Short Answer:

Bathymetric LiDAR is a special type of LiDAR technology used to measure underwater depths and map the bottom surface of rivers, lakes, and coastal areas. It works by sending green laser pulses from an aircraft toward the water, which can penetrate the surface and reflect off the underwater ground.

This method helps surveyors create accurate 3D maps of underwater terrain without using boats or manual depth measuring tools. Bathymetric LiDAR is useful in civil engineering for harbor design, bridge construction, flood studies, and environmental monitoring.

Detailed Explanation:

Bathymetric LiDAR

Bathymetric LiDAR is an advanced remote sensing technique used to measure water depth and map underwater surfaces. The word “bathymetric” comes from “bathymetry,” which means the study of underwater depth. LiDAR stands for Light Detection and Ranging, a method that uses laser pulses to determine distances. Unlike regular (topographic) LiDAR that maps land, bathymetric LiDAR is designed to work through water.

This system is usually mounted on an aircraft, helicopter, or drone. It sends out two types of laser beams—infrared and green. The infrared beam reflects off the water surface, while the green laser penetrates the water and reflects off the bottom. By measuring the time difference between these two reflections, the system calculates the depth of the water.

Bathymetric LiDAR is highly valuable in surveying because it allows large water bodies to be scanned quickly and safely from the air. It helps create digital terrain models of riverbeds, lake floors, and coastal zones, which are important for construction and environmental projects.

How bathymetric LiDAR works

1. Laser emission: The LiDAR device emits two types of light—infrared (for the water surface) and green (for the underwater ground).
2. Light reflection: The infrared pulse reflects immediately from the water surface. The green pulse travels through the water, hits the bottom, and bounces back.
3. Time measurement: The time taken by each pulse to return is recorded. Since the speed of light in water is known, the depth can be calculated.
4. Position tracking: GPS and motion sensors are used to track the exact location and orientation of the aircraft or drone during the scan.
5. Data processing: The collected data is processed to generate 3D maps and underwater terrain models.

Applications in civil engineering

Bathymetric LiDAR is used in many civil engineering and infrastructure projects:

• Bridge and pier design: Helps engineers understand the river or seabed below construction sites.
• Floodplain mapping: Provides accurate underwater data for flood risk analysis and planning.
• Coastal engineering: Used for shoreline management, erosion studies, and designing breakwaters or sea walls.
• Harbor and port planning: Maps the depth and shape of the sea floor for safe ship navigation and port construction.
• Dam inspection and reservoir studies: Monitors silt buildup and underwater structures without draining water.

Advantages of bathymetric LiDAR

• Fast data collection: Can cover large water areas quickly from the air.
• Safe operation: Reduces the need for boats or divers in dangerous or hard-to-reach locations.
• Accurate results: Provides high-resolution data on both water surface and bottom.
• Environmental monitoring: Useful for studying aquatic habitats and sediment changes.
• Integration with land surveys: Can be combined with topographic LiDAR to create full land-and-water terrain models.

Conclusion:

Bathymetric LiDAR is a laser-based surveying method used to measure underwater depths and map the floor of rivers, lakes, and coastal zones. It works by using green laser light that passes through water and reflects from the bottom. This method is accurate, fast, and safe, making it extremely useful in civil engineering for designing and monitoring structures related to water bodies.