STAR - GOESR Vegetation Health :

Javascript is currently disabled on this computer. Without javascript, many display enhancements do not work; however, all content should be fully visible and accessible.

MSG/SEVIRI -- Effective BT for IR bands

Since May 5 2008 08:00UTC, EUMETSAT changed the definition of radiance in L1.5 level SEVIRI images to "effective" radiance.

Since then, the "equivalent blackbody temperature" will be calculated by Planck function using the calibration parameters provided by McIDAS system at SSEC. Before that time, the "spectral blackbody temperature" is returned by the same procedure. EUMETSAT provided a quick fix method (polynomial fit, not shown) to convert the "spectral blackbody temperature" to "equivalent blackbody temperature".
The figure below shows the difference between the two kinds of brightness temperature.

Figure (a) the relative difference of radiance calculated from the same radiance-count values by using the calibration parameters before (ex: 05/03/2008 ) and after (ex; 05/07/2008) the date EUMETSAT changed the definition of radiance. It shows the difference is very small: up to 0.0006%.
Figure (b) shows the corresponding BT for each radiance count.
Figure (c) assumes the input is the "spectral radiance". It shows the difference of "effective BT from the spectral radiance by without using polynomial fit correction" and "spectral BT by directly applying Planck function". It is consistent with the result shown in EUMETSAT document "pdf_msg_planned_change_level15.pdf" . The difference is significant so that we have to do correction to calculate "effective BT" from the "spectral radiance".

Figure (d) assumes the input is the "spectral radiance". It shows the difference of "effective BT from the spectral radiance by using polynomial fit correction" and "spectral BT by directly applying Planck function". The difference it is about -1.2K to 1.0K. The difference is reduced by polynomial fit correction.