The Solar Irradiance Data Preprocessing In Solar Radiation Monitor

The total solar irradiance is defined as: the average of solar energy received by the outer surface of the Earth's atmosphere(unit:W / m~2). When the distance between Sun and Earth is 1 AU, this solar irradiance value is called the solar constant. Solar constant reflecting the energy characteristics of solar radiation, which is changed over time. To understand the process of change, measuring the solar constant has very important significance on understanding of climate change and controlling of the global environment.Solar radiation monitor is installed in satellite FY-3 to measure the solar irradiance. Solar radiation monitor is composed of wide field absolute radiometer (or power calibration radiometer) and it does not depend on any radiation standard. With this absolute radiometer to measure solar irradiance, the solar constant access to accurate data because calibration process used method of electric power alternative radiation power. Solar radiation monitor is point to the sun installed, which uses of wide-field absolute radiometer measure of solar irradiance during the sun flight over the radiometer field of view. Solar radiation monitor consists of three identical absolute radiometer, with the satellite X-axis (the satellite orbital plane) are 22°,27°,32°. During the working life, incident sunlight of the satellite with the satellite orbital plane vector angle changes between the 15°-38°. The three absolute radiometer to measure solar irradiance field of view are±9.3°, which ensures on-orbit solar radiation monitor can be measured solar irradiance data every day and every lap.This paper first describes the principle of solar radiation monitoring and measurement processes. During the sun sweep of the field of view of solar radiation monitor, varying function of incident angle and radiometer receiver cavity temperature response is studied. Calibration of time-varying incident angle for solar radiation monitor is also discussed in this paper. The absolute radiometer of the solar radiation monitor detects small changes of the radiation through electrical calibration. Radiation power of these small changes is influential to received solar radiation. Radiometer cavity receives changes of radiation power is actually caused by the changing angle of incident sunlight. The absolute value of temperature response of radiometer cavity can be calculated by solving the cavity temperature response function. Cavity temperature default value ratio responses value is defined as the angle correction factor. Use of the distance correction and angle correction to the original solar radiation, resulting in solar constant value.Satellite FY-3 has measured more than 32,000 sets of data in the past two years. The data changes through the amendment of this observation angle and the obtained value of solar constant is 1368±4 W / m~2 which the uncertainty is 0.3%. This result is corresponding well to World Meteorological Organization recommended value 1367±7 W / m~2 and the data measured on other satellite in the same period.