Weather radar is a remote sensing instrument using microwave energy between X-band (3 cm wavelength) and S-band (10 cm wavelength). A short pulse of high power microwave energy is produced by a magnetron in the transmitter system and this energy is focused by an antenna system into a narrow beam. This pulse of energy travels through the atmosphere at the speed of light (3 x 10 ⁸ ms^-1). When a target such as a raindrop is encountered, some of the energy is scattered of which a minute fraction is in the direction back to the antenna system were a sensitive receiver system is used to process and amplify this received power into useful data. From the azimuth and elevation information on the pointing direction of the antenna, the time between transmitting and receiving and the power of the received signal, the target location can be determined as well as its intensity or reflectivity.

dBZ is the unit used we use for reflectivity in meteorology. dBZ is related to the number of drops per unit volume and the sixth power of their diameter and it can be related to rainfall rate through an empirical relationship called a Z-R relationship.

In the table below a guideline on the interpretation of dBZ factors are given.

Please take note that various atmospheric and environmental conditions can negatively affect radar data and caution should be exercised when interpreting the information. Some of these effects include:

• returns from mountains and other non-meteorological targets,
• attenuation of the radar signal when viewing weather echoes through areas of intense precipitation(with C-band radars),
• temperature inversions in the lower layers of the atmosphere which bend the radar beam in such a way that ground clutter is observed where normally not expected,
• the “bright band” which is a layer of enhanced reflectivity caused by the melting of ice particles as they fall through the O^oC level in the atmosphere and which can result in over-estimation of rainfall.