Vaisala Energy Support
What is the Vaisala 1.2 dataset?
The Vaisala 1.2 dataset is the third dataset created by Vaisala, then 3TIER. The main change from the V1.1 dataset was increasing the temporal resolution of the MODIS aerosol and water vapor inputs from monthly to daily. Four MODIS data streams are still used to derive the satellite aerosol values.
The clear sky model used is based on the Perez SUNY v1.0 methodology, as described in R. Perez et al., “A new operational model for satellite-derived irradiances: Description and validation," Solar Energy, Vol. 73, Iss. 5, November 2002, pages 307-317.
The primary difference between the Vaisala 1.2 and Perez v1.0 clear sky algorithms is that the Linke coefficient used here is derived using a Vaisala proprietary method incorporating the MODIS aerosol optical depth and water vapor dataset mentioned above, using Ineichen's “Conversion function between the Linke turbidity and the atmospheric water vapor and aerosol content,” Solar Energy, 82, 1095-1097.
Vaisala uses a proprietary cloud index calculation methodology to compute cloudy sky irradiance. To derive the cloud index, the satellite radiance measurements are first processed to account for instrument degradation over time. The Vaisala cloud algorithm then divides the satellite measurements into bins by solar azimuth and zenith angle, and treats each bin independently for the calculation of a cloud index. The fit between cloud index, clear-sky GHI, and observations is done on a per satellite basis.
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