach the surface, the resulting ground model may contain gaps or require more interpretation.
2. Low-level vegetation
Groundcover and understorey can be just as important as the upper canopy. Thick shrubs, grass or low branches may obscure the terrain even where gaps exist between taller trees.
3. Sensor capability
Different LiDAR sensors have different pulse rates, return capabilities and operating characteristics. The selected equipment should suit the size, vegetation and accuracy requirements of the site.
4. Flight planning
Flight altitude, speed, overlap and the direction of flight lines affect the density and distribution of recorded points.
Additional overlap or multiple flight directions may provide more opportunities to record the ground around vegetation.
5. Terrain
Steep slopes, gullies, embankments and sudden changes in elevation can make the ground harder to record and classify.
The final result depends on more than the number of points collected. The quality, distribution and classification of those points also matter.
Is LiDAR Better Than Photogrammetry for Vegetated Land?
LiDAR and photogrammetry are both valuable aerial survey methods, but they collect information differently.
Photogrammetry uses overlapping photographs to reconstruct the visible surface. It works particularly well across open ground, stockpiles, cleared construction sites and areas where detailed colour imagery is required.
However, if the ground cannot be seen in the photographs, photogrammetry generally cannot recreate it accurately.
LiDAR may be more suitable for a topographic survey under vegetation because some laser pulses can reach the terrain through gaps in the canopy.
| Project requirement | LiDAR | Photogrammetry |
| Map visible vegetation | Yes | Yes |
| Record ground through canopy gaps | Often suitable | Usually limited |
| Produce detailed colour imagery | Limited unless combined with a camera | Yes |
| Create a bare-earth terrain model | Often suitable | Difficult where the ground is hidden |
| Capture an open construction site | Yes | Yes |
| Produce a photo-realistic model | Usually requires imagery | Yes |
Neither method is automatically better for every project. Some sites benefit from a combined workflow that provides both terrain data and current aerial imagery.
What Can Be Delivered from a Vegetation LiDAR Survey?
The deliverables should be selected around the decisions the client needs to make.
A UAV LiDAR vegetation mapping survey may provide:
- A classified three-dimensional point cloud
- A bare-earth digital terrain model
- A digital surface model showing vegetation and structures
- Contours
- Cross-sections
- Hillshade or terrain visualisations
- Vegetation-height information
- CAD or GIS-compatible files
- Geo-referenced aerial imagery
- A report outlining survey control and accuracy
A bare-earth model represents the estimated ground surface after vegetation and other above-ground points have been classified and excluded. It should not be confused with the complete point cloud, which may retain trees, buildings and other features.
When May Drone LiDAR Not Be Enough?
Drone LiDAR is a useful tool, but it is not a guaranteed solution for every heavily vegetated site.
Challenges may include:
- Extremely dense or continuous canopy
- Thick understorey close to the ground
- Limited or uneven ground returns
- Water-covered areas
- Steep or complex terrain
- Restricted airspace
- Features requiring direct observation
- Projects with strict engineering, cadastral or legal requirements
In these conditions, LiDAR may need to be supported by GNSS observations, total-station measurements, terrestrial laser scanning, or conventional ground surveying.
Frequently Asked Questions
1. Can drone LiDAR map the ground beneath dense forest?
It may record the ground through openings in a dense canopy, but results vary. Continuous canopy and thick understorey can reduce the number of ground returns and leave gaps in the terrain data. Site conditions should be assessed before the expected coverage and accuracy are confirmed.
2. Can LiDAR distinguish vegetation from the ground?
LiDAR records points from different surface levels. Processing software and survey review can classify these points as ground, low vegetation, medium vegetation, high vegetation, structures or other features. The classification should be checked before the ground surface is used for project decisions.
3. Is drone LiDAR more accurate than photogrammetry beneath trees?
LiDAR is generally better suited to terrain hidden beneath vegetation because photogrammetry relies on visible ground in photographs. However, accuracy still depends on survey control, point distribution, flight planning, equipment and processing. LiDAR is not automatically accurate simply because it can record some ground returns.
4. What is the difference between a DTM and a DSM?
A digital terrain model, or DTM, represents the estimated bare-earth surface. A digital surface model, or DSM, represents the upper visible surfaces, which may include tree canopies, buildings and other objects above the ground.
5. Can LiDAR data be used for engineering design?
LiDAR data may support engineering design when it has been captured, controlled, processed and verified to the required standard. Some projects also require ground surveying to capture obscured features, breaklines, boundaries or critical design points. The intended engineering use should be established before the survey methodology is selected.