Weather radar consists of a rotating dish protected by a large white dome; this dish sends pulses of energy the radar beam into the atmosphere to detect objects like rain or hail.
If the radar beam encounters an object, some of the radiation will bounce off of it and return to the radar site. The strength of the return beam and the time it takes for the pulse to return to the radar dish allows us to see how heavy the precipitation is and how far away it is from the radar site.
The resulting data is displayed on a map using a rainbow scale that typically spans from light blue to dark red and purple, with cooler colors indicating lighter precipitation and warmer colors showing heavy precipitation. Solid batches of oranges, reds, and purples on a radar image usually indicate an intense thunderstorm. A recent development in radar technology called "dual polarization" allows the radar to send out two beams of energy—one that is oriented horizontally and another oriented vertically.
This dual radar beam allows us to see the size and shape of the objects falling through the atmosphere. This is important as it can tell us the difference between rain, hail, snow, sleet, and foreign objects like tornado debris. The National Severe Storms Laboratory calls this "the most significant enhancement ever made to the nation's radar network since Doppler radar.
The only downside to dual polarization technology is caused by the Earth itself. As the radar beam gets farther away from the radar site, it climbs higher off of the ground due to the curvature of the Earth.
Most people are familiar with the green, yellow, and red pictures that radar generates because they see them on TV, but radar actually gives a meteorologist more information about the atmosphere than a simple image of rain. A radar sends out a beam of radiation into the atmosphere.
If there is rain falling, the radiation hits that rain and bounces back to the radar. Depending on how much energy is reflected back to the radar and how fast that radiation is bounced back, we can determine where and how heavy the rain is.
The radar then sends this information through a computer that gives us the pretty green, yellow and red maps you see on TV when we are tracking storms and rain. Typically, the heavier the rain, the warmer the color. So, green usually means light rain, yellow means moderate rain, and red means heavy rain or hail.
So, how exactly does it work? A modern Doppler radar system consists of a large radar dish housed inside an even larger hexagonal dome to protect it from the elements. The radar dish can rotate degrees in the horizontal and approximately 20 degrees in the vertical. As the radar antenna turns, it emits extremely short bursts of radio waves, called pulses and waits for these pulses to return during the "listening period". Each pulse lasts about 0.
The transmitted radio waves move through the atmosphere at around the speed of light. Once it hits a target such as a raindrop or snowflake, the radio waves are scattered with some of the energy returning back to the radar.
By utilizing the Doppler Effect, Doppler radars provide information regarding the movement and positions of targets. After the radar emits a pulse of radio waves, it tracks the phase shift between the transmitted radio wave and the received echo. This phase shift shows whether the target is moving directly toward or away from the radar, called its radial velocity.
0コメント