Observations with “Clear Air” Radars

Abstract

In the previous Chapters we have largely dealt with microwave weather radars of the type which are used in operational meteorology to observe weather systems associated with precipitation. We referred briefly (Chapter 2) to scattering and reflection in the clear air due to discontinuities or fluctuations in radio refractive index and mentioned that echoes due to such phenomena are better observed at longer wavelengths i.e. in the UHF and VHF frequencies. We also discussed briefly (Chapter 4) several clear air phenomena, besides hydrometeors, which can be detected by microwave radar. In the present Chapter, we shall deal with VHF and UHF radar systems which are particularly suited for clear air observations, and are called “clear air” radars. It has been recognised in recent years that, despite their name, these radars are capable of detecting echoes from hydrometeors also. This capability, which will also be discussed in this chapter, is the reason for the use of the inverted commas with the name “clear air”. Some authors prefer to call them simply VHF/UHF radars.