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IR20 & IR20WS pyrgeometer

Research grade pyrgeometers

IR20 is a research grade pyrgeometer suitable for high-accuracy longwave irradiance measurement in meteorological applications. Thanks to Hukseflux’  technological innovation, IR20 is offered at a significantly lower price level than competing models of the same performance level. IR20 is capable of measuring during both day and night. In absence of solar radiation, model IR20WS offers even better accuracy because of its wider spectral range.

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IR20 and IR20WS research grade pyrgeometers

IR20 measures the longwave or far-infra-red radiation received by a plane surface, in W/m², from a 180° field of view angle. In meteorological terms pyrgeometers are used to measure “downward and upward longwave irradiance” (WMO definition). Longwave radiation is the part of radiation that is not emitted by the sun. The spectral range of longwave radiation is not standardised. A practical cut-on is in the range of 4 to 5 x 10⁻⁶ m. IR20 has a dome with a solar blind filter with a cut-on at 4.5 x 10⁻⁶ m, making it suitable for day- and night observations. Model IR20WS has a wide spectral range with a cut-on at 1.0 x 10⁻⁶ m. It offers a superior accuracy under conditions during night-time, when solar radiation is absent.

IR20 Pyrgeometer benefits

  • breakthrough pricing for a pyrgeometer of this performance level as a result of Hukseflux’ technological innovation.
  • correction of temperature dependence by use of the measurement function. This is far more accurate than temperature compensation in the instrument, especially at very low and high temperatures. Every pyrgeometer is supplied with temperature coefficients to enter into the equation.
  • high sensitivity. With sufficient input signal a typical datalogger no longer significantly contributes to the uncertainty of the measurement.
  • low thermal-resistance of the sensor. Competing designs need a significant correction for the difference in temperature between pyrgeometer body and sensor surface. For IR20 this is not needed.
  • fast response time (3 s). A low response time is a benefit for measurements on moving platforms such as aircraft and buoys.
  • on-board heater. Heating prevents condensation of water on the pyrgeometer dome which, when occurring, leads to very large measurement errors.
  • instrument cut-on wavelength (5 %) and the two 50 % transmission points are displayed on the product certificate for individual sensors


Measurand longwave radiation
Optional measurand sky temperature
Sensitivity (nominal) 17 x 10⁻⁶ V/(W/m²)
Spectral range  IR20 4.5 to 40 x 10⁻⁶ m (nominal)
Spectral range IR20WS 1.0 to 50 x 10⁻⁶ m
IR20WS restrictions for use only in the absence of solar radiation
Field of view angle 180 °
Response time  (95 %) 3 s
Rated operating temperature range -40 to +80 °C
Temperature dependence < ± 0.4 %  (-30 to +50 °C)
Calibration traceability to WISG
Optional traceability to blackbody (ITS-90)
Temperature sensor 10 kΩ thermistor
Heater 12 VDC, 1.5 W
Standard cable length 5 m
  • longer cable, in multiples of 5 metres
  • blackbody calibration (ITS-90)
  • VU01 ventilation unit is designed for use with IR20 / IR20WS pyrgeometer


Suggested use

  • climatological networks
  • extreme climates (polar / tropical)
  • moving platforms (aircraft, buoys)
  • uncertainty assessment (IR20 + IR20WS)
  • calibration reference (IR20WS)
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