Radar Basics

MST-Radar

MST-Radar (Mesospheric Stratospheric Tropospheric Radar) or VHF profiler is a high-sensitivity, high-resolution radar that typically operates at frequencies around 50 MHz. They allow observations of the structure and wind fields in the middle atmosphere with unprecedented height and time resolution. Radars that are similar in structure but operate at slightly higher frequencies are Stratosphere-Troposphere (ST) radars. The MST-Radar is an instrument capable of providing estimates of atmospheric parameters with high resolution which is essential in the study of different dynamical processes in the atmosphere.

An MST radar is comprised of a high resolution two-dimensional phased array of two orthogonal sets of Yagi-Uda antennas (one for each polarization). It uses high power transmitters in the region of Megawatts with both coded or uncoded waveforms. Both polarisations are simultaneously processed in phase-coherent receivers with quadrature channels. The signal processor consists of two identical channels of A/D converter, decoder, and integrator.

The scattering and reflection mechanisms responsible for the MST-Radar echo signals are caused by fluctuations of the refractive index due to varying density of the atmosphere (so-called “clear air echoes”). A second cause is the thermal or Thomson scattering, often referred to as incoherent scatter. It arises by free electrons in the ionosphere and the echo signal is characterized by the statistical fluctuations of electron density due to random thermal motions of electrons and ions.