Radiometry

Radiometry is the science of measuring electromagnetic radiation and its application in physics , astronomy, and geophysics . It is related to photometry and represents the extension of this "measurement of light " into the areas of infrared and ultraviolet , but also of gamma rays .

Basics

The quantitative measurement of radiation intensities is carried out with different types of detectors . They convert part of the radiation into heat or an electrical signal , from which conclusions can be drawn about the type of radiating surface and its temperature , among other things . The theoretically ideal “ black body ” and the radiation laws that apply to it often serve as a comparison .

Radiometric quantities

In order to be able to describe the properties of the radiation source, receiver and irradiated material, seven radiometric quantities have been defined. They correspond to seven photometric quantities, which are their spectrally weighted special case because of the limited wavelength interval of visible light - the light sensitivity curve standardized by the CIE .

radiometric quantity	Symbol a)	SI unit	description	photometric equivalent b)	symbol	SI unit
Radiant flux radiant power, radiant flux, radiant power	${\displaystyle \Phi _{\mathrm {e} }}$	W ( watt )	Radiant energy through time	Luminous flux luminous flux, luminous power	${\displaystyle \Phi _{\mathrm {v} }}$	lm ( lumens )
Radiant intensity irradiance, radiant intensity	${\displaystyle I_{\mathrm {e} }}$	W / sr	Radiation flux through solid angles	Luminous intensity luminous intensity	${\displaystyle I_{\mathrm {v} }}$	cd = lm / sr ( candela )
Irradiance irradiance	${\displaystyle E_{\mathrm {e} }}$	W / m 2	Radiation flux through the receiver surface	Illuminance illuminance	${\displaystyle E_{\mathrm {v} }}$	lx = lm / m 2 ( lux )
Specific radiation emission current density, radiant exitance	${\displaystyle M_{\mathrm {e} }}$	W / m 2	Radiation flux through the transmitter surface	Specific light emission luminous exitance	${\displaystyle M_{\mathrm {v} }}$	lm / m 2
Radiance radiance, radiance, radiance	${\displaystyle L_{\mathrm {e} }}$	W / m 2 sr	Radiant intensity through effective transmitter area	Luminance luminance	${\displaystyle L_{\mathrm {v} }}$	cd / m 2
Radiant energy amount of radiation, radiant energy	${\displaystyle Q_{\mathrm {e} }}$	J ( joules )	by radiation transmitted energy	Amount of light luminous energy, quantity of light	${\displaystyle Q_{\mathrm {v} }}$	lm · s
Irradiation irradiation, radiant exposure	${\displaystyle H_{\mathrm {e} }}$	J / m 2	Radiant energy through the receiver surface	Exposure luminous exposure	${\displaystyle H_{\mathrm {v} }}$	lx s
Radiation yield radiant efficiency	${\displaystyle \eta _{\mathrm {e} }}$	1	Radiation flux through absorbed (mostly electrical) power	Luminous efficiency (overall) luminous efficacy	${\displaystyle \eta _{\mathrm {v} }}$	lm / W

^a)The index "e" is used to distinguish it from the photometric quantities. It can be omitted.

^b)The photometric quantities are the radiometric quantities, weighted with the photometric radiation equivalent K , which indicates the sensitivity of the human eye.

As radiation flux density (also irradiance ) referred to the radiant flux (weighted physiologically: luminous flux ) of the surface element crosses. The radiation energy that falls on a surface element per period of time is referred to as irradiance , physiologically weighted as illuminance . ${\displaystyle E}$ ${\displaystyle \Phi }$ ${\displaystyle \Phi _{\mathrm {v} }}$ ${\displaystyle \mathrm {d} A}$ ${\displaystyle \mathrm {d} t}$ ${\displaystyle \mathrm {d} A}$ ${\displaystyle E}$ ${\displaystyle E_{\mathrm {v} }}$

${\displaystyle E={\frac {\mathrm {d} ^{2}Q}{\mathrm {d} A\cdot \mathrm {d} t}}\left(\mathrm {\frac {Ws}{m^{2}\cdot s}} \right)={\frac {\mathrm {d} \Phi }{\mathrm {d} A}}\left(\mathrm {\frac {W}{m^{2}}} \right)}$

The radiation energy that emanates from a surface element per time period is called specific radiation , physiologically weighted as specific light radiation . ${\displaystyle \mathrm {d} t}$ ${\displaystyle \mathrm {d} A}$ ${\displaystyle M}$ ${\displaystyle M_{\mathrm {v} }}$

${\displaystyle M={\frac {\mathrm {d} ^{2}Q}{\mathrm {d} A\cdot \mathrm {d} t}}\left(\mathrm {\frac {Ws}{m^{2}\cdot s}} \right)={\frac {\mathrm {d} \Phi }{\mathrm {d} A}}\left(\mathrm {\frac {W}{m^{2}}} \right)}$

The radiance (also radians ) is defined as total radiance of the radiation energy per time period by an area element in a predetermined direction in a Raumwinkelement goes or comes from this. Physiologically weighted, one speaks of the luminance , which indicates the perception of brightness. is the apparently shining surface. ${\displaystyle L}$ ${\displaystyle L_{\Omega }}$ ${\displaystyle \mathrm {d} A}$ ${\displaystyle \mathrm {d} \Omega }$ ${\displaystyle \mathrm {d} A\cos \theta }$

${\displaystyle L_{\Omega }={\frac {1}{\cos \theta }}\cdot {\frac {\mathrm {d} ^{2}\Phi }{\mathrm {d} A\ \mathrm {d} \Omega }}={\frac {\mathrm {d} I(\theta )}{\mathrm {d} A\cos \theta }}\left(\mathrm {\frac {W}{m^{2}\cdot sr}} \right)}$

${\displaystyle \theta }$is the angle between the light source and the surface normal

Radiometer

The detectors for the physical measurement of radiation quantities are called radiometers . Of the above five quantities, the main measurements are the amount of radiation, the irradiance and the radiance.

A radiometer consists of the input optics (or the measurement opening / antenna), the spectral filter , the actual sensor , the associated electronics and the display device or display.

Gamma radiometry

→ Main article : Radiometric dating

The radiometry of gamma radiation is an important method in geophysics and other geosciences to determine rocks and their material content. The basis is the radioactivity of the nuclides they contain, i.e. their spontaneous conversion into other chemical elements. The high-energy gamma radiation that occurs during decay processes has a typical energy distribution for each nuclide, the so-called gamma spectrum. The quantitative analysis of the natural isotopes (especially uranium, thorium, potassium-40 and carbon-14) allows a characterization of the rocks.

literature

• Noboru Ohta, Alan R. Robertson: Colorimetry: Fundamentals and Applications , Wiley-IS & T Series, West Sussex 2006. ISBN 978-0-470-09473-0
• Bergmann, Schaefer, Textbook of Experimental Physics Vol. 3 "Optics", De Gruyter, Berlin, New York, 1993

Web links

Commons : Radiometry  - collection of images, videos and audio files

• Infrared radiometry ( Memento from May 16, 2006 in the Internet Archive )