NASA-SSE satellite data

NASA-SSE (Surface Meteorology and Solar Energy programme) are monthly data, average of 1983-2005 satellite measurements, provided for any cell in a grid of 1°x1° over the world (1° latitude is 111 km). See the Nasa SSE site for further information.

Also available from this database, but direct import not implemented in PVsyst: irradiances or temperatures in daily values for any period in the 1983-2005 range.

Details of the method

In contrast to ground measurements, the SSE data set is a continuous and consistent 22-year global climatology of insolation and meteorology data. It is derived from several databases, including "Goddard Earth Observing Systems (GEOS-1), the International Satellite Cloud Climatology Project (ISCCP D-1), from data of the Geostationary and Polar satellite for Environmental Observation (GOES and POES), the European Geostationary satellite Meteosat, and Japanese ones. etc.

Although the SSE data within a particular grid cell are not necessarily representative of a particular microclimate, or point, within the cell, the data are considered to be the average over the entire area of the cell. For this reason, the SSE data set is not intended to replace quality ground measurement data. Its purpose is to fill the gap where ground measurements are missing, and to augment areas where ground measurements do exist.

Accuracy

The accuracy of Satellite measurements has been evaluated using numerous ground-based measurements. Although the reliability of these ground measurements themselves is not always well assessed, the NASA estimates that the RMS Error on monthly values is around 13-16%, and the Mean Bias Error (MBE) lies between -2% and +0.7%.

Further information about the data generation

The solar energy data is generated using the Pinker/Laszlo shortwave algorithm. Cloud data is taken from the International Satellite Cloud Climatology Project DX dataset (ISCCP). ISCCP DX data is on an equal area grid with an effective 30x30 km pixel size. The output data is generated on a nested grid containing 44,016 regions. The nested grid has a resolution of one degree latitude globally, and longitudinal resolution ranging from one degree in the tropics and subtropics to 120 degrees at the poles. This, in turn, is mapped to a one degree equal-angle grid (360 longitudes by 180 latitudes). The remapping method is by replication, wherein any grid region that is larger than 1x1 degree is subdivided into 1x1 degree regions, each with the same value as the original.