Light Detection and Ranging (LiDAR)

Basics

• First used in 1960
• Early systems collected profile elevations
• Based on the travel time of the speed of light
• Active remote sensing system

How

LiDAR emits laser pulses at high rates.

• Pulse repetition frequency > 100,000 per second
• Pulse travels at the speed of light

\[ R = \frac{1}{2}tc \]

Where \(R\) is the range between the sensor and the object, \(t\) is the travel time of the laser pulse to the target and back to the sensor, and \(c\) is the speed of light.

Data Collection

Uses a combination of:

• Laser scanner
• GPS
• Inertial measurement unit
  • Pitch, roll, yaw

Elevation mapping uses eye-safe NIR light (1040 - 1060 nm), while bathymetric LiDAR uses blue-green lasers (532 nm).

• Can be collected at night.
• Laser footprint varies with the scan angle and topography.

Instantaneous laser footprint (\(F_{P_{inst}}\)) is computed as:

\[ F_{P_{inst}} = \frac{h}{\cos^2 (\theta_{inst})} \gamma \]

Where \(h\) is the altitude of the sensor above ground level, \(\theta_{inst}\) is the scan angle, and \(\gamma\) is the beam divergence.