Almost unknown to the public, a constellation of satellite guardians is flying overhead, and all it takes is a phone call for them to intervene when a country is hit by a storm, earthquake, tsunami or flood.

Armed with cameras or ground radar, these Earth-observation satellites were sent into orbit for scientific and commercial missions.

But under an international agreement, they can also be called on for humanitarian work.

Assigned to fly over a disaster zone, they send back high-resolution images that can be crucial for rescue teams on the ground.

Which towns or streets are most at risk of flooding? What route can be found for relief trucks after a bridge has collapsed? And where is a secure location to pitch tents for survivors?

This pooled effort gathers 14 space agencies or national organisations, which together have 20 satellites, ranging from France’s SPOT commercial satellite to the United States’ scientific satellite, Landsat.