Definition of Terms
Sensors are the device recording information on the objects of interest; this can refer to either the entire sensor system (e.g., camera) or the actual sensing device (e.g., Charge Couple Devise or CCD). Cameras are the most typical sensor system, recording the frequency and intensity of visible and near visible portions of the electromagnetic radiation (EMR). All aerial imaging sensors record some portion of the Electromagnetic Spectrum, though many of them are imperceivable to humans. Radar was one of the first examples.
Passive sensors are by the most common type; they record the EMR that reaches the sensor without emitting. Cameras for example, record EMR which is typically produced by the sun, though flashes and indoor lighting are also potential sources.
Adjusting photos to correct distortions due to topographic relief, lens distortion, and camera tilt.