Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Estimation of Scale Dependent Effective Roughness Lengths for Momentum Withlaser and Radar Altimeter Data

item Massimo, Menenti - DLO-WINAND STARING CTR
item Ritchie, Jerry
item Parry, Robert
item Pachepsky, Yakov - DUKE UNIVERSITY
item Gimenez, Daniel
item Leguizamon, Simon - DLO-WINAND STARING CENTRE

Submitted to: John Wiley Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 3, 1996
Publication Date: N/A

Interpretive Summary: Landscape roughness affects wind movement that in turn affects aerodynamic roughness. Estimates of aerodynamic roughness are key to understanding heat and water loss from the landscape at local and regional scales. This paper discusses techniques for using airborne laser measurements of landscape roughness to estimate aerodynamic roughness. Estimates of aerodynamic roughness from the airborne laser data were similar to estimates made using classical techniques. Different mathematical techniques (fractal, fourier transforms, wavelets transforms) gave consistent estimates of landscape roughness scales. Using airborne laser measurements of the landscape roughness and the mathematical procedures described, local and regional estimates of aerodynamic roughness can be made effectively and efficiently. These estimates will allow water management specialists (USDA-NRCS, USGS, BLM, and COE) to better understand water and heat loss from the landscape thus, allowing them to develop better management plans to conserve and allocate water especially in semiarid environments. Better conservation and allocation of limited water supplies benefit agricultural and public users.

Technical Abstract: The geometry of the land surface controls momentum transport at different heights over a composite landscape at different horizontal length scales. With increasing reference height in the surface layer, the effect of the interspersed lower vegetation combines with the effect of larger obstacles (tress), and the topography. This paper discusses the determination of aerodynamic roughness lengths at various length scales using high resolution airborne laser measurements and low resolution radar altimeter observations. To estimate length scales of composite landscapes, different statistics (autocorrelation function, power spectrum, different fractal techniques and wavelet transform) of the laser measurements have been used. The airborne laser measurements have been used to estimate the local aerodynamic roughness length (interspersed vegetation) and subsequently to estimate an effective roughness length by including the geometry of shrubs, trees, and topography. Values of the local roughness agreed with wind profile measurements. Fractal techniques provided consistent estimates of the shorter, a-periodic length scales. Fourier (power spectrums) and wavelets transform gave consistent values of the topography wavelengths.

Last Modified: 4/16/2014
Footer Content Back to Top of Page