Doppler radar provides early warning for severe weather.

During a severe storm, you can watch a local weathercaster showing where the storm is located, how heavy the precipitation is, where there is hail likely falling, and any likelihood of tornadoes. This is all done with a weather tool known as doppler radar. 

What is Simple Radar and Doppler Radar?

RADAR is an acronym that has become a word: RAdio Detection And Ranging. Radar was developed in the late 1930’s and has been continuously improved since.

• Simple radar uses short pulses of electromagnetic energy that is sent out by the radar. Some of these pulses will bounce off an object, then part of the pulse will bounce back to the radar and is detected. This was shown as blips or blobs on a screen with a sweeping line that updates the screen as it passes over. Radars use energy called radio waves, which are much longer wavelengths than sunlight.
   
• Doppler Radar is a type of radar that uses the Doppler Effect to detect the direction and speed of precipitation and air motion.
  • Consider the pitch change of a car as it approaches and passes you, Doppler radar identifies whether wavelengths are compressed or stretched out to determine the direction and speed of detected precipitation.
  • This system filters out things that aren't precipitation and air movement that may show up on a radar screen. 
  • Wavelengths of about 1 to 30 centimeters, or about a quarter inch to a foot, are used for Doppler radar, depending on specific functions. These radar systems can also raise and lower the antenna, scanning a greater vertical slice of the atmosphere.
  • The farther away from the radar, the less weather can be detected near the ground. Since the pulse moves in a direct line, it cannot follow the curvature of the earth. 
     

New Technology

Additional technologies enhance Doppler radars effectiveness. Dual polarization allows the pulses sent out to be vertical (think of waves moving up and down) and horizontally (waves moving from side to side), that shows more detail. 

Phased array systems use several antennas to send out pulses which can look at multiple elevations of a storm at once. Older systems must raise and lower the antenna and takes several minutes to complete the scanning cycle.