LiDAR Canopy Penetration: How Much Reaches the Ground?

LiDAR technology has revolutionized mapping and surveying by providing highly accurate, 3D terrain models through laser scanning. One of its most impressive features is the ability to capture the terrain beneath dense vegetation—a task that traditional photogrammetry struggles with. But how does LiDAR work in heavily forested or densely vegetated areas, and what percentage of laser pulses actually penetrate the canopy to reach the ground?

How LiDAR Works in Vegetation

LiDAR (Light Detection and Ranging) sends laser pulses from a sensor (mounted on a UAV or aircraft) toward the Earth's surface. These pulses bounce back to the sensor when they hit objects, and the time it takes for the pulses to return is used to calculate distances. This allows LiDAR to generate a detailed 3D point cloud that models the surface.

LiDAR's ability to capture multiple "returns" from a single laser pulse is key in areas with vegetation. As the pulse travels downward, it may hit leaves, branches, or other vegetation layers (first returns) before eventually reaching the ground (last return). This is why LiDAR is so effective at mapping areas under dense tree canopies—unlike traditional methods, it can “see” through the layers of vegetation.

What Percentage of Laser Pulses Penetrates the Canopy?

In dense forests, like tropical rainforests, 10% to 30% of LiDAR pulses typically make it through the canopy and reach the ground. However, this percentage varies significantly depending on several factors:

1. Vegetation Density: In forests with thicker canopies, fewer pulses will penetrate to the ground. In contrast, in open forests or areas with sparse vegetation, more laser pulses will reach the ground.

2. Seasonality: In deciduous forests, LiDAR data collection during the leaf-off season will have higher ground penetration rates. Without leaves blocking the way, more pulses will travel through to reach the ground.

3. LiDAR System Characteristics: The specifications of the LiDAR system, such as the wavelength of the laser and the pulse repetition rate, also impact how much data can be captured beneath the canopy. Longer wavelengths (like near-infrared) tend to have better penetration in vegetation.

4. Environmental Conditions: Humidity, cloud cover, and even the moisture content in leaves can affect how laser pulses behave when passing through vegetation. In humid or wet conditions, the ability of LiDAR to penetrate can be reduced.

Multiple Returns: How LiDAR Handles Dense Vegetation

LiDAR’s strength lies in its ability to capture multiple returns from the same pulse. The first return represents the top of the canopy, while subsequent returns might represent mid-canopy layers, the understory, and finally the ground. This ability makes it possible to generate a Digital Elevation Model (DEM), which strips away the surface features (trees, buildings, etc.) to display the true terrain below.

In particularly dense vegetation, ground returns may be sparse, requiring ground verification methods (like placing ground control points) to ensure accuracy. Nonetheless, the data LiDAR captures remains more detailed than what traditional surveying methods can provide.

Applications of Canopy-Penetrating LiDAR

LiDAR's ability to penetrate vegetation has a wide range of applications in fields such as:

• Forestry Management: LiDAR is used to assess forest density, biomass, and canopy structure. By capturing multiple layers of the forest, foresters can better understand the health and growth patterns of the ecosystem.

• Environmental and Conservation Work: LiDAR helps map wetlands, floodplains, and other sensitive areas that are difficult to survey using traditional methods. This is especially useful in monitoring areas prone to erosion, land degradation, or habitat loss.

• Civil Engineering and Infrastructure Development: Engineers rely on LiDAR to produce accurate topographic maps in forested areas, ensuring they account for terrain changes when planning roads, utilities, and other infrastructure.

  
  

Conclusion

LiDAR’s ability to penetrate dense vegetation makes it a valuable tool for topographic surveys in forested areas. While typically only 10% to 30% of laser pulses reach the ground in dense forests, the resulting data is still far more comprehensive than other mapping methods, such as photogrammetry. With its capacity for multiple returns and high accuracy, LiDAR enables detailed Digital Elevation Models (DEMs), making it indispensable for professionals in fields ranging from forestry to civil engineering.

Before - shows canopy and vegetation

After - Canopy and vegetation removed to show ground hits.