Passive sensors, like cameras, are sensitive to energy sources being emitted or reflected off an object. All remote sensing systems collect, record, store, and analyze information. Digital remote sensing systems convert electromagnetic energy to numeric values, which are stored on an electromagnetic tape. Rows of pixels form scan lines. Many scan lines are used to construct an image.
Electromagnetic energy is used to produce images using remote sensing devices.
Radar is used to produce black and white images that etch the landscape even on a cloudy day. These images can be color-enhanced. Near-infrared images are used to detect vegetation. Healthy vegetation emits infrared and appears darker or red when color-enhanced. During World War II, this technology was used to detect camouflage consisting of dead foliage.