URBMAT : an urban canyon sampling format for nocturnal long wave radiation regime modelling
| dc.contributor.author | Wakefield, Philip M. | en_US |
| dc.date.accessioned | 2024-08-15T20:12:22Z | |
| dc.date.available | 2024-08-15T20:12:22Z | |
| dc.date.copyright | 1987 | en_US |
| dc.date.issued | 1987 | |
| dc.degree.department | Department of Geography | |
| dc.degree.level | Master of Arts M.A. | en |
| dc.description.abstract | The study of long wave radiation regimes within urban canyons is an area of urban climatology requiring more intensive and extensive investigation. Long wave irradiances that create these regimes are the principal sources and sinks of energy for energy budgets in the urban canyon at night under clear, calm and dry conditions. It is desirable to model urban nocturnal long wave radiation regimes to save time and costs incurred in direct measurement as well as lend insight and understanding into the theoretical controls of the irradiances. This research focuses on URBMA T which addresses the three preconditions deemed necessary for the development of "good" models. These preconditions include the clear and concise identification of those variables, properties and factors that may be relevant to modelling; a thorough knowledge of those instruments available for measuring specific variables; and the development of standardized methods for sampling the relevant variables in urban canyon, vegetative and building air-volumes. The principal dependent variables that should be modelled are radiant surface temperatures and radiant sky temperatures. These temperatures can be employed in the Stefan-Boltzmann Law to yield a value for long wave irradiance. The key independent variables suggested by this research are associated with the urban canyon, vegetative and building air-volumes. They are the dry-bulb air temperature and wind speed in each air-volume as well as the wet-bulb air temperature in the urban canyon air-volume. Net long wave irradiances are recommended as a "test" variable to be used for model validation. The key properties for consideration in model development are the emissivity and thermal conductivity of surface materials. Key factors include aspect, height or depth of vegetative canopies, vegetative canopy cover, thickness of materials, and viewfactors for the sky and urban surf aces. Radiant temperatures can be measured using a compact and portable infrared radiometer affixed to a tripod. A guide is provided to assist in setting up the radiometer when surface temperatures on vertical surfaces are to be sampled. When dry-bulb and wet-bulb air temperatures are to be sampled concurrently, an aspirated psychrometer can be used. A thermistor - thermometer can be used when the dry-bulb air temperature is to be sampled alone. Wind speeds should be measured using a hot-wire or hot-film anemometer. The hot- wire anemometer used in this research was very sensitive to movements of air. It was determined that an average between a high and low measurement of wind speed over a 10 second time interval could be used to represent a single wind speed measurement for a specific sampling location. Air temperatures and wind speed are measured in air-volumes at an instrument height ranging between 1.0 and 1.5 metres above the floor of the room or urban canyon. Vertical and horizontal surface areas can be sampled for radiant surface temperature by either single measurements at the surface's centre or by traversing the surface when the centre is not accessible. Radiant sky temperatures can be measured at 0°, 41 °, 60° and 76° from the zenith in the N, E, Sand W directions where the radiometer is placed at the urban canyon centre. Net long wave irradiances can be sampled at the centre of the urban canyon at an instrument height between 1.0 and 1.5 metres using either a net pyrradiometer or a net pyrgeometer. Air temperatures and wind speeds in air-volumes can be sampled at the centre of the urban canyon for homogeneous canyon floors and at the centre of a room. Vegetative air-volumes are sampled for air temperature and wind speed halfway between the trunk or ground surface and the outer edge of the canopy. Where the urban canyon floor is heterogeneous, single measurements for air temperature and wind speed taken at the centre of individual surface areas can be averaged using a weighting factor based on the surfaces' areas. In addition, this research introduces the concept of surface elements, configurations and components. Formulae for deriving sampling intervals are developed based on areal dimensions and the desired accuracy of results. Further, a viewfactor model is introduced that may enhance the development and use of subsequent models. | |
| dc.format.extent | 241 pages | |
| dc.identifier.uri | https://hdl.handle.net/1828/20020 | |
| dc.rights | Available to the World Wide Web | en_US |
| dc.title | URBMAT : an urban canyon sampling format for nocturnal long wave radiation regime modelling | en_US |
| dc.type | Thesis | en_US |
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