In order to understand the complex dynamics of the urban environments discussed above it is necessary to have detailed observations of some key variables describing the state of the physical environment. Variables like air temperature, surface temperature, wind speed and direction, precipitation, humidity and particulate concentrations have a direct impact on human health and comfort, yet the dynamics of the processes controlling them are still not well understood in the urban context. In part, this is because it is often difficult, or prohibitively expensive to make direct measurements of these quantities at the spatial and temporal scales necessary to understand the processes controlling them. Remote sensing, however, provides ways to make indirect measurements as proxies for many of these quantities. The advantage of remotely sensed observations is that they can often be made over very large areas so as to provide a synoptic “snapshot” of the spatial variation in the physical quantity. Multiple synoptic images can be combined with in situ measurements to provide better spatial and temporal resolution of the quantities than could be provided by in situ measurements alone. It is critical, however, that remotely sensed observations be calibrated with in situ measurements. At present, there are several airborne and satellite-based remote sensing tools capable of measuring physical quantities across an enormous range of temporal and spatial scales. An excellent synopsis of spatial and temporal resolutions offered by various sensors useful for urban environmental observations is provided by Jensen and Cowen (1999).