radiometry


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Radiometry

A branch of science that deals with the measurement or detection of radiant electromagnetic energy. Radiometry is divided according to regions of the spectrum in which the same experimental techniques can be used. Thus, vacuum ultraviolet radiometry, intermediate-infrared radiometry, far-infrared radiometry, and microwave radiometry are considered separate fields, and all of these are to be distinguished from radiometry in the visible spectral region. Curiously, radiometry in the visible is called radiometry, optical radiation measurement science, or photometry, but it is not called visible radiometry. See Electromagnetic radiation, Infrared radiation, Light, Ultraviolet radiation

Any radiation detector (such as a thermometer) that responds to an increase in temperature caused by the absorption of radiant energy is known as a thermal detector. Similarly, any detector (such as a photochemical reaction) that responds to the excitation of a bound electron is called a photon or quantum detector.

Liquid-in-glass thermometers are sluggish and relatively insensitive. The key to developing thermal detectors with better performance than liquid-in-glass thermometers has been to secure a large and rapid rise in temperature associated with a high sensitivity to temperature changes.

Thermal detectors have been based upon a number of different principles. Radiation thermocouples produce a voltage, bolometers undergo a change in resistance, pyroelectric detectors undergo a change in spontaneous electric polarization, and the gas in pneumatic detectors (Golay cells) and photoacoustic detectors expands in response to incident radiation. The periodic expansion and contraction of the gas in response to high-frequency modulated radiation is detected by a sensitive microphone in the case of the photoacoustic detector. The Golay cell, on the other hand, uses a sensitive photomultiplier and a reference beam of light to detect distortion of a flexible membrane mirror caused by the expansion and contraction of the gas. See Bolometer, Pyroelectricity, Thermocouple

The main problem with thermal detectors is that they respond not only to electromagnetic radiation but to any source of heat. This makes their design, construction, and use rather difficult, because they must be made sensitive to the radiation of interest while remaining insensitive to all other sources of heat, such as conduction, convection, and background radiation, that are of no interest in the particular measurement.

Photon detectors respond only to photons of electromagnetic radiation that have energies greater than some minimum value determined by the quantum-mechanical properties of the detector material. Since heat radiation from the environment at room temperature consists of infrared photons, photon detectors for use in the visible can be built so that they do not respond to any source of heat except the radiation of interest.

Following the introduction of planar silicon technology for microelectronics, the same technology was quickly exploited to make planar photodiodes based on the internal photoelectric effect in silicon. In these devices, the separation of a photogenerated electron-hole pair by the built-in field surrounding the p+n junction induces the flow of one electron in an external short circuit (such as the inputs to an operational amplifier) across the electrodes. The number of electrons flowing in an external short circuit per absorbed photon is called the quantum efficiency. The use of these diodes has grown to the point where they are the most widely used detector for the visible and nearby spectral regions. Their behavior as a radiation detector in the visible is so nearly ideal that they can be used as a standard, their cost is so low that they can be used for the most mundane of applications, and their sensitivity is so high that they can be used to measure all but the weakest radiation (which requires the most sensitive photomultipliers). See Semiconductor diode

Research efforts have been directed at producing photon detectors based on more exotic semiconductors, and more complicated structures to extend the sensitivity, time response, and spectral coverage.

radiometry

[‚rād·ē′äm·ə·trē]
(physics)
The detection and measurement of radiant electromagnetic energy, especially that associated with infrared radiation.
References in periodicals archive ?
13th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment, Pasadena, CA.
Drummond, (ed) Precision Radiometry, Advances in Geophysics, Academic Press 14, 415 pp.
Digital correlators for synthetic aperture interferometric radiometry," IEEE Trans.
Skou, "Synthetic aperture radiometry evaluated by a two-channel demonstration model," IEEE Trans.
Torres, "Radiometric sensitivity computation in aperture synthesis interferometric radiometry," IEEE Trans.
Identifying optimal spectral bands to assess soil properties with VNIR radiometry in semi-arid soils.
Actinometry was not used because it is time consuming and expensive when compared to radiometry.
These chargeability highs and discontinuities suggested that diorite porphyry intrusion had been intensively fractured and sulphur mineralization had been emplaced throughout these fracture areas (Figure 13a, b) Interpreting inferred structural features was complex Most linear features did not coincide with 20m to 310m or the interpreted applied radiometry, magnetic and IP methods However, the interpreted linear features showed that intrusive bodies and host rocks had been intensively fractured, allowing the flow of mineralized solutions.
such as radiometry, elevation, range or GPS co-ordinates.
The CIE has published three new reports: Emergency Lighting in Road Tunnels; Practical Daylight Sources for Colorimetry; and Proceedings of CIE Expert Symposium on Spectral and Imaging Methods for Photometry and Radiometry.
Nevertheless, a strict separation of areas affected by heavy metal pollution was not possible due to the fact that there is an uncertainty of the discrimination interval between two classes that are similar in terms of radiometry.
Training in chemical engineering and with a long career in the plastics business, he covers the fundamentals of radiation science and technology, curing equipment, processes for ultraviolet and electron beam radiation in turn, coating methods using the technology, applications, dosimetry and radiometry, safety and hygiene, and recent developments and trends.