Note about the former service about Linke turbidity factor (TL) database in the Helioserve web site, now redirected to the SoDa web service for the TL.

The Helioserve web site has been integrated inside the HelioClim web site.

One may obtain on-line values of the Linke turbidity factor through the SoDa web service (see "climatological data") for any site in the whole world.

This worldwide database of the Linke turbidity factor (see maps below) as well as the database for elevation (orography) can be obtained at: Les Presses, Ecole des Mines de Paris. Contact .

These files of the Linke turbidity factor database contain the twelve monthly values of the Linke turbidity factor and the elevation value of a geographical place, given by latitude and longitude. Latitude is positive North, longitude is positive eastwards of longitude 0. The data are in gridded, raw format, 1 byte per value (2 for elevation), 2160 rows and 4320 columns. Cell size is 5' (that is approximately 10 km at mid-latitude). Upper left corner is 90 N, 180 W. Then, point 90 N, 179.5 W etc. Lower right is 90S, 180 E.
The Linke turbidity factor has no unit. It typically ranges between 3 (clear skies) to 7 (heavily polluted skies). The factor was multiplied by 20 for storage. A value of 70 means a Linke turbidity factor equal to 3.5.
The database is also available in ArcInfo/ArcGrid ASCIIGRID.

The way of constructing the database is explained below. More information.

Within the project SoDa (funded by the European Commission), we have created maps of the TL for each cell of 5 minutes of arc angle world-wide. For each month, we combined TL extracted from radiation data and TL extracted from the SRB gridded data from NASA. In order to cope with the large differences in spatial resolution, we also used water vapour maps and orography maps in the fusion methodology.

The errors were assessed by cross-checking, that is removing one station (out of approx. 220), making calculation for this site (using the elevation database and not the actual elevation) and computing the discrepancy. The bias was found to be 0.01 and the rmse 0.73 as an annual average with slight deviations from month to month. These values are of better quality than what was offered in Helioserve and are covering the whole world. Hence, we decided to remove our offer and to redirect requests to the SoDa service.

See the maps for January, February, March, April, May, June, July, August, September, October, November, December.

This work was performed by Jan Remund (Meteotest), Mireille Lefèvre, Michel Albuisson, Thierry Ranchin and Lucien Wald (Armines / Ecole des Mines de Paris) with the help of Lamissa Diabaté (UFAE, Bamako).