Effects
of urban surface geometry on remotely-sensed
surface temperature
Author(s): J. A. Voogt T. R. Oke
Source: International Journal of Remote Sensing
Volume:
19 Number: 5 Page: 895 – 920
Abstract: Direct observations of urban surface
temperature in
daytime are made using a thermal scanner mounted in a helicopter over
three
land-use areas in Vancouver, B.C. The results reveal strong
directional
variations in the observed apparent surface temperature. The variations
arise
due to the differential patterns of irradiated and shaded surfaces
within the
sensor field of view created by the three-dimensional urban surface
structure
and the position of the Sun. The directional variations may be
considered to be
a form of effective anisotropy due to the large scale roughness of the
urban
surface. Variations in excess of 9 C were measured over a downtown
area. Urban
residential and light industrial land-use areas also exhibited strong
effective
anisotropy. The directional temperature variations are of similar
magnitude to
atmospheric corrections applied to thermal imagery. This implies that
effective
anisotropy should receive serious consideration in the interpretation
of
thermal imagery obtained over urban areas. The scale dependence of the
effective anisotropy is discussed.