Researchers used the advanced Rotating Shadowband Spectrometer (aRSS) located at ARM’s Southern Great Plains (SGP) site in Oklahoma, to retrieve the mean and variance of the photon path length distribution in two spectral bands. Measurements from previous instruments have been used to retrieve the mean photon path length in the oxygen A-band (763 nm). Measurements from the aRSS, which has triple the resolution of previous instruments, allowed the first retrievals of the statistics of the path length distribution, and hence the variance, in a water vapor band (820 nm). Because the scattering properties of cloud particles vary slowly with wavelength in this region of the solar spectrum, researchers can assume that they are the same at both these wavelengths and therefore use the pair of measurements to draw conclusions about the scattering properties of the atmosphere. To read the full story, see the Sample Results of ARM Research Highlight.