Electromagnetic Waves

 Electromagnetic energy is emitted in the form of waves.  Radar emits powerful electromagnetic energy into the atmosphere, in order to detect meteorological phenomena.  The electromagnetic energy is emitted in bursts, or pulses, through a directional beam.  Pulsed energy is radiated back (backscattered) to the radar from meteorological and non-meteorological targets.  Larger particles will reradiate more energy than smaller sized particles due to the particle diameter.  Water coated ice particles reradiate more energy than water droplets of the same size because of their highly reflective state.

Electromagnetic energy has three important characteristics: wavelength, amplitude, and frequency. These characteristics will affect radar performance.

 Wavelength.  The wavelength of the energy is typically measured in centimeters (cm) between successive troughs or crests in the sine waves.   Other factors being equal, the echo return from clouds or precipitation increases with shorter wavelengths.  Within the wavelengths used for weather radar, the smaller droplets are more visible to the radar at the shorter wavelengths and are more transparent at the longer wavelengths.

 Amplitude.  A wave's height is called amplitude. Amplitude represents the amount of energy or power contained within the wave, with higher amplitudes associated with more returned power.

 Frequency.  Radar frequency refers to the number of completed waves (cycles) per second.  Frequency and wavelength are closely related, and changes in one have a direct impact on the other. 

Concept Mapping Toolkit
Insitute for Human and Machine Cognition
The University of West Florida