Incoherent Scatter RADAR measures ion velocity (from Doppler shift) and flow and thereby yields the perpendicular electric field component

What will the RADAR electromagnetic radiation scatter from? It was originally hypothesized that it would scatter from electrons. Scattering of electromagnetic radiation of frequency f1 from moving electrons would lead to a frequency f2 i.e. would create a frequency shift due to the Doppler effect. It had therefore been presumed that the mean thermal electron velocity would be provided.
Surprisingly, the first experiments showed that ion velocity was provided. (Slide 4) "This is explained by the fact that, when the probing wavelength is greater than the Debye length, the electrons are linked to the ions through the Debye cloud around them, and part of the scattered signal (the ion line) is characterized by ion properties. f(T) gives the line-of-sight component of the mean ion velocity V(i). If several positions are used, the complete vector flow velocity can be found."
"In the F region the ion flow velocity yields the perpendicular electric field components via the relationship E(p)= B*V(i).
"The ion flow velocity parallel to B is much more complicated, since many factors contribute, such as the component of the neutral wind along B, the ion pressure gradient, and gravitational forces".
"The Full Spectrum"
(Slide 6) "The first simultaneous observations of both ion and electron scattering lines (called plasma lines). The data were taken in the altitude range 1460–2486km over Arecibo, where H+ is the dominant ion."
Except for RADAR, also LIDAR can be used. We refer to Rayleigh scattering from air molecules and Mie scattering from aerosols and clouds. Please refer to attached figure which also shows meteor trails for which we distinguish head and tail scattering referred to as head and trail echos.
"The first incoherent scatter radar (ISR) site was Arecibo, Puerto Rico, in 1959. At the time of writing, there are 15 such sites (slide 3).

Measurement of air molecule velocity for determination of wind speed

Use of LIDAR and calculation of frequency-shift (Doppler-shift)
The ESA Aeolus satellite uses Aladin, a pulsed UV LIDAR (355 nm, circularly polarized, 50 Hz).
In order to determine the speed of the wind, we measure the velocity of air molecules (and/or aerosols).
An instrument emits light and processes the backscattered light which has been frequency-shifted due to the Doppler effect.
The frequency shift allows the determination of the molecule velocity.
Excerpt from (pdf) (Indirect link:
"The temperature-dependent Brownian motion of air molecules causes scattered light to become broadened in frequency. Pressure fluctuations by acoustic waves cause an additional modulation to the frequency distribution of the scattered light, which is described by Brillouin scattering theory."
Therefore, "the monochromatic Aladin emitted laser light that is backscattered by molecules undergoes a frequency broadening which is both temperature (Rayleigh) and pressure (Brillouin) dependent."
"The higher the temperature and atmospheric pressure, the broader and more modulated the backscattered laser signal becomes."
"Backscattered laser light, thus, needs to be temperature and pressure corrected before the Doppler shift between the emitted and received laser light can be determined. The resulting Doppler shift is used to retrieve the speed of the air molecules (...)"
Suggested image reference:
Figure 6 from 
"Mie scatter occurs when the particle size moves out of the Rayleigh range into a size comparable to the lidar wavelength. The most important Mie scatter is from noctilucent clouds".



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Bepi-Colombo, 1ère Mission Mercure ESA-JAXA (Japon)
Cartographie de champs magnétique et de magnétosphère
Deux sondes: MPO (Mercury Planetary Orbiter) par ESA, MMO (Mercury Magnetospheric Orbiter) par JAXA
Maîtrise/coordination CNES: Huit laboratoires français participent à la conception de 6 des 16 instruments de la mission (IAS, IPGP, IRAP, LAM, LATMOS, LESIA, LPC2E, LPP).
L'instrument SORBET: récepteur radiofréquences (hautes-radiofréquences ou HF) 2.5kHz-10MHz
Créé par LESIA, laboratoire de l'Obsérvatoire de Paris
"La figure représente la puissance électrique (brute en dB) collectée à l’entrée du récepteur SORBET, en fonction du temps et de la fréquence, le 9 novembre 2018. On peut distinguer trois périodes correspondant à des modes de fonctionnement PWI très différents (...)."