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Radiation

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Description

In the field of meteorological measurements, solar radiation has become an important topic of study.

There are several types of radiation sensor allowing you to quantify the different types of radiation:

METEO OMNIUM defines the equipment to be installed according to client requirements.

For more information on the concept of radiation, see the section on solar radiation.

Pyranometer

The pyranometer is a global radiation sensor.
It is a heat flux sensor used for measuring the amount of solar energy in natural light. It is used to measure the total power of solar radiation in watts per square meter. It is sensitive in a spectral range (determined in nanometers) which is a function of the filter used.

Pyranometer example 1

Mechanical characteristics:

Dimensions : 110mm (W) x 68mm (H), 32mm (dome width)

Main features:

Spectral range : 300 to 2800 nm
Maximum sunlight : 2000 W/m²
Sensitivity : 5 to 20 μV/W/1/m2
Temperature range : -40°C to +80°C
Temperature dependence : <5% (-10°C to +40°C)
Response time : <18s
Field of vision : 180°
Tilt error (up to 80° with radia. 1000W/m²) : <20W/m²

ISO rating : second class

pyranometre-kipp-zonen-cmp3

Pyranometer example 2 

Mechanical characteristics:

Dimensions : 150mm (W) x 68mm (H), 50mm (dome width)
Weight :
600g

Main features:

Spectral range : 285 to 2800 nm
Maximum sunlight : 4000 W/m²
Sensitivity :
7 to 14 μV W-1 m2
Temperature range :
-40°C to +80°C
Temperature dependence :
<1% (-10°C to +40°C)
Response time : <5s
Field of vision :
180°
Tilt error (up to 80° with radia. 1000W/m²) :
<10W/m²

pyranometre-kipp-zonen-cmp11

Pyrgeometer

The pyrgeometer is a sensor of atmospheric radiation.
It is a hemispherical radiometer used to measure the incident infrared radiative flux on the surface of the Earth in all directions (solid angle of 2∏) and due to long wave radiation from the atmosphere or that emitted and reflected by the ground.

Mechanical characteristics:

Dimensions : 110mm (W) x 68.3mm (H), 30mm (dome width)
Weight : 600g

Main features:

Spectral range : 4500 to 42000 nm
Measurement range : -250 to +250 W/m²
Sensitivity : 5 to 15 μV W-1 m2
Temperature range : -40°C to +80°C
Temperature dependence : <5% (-10°C to +40°C)
Response time : <18s
Field of vision : 150°
Non-linearity : <1%

pyrgeometre-kipp-zonen-cgr3

Pyrheliometer

The pyrheliometer is a direct radiation sensor.

Mechanical characteristics:

Dimensions : 316mm (W) x 76mm (H)
Weight :
900g

Main features:

Spectral range : 200 to 4000 nm
Maximum sunlight : 4000 W/m²
Sensitivity : 7 to 14 μV W-1 m2
Temperature range : -40°C to +80°C
Temperature dependence : <0,5% (-20°C to +50°C)
Response time : <5s
Field of vision : 5 ±0,2°
Non-linearity : <0,2%

ISO rating : first class

pyrheliometre-kipp-zonen-chp1

The pyrheliometer is linked to a "Sun Tracker".
This device allows you to point the pyrheliometer at the sun.

Sun Tracker

Mechanical characteristics:

Dimensions : 500 x 340 x 380 mm (without stand)
Weight :
23kg (tracker) / 5kg (stand)

Main features:

Pointing accuracy : <0,05°
Power supply : 18 to 30 volts DC
Consumption :
21W (13W at night)
Temperature range :
-20°C to +50°C 
Angular velocity : up to 5°/s

ISO rating : first class

suntracker-kipp-zonen-solys2

Solar radiation

During the day, when solar radiation reaches the upper troposphere, a dangerous proportion of the spectrum (such as UVB and UVC) has been removed or minimised.
At this level, the incident radiation interacts with the air, atmospheric moisture and potentially dust and chemical sprays.
This divides the energy into four components which are direct waves, reflected, disseminated and absorbed.

Some definitions may thus be established:

  • diffused radiation : radiation received indirectly as a result of scatter due to air molecules (O2 and N2), clouds, fog, mist, dust or other obstructions in the atmosphere or on the ground
  • direct radiation : solar radiation from the sun directly without reflecting off clouds, dust, soil or other objects. Also referred to as direct and normal radiation, referring to the portion of sunlight that comes directly from the sun and that reaches the surface at an angle of 90°.

It may be interesting to illustrate the concept of radiation using images:

ciel1 In a clear sky, the direct radiation is maximum. However the diffused radiation (about 50% of total) can not be ignored.
ciel2 When the cloud cover is partial, a mixture of diffused and direct radiation is received at ground level. It varies depending on the position of the clouds. In some cases, the overall radiation can be amplified by 20% compared to the level of radiation from a clear sky due to the reflection of direct radiation on the edges of clouds.
ciel3 In diffused sunlight, almost all the radiation is re-transmitted, except infra-red.
ciel4 In a cloud cover situation, no direct radiation is received and depending on the type of cloud, radiation can be reduced by up to 15-20% of the radiation observed with a clear sky.