Dual-polarized radar technology is important because it can accurately predict the amount of potential rainfall. These perpendicular fields bounce off of an object and return back to the radar which then gives information on the horizontal and vertical dimensions of particles, hydrometeors, and/or biological targets within the observable range of a given radar site. Dual-polarized radars send both horizontal and vertical electromagnetic waves to examine a variety of particle, hydrometeor, and/or biological target types existing within different types of air masses. Dual-polarization revolutionized radar technology by providing better resolution and a clearer view of storms and corresponding storm structure which is critical for real-time forecasting and research purposes. Each VCP therefore can provide a different perspective of the atmosphere.ĭoppler radars were upgraded to Dual-polarized radar technology because the earlier WSR-88D style radar technology in operations at the time was becoming outdated. These different VCPs have varying numbers of elevation tilts and rotation speeds of the radar itself. Within these two operating states there are several VCPs the NWS forecasters can utilize to help analyze the atmosphere around the radar. This is when the meteorologists switch the radar to precipitation mode. At the same time, meteorologists want to see higher up in the atmosphere when precipitation is occurring to analyze the vertical structure of any storms. When precipitation is occurring, the radar does not need to be as sensitive as in clear air mode as rain provides plenty of returning signals. In this mode, the radar is in its most sensitive operational state. Clear Air mode is used when there is no rain within the range of the radar. There are two main operating states of the Doppler radar Clear Air Mode and Precipitation Mode. A VCP consists of the radar making multiple 360° scans of the atmosphere, sampling a set of increasing elevation angles. “When it comes to understanding how a Doppler radar works, a radar continuously scans the atmosphere by completing volume coverage patterns (VCP). The direction the radar is pointing then helps to locate both the position and relative distance of a given storm. Measuring the time it takes for the radio wave to leave the radar and return can tell us how distant the storm is from a given location. The intensity of this received signal, called the radar echo, indicates the intensity of the precipitation being observed at a specific time. When the energy is sent back, it is detected by the radar’s receiver. Precipitation scatters these waves, sending back some energy to the transmitter. By measuring the shift, or change in phase between a transmitted pulse, the target’s movement directly toward or away from the radar is calculated. The radar transmits pulses of radio waves and keeps track of the phase (i.e., shape, position, and form) of the pulses being sent away from the radar site. The transmitter sends out pulses of radio waves. ![]() A radar unit consists of a transmitter and a receiver. This is often experienced when an emergency vehicle drives past with its siren blaring or within the context of hearing an approaching train reaching a station platform.ĭoppler radar systems provide information regarding the movement of targets as well as their position with time. As the object moves away from a given location, the sound waves are then stretched, leading to a lower frequency. If an object emits sound waves as it approaches a location, the waves are compressed and consequently will then lead to a higher frequency being observed. The phase shift effect is similar to the "Doppler shift" which can be observed under many circumstances with sound waves movement/propagation. A positive phase shift implies forward motion toward the radar and a negative shift suggests retreating motion away from the radar. The Doppler effect is effectively a phase shift change in frequency or wavelength which is caused by the distance between the object being observed and the observer. This phenomenon became known as the Doppler effect. In 1842, an Austrian physicist by the name of Christian Andreas Doppler described how the frequency of light and sound waves were affected by the relative motion of an object.
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