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6.1 Introduction
Radiometric instruments vary in what they are intended to measure, how they do it, how complicated and expensive they are, how rugged, and in a number of other ways. In this chapter, the simplest of radiometers is considered, the components of radiometers are described, and spectral radiometers are covered.
6.2 Instrumentation Requirements
It surely comes as no surprise that different instruments have different requirements. For instance, the required accuracy and repeatability vary greatly with the application. A device meant for routine maintenance in the factory might have a radiometric uncertainty of about 20%, yielding a temperature uncertainty of a few degrees, whereas several different bureaus of standards have strived for uncertainties of 0.01%.
6.2.1 Ideal radiometer
It is hard to describe one ideal radiometer, but, in general, they should all measure the radiometric property accurately, precisely, and repeatedly. They should be simple to use, with easily interpreted outputs; of course, the ideal radiometer should be free of defects. Some need to be quite rugged for field use, but all should be able to withstand the environment or environments to which they are exposed. They should be sensitive and have a wide dynamic range, or they should at least be sensitive enough for the task at hand and have sufficient dynamic range for their use.
6.2.2 Specification sheet
In the fervent hope that you can obtain the ideal radiometer, the following specification sheet is presented. It may not be complete for all applications, and not all applications need all of these specifications, but it is a good start and a good guide.
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