- Electromagnetic Radiation: It is a form of energy that travels in waves at the speed of light.
- Wavelength & Frequency: Long wavelength = low frequency; short wavelength = high frequency (measured in hertz).
- Electromagnetic Spectrum: Includes gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves.
- Visible Spectrum: Ranges from about 0.4 to 0.7 microns (violet to red); only a small part of the total spectrum.
- Electromagnetic Energy Principle: All objects above 0 K emit energy; hotter objects emit more energy and shorter wavelengths.
- Sensing Systems:
Passive system uses natural energy (e.g., camera).
Active system sends its own energy (e.g., radar). - Effects of Atmosphere: Gases and dust absorb and scatter radiation; certain “windows” allow energy to pass for remote sensing.
Formulae [1]
Formula: Representative Fraction (R.F.)
\[\boxed{\text{Representative Fraction (R.F.)}=\frac{\text{Cameral Focal Length (Cf)}}{\text{Elevation of Camera (H)}}}\]
Key Points
Key Points: Introduction of Remote Sensing
- Meaning of Remote Sensing: It is the process of collecting information about objects or areas from a distance, without direct contact.
- Basis of Remote Sensing: It works by detecting reflected or emitted electromagnetic energy from objects.
- Natural & Artificial Sensors: Human senses act as natural sensors, but special instruments are used as remote sensors.
- Types of Remote Sensors: Main instruments are Radiometer, Audiometer, Magnetometer and Gravimeter.
- Uses: These instruments measure radiation, sound waves, magnetic field and gravity to study earth features, ocean floor and natural resources.
Key Points: Zones of Remote Sensing
- Gamma Ray Region: Used to detect radioactive minerals like uranium, thorium and potassium for geological studies.
- Ultraviolet Region: Helps in identifying minerals, soils and water bodies; useful in mineral and ocean studies.
- Visible Region: Most commonly used in remote sensing; uses cameras and scanners on aircraft and satellites.
- Infrared Region: Detects thermal energy; useful in studying forest fires, crop health, soil moisture and geological features.
- Multispectral Remote Sensing: Uses multiple spectral bands to get detailed and accurate information about land, soil and vegetation.
- Microwave Region (Radar): Works in all weather and day-night conditions; can penetrate clouds and haze.
- Radar/SLAR Imaging: Produces sharp images of terrain; useful for mapping landforms and surface features.
Key Points: Electromagnetic Spectrum and Energy
Key Points: Photography
- Aerial Photography: It was the first remote sensing method used to collect geographical information about the earth.
- Historical Development: First aerial photographs were taken in 1909; its importance increased during World Wars.
- False Colour Photography: Developed during World War II; helps to distinguish vegetation, crops, water pollution and land use.
- Scale of Aerial Photograph: Scale depends on camera focal length and height of the camera above ground.
Key Points: Remote Sensing from Spacecrafts
- Remote Sensing from Spacecraft: Satellites take photographs and collect data from space, covering very large areas.
- Advantages: Greater perspective, wide (synoptic) coverage and rapid repetitive coverage of the earth.
- Types of Sensors: Both active and passive sensors are used on satellites.
- Important Satellites:
TIROS (1960) – weather observation
LANDSAT (from 1972) – earth resource study
ERS – radar and microwave sensing - LANDSAT Uses: Studies agriculture, forests, oceans, geology, hydrology and land use.
- Radar Satellites: Can work day and night and through clouds, mist and fog.
- India’s Contribution: National Remote Sensing Agency (NRSA), Hyderabad, established in 1972, plays an important role in remote sensing.
Key Points: Geology and Mineral Resources
- Geology & Mineral Resources: Remote sensing helps in studying faults, fractures and locating mineral resources (Project Vasundhara).
- Forest Mapping: Used to estimate forest cover and identify dense, open and mangrove forests.
- Wasteland Mapping: Helps in identifying and classifying wasteland areas across India.
- Water & Soil Mapping: Used for groundwater potential maps and nationwide soil resource mapping.
- Drought Monitoring: Helps in early warning and management of drought conditions.
- Urban & Landuse Studies: Used to study urban sprawl and land use changes in major cities.
- Snow & Marine Studies: Helps in estimating snow melt runoff and identifying marine fishery potential zones.
Key Points: Application of Remote Sensing in Geography
- Importance in Geography: Remote sensing provides quick, accurate and reliable data for studying physical and human features.
- Agriculture & Land Use: Used for crop estimation, yield prediction, land use mapping and drought monitoring.
- Water Resources: Helps in flood mapping, groundwater potential mapping and identifying erosion-prone areas.
- Ocean & Coastal Studies: Used for monitoring coastal environment and studying marine resources.
- Forestry & Environment: Helps in forest mapping, forest density study and assessing environmental impacts.
