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Sensing little knowledge: what is photosynthetically active radiation

by:Rika Sensors     2021-12-06
Sensing little knowledge: what is photosynthetically active radiation
In the past few days, when I was learning about strawberry planting skills, I learned a new word:

photosynthetic active radiation.

The curiosity for knowledge prompted the editor to study seriously.

Although I haven't learned how to grow strawberries,

the little sensor knowledge is lit up!

Today, I will report to you and share a little knowledge about photosynthetically active radiation~

What is photosynthetically active radiation?

Photosynthetic active radiation means that green plants can be The solar radiation energy absorbed and converted by pigments.

The wavelength range of photosynthetically active radiation is 380~710nm, which basically coincides with visible light. The proportion of photosynthetically active radiation in the direct solar radiation increases with the increase of the solar altitude, up to 45%. In the scattered radiation, the proportion of photosynthetically active radiation can reach as much as 60 to 70%, so cloudy days increase the proportion of PAR. On average, photosynthetically active radiation accounts for about 50% of the total solar radiation.

Why do we need to monitor photosynthetically active radiation?

For plant growth, photosynthetically active radiation is a very important environmental element. In facility agriculture planting, different crop varieties and different growth stages require different light intensity and duration. To achieve a good planting effect, it is necessary to adjust the appropriate light intensity and time according to the growth and development of plants. Therefore, reasonable regulation of photosynthetically active radiation can not only effectively save light and electricity, but also further improve crop yield and quality.

How to monitor photosynthetically active radiation

There are three measurement systems for photosynthetically active radiation:

1. Optical system. This system is based on the response characteristics of the human eye to brightness. The instruments include illuminance meters, etc. The physical quantity observed is the luminous flux density of the visible light band emitted by the radiation source, which is measured by illuminance (lx).

2. Energetics system. Using thermocouples as sensors, there are sky pyranometers, direct pyranometers, net pyranometers, spectroradiometers, etc., to measure radiation from the perspective of capability. The radiant flux density in a certain characteristic wavelength range, that is, the photosynthetic effective wavelength band, is also measured as irradiance (Wm-2).

3. Quantum system. Using silicon and selenium photocells as sensors to measure the amount of radiation from the perspective of light quantum, there are light quantum flux meters. It is measured by light quantum flux density (umol m-2 s-1).

The photosynthetically active radiation can be directly measured with an instrument. For example, the photoelectric sensing principle is used to measure the photosynthetically active radiation sensor equipped with high-precision photoelectric sensing elements. When there is light, the light is focused by the lens by the projector, and then transmitted to the receiver lens, and then to the receiving sensor. The sensor converts the received light signal into an electrical signal and transmits it to the platform, which can effectively measure the environment in the environment. The amount of photosynthetically effective radiation.

The photosynthetically active radiation can also be estimated by direct solar radiation. In order to obtain the proportional coefficients between direct solar radiation and scattered radiation and photosynthetically active radiation, the heliograph or sky pyrometer and photosynthetically active radiance meter can be simultaneously observed to calculate the coefficient values u200bu200bof the day, month, season and year and their mutual The Soviet Union X. Mordau et al. studied the quantitative relationship between direct solar radiation (S), diffuse radiation (D) and photosynthetically active radiation (Qp), listed the calculation formula and pointed out that at mid-high latitudes 4 When the solar altitude is not less than 20° at noon in September, the calculation error of this formula for the total daily or monthly total photosynthetically active radiation does not exceed 5%. The calculation formula is: Qpu003d0.43S+0.57D.

With the continuous development of my country's agriculture, how to conduct agricultural production more efficiently and energy-saving has become a problem that needs to be considered on the road of my country's agricultural development. By mastering the influence of photosynthetically active radiation intensity on crop growth and development, the yield and quality of crops can be further improved.



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