Portable spectral profiler probe for rapid snow grain size stratigraphy

We present a portable spectral profiler probe to measure snow grain size stratigraphy in mountain snowpack at up to 5 mm vertical resolution, without the need for snow pit excavation. The probe infers grain size using near-infrared reflectance spectroscopy by inserting into the snowpack an optical package consisting of a light source and fiber optic receiver, which views the snow laterally and sends the collected reflected light to a spectrometer at the surface. The instrument can be easily dismantled and transported in a backpack, and rapidly deployed in the field. Grain size profiles from the probe, along with snow-pit contact spectroscopy and hand lens measurements were gathered and compared during winter and spring 2010 field campaigns in Colorado. Results from the probe agree to within 30% with snow-pit contact spectroscopy measurements, except when thin layers are present, which are detected at better vertical resolution by the profiler probe. The results highlight the lateral heterogeneity inherent in most mountain snowpacks, which is impractical to measure with conventional techniques. This type of measurement, along with density measurements, can greatly impact the accuracy of remote passive and active microwave retrievals.