A net radiometer is an actinometer designed to measure the net radiation at the Earth’s surface. This device is useful for measuring direct incoming short wave radiation, reflected short wave radiation, diffused long wave radiation by sky and long wave radiation emitted by the ground surface.
Operation of Net Radiometers
A typical net radiometer consists of a thermopile sensor with upper and lower surfaces forming the outer sensing surfaces of the radiometer. The surface that absorbs the most radiation gets heated up rapidly, and its temperature will be greater than that of the opposing surface. As a result, a temperature difference is created between the two sides of the sensor. This difference in temperature is then converted into a voltage by the Seebeck effect.
The voltage output using this instrument is a measurement of the difference in incident radiation between the two surfaces using a calibration factor. The sensing surfaces are protected from convective heat exchange and weather condition by polyethylene windshields.
Net radiometers are commonly used in meteorological stations, solar energy studies and building physics.
Types of Commercially Available Products
The following are the net radiometers available in the market:
- NR01 Net Radiometers – Developed by Hukseflux Thermal Sensors, NR01 net radiation sensors allow separate measurements of solar and long-wave radiation, facing both up and down. They can be easily connected to commonly used data logging systems. The advantages of NR01 sensors include light weight, ease of leveling, solar offsets in the longwave measurement and pyrgeometer heating.
- MR-60 Net Radiometers – MR-60 radiometers developed by Eko Instruments are 4-component radiometers that measure solar short-wave radiation in the visible to near/mid-infrared region and earth long-wave radiation in the far-infrared region. These sensors can also measure albedo and radiation balance.
- SNR01 Net Radiometers – Dynamax’s SNR01 radiometers incorporate four separate sensors for measuring total global and surface reflected short-wave solar irradiance, and the far infrared long-wave radiation components. A key advantage to the SNR01 radiometers includes integrated two-axis leveling assembly for improved in-field level adjustment, decreased FIR sensor/pyrgeometer window thermal offset error and reduced instrument weight.