News: Remote sensing has transformed how scientists study the Earth, enabling them to map forests, water bodies, crops, and mineral deposits without ever setting foot on the ground.
About Remote Sensing
- Meaning: Remote sensing is a technology that allows scientists and engineers to study the earth’s surface and subsurface without physical contact.
- Working Principle: It uses satellites, aircraft, and drones equipped with sensors to collect information from a distance.
- The Sun emits visible as well as invisible electromagnetic radiation such as infrared and ultraviolet light. Different materials on Earth, including plants, water, soil, and rocks, reflect and absorb this energy in unique ways.
- These unique patterns are called spectral signatures and act like fingerprints for identifying materials. Sensors analyse reflected energy to determine the type, condition, and composition of objects on the ground.
- Uses of Remote Sensing Technique
- Vegetation, forest health, and carbon mapping: Remote sensing can distinguish between different plant communities and tree species across large forest areas.
- Scientists use the Normalised Difference Vegetation Index (NDVI) to assess plant health using spectral signatures.
- High NDVI values indicate healthy vegetation, while low values may indicate stress, disease, or lack of water.
- Mapping surface water and monitoring water quality: Satellites use optical indexing and synthetic aperture radar (SAR) to map rivers, lakes, wetlands, and floods.
- Water reflects visible green light but absorbs near-infrared and shortwave infrared radiation.
- Scientists use the Normalised Difference Water Index (NDWI) to identify water bodies in satellite images.
- The Modified NDWI (MNDWI) is especially useful in urban areas to distinguish water from building shadows.
- Mineral detection and hyperspectral remote sensing: Hyperspectral sensors split reflected sunlight into hundreds of narrow wavelength bands.
- These sensors generate detailed spectral signatures for every pixel in an image.
- Hyperspectral data can identify specific minerals, rock types, and even nutrient deficiencies in plants.
- Oil and gas exploration from space: Oil and gas sometimes leak slowly upward through cracks in the Earth, a process known as micro-seepage.
- This seepage alters soil chemistry and slightly stresses vegetation, causing subtle colour changes.
- Satellites can detect these changes to identify potential drilling locations.
- Groundwater mapping using gravity: Underground water increases the gravitational pull of an area.
- Example – NASA’s GRACE mission measured tiny changes in gravity using two satellites flying in formation.
- Vegetation, forest health, and carbon mapping: Remote sensing can distinguish between different plant communities and tree species across large forest areas.
