Clear-Air Data

  • Good, useable data is often collected in "clear-air" conditions, i.e., in the absence of clouds and precip
  • Originally, "clear-air" echoes were called "angel", or "ghost" echoes
  • There are two possible scattering mechanisms possible:

1) Scattering from refractive index gradients on scale of l/2

  • This is often referred to as "Bragg Scattering"
  • for Bragg scattering
  • This suggests using long wavelengths to more effectively detect refractive index gradients - this is essentially what a profiler is doing, remember, the profiler wavelengths are quite large

2) Particulate scattering from insects and birds

  • Then have rayleigh scattering where
Which scattering mechanism is still somewhat of a matter of debate, though the growing consensus is that most clear-air data is scattering from insects.

So, why do you get areas of enhanced clear-air echoes that appear to be some what linear????