Solar irradiance at the top of the atmosphere on a plane normal to the incident radiation, and at the mean distance of the Earth from the Sun. Solar irradiance is also referred to as the solar constant. In satellite remote sensing, the solar irradiance is used as an onboard calibration of visible band sensors. Some climate studies suggest that small variations in the solar irradiance associated with solar activity over days to decades may have an effect the Earth's climate. The intensity of the sun's radiation at different wavelengths. The radiation is generally given in terms of solar constant S, defined in terms of flux of total radiation received outside the earth's atmosphere per unit area at mean sun earth distance., and has the value S = 1.34 X 10*6 ergs cm*-2 sec*-1.
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre (W/m2) in SI units. Solar irradiance is often integrated over a given time period in order to report the radiant energy emitted into the surrounding environment (joule per square metre, J/m2) during that time period. This integrated solar irradiance is called solar irradiation, solar exposure, solar insolation, or insolation. Irradiance may be measured in space or at the Earth's surface after atmospheric absorption and scattering. Irradiance in space is a function of distance from the Sun, the solar cycle, and cross-cycle changes. Irradiance on the Earth's surface additionally depends on the tilt of the measuring surface, the height of the Sun above the horizon, and atmospheric conditions.Solar irradiance affects plant metabolism and animal behavior. The study and measurement of solar irradiance have several important applications, including the prediction of energy generation from solar power plants, the heating and cooling loads of buildings, climate modeling and weather forecasting, passive daytime radiative cooling applications, and space travel.
