INSTRUMENT 05 OF 5 . GEN 2GNSS Reflectometry
GNSS Reflectometry
It reads the surface winds inside a hurricane—through the rain. By listening to GPS signals reflected off the ocean, it measures winds in rain-wrapped storm cores that challenge traditional satellite sensors. Over land, the same technique reveals soil moisture and flooded areas.
Overview
A GNSS signal reflects from the wind-roughened ocean and is captured by a low-orbit receiver. The shape and strength of the reflected signal reveal surface roughness, which is used to retrieve ocean-surface wind speed—even through heavy rain.
- Method
- Passive bistatic sensing
- Signal source
- GNSS L-band signals
- Primary output
- 10 m ocean wind speed
Read the shimmer, get the wind.
Think of moonlight on water. On a still night the reflection forms a sharp, bright streak. When the wind picks up, that streak spreads into a wide, fuzzy shimmer - and the rougher the water gets, the more the reflection spreads.
GNSS reflectometry does exactly this, but with GPS signals instead of moonlight. A calm sea reflects GPS signals more like a mirror; a wind-roughened sea scatters them across a wider area. Read how scrambled the reflection is and you can work backward to the surface wind speed.
And because GPS signals punch through heavy rain, it can read that shimmer even in the heart of a hurricane, where a visible camera would see only a wall of clouds.
Borrow a signal, catch the bounce
A GPS satellite's signal travels down and reflects off the sea. A low-Earth orbit receiver catches that bounce - and the shape of the returned signal encodes how rough the surface is.
A glassy sea returns a sharp, mirror-like specular signal; a wind-whipped sea scatters it into a broader, fuzzier return. Measure that scattering and you can work backward from surface roughness to wind speed. It carries no transmitter of its own - it reads signals already in orbit.
One bounce, the surface laid bare
A surface-state modality: the ocean’s wind and roughness, and — over land — how wet the ground is and where the water is spreading.
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Ocean surface wind speed (10 m)
Through heavy rain — including the tropical-cyclone inner core.
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Ocean surface roughness
The surface scattering signature the wind speed is read from.
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Soil moisture
Top-layer wetness — heritage product cross-calibrated to NASA’s SMAP.
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Flood & inundation extent
Surface-water detection and fractional inundation mapping.
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Sea ice & freeze / thaw
Detection of changing surface states across ocean and land.
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Air–sea heat flux
Derived by combining GNSS-R winds with atmospheric and ocean state data.
The wind that is hardest to see from space
A scatterometer reads ocean wind by bouncing its own radar off the sea - but heavy rain scrambles that signal, so it goes blind in exactly the rain-wrapped core where a hurricane's most dangerous winds live. Visible and infrared imagers can see the storm's clouds, but not the ocean surface beneath them.
GNSS reflectometry can reach the ocean's surface because it borrows the long-wavelength GPS signals already in orbit - which pass through heavy rain, allowing the instrument to measure surface winds deep inside the hurricane inner core. It opens the single most under-observed regime in the most dangerous storms.
Constellation Foundation
GNSS Reflectometry reveals what is happening at the surface - even through heavy rain. The rest of the constellation fills in the atmosphere and precipitation above it.
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