  Wind-blown snow particles often contaminate Terrestrial Laser Scanning (TLS)
data of snow covered terrain. However, common filtering techniques fail to
filter wind-blown snow and incorrectly filter data from the true surface due to
the spatial distribution of wind-blown snow and the TLS scanning geometry. We
present FlakeOut, a filter designed specifically to filter wind-blown
snowflakes from TLS data. A key aspect of FlakeOut is a low false positive rate
of \num{2.8e-4} -- an order of magnitude lower than standard filtering
techniques -- which greatly reduces the number of true ground points that are
incorrectly removed. This low false positive rate makes FlakeOut appropriate
for applications requiring quantitative measurements of the snow surface in
light to moderate blowing snow conditions. Additionally, we provide
mathematical and software tools to efficiently estimate the false positive rate
of filters applied for the purpose of removing erroneous data points that occur
very infrequently in a dataset.
