Electromagnetic radiation radiometry

The various terms that are used for the description of the emission of electromagnetic radiation from a radiant source or for the receipt of electromagnetic radiation by a specified surface element are summarized in Tab. 3-9. The terminology of electromagnetic radiation measurement is divided into radiometry and the subset of photometry (Fig. 3-18). The former is the science that involves the energy measurement of electromagnetic radiation in general. The latter is applied for the same purpose when visible radiation is to be described or measured in relation to the human eye s response. Important photometric quantities are for example luminous flux, luminous intensity, illuminance and luminance (McCluney, 1994). Every photometric quantity has its counterpart in radiometry, and vice versa. 

The measure for the burden on human beings is the equivalent dose, stated in Sieverts (1 Sv = 1 J/kg, standardized to electromagnetic radiation). It takes into account the varying degrees of potential hazard from the different kinds of radiation. Table 7 shows the applications of radiometry classified according to fields. 

Irradiance is a radiometry term for the power of electromagnetic radiation at a surface, per unit area, which is used when the electromagnetic radiation is incident on the surface. The SI unit for this quantity is watts per square meter (W/m ), which is sometimes called http //en. wikipedia.org/wiki/Intensity. This quantity... 

Radiometry. Radiometry is the measurement of radiant electromagnetic energy (17,18,134), considered herein to be the direct detection and spectroscopic analysis of ambient thermal emission, as distinguished from techniques in which the sample is actively probed. At any temperature above absolute zero, some molecules are in thermally populated excited levels, and transitions from these to the ground state radiate energy at characteristic frequencies. Erom Wien s displacement law, T = 2898 //m-K, the emission maximum at 300 K is near 10 fim in the mid-ir. This radiation occurs at just the energies of molecular rovibrational transitions, so thermal emission carries much the same information as an ir absorption spectmm. Detection of the emissions of remote thermal sources is the ultimate passive and noninvasive technique, requiring not even an optical probe of the sampled volume. 

The word radiometry describes the detection and measurement of radiated electromagnetic energy, and is also used to describe the prediction and calculation of the power transferred by radiation from one object or surface to another. The concepts of radiometry are so similar to those of photometry (related to vision and detection by the human eye) and to the transfer of photons that it is convenient to discuss all three together. In fact, we rarely need to distinguish between the three disciplines, and we will use the word radiometry to cover all three. The radiometric calculations described in this chapter are a necessary part of the characterization of detectors and the prediction of signal and noise levels. 

---