Satellites warn of storms before they hit, map floods and damage afterwards, and keep communication working when ground networks fail.
When a cyclone or flood strikes, officials need answers fast. Which villages are under water? Which roads are cut? Satellites can see a whole state in one pass, including places no one can reach. ISRO's Disaster Management Support Programme uses space data for floods, landslides, cyclones, forest fires, earthquakes, drought and more.
ISRO's National Remote Sensing Centre runs a Decision Support Centre for all major disaster types. During major floods and cyclones it maps the affected area and sends the maps to state and central relief departments and the Ministry of Home Affairs, in near real time.
For floods, NRSC says microwave (radar) data are the most useful, because clouds usually block optical cameras while the water is rising. Radar satellites such as EOS-04 list flood mapping among their main uses. Maps and other information are shared with administrators through ISRO's National Database for Emergency Management (NDEM) geoportal.
No single country has a satellite overhead at the right moment for every disaster. The International Charter Space and Major Disasters solves this by pooling satellites. ISRO joined in 2000. NRSC says the Charter has 17 member organisations and serves more than 120 countries. Since 2021 alone, ISRO has responded to 153 Charter activations with almost 700 Earth-observation products. India took the Charter's lead role from April to October 2025.
India also receives Charter data when disasters strike at home, and ISRO also works with the Sentinel Asia network.
Satellites help before a disaster too. Weather satellites like INSAT-3DS track cyclones as they approach the coast. INSAT-3DS also carries a satellite-aided search and rescue transponder. And NavIC's IRNSS-1A broadcasts warnings about cyclones, tsunamis and high waves to fishermen at sea.
Filter to Earth observation and count the low sun-synchronous satellites passing over India today: each pass is a chance to image a disaster zone. See India's Earth-observation fleet
Flood mapping from radar is, at heart, counting pixels.
Calm open water acts like a mirror for radar: the pulse bounces away from the satellite, so flooded areas return very little energy and look dark. Fields, trees and buildings scatter energy back and look brighter. An analyst (or algorithm) sets a brightness threshold, marks every pixel below it as water, then removes permanent water bodies using a pre-flood image.
Area follows directly. With 10 m pixels, each pixel is 100 m². If 2,500,000 pixels are newly marked as water:
area = 2,500,000 × 100 m² = 2.5 × 10⁸ m² = 250 km²
Overlaying this on village boundaries and road maps gives the lists relief teams need.
Timing is the hard part. A single satellite with a 12-day repeat might not pass over a flood until the water has gone. Pointing the sensor sideways helps, and so does combining many satellites. Roughly, if several independent satellites each offer a pass every 12 days, the expected wait for the first one shrinks as the number of satellites grows; with 12 such satellites spread evenly in time, there would be about one opportunity per day. This is exactly why the International Charter pools satellites from many agencies, and why NRSC combines Indian satellites with Charter requests for non-Indian ones.
Cyclones are different: they are followed continuously from geostationary orbit, so the problem there is not waiting for a pass but interpreting cloud patterns, as described in tracking cyclones.
Floods usually come with thick cloud, which blocks optical cameras; radar sees through cloud and works at night.
A voluntary, non-binding arrangement in which member space agencies provide Earth-observation data and products to countries hit by major disasters.
1,000,000 × 100 m² = 100 km².