  Snow is a highly complex medium composed of ice crystals of various shapes
and sizes. Knowledge of its intrinsic optical properties such as the scattering
and absorption coefficient is tantamount to radiative transfer models in
climate research. The absorption coefficient, in particular, allows us to
access information about light-absorbing particles contained in the snow. In
contrast to snow's apparent properties like the albedo, measuring the intrinsic
properties is challenging. Here, we present a simple apparatus that can measure
bulk optical properties of snow using readily available components and a
smartphone camera, and a robust diffuse-optical framework for data analysis. We
demonstrate the instrument both on scattering phantoms with known scattering
and absorption coefficient as well as in the field. Its low cost, simplicity
and portability uniquely qualify this setup for large-scale field work,
undergraduate education and citizen science.
