Short note: Types of remote sensing

Remote sensing records information about the Earth's surface from a distance using electromagnetic energy.

Types of remote sensing

1. By energy source
   • Passive: uses natural energy, mainly reflected sunlight or emitted thermal radiation (e.g. Landsat, Sentinel-2, aerial photography).
   • Active: the sensor sends its own energy and records the return (e.g. radar/SAR, LiDAR).
2. By platform: ground-based, airborne (aircraft, drones) and spaceborne (satellites).
3. By wavelength region: visible and near-infrared, thermal infrared and microwave remote sensing.
4. By number of bands: panchromatic, multispectral and hyperspectral.

Applications

• Land use and land cover mapping: classification of urban, agricultural, forest and water areas from multispectral images.
• Route and site selection: alignment of roads, canals, pipelines and transmission lines, and choice of dam, bridge and airport sites using terrain, drainage and geology.
• Water resources: mapping of rivers, lakes and catchments; snow and glacier monitoring; flood extent and flood-plain mapping; watershed management.
• Geology and soil: identification of rock types, faults and lineaments, landslide-prone slopes and soil types for foundation and slope-stability studies.
• Disaster management: assessment of damage after earthquakes (e.g. Gorkha 2015), floods and landslides, and hazard mapping.
• Urban planning: monitoring of urban growth, infrastructure inventory, and change detection.
• Environmental monitoring: vegetation health, erosion, deforestation, pollution of water bodies, and impact assessment of projects.
• Construction and survey: topographic mapping, DEM and contour generation.