What is "Remote Sensing?"
At the most basic level, "remote sensing" refers to the use of aerial imagery to study conditions on and changes to the Earth's surface. This process relies on discerning wavelengths in the visible light spectrum. Imagery "platforms," the objects on which sensors are placed in order to obtain imagery, range from trucks with crane-like appendages to advanced satellites; indeed, black-and-white photographs taken from hot air balloons are early examples of remote sensing. What platform is deployed, and which types of sensors are used, depend on the objective and scope of the examination.
A remote sensor is either "active" or "passive;" active sensors produce their own energy, which is used to identify wavelengths, while passive ones detect energy reflected from the Earth's surface.
Consideration must be given to the spatial and spectral nature of the region being photographed, as this has ramifications for the quality of imagery produced. Spatial resolution refers to the ability to distinguish objects from each other - how well they can be discerned - on the ground, while spectral resolution concerns how many spectral bands a sensor can observe. In urban areas, this is particularly relevant given the distinct nature of attributes of the built environment.