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United States Department of Agriculture

Agricultural Research Service

Title: Effective Aerodynamic Roughness Estimated from Airborne Laser Altimeter Measurements of Surface Features

Authors
item DE Vries, Arjen - UNIV. GRONINGEN, NL
item Ritchie, Jerry
item Klaassen, Wim - UNIV. GRONINGEN, NL
item Menenti, Massimo - WINAND STARING CENTER, NL
item Kustas, William
item Rango, Albert
item Prueger, John

Submitted to: International Journal of Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 2, 1998
Publication Date: N/A

Interpretive Summary: It would be an advantage to use measurements of land surface characteristics instead of wind flow characteristics to estimate the effective aerodynamic roughness for large areas since wind flow data are often not available. A method is presented to derive aerodynamic roughness of complex landscape areas from laser altimeter measurements of land surface roughness. Estimates of aerodynamic roughness made with the method were comparable to estimates made with wind profile data. These results show that estimations of aerodynamic roughness of a complex terrain are possible using simple terrain features computed from laser altimeter data or other topographic data. This method opens the possibility of estimating aerodynamic roughness over large areas where wind flow characteristics are not available. Such estimates of aerodynamic roughness are necessary in order to accurately estimate water loss by evapotranspiration from the landscape.

Technical Abstract: Aerodynamic roughness length (z0) and displacement height (d0) are important surface parameters for estimating surface fluxes in numerical models. These parameters are generally determined from wind flow characteristics measured at meteorological towers. It would be an advantage to use measurements of land surface characteristics instead of wind flow characteristics to estimate the z0 and d0 for large areas. The current research evaluates the use of laser altimeter data to obtain these land surface characteristics. Data were collected at the USDA ARS Jornada Experimental Range over a coppice dune covered by honey mesquite with flat and mostly bare interdunal areas. For this analysis, three 450 m laser transects with a 2 cm measurement interval were used. The distribution and size of the dunes was calculated from these laser transects and used to compute z0. Analysis gave an average z0 = 4.7 cm and d0 = 70 cm for the three laser transects, which compares to z0 = 7 cm and d0 = 98 cm calculated from wind profile data measured at a 10 m tower near the laser transects. These results show that the estimation of z0 and d0 for a complex terrain is possible using simple land surface features computed from high resolution laser altimeter data.

Last Modified: 9/21/2014
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