Push broom scanner
A push broom scanner, also known as an along-track scanner, is a device for obtaining images with spectroscopic sensors. The scanners are regularly used for passive remote sensing from space, and in spectral analysis on production lines, for example with near-infrared spectroscopy used to identify contaminated food and feed. The moving scanner line in a traditional photocopier (or a scanner or facsimile machine) is also a familiar, everyday example of a push broom scanner. Push broom scanners and the whisk broom scanners variant (also known as across-track scanners) are often contrasted with staring arrays  (such as in a digital camera), which image objects without scanning, and are more familiar to most people. In orbital push broom sensors, a line of sensors arranged perpendicular to the flight direction of the spacecraft is used. Different areas of the surface are imaged as the spacecraft flies forward. A push broom scanner can gather more light than a whisk broom scanner because it looks at a particular area for a longer time, like a long exposure on a camera. One drawback of push broom sensors is the varying sensitivity of the individual detectors. Examples of spacecraft cameras using  push broom imagers include Mars Express's High Resolution Stereo Camera, Lunar Reconnaissance Orbiter Camera NAC, Mars Global Surveyor's Mars Orbiter Camera WAC, and the Multi-angle Imaging SpectroRadiometer on board the Terra satellite.