Re: Visibility and wavelength

[John Brownlee <jonnie@chronic.lpl.arizona.edu>]

Hi Rick,

	It's a question of scattering, for most particle sizes. Depending
on the size distribution of particles, different wavelength regimes will be
dominated by scattering while others won't. The key would be to find a
region of the spectrum where A. scattering is minimal, and B. water
absorbtion is also minimal. The Air Force's declassified millimeter wave
imager is used in exactly this way for seeing in adverse weather; the
scattering by water droplets is minimal and the absorbtion is too. So, the
imager can "see" in a manner which is akin to regular optical vision
(making it easier on the pilot) and cut through zero-zero visibility.
	I am assuming a lot here about the particle size, and whether the
scattering law is geometric, Mie or what-have-you. This is a topic of
current research for me (it piqued my interest), so if anyone out there in
TV-land has any leads or references on long wavelength attenuation by
seawater, I'd love to hear 'em. This may be impossible, but the technology
to image in these different wavelength regimes has only existed for a few
years really. This is the sort of thing which was probably considered
before, but maybe wasn't possible due to contraints on detectors. It is
also entirely possible that this sort of study has never been done, and
some poor bastard (not unlike myself) will wind up measuring the
attenuation function personally.
	Let you know what I find,

							John

John Brownlee
Lunar and Planetary Lab
University of Arizona
jonnie @ lpl . arizona . edu