In 1858 Gaspard-Felix Tourmachon used the newly invented camera to take the first photograph of the Earth from a balloon over France. Today remote sensing is used for astronomy, military intelligence, cartography, meteorological observation, geological, biological, and even archeological investigation.
Remote sensors can be passive or active.
Active remote sensors, like radar, emit energy pulses that are reflected off an object and detected. 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.