training course on weather radar systems - RTC, Regional Training ...

MODULE A- INTRODUCTION TO RADAR
polarizations. Although there are many different ways to mix the horizontal and vertical pulses
together into a transmission scheme, the most common method is to alternate between horizontal
and vertical polarizations with each successive pulse. That is, first horizontal, then vertical, then
horizontal, then vertical, etc. And, of <strong>course</strong>, after each transmitted pulse there is a short listening
period during which the radar receives and interprets reflected signals from the cloud.
Since polarimetric radars transmit and receive two polarizations of radio waves, they are
sometimes referred to as dual-polarization radars. The difference between non-polarimetric and
polarimetric radars is illustrated below:
4.13. Terminal Doppler Weather Radars (TDWR)
Terminal Doppler Weather Radars a member of weather radars family used generally at the
airports for supporting the aviation safety. TDWRs have the capability of detecting wind
parameters indicating connective microbursts, gust fronts, and wind shifts. It provides a new
capability for the dissemination of radar derived, real-time, and warnings and advisories. The
characteristics of the TDWR make it well suited for additional applications. Its narrow beam and
aggressive ground clutter suppression algorithms provide excellent data on boundary layer
reflectivity and winds – in particular the locations of thunderstorm outflow boundaries.
Similarly, its narrow beam (0.5 deg) could be useful for detection of severe weather signatures
(e.g., tornado vortices) with small azimuth extent.
4.14. Wind Profilers
Wind profilers are specifically designed to measure vertical profiles of horizontal wind speed
and direction from near the surface to above the tropopause.
Obtaining wind profiles consistently to the tropopause in nearly all weather conditions requires
the use of a relatively long wavelength radar. 404 MHz Wind profilers are relatively low-power,
highly sensitive clear-air radars, operating at a wavelength of 74 centimeters. The radars detect
fluctuations in the atmospheric density, caused by turbulent mixing of volumes of air with
slightly different temperature and moisture content. The resulting fluctuations of the index of
refraction are used as a tracer of the mean wind in the clear air. Although referred to as clear-air
TURKEY RADAR TRAINING 1.0 / ALANYA 2005 41