ABSTRACT
Since most radio receivers are narrowband instruments and many of the detectors used for far-infrared (FIR) and microwave observations operate over restricted wavebands, essentially all their observations come under photometry and have therefore been covered in Sections 1.1 and 1.2. Likewise extreme ultraviolet (EUV), x-ray, and g-ray detectors often have some intrinsic sensitivity to wavelength (i.e., photon energy) and so automatically operate as photometers or low-resolution spectroscopes. Their properties have been covered in Section 1.3. In this section, we are thus concerned with photometry as practiced over the near ultraviolet, visible, near-infrared (NIR), and mid-infrared (MIR) regions of the spectrum (roughly 100 nm to 100 mm).
