Scintillometer-Based Estimates of Sensible Heat Flux Using Lidar-Derived Surface Roughness

Abstract

The estimation of sensible heat flux, H, using large aperture scintillometer (LAS) under varying surface heterogeneity conditions was investigated. Surface roughness features characterized by variable topography and vegetation height were represented using data derived from the highly accurate light detection and range (lidar) techniques as well as from traditional vegetation survey and topographic map methods. The study was conducted at the Cibola National Wildlife Refuge, Southern California, over a riparian zone covered with natural vegetation dominated by tamarisk trees interspersed with bare soil in a region characterized by arid to semiarid climatic conditions. Estimates of H were obtained using different representations of surface roughness features derived from both traditional and lidar methods to estimate LAS beam height [z(u)] at each increment u along its path, vegetation height (h c ), displacement height (d), and roughness length (z 0 ) combined with the LAS weighing function, W(u), along the path. The effect of the LAS 3D footprint was examined to account for the contribution from the individual patches in the upwind direction, hence on the estimates of H. The results showed better agreement between LAS and Bowen ratio sensible heat fluxes when lidar-derived surface roughness was used, especially when considering the LAS 3D footprint effects. It was also found that, under certain conditions, the LAS path weighted h c and d obtained using the LAS weighting function W(u) is a good approximation of the 3D weighted footprint values.

Estimation of turbulent sensible heat and momentum fluxes over a heterogeneous urban area using a large aperture scintillometer

“…W (r) is the LAS weighting function, which has a mathematical bell-shape curve with a maximum value in the middle of the optical path (e.g., Chehbouni et al, 2000;Meijninger and De Bruin, 2000;Timmermans et al, 2009;Geli et al, 2012):…”

“…When calculating turbulent sensible heat flux using the scintillation method, previous studies have used various nondimensional similarity functions (e.g., Meijninger and De Bruin, 2000;Lagouarde et al, 2006;Evans et al, 2012;Geli et al, 2012). Along with the surface-layer structure function suggested by Andreas (1988), the function by De Bruin et al (1993) has been popularly used, which is given for unstable conditions (z/L < 0) as follows: Foken and Kretschmer (1990) and Thiermann and Grassl (1992) proposed different functional forms as follows:…”

Uso de datos satelitales MODIS y balance de energía para estimar la evapotranspiración

“…La descripción de T * y u * , así como una descripción detallada de la teoría de scintilometría puede revisarse en Solignac et al (2009), Zeweldi et al (2010, Samain et al (2012); Geli et al (2012) y Liu et al (2013). Para determinar el valor del flujo de calor latente (LE) se utilizó la ecuación de balance de energía (ecuación 2).…”

“…The description of T * and u * , as well as a detailed description of the scintilometry theory can be reviewed in Solignac et al (2009);Zeweldi et al (2010); Samain et al (2012); Geli et al (2012) and Liu et al (2013). The energy balance equation (equation 2) was used to determine the value of the latent heat flux (LE).…”

LAS-Derived Determination of Surface-Layer Sensible Heat Flux over a Heterogeneous Urban Area

“…LAS 가중 함수는 광학 경로의 중심에 서 최대값을 가지는 종형(bell-shaped) 함수 형태를 가 진다 (Frehlich and Ochs, 1990;Geli et al, 2012) (이 후부터 은 간단히 으로 쓰기로 한다.). 대기 굴절률의 섭동은 난류에 의한 기온과 습도의 섭동에 기인하므로, 측정되는 은 온도 구조 매개 변수( ), 습도 구조 매개변수( ), 그리고 이들의 비선형 상호작용에 의한 구조 매개변수( )로 표현 할 수 있으며, 기압 섭동에 의한 효과는 무시할 수 있 다 (Hill et al, 1980).…”