Editorial Feature

What is a Pyrgeometer?

A pyrgeometer is an instrument for measuring the infrared radiation spectrum in the atmosphere, which extends from 4.5 to 100 µm.

This instrument has different sensitivity to short and long-wave radiations. It is designed for both material testing research and atmospheric applications.

Long-wave radiations are emitted by all objects existing on the Earth. However, the main purpose of a pyrgeometer is to perform meteorological observation of atmospheric radiation and the net radiation from between the earth and the atmosphere.

Working Principle

The pyrgeometer is operated based on the principle that radiant energy is converted into heat energy, which can be measured by a thermopile.

This instrument consists of a silicone dome to isolate long-wave radiation from solar short-wave radiation during daytime. It also includes a vacuum-deposited interference filter having a transmission range of approximately 3.5 to 50 µm, and a shielded case to minimize heating of the instrument due to solar radiation.

Thermistors are employed to monitor the temperatures of the dome, case and environmental thermal infrared irradiance.

A detector that is coated with a black paint detects a net signal from various sources including emissions from the dome, case and targets in its field of view.

The incoming radiation is absorbed by the detector, and the heat flows through the instrument body. The thermal gradient across the thermopile creates a voltage that is relative to the net radiation.

The spectral range of the incoming radiation is restricted by the filter that eliminates unwanted solar radiation. Thus, the thermal infrared irradiance can be measured in watts per square meter.

Since the case is protected from solar radiation, its temperature is considered as the air temperature, which provides the degree of thermal emission by the atmosphere. Conversely, the dome is unprotected from heat. Therefore, the difference between thermal emissions of the dome and case provides an erroneous signal which has to be eliminated.

Applications

Atmospheric radiations from water vapours, clouds, and CO2 become the core measurement factors for the pyrgeometer. The pyrgeometer is also used for material testing research applications and low temperature applications of the sensors applied in aircraft observations.

Products on Market

The following are the list of pyrgeometers that are currently available in the market:

CGR 3

Developed by Kipp and Zonen, the CGR 3 pyrgeometer is capable of generating a voltage that is proportional to the net radiation in the far infrared region. For this reason, the device features a temperature sensor, silicon window and solar-blind filter.

It also includes a newly designed sunscreen that covers both the body and connector to improve the accuracy of the device.

IR02 Pyrgeometer

IR02 pyrgeometer is a sensor developed by Hukseflux Thermal Sensors to serve meteorological outdoor experiments. This instrument measures far infrared radiation flux.

With the help of a thermopile sensor, the device generates a small output voltage that is relative to the flux created between the device and the object within the field of view. The device can be directly connected to data-logging systems.

The key benefits of IR02 pyrgeometer are as follows:

  • It prevents dew deposition
  • It has improved measurement accuracy.

References

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