Recent advances in radar instrumentation and techniques for studies of the mesosphere, stratosphere, and troposphere

The last few years have seen several significant advances in mesosphere-stratosphere-troposphere (MST) radar studies. This is true with respect to studies ranging from MF through VHF and up to UHF. These advances have been in each of the areas of equipment, techniques, and general radar theory. In this short paper we will highlight some of these advances and discuss their significance in the longer-term application of MST radar techniques. We will concentrate primarily on discussion about instrumentation and the raw products (powers, radial velocities, and spectral widths) produced by the systems, with some reference to the nature of the radio wave scattering entities. Quantities which are derived from the measurements of these raw quantities like gravity wave fluxes, tidal studies, and so forth will not generally be considered in any detail. Sample advances include new methods of data analysis (both on-line and post-collection), lightning detection, rainfall measurement, and temperature determination. Other interesting applications include simultaneous application of MST techniques with other procedures such, as in radio acoustic sounding (RASS) and the artificial periodic inhomogeneity (API) method. Areas of advance in terms of understanding scattering mechanisms include new insights into the controversy about the nature of aspect-sensitive scattering (specular reflection compared with anisotropic turbulence) and improvements and refinements in our measurements of turbulence with these radars. Radars working at frequencies other than those mentioned, especially L and S band (1215-1710 and 1710-2700 MHz respectively), have also been used with good success, and these will be discussed where appropriate. The paper will concentrate on radars which can employ clear-air scattering; we will not consider in much detail systems which rely predominantly on precipitation and other scattering targets embedded in the air.