Maps in real time "Hc3v4-15mapGHI"

Summary  -  In practice   -   Methodology

Last update: Apr. 2015

Summary

Annual subscription to 15 min Global Horizontal Irradiation bitmap Maps in Wh/m² and in TIFF format delivered in real time (h-15 min) on a given area, during daylight time from 3:00 TU to 20:45 UT.

Date: service available since March 2011

The pixel resolution is the Meteosat native pixel size over the zone and the projection is the Meteosat satellite native projection.

The maps are retrieved by the Customer through a Wget type command or an http request directly in a specific directory on the soda-is server machine. The Customer is identified through a login and password.
A mirror backup server (http://pro.soda-is.com/) is available to increase the reliability of the service.

In practice

Inputs:

The Customer communicates the rectangular box over the area cover by the service.

Outputs:

To limit the load on the service, the GHI values are divided by a factor of 1.2 to be stored in 8 bit TIFF format, leading to the approximate precision of 1 watt.

It is also possible to GHI maps with a 10^-2 precision in 16 bit TIFF images.

Archive: please note that the Hc3v4-15mapGHI maps are conserved for the last 4 weeks.

Methodology

The Hc3v4-15mapGHI includes the post-processing layers that are available in the time series HC3v4. Here they are:

  1. Each pixel is re-interpolated in time at an exact 15 min UTC
  2. All pixels where sun elevation is below 2 degrees are interpolated
  3. Altitude correction (using SRTM Altitude database)
  4. Kc-max correction
  5. Bias correction

1. Each pixel is re-interpolated in time at an exact 15 min UTC

To be able to apply the re-interpolation, this step implies to already have the next slot. Let's take as example Germany maps today at 10:15.

HC15mapGHI creates a new map [server]/germany/germany_irr_1504221000.tif. It contains GHI irradiation extracted from the sole 1504221000 MSG slot, i.e. irradiation at approximately 10:11 UT for Germany.

Hc3v4-15mapGHI generates 2 maps:

  • [server]/germany-hc3v4/germany_irr_1504221000.tif contains GHI irradiation from 09:45 to 10:00 UT. This map is final.
  • [server]/germany-hc3v4/germany_irr_1504221015.tif contains GHI irradiation from 10:00 to 10:15 UT. This map is a 4 minutes forecast (for Germany) and will be updated 15 minutes later.

2. All pixels where sun elevation is below 2 degrees are interpolated

When the sun elevation is below 2 degrees, the previous service without post-processing layers (HC15mapGHI) was generating no data (pixel = 254). In the new service HC3v4-15mapGHI, the irradiation values are interpolated using an interpolation based on the persistance of the clearness index Kc (GHI/GHI_clearsky.

NB: this remark can be generalized for every missing MSG slot. The previous service without post-processing layers was generating no map for Germany, whereas the new service provides an interpolated maps based on Kc persistance.

3. 4. 5. Altitude, Kc_max and bias corrections

Altitude correction and Kc-max correction are bug fixes for altitude and albedo errors.

Bias correction is a global calibration of hc3v4 w.r.t. BSRN stations.