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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, thoughdid this test, and everything is ok, see below. |
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. |
...
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 | |
|
Ground point latitude and longitude | LAT_GEO, LON_GEO | |
|
Spacecraft altitude | RAD_GEO | |
|
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 | |
|
X-axis direction | RA_SCX, DEC_SCX | |
|
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, thoughdid this test, and everything is ok, see below. |
Rocking angle | ROCK_ANGLE | |
|
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 | |
|
Live time | LIVETIME | | Differences are due to the bug already found in the old FT2 code. See below. |
There are still some differences in some quantities related to the EarthCoordinate class of the astro package. By looking at the time histories, all the differences are before a certain date, thus they are almost certainly related to a bug-fix in the astro package. (to be confirmed)
Orbital Pole
I repeated the comparison between the RA_NPOLE and DEC_NPOLE quantities, but comparing a given i-th bin of the old version of the FT2 files with the i-th-1 bin in the new FT2 file, to solve the discrepancy in the computation method. As expected, the differences vanish:
Livetime
As already found in my former test (see the mother page), the old code had a bug in the livetime computation. Here I show the difference in livetime between the two codes, as function of time, thus on the y-axis there is the usual fractional difference, while on the x-axis there is the MET time (in seconds):
(text continue below the gallery, click on an image to enlarge it)
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