A Model to Calculate what a Remote Sensor 'Sees' of an Urban Surface
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Whilst the measurement of radiation emissions from a surface is relativelystraightforward, correct interpretation and proper utilization of the informationrequires that the surface area `seen' be known accurately. This becomes non-trivialwhen the target is an urban surface, due to its complex three-dimensional form andthe different thermal, radiative and moisture properties of its myriad surface facets.The geometric structure creates shade patterns in combination with the solar beamand obscures portions of the surface from the sensor, depending on where it is pointing and its field-of-view (FOV). A model to calculate these surface-sensor-sun relations (SUM) is described. SUM is tested against field and scale model observations, and theoretical calculations, and found to perform well. It can predict the surface area`seen' by a sensor of known FOV pointing in any direction when placed at any pointin space above a specified urban surface structure. Moreover, SUM can predict theview factors of the roof, wall and ground facets `seen' and whether they are sunlit orshaded at any location and time of day. SUM can be used to determine the optimalplacement and orientation of remote sensors to study urban radiation emissions; ifthe facet temperatures are known or modelled it can calculate the average temperatureof the system, and it can determine the directional variation of temperature (anisotropy) due to any particular surface-sensor-sun geometric combination. Thepresent surface geometry used in SUM is relatively simple, but there is scope to makeit increasingly realistic.