The next generation of weather radars, which are currently being installed throughout the United States, will improve observations of the interior of storm systems. These radars are called dual-polarization radars.
Radar, an acronym for Radio Detection And Ranging, consists of a transmitter and a receiver. The transmitter emits pulses of radio waves outward in a circular pattern.
Precipitation scatters these radio waves, sending some energy back to the transmitting point where it is detected by the radar’s receiver. The intensity of this received signal, called the radar echo, indicates the intensity of the precipitation.
A radio wave is electromagnetic energy. That means it has electric and magnetic fields, which are oriented perpendicular to one another. The orientation of these oscillations is referred to as polarization.
It’s the same principle at work in a polarizing filter for a camera, or polarizing sunglasses. Rotate the filter, or glasses, while looking through them at a portion of the sky away from the sun; at a certain orientation, the intensity of the sky’s light will be reduced. This is because the filter is removing polarized light that is not aligned with the filter.
Typical weather radars transmit and receive radio waves with a single orientation of the electric field. Dual-polarization radars emit radio waves that alter their transmitted pulse between horizontal and vertical polarizations. The additional information on polarization improves the precipitation rate measurement as well as determining the type of precipitation (snow, rain, freezing rain and hail).
