Rapid methods to estimate sky‐view factors applied to urban areas

A common parameter used to characterize the geometry of urban canyons is the sky-view factor (ψs). Here, two simple alternatives are presented that can be used both objectively and rapidly to estimate ψs. The first method uses a Nikon CoolPix 950 digital camera fitted with a Nikon FC-E8 fisheye lens. The second method involves a LI-COR LAI-2000 Plant Canopy Analyzer to measure automatically diffuse non-interceptance (DIFN) light using a fisheye optical sensor. Through a series of intercomparisons for urban canyons of known geometry, the digital camera is shown to provide accurate estimates of ψs. The LAI-2000 also performs well, although it tends to over-estimate ψs (for the conditions considered here, the mean absolute error is 0.04), and has a more restricted set of sky conditions under which it performs well (ideally, uniform overcast skies). For both methods, data collection and post-processing is rapid, and storage of data is straightforward. Thus, mobile data collection is possible which allows detailed information on the spatial variability of ψs in urban areas to be determined. An example of such an application for a small US city, Bloomington, IN, is presented. Copyright © 2001 Royal Meteorological Society

[1]  J. Monteith,et al.  Boundary Layer Climates. , 1979 .

[2]  Ingegärd Eliasson,et al.  Urban nocturnal temperatures, street geometry and land use , 1996 .

[3]  Hans Peter Schmid,et al.  Measurements of CO2 and energy fluxes over a mixed hardwood forest in the mid-western United States , 2000 .

[4]  I. D. Watson,et al.  Graphical estimation of sky view-factors in urban environments , 1987 .

[5]  Gerald Mills,et al.  Simulation of the energy budget of an urban canyon. II: Comparison of model results with measurements , 1993 .

[6]  Douw G. Steyn,et al.  The calculation of view factors from fisheye‐lens photographs: Research note , 1980 .

[7]  T. Oke.  Canyon geometry and the nocturnal urban heat island: Comparison of scale model and field observations , 1981 .

[8]  I. D. Watson,et al.  The determination of view-factors in urban canyons , 1984 .

[9]  J. Mattsson,et al.  Canyon geometry, street temperatures and urban heat island in malmö, sweden , 1985 .

[10]  H. Swaid,et al.  The role of radiative-convective interaction in creating the microclimate of urban street canyons , 1993 .

[11]  Yasushi Sakakibara,et al.  A numerical study of the effect of urban geometry upon the surface energy budget , 1996 .

[12]  B. Holmer,et al.  Eine einfache operative Methode für die Bestimmung von „Sky View Factors“ in unregelmäßigen Straßenschluchten mittels Fischauge-Photos , 1992 .

[13]  T. Gustavsson.  A study of air and road‐surface temperature variations during clear windy nights , 1995 .

[14]  K. Blennow.  Sky View Factors from High-Resolution Scanned Fish-eye Lens Photographic Negatives , 1995 .

[15]  J. Norman,et al.  Instrument for Indirect Measurement of Canopy Architecture , 1991 .

[16]  C. S. B. Grimmond,et al.  An urban canyon energy budget model and its application to urban storage heat flux modeling , 1998 .

[17]  J. E. Hay,et al.  The Determination of Sky View-Factors in Urban Environments Using Video Imagery , 1986 .

[18]  A. Arnfield,et al.  CANYON GEOMETRY, THE URBAN FABRIC AND NOCTURNAL COOLING: A SIMULATION APPROACH , 1990 .

[19]  J. A Clark,et al.  A simple «equal area» calibration for fisheye photography , 1988 .

[20]  T. Oke,et al.  Wind, temperature and stability conditions in an east-west oriented urban canyon , 1988 .