The Multispectral Scanners (MSSs) were the first multispectral sensors to monitor Earth's resources from space. Developed by Santa Barbara Research Center for NASA's Goddard Space Flight Center, the first MSS was carried aboard the Earth Resources Technology Satellite (ERTS 1), subsequently renamed Landsat 1. Five MSS sensors have been flown, and the sensors on Landsats 4 and 5 are currently operational. The instrument operates by repeatedly scanning a 24-element fiber-optic array from west to east across Earth's surface; the orbital motion of the spacecraft provides a natural north-to-south scanning motion. Then, a separate binary-number array for each spectral band is generated. Each number corresponds to the amount of energy reflected into that band from a specific ground location. In the ground-processing system, the binary number arrays are either directly interpreted by image-classification software or reconstructed into images. The MSS ushered in an era of hitherto unimagined synoptic knowledge of Earth. An extraordinary number of uses for MSS data emerged as data were acquired and disseminated: land-use planning, vegetation inventories, crop growth and health assessments, and cartography, to name a few. The MSS was an experimental system that exceeded its designers' most optimistic expectations, not only in the quality of data obtained, but also in the large user community that developed.

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