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Title: EFFECTIVE AERODYNAMIC ROUGHNESS ESTIMATED FROM AIRBORNE LASER ALTIMETER MEASUREMENTS OF SURFACE FEATURES

Author
item DEVRIES, A - DEPT. OF WATER RESOURCES
item Kustas, William - Bill
item Ritchie, Jerry
item KLAASSEN, W - UNIVERSITY OF GRONINGEN
item MENENTI, M - UNIVERSITY LOUIS PASTEUR
item Rango, Albert
item Prueger, John

Submitted to: International Journal of Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2001
Publication Date: 7/1/2003
Citation: DEVRIES, A.C., KUSTAS, W.P., RITCHIE, J.C., KLAASSEN, W., MENENTI, M., RANGO, A., PRUEGER, J.H. 2003. EFFECTIVE AERODYNAMIC ROUGHNESS ESTIMATED FROM AIRBORNE LASER ALTIMETER MEASUREMENTS OF SURFACE FEATURES. INTERNATIONAL JOURNAL OF REMOTE SENSING. 24:1545-1558.

Interpretive Summary: Large scale estimates of the water loss or heat are important to understanding the impact that changing the land surface has on the global climate. One of the major areas of concern is the semi-arid environment because of the large areas around the world and the fragile nature of these areas. A study was conducted to determine if there are more effective methods of characterizing the surface features of the land surface needed for estimating the energy exchange between the surface and the atmosphere. We conducted a study at the Jornada Experimental Range near Las Cruces, New Mexico to compare different methods of measuring the earth's surface. The use of airborne laser to measure surface features provides a reliable and effective method for evaluating the surface. This information will help other scientists understand these methods and their application to other regional and global scale studies.

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 using logarithmic wind profiles measured at a meteorological tower or by balloon release. 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. Important land surface characteristics are the size and distribution of roughness elements (obstacles). This research evaluates the use of high resolution laser altimeter data to obtain these land surface characteristics. Data were collected at the US Department of Agriculture, Agriculture Research Service (USDA-ARS), Jornada Experimental Range in southern New Mexico, USA over a coppice dune dominated area. These dunes are covered by honey mesquite (Prosopis glandulosa Torr.) 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 dunes were calculated from these laser transects and used to compute z0. Analysis gave an average z0=4.3 cm and d0=70 cm for the three laser transects, which compares to z0=7+4cm and d0=98+48 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.