Fresh snow, peak accumulation, and ablation-Sun Cup snow surface datasets for evaluation of geometry aerodynamic roughness code

These three datasets have been prepared to assess a computer code for the computation of the geometric-based aerodynamic roughness length z0. using the Lettau (1969; https://doi.org/10.1175/1520-0450(1969)008%3C0828:NOARPE%3E2.0.CO;2) formulation. They are at an extend of 1000 by 1000 pixels and in units of meters. They are in ASCIIGRID fomat ingestable by GIS software. 

The fresh snow surface is at a 0.001 m (1 mm) resolution and the data were collected on 2021-04-19 in Fort Collins, Colorado USA. The ablation-sun cup surface is at a 0.005 m (5 mm) resolution and the data were collected on 2017-06-13 in the headwaters of the Poudre River, near Milner Pass, Colorado USA. Both datasets were collected with a Faro Focus3D X 130 model Terrestrial lidar Scanner. The raw point cloud data were interpolated to the stated resolution using kriging with the SURFER software.

The peak accumulation dataset is at a 1 m resolution for the Niwot Saddle near Niwot Ridge, Colorado and were collected on 2010-05-20 using airborne lidar (see Harpold et al., 2014 https://doi.org/10.1002/2013WR013935 and Sexstone et al., 2022; https://doi.org/10.18172/cig.4951 for the raw data). The data were in gridded format, but linearly and then non-linearly detrended.

Methods

Two datasets (fresh snow and sun cups) were collected with a Faro Focus3D X 130 model Terrestrial lidar Scanner.
The fresh snow (FS-FC) dataset was collected during a new snowfall event on 2021-04-19 in Fort Collins Colorado with snow snowcover existing on the ground. The FS-FC raw point cloud was at a resolution finer than 1 mm.
The ablation-sun cup (SC-PH) dataset were collected when substantial sun cups were present during snowmelt on 2017-06-13 in the headwaters of the Poudre River, near Milner Pass, Colorado. The SC-PH raw point cloud was at a resolution of about 3 mm. The ablation-sun cup data were collected as three separate scans due to the nature of the surface, i.e., sun cups. The three point cloud were sewn together with Cloud Compare, an open-source software for 3D point cloud and mesh analysis.

Each of the raw point cloud (FS-FC and SC-PH) (three sewn together for SC-PH) was processed using Cloud Compare. The scans were cropped to the area of interest, ensuring that the dataset was limited to the preferred geographic region or feature under study. Any rogue points, such as noise or erroneous data points often caused by environmental, were identified and removed to enhance the accuracy and clarity of the dataset.

The cropped point cloud was interpolated using kriging in Golden Software’s Surfer program.
Each gridded dataset was detrended in the X and Y directions to reduce bias from sloping surfaces.
The original data for the third dataset (peak accumulation at Niwot Saddle, PA-NS) was already in the public domain (see Harpold et al., 2014 https://doi.org/10.1002/2013WR013935 and Sexstone et al., 2022; https://doi.org/10.18172/cig.4951 for the raw data). Those data are at a 1 m resolution. The data herein were linearly detrended, then detrended using a third order polynominal, and then linearly detrended again. The third order polynomial detrending remove the influence of the hillslope.