RADAR
Weather radar is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail, etc.). Modern weather radars are mostly Doppler radars, capable of detecting the motion of rain droplets in addition to the intensity of the precipitation. Both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather.
During World War II, radar operators discovered that weather was causing echoes on their screen, masking potential enemy targets. Techniques were developed to filter them, but scientists began to study the phenomenon. Soon after the war, surplus radar were used to detect precipitations. Since then, weather radar has evolved on its own and is now used by national weather services, research departments in universities as well as in television broadcasts. Raw images are routinely used and specialized software can take radar data to make short term forecast of future positions and intensities of rain, snow, hail, and other weather phenomena. Their output is even incorporated into numerical weather prediction models to improve analyses and forecasts.
The phase shift effect is similar to the "Doppler shift" observed with sound waves. With the "Doppler shift", the sound pitch of an object moving toward your location is higher due to compression of sound waves. As an object moves away from your location, sound waves are stretched resulting in a lower frequency. You have probably heard this effect from an emergency vehicle or train. As the vehicle or train passes your location, the siren or whistle's pitch lowers as the object passes by.
For the Doppler radar, atmospheric objects moving inbound (toward the radar) produce a positive shift in frequency of the radar signal. Objects moving away from the radar (outbound) produce a negative shift in frequency. It is this change in frequency that allows us to "see" motion in the atmosphere. The larger the phase shift, the greater the target's radial velocity.
During World War II, radar operators discovered that weather was causing echoes on their screen, masking potential enemy targets. Techniques were developed to filter them, but scientists began to study the phenomenon. Soon after the war, surplus radar were used to detect precipitations. Since then, weather radar has evolved on its own and is now used by national weather services, research departments in universities as well as in television broadcasts. Raw images are routinely used and specialized software can take radar data to make short term forecast of future positions and intensities of rain, snow, hail, and other weather phenomena. Their output is even incorporated into numerical weather prediction models to improve analyses and forecasts.
The phase shift effect is similar to the "Doppler shift" observed with sound waves. With the "Doppler shift", the sound pitch of an object moving toward your location is higher due to compression of sound waves. As an object moves away from your location, sound waves are stretched resulting in a lower frequency. You have probably heard this effect from an emergency vehicle or train. As the vehicle or train passes your location, the siren or whistle's pitch lowers as the object passes by.
For the Doppler radar, atmospheric objects moving inbound (toward the radar) produce a positive shift in frequency of the radar signal. Objects moving away from the radar (outbound) produce a negative shift in frequency. It is this change in frequency that allows us to "see" motion in the atmosphere. The larger the phase shift, the greater the target's radial velocity.