ABSTRACT
This chapter reviews some key general concepts and detector properties, which will be relevant to the design and performance of astronomical detection systems across the electromagnetic spectrum. The measurement of a physical parameter involves the conversion of the input quantity, electromagnetic power, for instance, into some easily measurable output quantity, such as voltage or current, by a transducer. In many cases, the electromagnetic radiation to be measured (the signal) is accompanied by a constant, or slowly varying, amount of unwanted additional radiation. The presence of background radiation often degrades the quality of measurement through contributing noise. Noise is any fluctuating unwanted contribution to the output signal that might affect the measurement by introducing uncertainty in the recorded value. Calibration is the process by which the measured signal is converted into astronomically meaningful units. The two most important kinds of calibration in astronomy are flux calibration and spectroscopic calibration.
