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08 Jan 2021
08 Jan 2021
Abstract. The aerodynamic roughness of heat, moisture and momentum of a natural surface is an important parameter in atmospheric models, as it co-determines the intensity of turbulent transfer between the atmosphere and the surface. Unfortunately this parameter is often poorly known, especially in remote areas where neither high-resolution elevation models nor eddy-covariance measurements are available. In this study we adapt a bulk drag partitioning model to estimate the aerodynamic roughness length (z0m) such that it can be applied to 1D (i.e. unidirectional) elevation profiles, typically measured by laser altimeters. We apply the model to a rough ice surface on the K-transect (western Greenland ice sheet) using UAV photogrammetry, and evaluate the modelled roughness against in situ eddy-covariance observations. We then present a method to estimate the topography at 1 m horizontal resolution using the ICESat-2 satellite laser altimeter, and demonstrate the high precision of the satellite elevation profiles against UAV photogrammetry. The currently available satellite profiles are used to map the aerodynamic roughness during different time periods along the K-transect, that is compared to an extensive dataset of in situ observations. We find a considerable spatiotemporal variability in z0m, ranging between 10−4 m for a smooth snow surface over 10−1 m for rough crevassed areas, which confirms the need to incorporate a variable aerodynamic roughness in atmospheric models over ice sheets.
Maurice van Tiggelen et al.
Status: open (until 05 Mar 2021)
Interesting work on your field work for the roughness project.
You cite our work as follows (line 192): "Fortunately, information smaller than the footprint diameter can be extracted from the ATL03 product, as shown
by Herzfeld et al. (2020)." and continue with "In the following part we describe a method to produce a 1 m resolution along-track surface height
estimation from the ATL03 raw photons signal."
In the paper cited as Herzfeld et al. (2020), we introduce the Density-Dimension Algorithm for ice surfaces, the DDA-ice, which facilitates surface-height determination at the 0.7m nominal along-tack resolution of the ATLAS iinstrumnet aboard ICESat-2 (under clear-sky atmospheric conditions). Please include reference to this capability in your manuscript. The way you have it written right now suggests that the DDa-ice retrieves something better than footprint size (70m) while your approach gets heights at 1m resolution.
The DDA-ice automatically adapts to several properties of the data (locally and the ground follower automatically adapts to surfce roughness.
In the introduction, you provide references ot previous work on surface roughness and its relationship to atmospheric processes in the boundary layer.
In the 1990s, we have conducted measurements of surface roughness on the Greenland ice sheet and written a fundamental paper on the relationship of surface roughness and melt energy, which was discussed with the last author in person - and with the first author sometime later via email.
Here is the reference:
HERZFELD, U.C., J.E. BOX, K. STEFFEN, H. MAYER, N.~CAINE (2003/2004, printed 2006), and
M.V.~LOSLEBEN, A case study on the influence of snow and ice surface roughness
on melt energy, Zeitschrift f"ur Gletscherkunde und Glazialgeologie, v. 39, p.~1-42
It would be good to see our work given due credit in this paper.
Next, I'm reading the drag context with interest.
Best regards, Ute Herzfeld and coauthors
Maurice van Tiggelen et al.
Dataset for figures Maurice van Tiggelen, Paul C. J. P. Smeets, Carleen H. Reijmer, Bert Wouters, Jakob F. Steiner, Emile J. Nieuwstraten, Walter W. Immerzeel, and Michiel R. van den Broeke https://doi.org/10.5281/zenodo.4386867
Maurice van Tiggelen et al.
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