- Net radiometer
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A net radiometer is a type of actinometer used to measure net radiation (NB) at the Earth's surface in meteorological applications. The name net radiometer reflects the fact that it is supposed to measure incoming minus upwelling radiation. It is most commonly used in the field of eco-physiology.
Contents
Terminology
Although there are many types of net-radiometers, the 4-component design at present is most popular for scientific applications.
A 4-component net-radiometer serves to measure the 4 separate components of the surface radiation balance. SWin or global solar radiation, SWout or reflected solar radiation, LWin or infrared emitted by the sky and LWout or infrared emitted by the ground surface. From these also parameter like SW “albedo”, “sky temperature”, “(ground) surface temperature” and off course “net-radiation” (net value of all SW and LW fluxes) can be calculated. A typical net radiometer does not require any power to operate.
The SW solar radiation spectrum extends approximately from 300 to 2800 nm. Pyranometers usually cover that spectrum with a spectral sensitivity that is as “flat” as possible. The longwave (LW) or far infrared (FIR) extends from 4500 to 50000 nm. This part of the spectrum is covered by a pyrgeometer.
Calculations
NOTE: the following formulas have T in kelvins. In order to have T in degrees Celsius, please add 273. With U voltage output of a sensor, 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) + 5.67.10-8 (Tpyrgeo)4
LWout = (Upyrgeo, down / Epyrgeo, down) + 5.67.10-8 (Tpyrgeo)4
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 deducted:
SWalbedo = SWin/SWout NOTE: the following formulas have T in kelvins. In order to have T in degrees Celsius, please add 273.
Tsurface = (LWout /5.67.10-8)1/4
Tsky = (LWin/5.67.10-8)1/4
The SW albedo and the Tsurface must be estimated from other sources, and the NR can be calculated using these plus the SWin and LWin measurements. SW albedo typically is assumed to be a constant, typically taken from local satellite observations; Tsurface can often be calculated from air temperature of ground temperature measurements.
Usage
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
Net-radiometers are not standardised.
References
Specifications, drawings and pictures courtesy of Hukseflux Thermal Sensors, www.Hukseflux.com
See also
Earth-based meteorological equipment and instrumentation Anemometer · Barograph · Barometer · Ceiling balloon · Ceiling projector · Ceilometer · Dark adaptor goggles · Disdrometer · Field mill · Hygrometer · Ice Accretion Indicator · LIDAR · Lightning detector · Nephelometer · Nephoscope · Pan evaporation · Pyranometer · Radiosonde · Rain gauge · Snowboard · Snow gauge · SODAR · Solarimeter · Sounding rocket · Stevenson screen · Sunshine recorders · Thermograph · Thermometer · Transmissometer · Weather balloon · Weather radar · Weather vane · Windsock · Wind profilerCategories:- Electromagnetic radiation meters
- Radiometry
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