Global Radiation (SIS) is the amount of incoming solar radiation (direct + diffuse). The acronym used here is SIS – solar incoming radiation at the Earth surface.
Direct Normalized Irradiance (DNI): Direct Irradiance is the amount of sunlight reaching the Earth surface directly, without beeing scattered at clouds, aerosoles or other particles in the atmosphere. The direct normalized irradiance (DNI) is calculated as if it would reach the surface perpendicular.
Sunshine Duration (SDU) provides the number of “sunny hours” per day or per month:
SDU = Sunny slots / all slots during daylight * daylength.
A slot is defined as sunny if the DNI > 120Wm-2. Slot: pixel in each satellite image considered. Considered are ½ hourly instantaneous data.
Daylength: period during which the sun elevation angle > 2.5°.
All three variables, Global Radiation (SIS), Direct Normalized Irradiance (DNI) and Sunshine Duration (SDU) are provided by the CM SAF. They are derived from MVIRI and SEVIRI sensors on Meteosat first and second generations, respectively, using the SARAH-2.1 retrieval.
The Climate Data Records of SIS, DNI and SDU cover the period January 1983 – December 2017. The Interim Climate Data Records of SIS, DNI and SDU provided in this cube cover the period January 2018 – December 2020.
For a quick overview on these data records as provided in the D&V cube refer to:
For further information please refer to: