CHAPTER VII - Standards and Calibration Uncertainty

Abstract

This chapter describes the radiometric standards and the role of the National Bureau of Standards (NBS) in providing measurement services in the United States. NBS' stated goal in radiometry and photometry is to make 1% measurements commonplace in the United States. There is an ongoing program to develop standards and calibration techniques directed toward the achievement of this goal. The optical radiation section of the NBS includes a photometric and radiometric dissemination group with activities that fall into three categories, namely, calibrations, intercomparisons, and developmental projects. The objective of the calibration of an electro-optical sensor, that the measurement must be independent of the sensor, requires that absolute or traceable standards should be available for use by the different observers who make such measurements from time to time. The concept of traceable standards, or standards, has less meaning for radiation standards than for the standard meter. The international standard of length is a bar of a platinum–iridium alloy called the standard meter. Copies of this primary standard are made—called secondary standards. The chapter also explains the use of a well-qualified receiver or detector of radiant energy. Absolute or self-calibrating thermal detectors are also available. It further discusses the uncertainty in the calibration of an electro-optical sensor in which the output is obtained in response to a standard source.