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)

Comments

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