Effects of Wavelength
on the ability to detect an object

The factors which govern the choice of a wavelength to be used in a particular radar include its sensitivity, which is its ability to detect weak targets at long range, the radar's ability to resolve small features, the types of targets to be studied, and the effects of the intervening atmosphere on the transmitted energy. Other factors also must be considered such as the radar's size, weight and cost. Most weather radars have wavelengths that range between 0.8 centimeters (cm) and 10.0 cm. Generally short wavelengths mean smaller and less expensive equipment.

Short wavelength radars are more effective in detecting small particles such as cloud droplets and drizzle drops. However, the short wavelength electromagnetic energy is also partially absorbed by these same particles (a process called attenuation). This makes it difficult to accurately measure the intensity of back-scattered energy for more distant targets that lie beyond the range of closer targets.

The main advantage of using longer wavelengths is that absorption by the intervening particles is drastically reduced. This means that a distant thunderstorm behind a closer thunderstorm will appear on the radar screen with its proper intensity. Since detecting severe weather is one of the most important missions of operational radars, such as the National Weather Service's WSR-88D Doppler radars, these radars typically use a long wavelength.

signal scattering
Terms for using data resources. CD-ROM available.
Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.

ray paths