This page offers access to pieces of software relating to

• Sun - Earth geometry,
• Sun geometry perceived by an observer,
• extraterrestrial radiation,
• as well as
• satellite Meteosat geometry,
• and conversion of image co-ordinates into geographical coordinates and vice-versa.

Other pieces of software are available for the implementation of the method Heliosat-2 for converting Meteosat images into irradiance maps:

• model ESRA for clear-sky,
• all libraries for the method Heliosat-2, including those relating to the solar geometry, clear-sky and Meteosat images (up to Meteosat-7 included).

A library in C for computing the solar geometry. The library "solar_geometry.c" comprises the following items:

• geometry of the solar beam,
• sunrise, sunset and daylength,
• changing the time system,
• position of the sun in the sky (see an execution of the code in applet Java. Is useful to check the correct implementation),
• extraterrestrial irradiation,
• integrated procedures providing the above parameters for a given day, or on monthly or yearly averages.

This library has been changed on 8 July 2004, to account for the differences between geographic and geocentric coordinates. This difference is only for latitude and reaches its maximum of 0.2 degree (approx. 20 km) at 45 degrees. Coordinates in equations for sun geometry are geocentric, while latitudes used by customers are geographic.

These libraries, in C, are for computing the geometry of the satellite (elevation, azimuth) with respect to the pixel, and to convert latitude - longitude into satellite co-ordinates row - columns and vice-versa.

• The library "meteosatlib.c" is valid for the satellites Meteosat-1 up to -7. More information. Please, take note that the navigation fo the images (i.e., the geometry of the images with respect to the geography) may change. This note lists such changes.
• The library "msg_geom_lib.c" is valid for the satellites Meteosat Second Generation (Meteosat-8 and followings). More information.

There are two Meteosat products treated in the library "meteosatlib.c" (Meteosat-1 to -7):

1. a high resolution image (noted HR) with 2500 lines and 2500 pixels per line oriented NW (lig 1, col 1) to SE (lig 2500, col 2500). The pixel size is 5 km at nadir. When such coordinates in lines and columns are used, they always refer to the image correctly oriented NW-SE. Note that the acquired image is actually inverse, taken from SE to NW, so that the first pixel acquired within a time frame is the south-easternmost pixel on the image (2500, 2500).
2. a B2 image (noted B2) with 416 lines and 416 pixels per line, subsampled from the high resolution as follows: starting from the first pixel acquired (2500, 2500) are taken each pixel every 6 lines and every 6 columns. These selected pixels are noted HRb2 in the high resolution product, and B2 in the B2 product. Thus, a pixel B2 represents a pack of 6x6 HR pixels whose south-easternmost one substitutes the other ones. Note that 6 cannot divide 2500, so that the B2 product ignores the last 4 lines and columns in the acquired direction. The first HRb2 pixel is positioned (10,10) on the high resolution image, while the last one is (2500, 2500) using a correctly oriented HR image.

The library "meteosatlib.c" comprises the following items:

• converting latitude - longitude to HR co-ordinates and reverse,
• converting latitude - longitude to B2 co-ordinates,
• relationship between HR pixels, HRb2 pixels and B2 pixels in their respective frames,
• elevation angle of the satellite seen from the ground and azimuth.

Meteosat Second Generation - Meteosat-8

The library "msg_geom_lib.c" comprises the following items:

• converting latitude - longitude to HR co-ordinates and reverse,
• converting latitude - longitude to 10 km co-ordinates,
• elevation angle of the satellite seen from the ground and azimuth,
• time lag between beginning of acquisition and current line.