Dec 02, 2012 Optical Radiation Measurements, Volume 1: Radiometry is an introduction to the measurement of optical radiant energy, with emphasis on the principles and generally applicable methods of radiometry. Topics range from basic concepts of radiant energy and its transfer to the calibration of instrumentation. This text covers the range of subjects necessary for the understanding of modern infrared-imaging systems at a level appropriate for seniors or first-year graduate students in physics or electrical engineering. The first six chapters focus on fundamental background issues of radiation detection, beginning with the basics of geometrical optics and finishing with a discussion of the figures of.
4-component net radiometer showing the instrument's main components: 2 pyranometers (with domes, one visible at right facing up and the second at right facing down obscured by the white radiation shield above it) and 2 pyrgeometers (flat windows, again one visible (facing up) and one obscured (facing down)). Dimensions: diameter of the pyranometer dome is 20 mm. Photo shows model NR01.
A net radiometer is a type of actinometer used to measure net radiation (NR) at the Earth's surface for meteorological applications. The name net radiometer reflects the fact that it measures the difference between downward/incoming and upward/outgoing radiation from Earth. It is most commonly used in the field of ecophysiology.
Working Principle[edit]
The net radiometer is based on a thermopile sensor whose warm joints are in thermal contact with the receiver while the upper cool joints are in thermal contact with the lower receiver. The temperature difference between the two receivers is proportional to the net irradiation. The temperature difference between hot and cold junction is converted into a voltage by Seebeck effect. Thetwo receivers are made from a portion of spherical coated Teflon®. The particular form of the two receivers provides a response in accordance with the cosine.The Teflon® coating, as well as allowing outdoor installation for long periods without risk of damage, can have a constant spectral response from ultraviolet (200 nm) up to far infrared (100 μm).
Installing and mounting the net radiometer for total irradiance measurements[edit]
To allow cleaning the two receiving surfaces regularly, LP NET 07 should be mounted in easily reachable places. The surfaces can be washed with plain water or pure ETHIL alcohol.Mount the instrument so that no shadow will be cast on it at any time of day and of the seasons, from obstructions such as buildings, trees, or any other obstacle.In the NORTHERN hemisphere, the net radiometer is normally oriented towards SOUTH, while it should be oriented NORTHWARD, in the SOUTHERN hemisphere.The instrument should be mounted at a height of at least 1.5 m above the ground. Please note that the flow on the lower receiver is representative of a circular area with a radius of 10 times the height.When installing the net-radiometer avoid, wherever possible, to touch the surfaces of the receiving net-radiometer.
Terminology[edit]
Although there are many types of net radiometers, the 4-component design at present is most popular for scientific applications.
![Radiometry And The Detection Of Optical Radiation Pdf To Jpg Radiometry And The Detection Of Optical Radiation Pdf To Jpg](/uploads/1/2/6/4/126474412/140125033.jpg)
A 4-component net radiometer serves to measure 4 separate components of surface radiation balance: SWin direct incoming short wave radiation, SWout or reflected short wave radiation, LWin diffused long-wave radiation from the sky and LWout long-wave radiation emitted by the ground surface. In net radiometers, shortwave radiation is measured with pyranometers which measure incoming shortwave radiation and reflected shortwave radiation (albedo), and longwave radiation is measured with pyrgeometers. The working range of pyranometers is 300 to 2800 nm wavelength and that of pyrgeometers is 4500 to 100000 nm wavelength.
The surface of the upper receiver measures the direct solar radiation plus the diffuse one and the radiation at longer wavelengths emitted from the sky (clouds), while the lower receiving area measures the solar radiation reflected from the ground (albedo) and the radiation length wavelengths emitted from the earth. The instrument is designed and constructed to be used outdoors in any weatherconditions. Besides its use in meteorology to measure energy balance, it can be used indoors for the measurement of radiant temperature (ISO 7726).
Cross section of a 4-component net radiometer showing the instrument's main components: (1) SWin solar radiation sensor or pyranometer, (2) LWin far infrared radiation sensor or pyrgeometer, (3) radiation shield, (4) leveling assembly for x and y axis, block plus bolts for x-axis adjustment (5) leveling assembly for x and y axis, horizontal rod, (6) connection body, containing Pt100 temperature sensor, heater and hole for users own temperature sensor (add cable gland M8), (7) LWout far infrared radiation sensor or pyrgeometer, (8) leveling assembly for x and y axis, bolts for y-axis adjustment, (9) SWout solar radiation sensor or pyranometer.
Calculations[edit]
NOTE: the following formulas have T in kelvins. Add 273.16 to convert to temperature in degrees Celsius.
U is the voltage output of a sensor, E is radiation at the sensor surface, up = upfacing instrument, down = downfacing instrument, SW = shortwave or solar radiation, LW = longwave or far infrared (FIR) radiation, in = incoming, out = outgoing, T = temperature, NR = net radiation.
SWin = Upyrano,up / Epyrano,up
SWout = Upyrano,down / Epyrano,down
LWin = (Upyrgeo,up / Epyrgeo,up) + 5.67×10−8Tpyrgeo4
LWout = (Upyrgeo,down / Epyrgeo,down) + 5.67×10−8Tpyrgeo4
NOTE: in the LWnet the instrument temperature is cancelled:
LWnet = (Upyrgeo,up / Epyrgeo,up) - (Upyrgeo,down / Epyrgeo,down)
SWnet = (Upyrano,up / Epyrano,up) - (Upyrano,down / Epyrano,down)
NR = SWnet + LWnet
Special parameters that can be deduced:
SWalbedo = SWin / SWout
Tsurface = (LWout / 5.67×10−8)1/4
Tsky = (LWin / 5.67×10−8)1/4
The SWalbedo and the Tsurface must be estimated from other sources, and the NR can be calculated using these plus the SWin and LWin measurements.
SWalbedo typically is assumed to be a constant, typically taken from local satellite observations; Tsurface can often be calculated from air temperature or ground temperature measurements.
Usage[edit]
Net radiometers are frequently used in meteorology, climatology, solar energy studies and building physics. They can be seen in many meteorological stations—typically installed horizontally.
Standardisation[edit]
Net-radiometers are not standardised.
Example of a domeless net radiometer. The sensor contains two black-surface sensors (second one not visible) and has a single output signal representing the total net radiation. This instrument is typically used for lower accuracy net radiation measurement.
See also[edit]
References[edit]
![Jpg Jpg](/uploads/1/2/6/4/126474412/679017487.jpg)
External links[edit]
- Specifications, drawings and pictures courtesy of Hukseflux Thermal Sensors, www.Hukseflux.com
- Specifications courtesy of Delta OHM www.deltaohm.com
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Net_radiometer&oldid=917531121'
In radiometry, radiant flux or radiant power is the radiant energy emitted, reflected, transmitted or received, per unit time, and spectral flux or spectral power is the radiant flux per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. The SI unit of radiant flux is the watt (W), that is the joule per second (J/s) in SI base units, while that of spectral flux in frequency is the watt per hertz (W/Hz) and that of spectral flux in wavelength is the watt per metre (W/m)—commonly the watt per nanometre (W/nm).
- 1Mathematical definitions
Mathematical definitions[edit]
Radiant flux[edit]
Radiant flux, denoted Φe ('e' for 'energetic', to avoid confusion with photometric quantities), is defined as[1]
where
- ∂ is the partial derivative symbol;
- Qe is the radiant energy emitted, reflected, transmitted or received;
- t is the time.
Spectral flux[edit]
Spectral flux in frequency, denoted Φe,ν, is defined as[1]
where ν is the frequency.
Spectral flux in wavelength, denoted Φe,λ, is defined as[1]
where λ is the wavelength.
Relationship with the Poynting vector[edit]
One can show that the radiant flux of a surface is the flux of the Poynting vector through this surface, hence the name 'radiant flux':
where
- Σ is the surface;
- S is the Poynting vector;
- n is a unit normal vector to that surface;
- A is the area of that surface;
- α is the angle between n and S.
But the time-average of the norm of the Poynting vector is used instead, because in radiometry it is the only quantity that radiation detectors are able to measure:
where < • > is the time-average.
SI radiometry units[edit]
Quantity | Unit | Dimension | Notes | |||||
---|---|---|---|---|---|---|---|---|
Name | Symbol[nb 1] | Name | Symbol | Symbol | ||||
Radiant energy | Qe[nb 2] | joule | J | M⋅L2⋅T−2 | Energy of electromagnetic radiation. | |||
Radiant energy density | we | joule per cubic metre | J/m3 | M⋅L−1⋅T−2 | Radiant energy per unit volume. | |||
Radiant flux | Φe[nb 2] | watt | W = J/s | M⋅L2⋅T−3 | Radiant energy emitted, reflected, transmitted or received, per unit time. This is sometimes also called 'radiant power'. | |||
Spectral flux | Φe,ν[nb 3] | watt per hertz | W/Hz | M⋅L2⋅T−2 | Radiant flux per unit frequency or wavelength. The latter is commonly measured in W⋅nm−1. | |||
Φe,λ[nb 4] | watt per metre | W/m | M⋅L⋅T−3 | |||||
Radiant intensity | Ie,Ω[nb 5] | watt per steradian | W/sr | M⋅L2⋅T−3 | Radiant flux emitted, reflected, transmitted or received, per unit solid angle. This is a directional quantity. | |||
Spectral intensity | Ie,Ω,ν[nb 3] | watt per steradian per hertz | W⋅sr−1⋅Hz−1 | M⋅L2⋅T−2 | Radiant intensity per unit frequency or wavelength. The latter is commonly measured in W⋅sr−1⋅nm−1. This is a directional quantity. | |||
Ie,Ω,λ[nb 4] | watt per steradian per metre | W⋅sr−1⋅m−1 | M⋅L⋅T−3 | |||||
Radiance | Le,Ω[nb 5] | watt per steradian per square metre | W⋅sr−1⋅m−2 | M⋅T−3 | Radiant flux emitted, reflected, transmitted or received by a surface, per unit solid angle per unit projected area. This is a directional quantity. This is sometimes also confusingly called 'intensity'. | |||
Spectral radiance | Le,Ω,ν[nb 3] | watt per steradian per square metre per hertz | W⋅sr−1⋅m−2⋅Hz−1 | M⋅T−2 | Radiance of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅sr−1⋅m−2⋅nm−1. This is a directional quantity. This is sometimes also confusingly called 'spectral intensity'. | |||
Le,Ω,λ[nb 4] | watt per steradian per square metre, per metre | W⋅sr−1⋅m−3 | M⋅L−1⋅T−3 | |||||
Irradiance Flux density | Ee[nb 2] | watt per square metre | W/m2 | M⋅T−3 | Radiant flux received by a surface per unit area. This is sometimes also confusingly called 'intensity'. | |||
Spectral irradiance Spectral flux density | Ee,ν[nb 3] | watt per square metre per hertz | W⋅m−2⋅Hz−1 | M⋅T−2 | Irradiance of a surface per unit frequency or wavelength. This is sometimes also confusingly called 'spectral intensity'. Non-SI units of spectral flux density include jansky (1 Jy = 10−26 W⋅m−2⋅Hz−1) and solar flux unit (1 sfu = 10−22 W⋅m−2⋅Hz−1 = 104 Jy). | |||
Ee,λ[nb 4] | watt per square metre, per metre | W/m3 | M⋅L−1⋅T−3 | |||||
Radiosity | Je[nb 2] | watt per square metre | W/m2 | M⋅T−3 | Radiant flux leaving (emitted, reflected and transmitted by) a surface per unit area. This is sometimes also confusingly called 'intensity'. | |||
Spectral radiosity | Je,ν[nb 3] | watt per square metre per hertz | W⋅m−2⋅Hz−1 | M⋅T−2 | Radiosity of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅m−2⋅nm−1. This is sometimes also confusingly called 'spectral intensity'. | |||
Je,λ[nb 4] | watt per square metre, per metre | W/m3 | M⋅L−1⋅T−3 | |||||
Radiant exitance | Me[nb 2] | watt per square metre | W/m2 | M⋅T−3 | Radiant flux emitted by a surface per unit area. This is the emitted component of radiosity. 'Radiant emittance' is an old term for this quantity. This is sometimes also confusingly called 'intensity'. | |||
Spectral exitance | Me,ν[nb 3] | watt per square metre per hertz | W⋅m−2⋅Hz−1 | M⋅T−2 | Radiant exitance of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅m−2⋅nm−1. 'Spectral emittance' is an old term for this quantity. This is sometimes also confusingly called 'spectral intensity'. | |||
Me,λ[nb 4] | watt per square metre, per metre | W/m3 | M⋅L−1⋅T−3 | |||||
Radiant exposure | He | joule per square metre | J/m2 | M⋅T−2 | Radiant energy received by a surface per unit area, or equivalently irradiance of a surface integrated over time of irradiation. This is sometimes also called 'radiant fluence'. | |||
Spectral exposure | He,ν[nb 3] | joule per square metre per hertz | J⋅m−2⋅Hz−1 | M⋅T−1 | Radiant exposure of a surface per unit frequency or wavelength. The latter is commonly measured in J⋅m−2⋅nm−1. This is sometimes also called 'spectral fluence'. | |||
He,λ[nb 4] | joule per square metre, per metre | J/m3 | M⋅L−1⋅T−2 | |||||
Hemispherical emissivity | ε | N/A | 1 | Radiant exitance of a surface, divided by that of a black body at the same temperature as that surface. | ||||
Spectral hemispherical emissivity | εν or ελ | N/A | 1 | Spectral exitance of a surface, divided by that of a black body at the same temperature as that surface. | ||||
Directional emissivity | εΩ | N/A | 1 | Radiance emitted by a surface, divided by that emitted by a black body at the same temperature as that surface. | ||||
Spectral directional emissivity | εΩ,ν or εΩ,λ | N/A | 1 | Spectral radiance emitted by a surface, divided by that of a black body at the same temperature as that surface. | ||||
Hemispherical absorptance | A | N/A | 1 | Radiant flux absorbed by a surface, divided by that received by that surface. This should not be confused with 'absorbance'. | ||||
Spectral hemispherical absorptance | Aν or Aλ | N/A | 1 | Spectral flux absorbed by a surface, divided by that received by that surface. This should not be confused with 'spectral absorbance'. | ||||
Directional absorptance | AΩ | N/A | 1 | Radiance absorbed by a surface, divided by the radiance incident onto that surface. This should not be confused with 'absorbance'. | ||||
Spectral directional absorptance | AΩ,ν or AΩ,λ | N/A | 1 | Spectral radiance absorbed by a surface, divided by the spectral radiance incident onto that surface. This should not be confused with 'spectral absorbance'. | ||||
Hemispherical reflectance | R | N/A | 1 | Radiant flux reflected by a surface, divided by that received by that surface. | ||||
Spectral hemispherical reflectance | Rν or Rλ | N/A | 1 | Spectral flux reflected by a surface, divided by that received by that surface. | ||||
Directional reflectance | RΩ | N/A | 1 | Radiance reflected by a surface, divided by that received by that surface. | ||||
Spectral directional reflectance | RΩ,ν or RΩ,λ | N/A | 1 | Spectral radiance reflected by a surface, divided by that received by that surface. | ||||
Hemispherical transmittance | T | N/A | 1 | Radiant flux transmitted by a surface, divided by that received by that surface. | ||||
Spectral hemispherical transmittance | Tν or Tλ | N/A | 1 | Spectral flux transmitted by a surface, divided by that received by that surface. | ||||
Directional transmittance | TΩ | N/A | 1 | Radiance transmitted by a surface, divided by that received by that surface. | ||||
Spectral directional transmittance | TΩ,ν or TΩ,λ | N/A | 1 | Spectral radiance transmitted by a surface, divided by that received by that surface. | ||||
Hemispherical attenuation coefficient | μ | reciprocal metre | m−1 | L−1 | Radiant flux absorbed and scattered by a volume per unit length, divided by that received by that volume. | |||
Spectral hemispherical attenuation coefficient | μν or μλ | reciprocal metre | m−1 | L−1 | Spectral radiant flux absorbed and scattered by a volume per unit length, divided by that received by that volume. | |||
Directional attenuation coefficient | μΩ | reciprocal metre | m−1 | L−1 | Radiance absorbed and scattered by a volume per unit length, divided by that received by that volume. | |||
Spectral directional attenuation coefficient | μΩ,ν or μΩ,λ | reciprocal metre | m−1 | L−1 | Spectral radiance absorbed and scattered by a volume per unit length, divided by that received by that volume. | |||
See also: SI·Radiometry·Photometry |
- ^Standards organizations recommend that radiometric quantities should be denoted with suffix 'e' (for 'energetic') to avoid confusion with photometric or photon quantities.
- ^ abcdeAlternative symbols sometimes seen: W or E for radiant energy, P or F for radiant flux, I for irradiance, W for radiant exitance.
- ^ abcdefgSpectral quantities given per unit frequency are denoted with suffix 'ν' (Greek)—not to be confused with suffix 'v' (for 'visual') indicating a photometric quantity.
- ^ abcdefgSpectral quantities given per unit wavelength are denoted with suffix 'λ' (Greek).
- ^ abDirectional quantities are denoted with suffix 'Ω' (Greek).
See also[edit]
References[edit]
- ^ abc'Thermal insulation — Heat transfer by radiation — Physical quantities and definitions'. ISO 9288:1989. ISO catalogue. 1989. Retrieved 2015-03-15.
Further reading[edit]
- Boyd, Robert (1983). Radiometry and the Detection of Optical Radiation (Pure & Applied Optics Series). Wiley-Interscience. ISBN978-0-471-86188-1.
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