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Exploring Snow Albedo Through Spectroscopic Analysis
Introduction/Application
During the summer months, we are often cautioned to prevent the harmful effects of overexposure to UV rays by wearing sunscreen to protect our skin, hats to protect our head, neck, and scalp, and sunglasses to protect our eyes. These precautions do not usually carry over to winter, where the greater concern is keeping our bodies warm and retaining heat in the much colder weather. Despite this, a similar damaging condition can occur during both seasons: photokeratitis, or sunburned eyes. While this is caused by longer daytimes during the summer, the condition can be caused during the winter by prolonged exposure to light from highly reflective snow. This reflective property is quantified as albedo, which is specifically a ratio of irradiance to radiosity or radiant flux. This term has a range of 0 to 1, with 0 being a surface that absorbs all incident radiation and 1 being a surface that reflects all incident radiation. For reference, Earth as a whole has an average albedo measurement around 0.3, while the Moon has an average albedo of 0.12. The albedo of snow can be highly variable, with values as high as 0.9 for fresh snow and as low as 0.2 for dirty snow. This value, along with peaks in the measured spectra, can be used to determine the age of snow, if it is melting, and if other particles and molecules are present. Such results are particularly useful when studying polar ice caps for effects from climate change.
This experiment aims to measure the albedo of snow utilizing our spectrometers. To obtain this value, we measured irradiance and radiant flux of the sample, which were used to calculate albedo. For comparison, we also performed pure reflectance measurements to see how closely they resembled the final albedo values. Because the typical albedo measurements cover a wavelength range of 300-3000 nm, we utilized both a UV/VIS and NIR spectrometer for these measurements. All snow measurements were performed just outside our office a day after moderate snowfall.