Radiometer and Optical Dome

 In meteorological observation, solar radiation is an indispensable measurement parameter. The observation of solar radiation includes total radiation, scattered radiation, direct radiation, reflected radiation, ultraviolet radiation etc. Analysis of solar radiation parameters plays a major role in the research of solar energy, meteorology, environmental ocean, agricultural ecology, building materials and other aspects.

Instruments for detecting solar radiation usually use a glass dome cover as windshield, which is often made of optical glass with high transmittance. The spectral range of the windshield is 280-3000nm. The optical dome isolates the sensor in the meter from the external environment and protects the sensitivity of the sensor. Besides, the optical dome effectively prevents the sensor from aging due to changes in the environment,  improves the anti-interference ability of the radiometer and prolongs the service life of the radiometer. The quartz dome is the most common optical dome used for the radiometer.

1. Different kinds of radiometers

Pyranometer

The total solar radiation is the sum of the direct solar radiation and the scattered solar radiation (global solar radiation) on the horizontal plane of a certain observation point on the earth. Pyranometer are widely used in greenhouses, laboratories, agriculture and scientific research to measure the intensity of solar radiation.

Reflection radiometer

The reflection radiometer is used to measure the total solar radiation with a spectral range of 0.28-3μm. It is also used to measure the solar radiation incident on the slope. If the sensing surface of the reflection radiometer is facing down, reflected radiation is measured. If the reflection radiometer adds a light-shielding ring, scattered radiation is measured. Therefore, it is widely used in solar energy, aging of building materials and air pollution.

Scattering Radiometer

Total radiation includes direct radiation and scattered radiation. Scattered radiation is short-wave radiation and must be measured with a radiometer. Scattering radiometers are used in weather stations and scientific research departments to continuously measure the intensity of scattered radiation in the sky. In order to prevent the influence of the environment on its performance, a two-layer quartz glass dome is used. The optical domes are ground by precise optical cold processing.

UV radiometer

The ultraviolet radiation sensor is a precision instrument used to measure solar ultraviolet radiation in the atmosphere.

A quartz glass cover is installed above the ultraviolet radiometer. The optical dome covers the spectral transmission range, reduces the influence of the external environment on the detector, and protect the sensor. The optical filter with optical coating is made through a special process. It receives ultraviolet light and prevents direct sunlight. The application of ultraviolet radiation meter includes ultraviolet forecast and detection, comprehensive environmental and ecological research, scientific research and academic experiment, medical protection, cosmetics research and development and weather and climate change research.

Spectroradiometer

The spectroradiometer accurately measures the total solar radiation, infrared, visible light and ultraviolet radiation. It is widely used in scientific research such as agricultural meteorology, plant physiology research, solar energy utilization, ocean survey, aging of building materials and air pollution.

To reduce the impact of weather changes on the performance of the spectroradiometer, it is equipped with optical domes. The inner cover is an optical dome made of quartz glass. The outer cover is an optical dome ground by precise optical cold processing.

Sunshine Duration Sensor

The sunshine duration sensor is used to continuously measure the sunshine duration. Due to the protection of the optical dome cover, it is capable of long-term observation outdoors. It is widely used in meteorology, environment, agriculture, scientific research, etc., to measure the sunshine duration.

2. How to choose suitable glass material for optical domes?

According to the environment and actual application, the material of the optical dome needs to have a wider transmittance of waveband. For the optical domes used in radiometers, the commonly used optical materials are N-BK7, N-BK10, UV fused silica, IR fused silica and sapphire.

N-BK7 is an economical choice that meets most measurement needs. Its spectral range (50% point) between 285nm and 2800nm.

Ultraviolet fused silica, its spectral range (50% point) is 190nm to 2750nm. Ultraviolet fused silica usually used in UV radiometers.

Infrared fused silica, whose spectral range (50% point) is between 200nm and 3600nm. Currently, it is the optical material with the best performance. Meanwhile, its price is more expensive than other optical materials.

The sapphire dome has the best spectral range. Its spectral range is from 190nm to 5500nm. However, the price of the sapphire is very expensive.

High-quality optical domes are an important optical component to ensure the accuracy of the radiometer. The concentricity, thickness irregularity and surface quality of the dome are the key parameters for high-quality domes.

CLZ Precision Optics has extensive experience in processing and producing high-precision optical domes. For the high-precision optical dome with a diameter of 40-50mm, we strictly control the concentricity and thickness irregularity of the optical dome <0.02mm. For high-precision optical domes with a diameter of 24-30mm, we control the concentricity and thickness irregularity to <0.01mm. The pyranometer with mentioned above parameters has excellent performance. The best material of optical dome is fused silica.

In 2017, CLZ Precision Optics upgraded the production process. In addition to producing N-BK7 dome and fused silica dome, we also produce high-precision sapphire domes. Although the sapphire dome is expensive, it has good performance and prospects.

3. Applications of radiometer

Automatic sun tracker

It loads with various types of solar radiometers. It possesses high tracking accuracy, excellent load capacity, and strong environmental adaptability. Under various extreme climatic conditions, it works stably. It is widely used in photovoltaic environmental monitoring, meteorological radiation observation, agricultural, forestry research and other research fields.

Comprehensive Observatory of Solar Radiation

The comprehensive observation station of solar radiation includes total radiation sensor, photosynthetic effective sensor, sunshine duration sensor, ultraviolet radiation sensor, illuminance sensor, direct radiometer, scattered radiometer, reflected radiometer and net radiometer.

Solar Radiation Recorder

There are mainly three types of solar radiation reaching the ground: ultraviolet radiation, infrared radiation and visible light radiation. Solar radiation of different wavebands has different effects on the growth of crops. Measuring and recording solar radiation with solar radiation recorders plays an important role in agricultural production.

CLZ Precision Optics Co., Ltd. specializes in the process of optical domes for meteorological instruments. We have provided domestic and foreign customers with high-precision domes made of various optical glass materials for a long time now. We look forward to providing high-quality optical domes for your radiometer. If you need optical domes for radiometers, please contact talia@clzoptics.com.