Radar
Also called: Radio detection and ranging · Topic: Remote Sensing, GIS and GNSS · NCERT: Class 11, Ch 6 "Introduction to Remote Sensing"
Meaning
Radar (radio detection and ranging) sends out its own microwave pulses and records the echoes that bounce back from objects. It is an active sensor because it brings its own energy, so it does not need sunlight. Microwaves pass through cloud, so radar can image the ground at night and in bad weather. This makes it ideal for India during the monsoon, when optical sensors only see cloud tops.
Example
India's RISAT-1 (2012) and EOS-04, also called RISAT-1A (2022), carry C-band radar. During monsoon floods in Assam's Brahmaputra valley, they can map flooded areas through thick cloud.
Don't confuse with
- Passive optical remote sensing: this records reflected sunlight. It needs daylight and clear skies.
- LiDAR: this is also active but uses laser light, which thick cloud blocks.
Related concepts
- Sensor
- Photographic sensor
- Multispectral scanner
- Swath
- Whiskbroom scanner
- Instantaneous field of view
- Pushbroom scanner
- Passive and active remote sensing
- Synthetic aperture radar
- LiDAR