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LiDAR in Remote Sensing



LiDAR (Light Detection and Ranging) is an active remote sensing technology that uses laser pulses to measure distances to the Earth's surface and create high-resolution 3D maps.

LiDAR sensors emit short pulses of laser light (usually in the near-infrared range) and measure the time it takes for the pulse to return after hitting an object.

Because LiDAR measures distance very precisely, it is excellent for mapping:

  • terrain

  • vegetation height

  • buildings

  • forests

  • coastlines

  • flood plains


✅ 1. Active Sensor

LiDAR sends its own laser energy, unlike passive sensors that rely on sunlight.

✅ 2. Laser Pulse

  • LiDAR emits thousands of pulses per second (even millions).

  • Wavelengths commonly used:

    • Near-Infrared (NIR) → land and vegetation mapping

    • Green (532 nm) → water/ bathymetry (penetrates shallow water)

✅ 3. Time of Flight (TOF)

The sensor measures the time taken for the laser to travel:

  • from the sensor → to the surface → back to the sensor.

Distance is calculated using:

Distance = (Speed of light × Time) / 2

This gives the exact elevation of the surface.

✅ 4. Point Cloud

LiDAR produces millions of points with x, y, z values.

This collection is called a point cloud, which forms a precise 3D model of the area.

Each point includes:

  • location

  • height

  • intensity (strength of return)

  • classification (ground, vegetation, building)

✅ 5. Multiple Returns

A single laser pulse may hit:

  • the top of a tree

  • branches

  • the ground

LiDAR records multiple returns:

  • First return → top of canopy/building

  • Intermediate returns → branches, shrubs

  • Last return → ground surface

This allows:

  • canopy structure mapping

  • forest biomass estimation

  • accurate ground surface (DEM) generation

✅ 6. DEM, DSM, and DTM

LiDAR is excellent for generating elevation models:

  • DSM (Digital Surface Model): includes buildings, trees

  • DTM / DEM (Digital Terrain Model): bare ground level

  • nDSM: canopy height = DSM – DTM

✅ 7. LiDAR System Components

A typical LiDAR system includes:

  • Laser

  • Scanner / mirror

  • GPS (Global Positioning System) → position

  • IMU (Inertial Measurement Unit) → orientation

  • Receiver sensor

Together, they ensure high-accuracy 3D measurements.

Types

1. Airborne LiDAR

Mounted on aircraft or drones.
Used for:

  • topographic mapping

  • flood modeling

  • forest studies

2. Terrestrial LiDAR

Mounted on tripod/ground vehicles.
Used for:

  • building mapping

  • cultural heritage documentation

  • highways & mining

3. Bathymetric LiDAR

Uses green laser (532 nm) to penetrate water.
Used for:

  • river bed mapping

  • shallow coastal studies

Applications

🌲 Forest & Vegetation

  • canopy height

  • biomass estimation

  • forest structure analysis

⛰ Terrain Mapping

  • high-resolution DEM/DTM

  • landslide and fault mapping

🏙 Urban Studies

  • building heights

  • 3D city models

  • urban planning

🌊 Hydrology and Flood Studies

  • floodplain mapping

  • drainage network extraction

🏛 Archaeology

  • detecting buried/hidden features

  • mapping ancient landscapes

🏞 Coastal & River Studies

  • shoreline change

  • bathymetry (water depth)


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