Estimation of effective aerodynamic roughness of Walnut Gulch watershed with laser altimeter measurements

A new method to estimate the effective aerodynamic roughness of a complex landscape is presented. High-resolution elevation profiles measured with an airborne laser altimeter have been used to compute geometrical parameters of three landscape elements of the Walnut Gulch experimental watershed, Arizona. Mean crop height, its standard deviation, and the frequency distribution (as a function of penetration depth) of plant elements hit by the laser beam have been calculated for short segments (1 m) measured over intervening grass between shrubs. Longer segments have been applied to obtain the mean height and spacing of taller shrubs and trees. Finally, laser profiles covering the entire watershed gave the mean amplitude and wavelength of hillocks and ridges. The aerodynamic roughness length of the intervening grass is estimated using the ratio of standard deviation to vegetation height, corrected for instrument noise, times mean height. An effective roughness length which parameterizes the total stress due to grass and taller shrubs and trees is calculated first. Finally, a watershed-scale effective roughness length is calculated combining the amplitude and wavelength of hillocks and ridges with the roughness length obtained in the previous step.

[1]  Jerry C. Ritchie,et al.  Comparison of laser and field measurements of vegetation height and canopy cover , 1994 .

[2]  I. Seginer.  Aerodynamic roughness of vegetated surfaces , 1974 .

[3]  G. L. Barker,et al.  Canopy Temperature Response to Water Stress under Partial Canopy , 1985 .

[4]  M. Raupach.  Drag and drag partition on rough surfaces , 1992 .

[5]  J. Garratt.  The Atmospheric Boundary Layer , 1992 .

[6]  W. B. Tucker,et al.  Classification and variation of sea ice ridging in the western Arctic basin , 1974 .

[7]  Jacob Davidian,et al.  Free-surface instability correlations, and Roughness-concentration effects on flow over hydrodynamically rough surfaces , 1966 .

[8]  R. Ketchumjr,et al.  Airborne laser profiling of the arctic pack ice , 1971 .

[9]  B. Choudhury,et al.  Estimate of the aerodynamic roughness parameters over an incomplete canopy cover of cotton , 1989 .

[10]  S. Arya,et al.  A drag partition theory for determining the large-scale roughness parameter and wind stress on the Arctic pack ice , 1975 .

[11]  J. K Marshall,et al.  Drag measurements in roughness arrays of varying density and distribution , 1971 .

[12]  R. Nelson,et al.  Determining forest canopy characteristics using airborne laser data , 1984 .

[13]  J. Wieringa.  Roughness‐dependent geographical interpolation of surface wind speed averages , 1986 .

[14]  Jerry C. Ritchie,et al.  Airborne Laser Measurements of the Surface Topography of Simulated Concentrated Flow Gullies , 1989 .

[15]  A.F.G. Jacobs.  Flow around a line obstacle , 1983 .

[16]  E. O'Loughlin,et al.  Flow Phenomena Near Rough Boundaries , 1969 .

[17]  Note on the Aerodynamic Roughness Length for Complex Terrain , 1978 .

[18]  E. F. Bradley,et al.  A wind tunnel study of turbulent flow over a two-dimensional ridge , 1990 .

[19]  E. Inoue,et al.  On the Turbulent Structure of Airflow within , 1963 .

[20]  P. J. Mason,et al.  On the parameterization of drag over small-scale topography in neutrally-stratified boundary-layer flow , 1989 .

[21]  Hans A. Panofsky,et al.  The geostrophic drag coefficient and the ‘effective’ roughness length , 1972 .

[22]  John L. Monteith,et al.  Vegetation and the atmosphere , 1975 .

[23]  Thomas J. Jackson,et al.  An Interdisciplinary Field Study of the Energy and Water Fluxes in the Atmosphere–Biosphere System over Semiarid Rangelands: Description and Some Preliminary Results , 1991 .

[24]  H. Lettau.  Note on Aerodynamic Roughness-Parameter Estimation on the Basis of Roughness-Element Description , 1969 .

[25]  Albert A. M. Holtslag,et al.  Flux Parameterization over Land Surfaces for Atmospheric Models , 1991 .

[26]  William P. Kustas,et al.  Aerodynamic parameters for a sparsely roughened surface composed of small cotton plants and ridged soil , 1990 .

[27]  William P. Kustas,et al.  Local energy flux estimates for unstable conditions using variance data in semiarid rangelands , 1994 .

[28]  E. F. Bradley,et al.  Drag due to regular arrays of roughness elements of varying geometry , 1973 .

[29]  W. Kustas,et al.  Wind profile constants in a neutral atmospheric boundary layer over complex terrain , 1986 .

[30]  Jerry L. Hatfield,et al.  Aerodynamic properties of partial canopies , 1989 .