Abstract. Terrestrial and airborne laser scanning and structure from motion
techniques have emerged as viable methods to map snow depths. While these
systems have advanced snow hydrology, these techniques have noted
limitations in either horizontal or vertical resolution. Lidar on an
unpiloted aerial vehicle (UAV) is another potential method to observe field-
and slope-scale variations at the vertical resolutions needed to resolve
local variations in snowpack depth and to quantify snow depth when snowpacks
are shallow. This paper provides some of the earliest snow depth mapping
results on the landscape scale that were measured using lidar on a UAV. The
system, which uses modest-cost, commercially available components, was
assessed in a mixed deciduous and coniferous forest and open field for a
thin snowpack (< 20 cm). The lidar-classified point clouds had an
average of 90 and 364 points/m2 ground returns in the forest and field,
respectively. In the field, in situ and lidar mean snow depths, at 0.4 m horizontal resolution, had a mean absolute difference of 0.96 cm and a root
mean square error of 1.22 cm. At 1 m horizontal resolution, the field snow
depth confidence intervals were consistently less than 1 cm. The forest
areas had reduced performance with a mean absolute difference of 9.6 cm, a
root mean square error of 10.5 cm, and an average one-sided confidence
interval of 3.5 cm. Although the mean lidar snow depths were only 10.3 cm in
the field and 6.0 cm in the forest, a pairwise Steel–Dwass test showed that
snow depths were significantly different between the coniferous forest, the
deciduous forest, and the field land covers (p < 0.0001). Snow
depths were shallower, and snow depth confidence intervals were higher in
areas with steep slopes. Results of this study suggest that performance
depends on both the point cloud density, which can be increased or decreased
by modifying the flight plan over different vegetation types, and the grid
cell variability that depends on site surface conditions.
