Space-based observation is well established as a means for collecting data for a wide variety of purposes. These missions include military reconnaissance, weather forecasting, agricultural analysis, commercial surveying, and search and rescue.
Satellites obtain images via optical cameras, infrared sensors, and radar (especially using synthetic aperture technique). Each modality has advantages and disadvantages, situations where it is optimal, and situations where its use is impossible. Often the combination of sensors (i.e., obtaining a multispectral image) optimizes the chances of detecting a given object or phenomenon.
Space-based observation can detect the presence of deceased humans and animals, or degraded crops. A reconnaissance satellite photographs a scene of interest, and transmits its images in digital form to an interpretation center on the ground, either directly, or relayed by a communications satellite. The value of the images depends on the type of image, its resolution, and the time elapsed between the occurrence of an event and receipt of imagery by a trained analyst.
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