Aerodynamic roughness length of crevassed tidewater glaciers from UAV mapping
The aerodynamic roughness length ( z 0 ) is an important parameter in the bulk approach for calculating turbulent fluxes and their contribution to ice melt. However, z 0 estimates for heavily crevassed tidewater glaciers are rare or only generalised. This study used uncrewed aerial vehicles (UAVs) t...
| Published in: | The Cryosphere |
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| Main Authors: | , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Copernicus Publications
2021
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/tc-15-5513-2021 https://doaj.org/article/65832a12c70149afbdae9a0ce2c77938 |
| Summary: | The aerodynamic roughness length ( z 0 ) is an important parameter in the bulk approach for calculating turbulent fluxes and their contribution to ice melt. However, z 0 estimates for heavily crevassed tidewater glaciers are rare or only generalised. This study used uncrewed aerial vehicles (UAVs) to map inaccessible tidewater glacier front areas. The high-resolution images were utilised in a structure-from-motion photogrammetry approach to build digital elevation models (DEMs). These DEMs were applied to five models (split across transect and raster methods) to estimate z 0 values of the mapped area. The results point out that the range of z 0 values across a crevassed glacier is large, by up to 3 orders of magnitude. The division of the mapped area into sub-grids (50 m × 50 m ), each producing one z 0 value, accounts for the high spatial variability in z 0 across the glacier. The z 0 estimates from the transect method are in general greater (up to 1 order of magnitude) than the raster method estimates. Furthermore, wind direction (values parallel to the ice flow direction are greater than perpendicular values) and the chosen sub-grid size turned out to have a large impact on the z 0 values, again presenting a range of up to 1 order of magnitude each. On average, z 0 values between 0.08 and 0.88 m for a down-glacier wind direction were found. The UAV approach proved to be an ideal tool to provide distributed z 0 estimates of crevassed glaciers, which can be incorporated by models to improve the prediction of turbulent heat fluxes and ice melt rates. |
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