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This is kind of a minor point, but may need to be clarified: During the time between the stop (LPASTOP) of a run and the LPASTART of the next (if a stop/start is issued outside an SAA passage - see above), the LAT will be dead as far as data taking is concerned. If a time interval is not explicitly included in an FT2 file, i.e., if the time of a START entry is not the same as the time of the previous STOP entry, we can just assume that the missing interval was dead time, right? \[anders\] Any time between an LPASTOP and the subsequent LPASTART is deadtime i.e. we did not take any data. |
(D. Band 4/6/07) First, is this an ICD/FFD issue, given that every row provides the start and stop time? Second, I think it makes sense to increase the time resolution when necessary--perhaps we should establish an angular change criterion?
2. DEADTIME column
(Digel) For reasons that I no longer recall, we originally decided to keep track of both accumulated livetime (in each 30 second interval) and accumulated deadtime (since the start of the mission). The Science Tools do not use the DEADTIME column and makeFT2 assigns the value 1-LIVETIME to the column anyway.
I propose to remove this column from the definition of FT2.
(D. Band 4/6/07) I concur with removing this column.
3. McIlwain coordinates
(Digel) These are geomagnetic coordinates and presumably useful in some way for studying variations in residual background. The actual model we are using for the background depends on geomagnetic latitude, however, rather than the McIlwain L, B. I'm not entirely sure that we need (i.e., that anyone will use) L, B, but I won't propose removing them. I would like to propose including geomagnetic latitude, however, as an additional column.
(D. Band 4/6/07) I concur with adding this column (especially since I don't have to do the calculation...).
4. IN_SAA column
(Digel) This is just a flag defined to be True if the LAT is in the SAA. Right now it is not entirely clear (to me) whether we will be getting spacecraft position and attitude information during SAA passages. This would have implications, e.g., for using the Low-Rate Science counters to monitor the boundaries of the SAA, and also would mean that an IN_SAA flag would be superfluous. I'll update (or remove) this entry when I find out the answer.
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So the IN_SAA flag remains relevant to the definition of FT2.
(D. Band 4/6/07) I understand this to mean that we will keep this column.
5. Extension Name for data extension in FITS file
(Stephens) I don't know if this has ever been discussed before but I noticed a discrepancy between the data and the documentation and thought I'd bring it up. We should verify that the science tools that both produce and consume this product are using the correct extension name (EXTNAME keyword value) for the extension containing the data and that that name matches what is in the documentation. The Science Data Products ICD and File Format documents list the extension name for this extension as 'LAT_POINTING_HIST'. It formerly used to be 'SC_DATA' and the last time I checked (mid-late January) the Science Tools were still set up to use this older name. While the name doesn't really matter, what does matter is that we are consistent across the tools and the documentation. The GSSC's data ingest system works off the ICD and that document is what the HEASARC will look to as well for the data formats so we need to keep it up to date and in sync with the software. Because of our requirements on data validation and tracking, if data arrives at the GSSC that doesn't match the format in those documents, the data will be rejected as bad. The bottom line is that we should settle on a name for this extension, have David Band put it in the document, make sure all the software are using that name, and be done with it.
(D. Band 4/6/07) I am not sure which name is older. I have not strong feelings one way or the other.