will see such terms as radiance, irradiance, luminance, illumination, illuminance, and the geometric relationship between the energy source and the surface. First of all, irradiance at certain point of a surface is the density of radiant flux ( power) per unit of surface area, while radiance at certain point of a surface in a. The amount of solar radiation incident on a tilted module surface is the component From these equations a relationship between Smodule and Shoriz can be.

### Average Solar Radiation | PVEducation

Similarly, the equivalent irradiance can be defined by: For example, the solar illumination received on land varies with the earth-sun distance, which varies during the year. The solar illumination integrated in the day j for a surface perpendicular to the sun is worth: The spectral solar irradiance shows large variations with wavelength.

Solar illumination at the top of the atmosphere according to the wavelength. To my knowledge, the most accurate measure available today is that of Thuillier et al. Irradiance is a useful quantity, but which still depends on the field of view of the detector. The narrower the field of view, the lower the irradiance. It also depends on the orientation of the detector with respect to the direction from which the light comes. For example, if the detector is oriented parallel to the direction of the photons, it will not receive light.

Conversely, when the detector is perpendicular to the light direction, it receives a maximum irradance.

To obtain a unit independent of the characteristics of the instrument, we will therefore have to define a new quantity yes, one more Definition of solid angle. As for the quantities above, the equivalent spectral radiance is defined as: When throughput is small, which is usually the case in remote sensing, we get: The radiance is a unit widely used in remote sensing, since it combines several advantages: The energy measured by a detector is proportional to the equivalent luminance.

FInally, the equation may be rewritten as: In equation 1all the variables are instrument characteristics, except the equivalent spectral luminance, which is independent of the characteristics of the instrument. The measurements obtained are therefore proportional to the radiance of the observed pixel, to a factor S.