Principle of measurement
Both radars transmit pulses that are backscattered by variations in the
atmospheric refractive index and then received. The variations in the
refractive index are due to turbulent flucuations in temperature and humidity
(troposphere and stratosphere) or concentrations of free electrons (mesosphere).
The different origins of the refractive index variations, in turn, result in
radar echoes received from two height regimes: 1 - 30 km and 60 - 90 km. The
mesospheric echoes strongly depend on the time of day and season. Utilizing the
Doppler shifts, the radar can measure three-dimensional velocity vectors
provided the main transmitting and receiving beams are cycled through at least
three non-coplanar orientations.