ABSTRACT
This chapter presents an overview of the technology used in acquiring digital images from space. It focuses on two different aspects of the acquisition phase: the sensor and the instrument that contains it. Digital data is acquired by two types of sensors; the older ones are based on the technology used in broadcast television, such as the vidicon tube, and the newer ones on charge-coupled device technology. Vidicon-type sensors are nonlinear under low and average illumination conditions but approach a linear response when the illumination is high. A sensor requires a discrete amount of time in which to accumulate enough photons with which to generate a strong signal. Electronic sensors, in general, have rather large dynamic ranges compared to those of computer video systems, human vision, or photographic films. Some of the most important characteristics of a sensor are its linearity, signal-to-noise level, sensitivity, wavelength response, size, ruggedness, charge transfer efficiency, and response to cosmic rays.
