Near infrared scattering by sunlit terrestrial clouds.
Level 5 - mechanism / opinion, no new human data
Non-clinical atmospheric physics observational study (Level 5 by design analogy)
PubMed 20048895 · doi:10.1364/AO.5.000555
What was done
Absolute radiance spectra of solar radiation scattered by terrestrial clouds were measured in the 1.15 µm to 3.6 µm wavelength range as a function of cloud type, cloud altitude, and scattering angle. The angular dependence of scattering efficiency was evaluated across multiple near-infrared wavelengths.
What was found
In the 2.6 µm to 2.9 µm region where single scattering dominates due to strong absorption, scattering efficiency increased nearly tenfold as scattering angles decreased from 150° to 45°. At other wavelengths in the 1.15–3.6 µm range, scattering efficiency increased approximately threefold across the same angular span. Ice clouds demonstrated characteristic spectral minima at 1.5 µm, 2.0 µm, and 2.8 µm corresponding to bulk absorption properties; the 1.5 µm and 2.0 µm minima were absent in liquid-water clouds.
Why it matters
These empirical measurements demonstrate that near-infrared spectral radiance patterns can distinguish ice clouds from liquid-water clouds, providing a basis for optical remote sensing and radiative transfer modeling of atmospheric clouds.
Limits
The abstract does not specify sample sizes (e.g., number of clouds, observation flights, or spectrum counts), specific measurement instruments, cloud altitudes tested, or quantitative measurement uncertainties.
Cited by
- supports Long-wavelength light is absorbed and scattered by water, resulting in slight attenuation and diffuse multi-angle arrival on cloudy winter days.