Precipitation

Water falling from the sky as rain, snow, sleet, or hail. Satellites estimate how much is falling and where, even over oceans and remote regions with no rain gauges.

Why it matters

Precipitation drives floods, droughts, water supply, and agriculture, and over much of the planet satellites are the only way to measure it — making space-based rainfall data critical for forecasting and disaster response.

Where you’ll meet it

• GPM (Global Precipitation Measurement) is NASA’s flagship rain and snow mission, with both radar and a microwave radiometer.
• IMERG is GPM’s blended product, merging many satellites into half-hourly global rainfall maps.
• TRMM, GPM’s predecessor, built the long-term record of tropical rainfall.

In plain terms

It’s like a global rain gauge stretched over the whole planet, catching showers over the open ocean and remote mountains where no one is standing with a bucket.