23.1 INTRODUCTION

As this handbook is being written, dramatic changes are taking place in the field of radar meteorology. While the majority of radar engineers are familiar with current operational meteorological radars, few are aware of the advances that have been made in the past two decades. For example, doppler radar meteorology, using modern digital signal-processing techniques and display technology, has moved ahead so rapidly that the United States is now planning to replace its existing operational weather radar network with a next-generation doppler system (NEXRAD). This system will provide quantitative and automated real-time information on storms, precipitation, hurricanes, tornadoes, and a host of other important weather phenomena, with higher spatial and temporal resolution than ever before.1 A second network of doppler radars, in airport terminal areas, will provide quantitative measurements of gust fronts, wind shear, microbursts, and other weather hazards for improving the safety of operations at major airports in the United States.1 ^,2 Next-generation doppler radars that use flat-plate antennas, color displays, and solid-state transmitters are now available for commercial aircraft. And many of these new technologies are being deployed in countries throughout the world.

In the research arenas, multiple-doppler radars are used for deriving three-dimensional wind fields.3 Airborne doppler radar4 ^,5 has been used to duplicate these capabilities, thus providing for great mobility. Polarization diversity techniques6 are used for discriminating ice particles from water, for improved quantitative precipitation measurement, and for detecting hail. And there is...