Atmospheric Measurements by VHF Pulsed Doppler Radar

In the past decade the technique of using sensitive Doppler radars to measure wind, turbulence, and stability in the free atmosphere has been developed. Because this technique can be used to study the atmosphere at all heights from near the ground up to about 100 km, it has been named the MST (mesosphere-stratosphere-troposphere) radar technique. Radars that are sensitive enough to make measurements in all three regions are called MST radars; those that can observe only in the troposphere and lower stratosphere are called ST radars. All MST and some ST radars operate in the VHF (30-300-MHz) frequency band. The history, design, measurement capability, and meteorological applications of the VHF MST radar technique are reviewed in this paper. The radar echoes come from refractive index structures in the air that have length scales of the order of half the radar wavelength, 3-4 m for VHF radars in use. The refractive index structures are primarily of two kinds: turbulent and laminar. The former results in turbulent scatter of the radar signal and the latter results in Fresnel (or partial) reflection. Meteorological applications include 1) measurement of wind profiles, particularly for the study of mesoscale phenomena such as gravity waves, fronts, jet steams, tides, wind variability, etc. These applications take advantage of the fact that wind profiles can be measured much more frequently with the MST radar technique than with other techniques. A frequency of about one profile per minute is typical. 2) Measurement of vertical winds.