An approach to deriving roughness length and zero-plane displacement height from satellite data, prototyped with BOREAS data

Abstract Global climate models typically use relatively crude estimates of roughness length, often based on constant values for land cover category. However, large variations may exist within any of the vegetation categories. Global large-scale estimates of roughness length, such as required by climate models, cannot rely on field experiments for practical reasons and must, therefore, be derived from satellite observations. This paper develops a satellite retrieval method for the roughness parameters, momentum roughness length, zo, and displacement height, d. The formulas, based on the observational data of Raupach [Raupach, M.R., 1992. Bound.-Layer Meteor. 60, 375–395; Raupach, M.R., 1994. Bound.-Layer Meteor. 71, 211–216] and Lindroth [Lindroth, A., 1993. Bound.-Layer Meteor. 66, 265–272], are applicable to most types of vegetation. Raupach relates the momentum roughness length and zero-plane displacement height to the frontal area index, λ, and to the height of the vegetation, h. The frontal area index is related to the shape of an average tree or plant crown and to the average density of the canopy elements. The crown shape factor includes the aspect (height-to-width) ratio of the crown and the geometric shape of the crown. Lindroth relates the momentum roughness length to the leaf area index (LAI) and to the height of the trees. The functional form of zo/h is peaked in both frontal area index, with the maximum occurring at λ=0.152, and average plant LAI (Lp), with the maximum occurring at Lp=0.878. As λ and Lp increase, d/h also increases and approaches an upper limit asymptotically at high values of λ and Lp. As the vegetation height is difficult to obtain from present satellite data, retrievals are restricted to fractional values (i.e. zo/h and d/h) for global application. This retrieval then requires data for the crown aspect ratio, the canopy density (fractional overstory canopy cover) and the LAI. Data from BOREAS (BOReal Ecosystem Atmosphere Study) are used to illustrate this satellite retrieval method.

[1]  J. Kondo,et al.  Numerical studies on the two-dimensional flow in horizontally homogeneous canopy layers , 1976 .

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

[3]  Lisa J. Graumlich,et al.  Interactive Canopies for a Climate Model , 1998 .

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

[5]  K. J. Schaudt,et al.  A New Method for Estimating Roughness Parameters and Evaluating the Quality of Observations , 1998 .

[6]  W. Massman,et al.  AN ANALYTICAL ONE-DIMENSIONAL MODEL OF MOMENTUM TRANSFER BY VEGETATION OF ARBITRARY STRUCTURE , 1997 .

[7]  Andrew J. Pitman,et al.  Assessing the Sensitivity of a Land-Surface Scheme to the Parameter Values Using a Single Column Model , 1994 .

[8]  J. Faundeen,et al.  The 1 km AVHRR global land data set: first stages in implementation , 1994 .

[9]  Ranga B. Myneni,et al.  Estimation of global leaf area index and absorbed par using radiative transfer models , 1997, IEEE Trans. Geosci. Remote. Sens..

[10]  Ruth S. DeFries,et al.  Subpixel forest cover in central Africa from multisensor, multitemporal data , 1997 .

[11]  D. Randall,et al.  A Revised Land Surface Parameterization (SiB2) for Atmospheric GCMS. Part I: Model Formulation , 1996 .

[12]  Ann Henderson-Sellers,et al.  Biosphere-atmosphere transfer scheme(BATS) version 1e as coupled to the NCAR community climate model , 1993 .

[13]  R. Dickinson.  Land Surface Processes and Climate—Surface Albedos and Energy Balance , 1983 .

[14]  Gregory S. Biging,et al.  Stochastic models for conifer tree crown profiles , 1997 .

[15]  Michael R. Raupach,et al.  Simplified expressions for vegetation roughness length and zero-plane displacement as functions of canopy height and area index , 1994 .

[16]  Z.‐L. Yang,et al.  Mapping surface‐cover parameters using aggregation rules and remotely sensed cover classes , 1997 .

[17]  R. DeFries,et al.  Derivation and Evaluation of Global 1-km Fractional Vegetation Cover Data for Land Modeling , 2000 .

[18]  G. Stanhill,et al.  Some results of helicopter measurements of the albedo of different land surfaces , 1970 .

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

[20]  Douglas A. Maguire,et al.  The relationship between gross crown dimensions and sapwood area at crown base in Douglas-fir , 1989 .

[21]  A. Lindroth.  Aerodynamic and canopy resistance of short-rotation forest in relation to leaf area index and climate , 1993 .

[22]  R. Shaw,et al.  Aerodynamic roughness of a plant canopy: A numerical experiment , 1982 .