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Quantity | Columns in the FT2 file | Histograms | Comment |
---|---|---|---|
Bin start and stop | START, STOP |
| No differences, by definition. |
Spacecraft position in ECI coordiantes (x,y,z) | SC_POSITION array |
| The differences in a very small number of bins are most probably due to Reason 1 above. |
Ground point latitude and longitude | LAT_GEO, LON_GEO |
| Reason 1. |
Spacecraft altitude | RAD_GEO |
| Reason 1. |
Zenith direction | RA_ZENITH, DEC_ZENITH |
|
|
McIlwain coordinates | L_MCILWAIN, B_MCILWAIN |
|
|
Geomagnetic latitude | GEOMAG_LAT |
| 16 percent of the time bins are in the underflow bin of the histogram. This is due to a known issue: on Feb. 2, 2010 we changed the quantity from unsigned to signed. Thus, all old FT2 files produced before that date have a always-positive GEOMAG_LAT, while the reprocessed ones have it signed from the beginning of the mission. |
South Atlantic Anomaly flag | IN_SAA |
|
|
Z-axis direction | RA_SCZ, DEC_SCZ |
| Reason 1. |
X-axis direction | RA_SCX, DEC_SCX |
| Reason 1. |
Orbital Pole direction | RA_NPOLE, DEC_NPOLE |
| Here there are considerable differences, because the new code compute the coordinates of the Orbital Pole in a different way respect to the old one. If vi is the position vector for the i-th bin in the FT2 file, the old code computed the orbital pole vector for the i-th bin as the cross product between vi-1 and vi, while the new code uses the product vi cross vi+1. Thus basically I should compare each i-th entry in the new set with the (i+1)th entry in the old one, to obtain the same results. I don't understand why the differences are basically only in the RA, though. |
Rocking angle | ROCK_ANGLE |
| Reason 1. |
LAT GNC mode | LAT_MODE |
|
|
LAT Configuration | LAT_CONFIG |
|
|
Data quality flag | DATA_QUAL |
| Need to check why there are these differences in a couple of runs. I suspect those are BAD runs, or runs with the new values for the DQM flag. |
Attitude quaternion | QSJ_1,QSJ_2,QSJ_3,QSJ_4 |
| Reason 1. |
Live time | LIVETIME |
| Differences are due to the bug already found in the old FT2 code. See below. |
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