Isn’t CLUSTER just a 3D-PTV? from the “Turbulence detected in Space” article

The article in Space by Michael Schirber is entitled “Turbulence detected in space”. It’s basically a pointer to the recent Physical Review Letters publication of Prof. Narita and his colleagues that work on the Cluster. Cluster it is a space exploration program that uses multiple sattelites to detect solar wind behavior. If you read the (popular) article, you can learn a bit about Turbulence:

Turbulence is quite common on Earth, as any frequent airplane passenger can attest. But even physicists get a little queasy when trying to explain the nature of this choppy, swirling flow.

“One cannot predict future behaviors with satisfactory accuracy,” says Yasuhito Narita of the Institute of Geophysics and Extraterrestrial Physics in Braunschweig, Germany. “Even a small deviation or uncertainty in the initial state will end up with a completely different state.”

and also about the so-called Chaos regimes:

Chaos reigns

It’s a bit of the butterfly-tornado connection from chaos theory. Without predictive mathematical equations for turbulence, scientists usually resort to statistical descriptions, like how much does the pressure or velocity vary over a certain distance. Researchers have done such detailed observations of the turbulence in wind tunnels and water pipes. Making similar measurements in space has been harder to do. Still, astrophysicists have inferred the presence of turbulence inside stars, among interstellar clouds, in black hole accretion disks and around Jupiter’s red spot. Single satellites have also studied the solar wind and have detected turbulent signals in the way this plasma flow changes with time. However, to make direct comparisons to models, researchers had to assume something about the size of wind variations.

But the interesting part is the following:

To avoid this ambiguity, multiple sensors are needed to measure the wind’s properties at several points. This is exactly what the Cluster suite of satellites was designed for.

One needs at least four spacecraft to obtain the spatial resolution in three dimensions,” Narita told “Cluster spacecraft provide a minimal set of the measurement points for this purpose.”
The four identical Cluster satellites orbit the Earth in a pyramid formation, collecting electric and magnetic field data. Of special interest is the Earth’s protective magnetosphere, where the planet’s magnetic field deflects the ionized solar wind, like air hitting a car’s windshield.

Isn’t it simply a 3D-PTV? Four cameras (i.e. spacecrafts) and spatial resolution in three dimensions?

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