Can LiDAR Penetrate Water?
What is LiDAR?
LiDAR (Light Detection and Ranging) uses pulsed laser light to measure to the ground or other surfaces. These light pulses, combined with other data from airborne systems, creates precise 3D information of the environment. While LiDAR is great for terrestrial mapping, its ability to penetrate water surfaces and measure underwater features depends on the type of LiDAR technology used.
How LiDAR Works
LiDAR systems work by sending laser pulses to a surface and measuring the time it takes for the light to return to the sensor. Those return times are calculated into distances and creates 3D models called point clouds. LiDAR is good for:
Measuring ground points under vegetation.
Mapping thin structures like power lines.
Combining image textures from photogrammetry to create highly detailed digital twins and 3D models.
But water is a challenge for traditional LiDAR systems.
Drone Surveying: Broader Applications
Drone surveying uses unmanned aerial vehicles (UAVs) with LiDAR and photogrammetry to collect spatial data from the air. This allows surveyors to create 3D models, maps and other deliverables with minimal ground based work.
Drone surveying goals:
Determining relative positions of objects or points on the Earth’s surface.
Measuring distances and angles between objects.
Preparing topographic maps and defining control points.
LiDAR and Water
When laser pulses hit water, they are absorbed and scattered by water molecules. How far LiDAR can penetrate water depends on:
Laser Wavelength: Shorter wavelengths in the blue-green spectrum can penetrate water better than longer wavelengths, like the infrared used for terrestrial mapping.
Water Clarity: Clearer water allows deeper penetration, murky water limits effectiveness.
Angle of Incidence: A steeper angle increases the chance of good reflections.
In general, terrestrial LiDAR systems can’t penetrate water and are not suitable for underwater mapping. For that purpose, specialized systems like Bathymetric LiDAR are needed.
Bathymetric LiDAR: The Solution for Underwater Mapping
Bathymetric LiDAR is designed for underwater mapping, using green laser light (532 nm) to penetrate water surfaces and measure the seafloor or other underwater features. They have:
Penetration Depth: Depending on water clarity, bathymetric LiDAR can penetrate up to 25 meters in clear water, perfect for shallow coastal areas and riverbeds.
High Resolution Mapping: Bathymetric LiDAR systems creates detailed maps of underwater environments, for applications like navigation, habitat mapping and coastal management.
Dual Capabilities: Many systems combine topographic and bathymetric technology, allowing for seamless mapping of land and water interfaces.
Drone Survey Deliverables
LiDAR and photogrammetry drone surveys produces:
3D Terrain Maps: 3D representation of terrain, used in construction and planning.
Topographic Maps: Large scale maps that show natural and man made features like waterways, woodlands and buildings.
Contour Maps: Maps with contour lines connecting points of equal elevation, for elevation analysis.
Digital Elevation Models (DEMs): Bare ground surface, without vegetation and buildings.
Colored Point Clouds: Photorealistic 3D point clouds that combines RGB images captured with photogrammetric cameras.
Industries using Drone Surveying
Drone surveys are changing:
Surveying: Complementing traditional methods with higher accuracy and speed.
Mining: Capturing geospatial data for infrastructure planning and volume calculations.
Agriculture: Monitoring crop health and field conditions.
Urban Planning: Informing resource allocation with up to date environmental data.
Construction: Creating Digital Terrain Models (DTMs) and DEMs for engineering projects.
LiDAR Alternatives for Underwater Mapping
While bathymetric LiDAR is great for some applications, other technologies are used in conjunction or as standalone solutions:
Sonar (Sound Navigation and Ranging): Uses sound waves to map underwater topographies, works well in deeper or murky water where light based systems struggle.
Satellite Imagery: Provides large scale visual data but lacks the resolution of LiDAR or sonar.
Underwater LiDAR Limitations
Despite the benefits, bathymetric LiDAR has:
Turbidity and Surface Conditions: Waves, suspended particles and algae can scatter or absorb the laser light, reducing accuracy.
Penetration Depth: Effective only up to shallow depths, especially in less clear water.
Equipment Costs: Specialized sensors and equipment are more expensive than traditional LiDAR systems.
Best Practices for Bathymetric Surveys
To get good data with bathymetric LiDAR:
Check Water Clarity: Choose survey locations with clear water whenever possible.
Optimize Wavelengths: Use green light.
Plan Surveys Around Weather: Avoid high waves or turbulence.
Combine Technologies: Use sonar or other methods to address turbid or deep water limitations.
Conclusion
Traditional LiDAR systems are not designed for underwater mapping, but bathymetric LiDAR is a great solution to get detailed data beneath the water surface. By using green wavelengths and combining topographic and bathymetric technology, these systems can map marine and coastal areas. By combining drone surveying with GNSS, photogrammetry and LiDAR, you can apply to many industries. Know the limitations and best practices to get the best results from your surveys.