...
The old code (ft2Util), written by Andrea Tramacere, has performed very well during the first 3 years of the mission. But , it has been patched a lot of times under the pressure of time, and it is now quite difficult to understand and to maintain. Thus we decided to rewrite it, taking into account all the things we learned during these 3 years.
...
The implementations are completely different, but from a conceptual point of view there are only three main differences:
...
- Handling of data gaps during the livetime computation: Fermi data on-ground can have two different kinds of gaps: gaps in the Digi file or gaps in the Merit file. The former type can be the results of a copy/download problem from the spacecraft or the ground stations, while the latter can be caused by a problem during the reconstruction (the Recon step). Both of them can also result from problems during the merging of different chunks of data. Note that all these problems are usually temporary, and gaps are usually filled with a roll back of the appropriate processing steps. The old code used to try to compensate for those gaps, by subtracting the corresponding deadtime from the livetime of the affected bin(s). The new code instead isolates the time span affected by these problems in single bins, which will have zero livetime, and thus will generate bad time intervals which will be excluded by downstream software (like the Science Tools).
- Sun coordinates: the new code now compute the Sun coordinates for each bin in the FT2 file.
- Exploit all the attitude information: the attitude information is issued by the spacecraft at 5 Hz, and it is formatted in ATT messages available on-ground in the so-called "Magic 7" files. The position information instead is issued by the spacecraft at 1 Hz. The old code used only those ATT messages issued contemporaneously to ORB messages, discarding the others. The new code instead keeps all the information. So when interpolation is needed, the old code have less information than the new one, slightly degrading the quality of the interpolations. The difference is anyway unimportant in most of the circumstances, leading to very small improvement in the quality of the interpolations and extrapolations of the satellite attidue.
Validation
Here I collect the results of the testing I performed, comparing the output generated by the old ft2Util code with the output generated by my code.
...