Environmental Engineering Reference
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capture more detailed effects of urban morphological features and underlying sur-
faces and building materials, at increasingly higher spatial resolutions, employ more
explicit and highly detailed sets of 3D canopy parameters and within-grid land use
classes.
A common requirement for environmental models is the description of the under-
lying surface layer. Technological advancements allow increasingly sophisticated
definitions of land cover characteristics (e.g., shape files with high resolution [~1 m]
definition of buildings and vegetation). Data of this type are now becoming routinely
available for many urban areas of the world with the information technology avail-
able to facilitate dissemination. In the United States, a pilot project is underway to
serve as a community-based technology enabler of such data; this or comparable
systems can be developed to handle the needs on an international basis (Chapter 1
of this volume). A community-based system should decrease administrative barriers
and increase international collaborative efforts to advance modeling tools.
15.5.2 Evaluation
Once the target variables and degree of precision needed for the application purpose
are identified (Table 15.1), it is necessary to determine whether the parameteriza-
tions are capable of reaching these targets. Several techniques are available.
•
Real scale measurements.
As measurements are taken in a real city, a model
should be able to reproduce them; however, very often it is difficult to have
enough measurements, and, where measurements are taken, its representative-
ness of the gridded fields must be ascertained. The model computes the equiva-
lent of a spatial average over the grid cell (usually a few kilometers or, at best,
several hundreds of meters). Outputs from models that introduce vertical reso-
lution within the UC and capture the effects of urban building and vegetation
features are virtual fields, and the task of evaluating such outputs is challenging.
Model-predicted vertical profiles of variables in the canopy reflect the aggregated
influence of all the canopy features as virtual elements within the grid. In reality,
such features take up finite volumes, and building-induced flows are subgrid fea-
tures. Thus, any single or set of measurements will not provide a representation
of the gridded fields but will, more or less, be under the influence of the near-
est buildings or obstacles. This is a design feature that has yet to be resolved in
developing field measurement strategies to evaluate predictions of within-canopy
fields.
Future guidance may come from insights gained using coupled UC models
and building-resolved flows, both of which are driven by the same set of build-
ing datasets. Currently, evaluations performed above the canopy layer (blending
layer) should not be subject to this conceptual difficulty, but, in and of itself, it
does not provide the requisite within-canopy evaluation.
•
Remote sensing data.
A variety of satellite platforms do now provide data on sur-
face variables and for urban areas. In particular, skin temperature is considered a
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