g43·concept
Passive microwave
A sensing approach that listens for the faint natural microwave energy that everything on Earth emits, rather than sending out its own signal. The instrument simply collects what the surface gives off.
Passive microwave
A sensing approach that listens for the faint natural microwave energy that everything on Earth emits, rather than sending out its own signal. The instrument simply collects what the surface gives off.
Why it matters
Microwaves pass through clouds and work day or night, so passive-microwave sensors can monitor soil, snow, sea ice, and rain even when visible and infrared instruments are blocked by weather or darkness.
Where you’ll meet it
- SMAP uses a passive-microwave radiometer to retrieve soil moisture worldwide.
- AMSR2 (and earlier AMSR-E) measures sea surface temperature, sea ice, snow, and rain by reading natural microwave emission across several frequencies.
- GPM’s GMI instrument uses passive microwave channels to sense precipitation from space.
In plain terms
It’s like feeling the warmth coming off a wall with your hand — you’re not shining a light on it, just sensing what it naturally gives off.