Net radiometer
Encyclopedia
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.
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.
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.
, climatology
, solar energy studies and building physics. They can be seen in many meteorological stations—typically installed horizontally.
Actinometer
Actinometers are instruments used to measure the heating power of radiation. They are used in meteorology to measure solar radiation as pyrheliometers.An actinometer is a chemical system or physical device which determines the number of...
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.
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
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
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 meteorologyMeteorology
Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...
, climatology
Climatology
Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences...
, solar energy studies and building physics. They can be seen in many meteorological stations—typically installed horizontally.
Standardisation
Net-radiometers are not standardised.See also
- radiometerRadiometerA radiometer is a device for measuring the radiant flux of electromagnetic radiation. Generally, the term radiometer denotes an infrared radiation detector, yet it also includes detectors operating on any electromagnetic wavelength....
- PyranometerPyranometerA pyranometer is a type of actinometer used to measure broadband solar irradiance on a planar surface and is a sensor that is designed to measure the solar radiation flux density from a field of view of 180 degrees...
- irradianceIrradianceIrradiance is the power of electromagnetic radiation per unit area incident on a surface. Radiant emittance or radiant exitance is the power per unit area radiated by a surface. The SI units for all of these quantities are watts per square meter , while the cgs units are ergs per square centimeter...
- Meteo-Technology instrumentation website