Parameterization of Urban Sensible Heat Flux from Remotely Sensed Surface Temperature: Effects of Surface Structure

Jinxin Yang,Qian Shi,Xiaoying Ouyang,Massimo Menenti,Zhifeng Wu,E Scott Krayenhoff

doi:10.3390/rs11111347

Abstract

Sensible heat exchange has important consequences for urban meteorology and related applications. Directional radiometric surface temperatures of urban canopies observed by remote sensing platforms have the potential to inform estimations of urban sensible heat flux. An imaging radiometer viewing the surface from nadir cannot capture the complete urban surface temperature, which is defined as the mean surface temperature over all urban facets in three dimensions, which includes building wall surface temperatures and requires an estimation of urban sensible heat flux. In this study, a numerical microclimate model, Temperatures of Urban Facets in 3-D (TUF-3D), was used to model sensible heat flux as well as radiometric and complete surface temperatures. Model data were applied to parameterize an effective resistance for the calculation of urban sensible heat flux from the radiometric (nadir view) surface temperature. The results showed that sensible heat flux was overestimated during daytime when the radiometric surface temperature was used without the effective resistance that accounts for the impact of wall surface temperature on heat flux. Parameterization of this additional resistance enabled reasonably accurate estimates of urban sensible heat flux from the radiometric surface temperature.

Highlights

Urban surface energy balance strongly modulates fair weather urban climates [1]
Rh, rh + rr, and rr were calculated with Equations (5) and (6) using the data generated with the Temperatures of Urban Facets in 3-D (TUF-3D) numerical experiments when λp varied from 0.05 to 0.60 and height to length (H/L) from 0.5 to 6
Direct predictions of urban sensible heat flux based on thermal remote sensing are still limited because of complications related to urban geometry

Summary

Introduction

Urban surface energy balance strongly modulates fair weather urban climates [1]. The replacement of soil or vegetation by impervious surfaces in urban areas reduces the potential for mitigation of ambient temperature through evaporation and transpiration [2,3,4]. The absorbed radiative energy is largely dissipated as sensible heat flux, warming the atmosphere. Turbulent heat exchange in urban areas is a major component of heat and mass transfer from the urban canopy to the atmospheric boundary layer, and sensible heat flux is a major component of turbulent exchange. Turbulent heat exchange in urban areas can be modeled by microclimate or computational fluid dynamics [5] numerical simulation models [6,7,8,9,10] or estimated by the bulk transfer approach [11,12,13]. The bulk heat transfer approach assumes the surface to be homogeneous and horizontal, with sensible heat flux being proportional to the surface–air temperature difference divided by aerodynamic resistance [17]

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