scholarly journals Sensitivity of BRDF, NDVI and Wind Speed to the Aerodynamic Roughness Length over Sparse Tamarix in the Downstream Heihe River Basin

2018 ◽  
Vol 10 (2) ◽  
pp. 56 ◽  
Author(s):  
Qiang Xing ◽  
Bingfang Wu ◽  
Nana Yan ◽  
Mingzhao Yu ◽  
Weiwei Zhu
Keyword(s):  
Wind Speed ◽  
River Basin ◽  
Roughness Length ◽  
Heihe River Basin ◽  
Heihe River ◽  
Aerodynamic Roughness Length ◽  
Aerodynamic Roughness

scholarly journals Aerodynamic roughness length estimation from very high-resolution imaging LIDAR observations over the Heihe basin in China

2010 ◽  
Vol 7 (3) ◽  
pp. 3397-3421 ◽  
Author(s):  
J. Colin ◽  
R. Faivre ◽  
M. Menenti
Keyword(s):  
Remote Sensing ◽  
Land Cover ◽  
River Basin ◽  
Surface Density ◽  
Roughness Length ◽  
Heihe River ◽  
Surface Model ◽  
Aerodynamic Roughness Length ◽  
Passive Remote Sensing ◽  
Aerodynamic Roughness

Abstract. Roughness length of land surfaces is an essential variable for the parameterisation of momentum and heat exchanges. The growing interest about the estimation of the surface turbulent flux parameterisation from passive remote sensing lead to an increasing development of models, and the common use of simple semi-empirical formulations to estimate surface roughness. Over complex surface land cover, these approaches would benefit from the combined use of passive remote sensing and land surface structure measurements from Light Detection And Ranging (LIDAR) techniques. Following early studies based on LIDAR profile data, this paper explores the use of imaging LIDAR measurements for the estimation of the aerodynamic roughness length over a heterogeneous landscape of the Heihe river basin, a typical inland river basin in the northwest of China. LIDAR points were used to extract a Digital Surface Model (DSM) and a Digital Elevation Model (DEM) from a single flight pass over an irrigated area covered by field crops, small trees arrays and tree hedges, with a ground resolution of 1 m and a total surface of 7.2 km2. As a first step, the DSM is used to estimate the plan surface density and frontal surface density of obstacles to wind flow and compute a displacement height and roughness length following strictly geometrical approaches. In a second step, both the DSM and DEM are introduced in a Computational Fluid Dynamics model (CFD) to calculate wind fields from the surface to the top of the Planetary Boundary Layer (PBL), and invert wind profiles for each calculation grid and compute a roughness length. Examples of the use of these three approaches are presented for various wind direction together with a cross-comparison of results on heterogeneous land cover and complex roughness element structures.

scholarly journals Aerodynamic roughness length estimation from very high-resolution imaging LIDAR observations over the Heihe basin in China

2010 ◽  
Vol 14 (12) ◽  
pp. 2661-2669 ◽  
Author(s):  
J. Colin ◽  
R. Faivre
Keyword(s):  
Remote Sensing ◽  
Surface Roughness ◽  
Land Cover ◽  
River Basin ◽  
Land Surface ◽  
Surface Density ◽  
Roughness Length ◽  
Aerodynamic Roughness Length ◽  
Passive Remote Sensing ◽  
Aerodynamic Roughness

Abstract. Roughness length of land surfaces is an essential variable for the parameterisation of momentum and heat exchanges. The growing interest in the estimation of the surface turbulent flux parameterisation from passive remote sensing leads to an increasing development of models, and the common use of simple semi-empirical formulations to estimate surface roughness. Over complex surface land cover, these approaches would benefit from the combined use of passive remote sensing and land surface structure measurements from Light Detection And Ranging (LIDAR) techniques. Following early studies based on LIDAR profile data, this paper explores the use of imaging LIDAR measurements for the estimation of the aerodynamic roughness length over a heterogeneous landscape of the Heihe river basin, a typical inland river basin in the northwest of China. The point cloud obtained from multiple flight passes over an irrigated farmland area were used to separate the land surface topography and the vegetation canopy into a Digital Elevation Model (DEM) and a Digital Surface Model (DSM) respectively. These two models were then incorporated in two approaches: (i) a strictly geometrical approach based on the calculation of the plan surface density and the frontal surface density to derive a geometrical surface roughness; (ii) a more aerodynamic approach where both the DEM and DSM are introduced in a Computational Fluid Dynamics model (CFD). The inversion of the resulting 3-D wind field leads to a fine representation of the aerodynamic surface roughness. Examples of the use of these three approaches are presented for various wind directions together with a cross-comparison of results on heterogeneous land cover and complex roughness element structures.

Spatiotemporal Variability of Potential Evaporation in Heihe River Basin Influenced by Irrigation

2020 ◽  
Author(s):  
Congying Han
Keyword(s):  
Wind Speed ◽  
Relative Humidity ◽  
Spatial Pattern ◽  
River Basin ◽  
Meteorological Factors ◽  
Heihe River Basin ◽  
Spatiotemporal Variability ◽  
Maximum Temperature ◽  
Heihe River ◽  
Potential Evaporation

<p><strong>Spatiotemporal Variability of Potential Evaporation in Heihe River Basin Influenced by Irrigation </strong></p><p>Congying Han<sup>1,2</sup>, Baozhong Zhang<sup>1,2</sup>, Songjun Han<sup>1,2</sup></p><p><sup>1</sup> State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100038, China.</p><p><sup>2</sup> National Center of Efficient Irrigation Engineering and Technology Research-Beijing, Beijing 100048, China.</p><p>Corresponding author: Baozhong Zhang ([email protected])</p><p><strong>Abstract: </strong>Potential evaporation is a key factor in crop water requirement estimation and agricultural water resource planning. The spatial pattern and temporal changes of potential evaporation calculated by Penman equation (E<sub>Pen</sub>) (1970-2017) in Heihe River Basin (HRB), Northwest China were evaluated by using data from 10 meteorological stations, with a serious consideration of the influences of irrigation development. Results indicated that the spatial pattern of annual E<sub>Pen</sub> in HRB was significantly different, among which the E<sub>Pen</sub> of agricultural sites (average between 1154 mm and 1333 mm) was significantly higher than that of natural sites (average between 794 mm and 899 mm). Besides, the coefficient of spatial variation of the aerodynamic term (E<sub>aero</sub>) was 0.4, while that of the radiation term (E<sub>rad</sub>) was 0.09. The agricultural irrigation water withdrawal increased annually before 2000, but decreased significantly after 2000 which was influenced by the agricultural development and the water policy. Coincidentally, the annual variation of E<sub>pen</sub> in agricultural sites decreased at -40 mm/decade in 1970-2000 but increased at 60 mm/decade in 2001-2017, while that in natural sites with little influence of irrigation, only decreased at -0.5mm/decade in 1970-2000 but increased at 11 mm/decade in 2001-2017. So it was obvious that irrigation influenced E<sub>pen </sub>significantly and the change of E<sub>pen</sub> was mainly caused by the aerodynamic term. The analysis of the main meteorological factors that affect E<sub>pen</sub> showed that wind speed had the greatest impact on E<sub>pen</sub> of agricultural sites, followed by relative humidity and average temperature, while the meteorological factors that had the greatest impact on E<sub>pen</sub> of natural sites were maximum temperature, followed by wind speed and relative humidity.</p>

Wind Profiles in Tropical Cyclone Stratiform Rainbands over Land

2013 ◽  
Vol 141 (11) ◽  
pp. 3933-3949 ◽  
Author(s):  
Shaunna L. Donaher ◽  
Bruce A. Albrecht ◽  
Ming Fang ◽  
William Brown
Keyword(s):  
Wind Speed ◽  
Tropical Cyclone ◽  
Roughness Length ◽  
Horizontal Wind ◽  
Ratio Method ◽  
Aerodynamic Roughness Length ◽  
Wind Structure ◽  
Aerodynamic Roughness ◽  
Wind Profiles ◽  
Radial Outflow

Abstract Observations of 14 stratiform periods in outer tropical cyclone rainbands are used to evaluate wind structure using a velocity–azimuth display (VAD) technique applied to KAMX (Miami) Weather Surveillance Radar-1988 Doppler (WSR-88D) data. These 14 cases occurred over land in southern Florida from Tropical Storm Fay and Hurricanes Gustav and Ike during 2008. Profiles show a maximum horizontal wind speed between 1000 and 1500 m in height, with occasional evidence of a secondary horizontal wind maximum near 3500–5000 m. Storm-relative wind components are calculated, and radial wind profiles show a mean transition from radial inflow at low levels to radial outflow around 2500–3000-m altitude. The radial inflow maximum is around 500 m, while maximum outflow is more variable. These profile characteristics are consistent with previous wind observations in rainbands over land and water. Changes in wind structure within one 4-h period are examined, with changes seen linked to the environmental influence on the rainband. All rainbands show a logarithmic wind speed decrease below 200 m. This layer is studied in detail using a log-wind fit method and a ratio method to calculate aerodynamic roughness length. Much lower ratios of surface to higher-level winds were found than in previous studies over open oceans. Another significant finding of this work is the lack of a constant aerodynamic roughness length despite similar storm wind profiles. These results are useful in broadening the understanding of low-level impacts of landfalling rainbands far from the storm center.

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