Karl D. Gordon
Summary: We need to do flats/illumination corrections for the 24 and 70 micron arrays which are dependent on scan mirror angle. Our current IOC/SV plans do not include enough such observations, especially for large source photometry and scan maps at slow and medium scan rate. To get the required number of calibration observations, we will need 34.4 hours.
In order to achieve scan mirror dependent flats/illumination corrections in a reasonable amount of time, it is assumed that they do not change as a function of time (i.e., from campaign-to-campaign). There is no reason to think that this assumption is not valid.
At present, flats/illumination corrections are expected to be needed for 24 and 70 micron data. We have confirmed with on-orbit data that we need them at 24 micron. it is assumed that the small size of the pickoff mirror contamination particles (when compared to the size of the 160 micron PSF) means that 160 microns will be unaffected. As such, we have included the numbers for 160 microns, but only for completeness.
First, we start with the number of unique scan mirror positions per standard AOR calibration cycle. A "-" means that mode does not exist for that array or that the same scan mirror positions are done in a previous AOR.
| Scan Mirror Positions Per Cycle | |||
|---|---|---|---|
| Mode | 24 | 70 | 160 |
| Compact Source | 7 | 6 | 6 |
| Large Source | 5 | 7 | 2 |
| Compact Source Super-Resolution | - | 9 | - |
| Large Source Super-Resolution | - | - | - |
| SED Mode | - | 2/chop | - |
| Scan Map, Fast | 33 | 33 | 33 |
| Scan Map, Medium | 25 | 25 | 25 |
| Scan Map, Slop | 11 | 11 | 11 |
Next, the number of DCEs needed to reach our target flat field/illumination correction S/N is needed. These numbers are from simulations of the sky and reflect the number of DCEs to overcome the confusion/cirrus noise, not necessarily the photon noise.
| Number of DCEs to get Target S/N | ||
|---|---|---|
| Array | target S/N | DCEs needed |
| 24 | 0.5% | 100 |
| 70 | 0.5% | 200 |
| 160 | 1.0% | 500 |
The number of DCEs at the same scan mirror position in a standard AOR calibration cycle is:
| DCEs at same Scan Mirror Position | |||
|---|---|---|---|
| Mode | 24 | 70 | 160 |
| Compact Source | 2 | 2 | 2 |
| Large Source | 4 | 2 | 8 |
| Compact Source Super-Resolution | - | 2 | - |
| Large Source Super-Resolution | - | - | - |
| SED Mode | - | 6/chop | - |
| Scan Map, Fast | 1 | 1 | 1 |
| Scan Map, Medium | 1 | 1 | 1 |
| Scan Map, Slop | 1 | 1 | 1 |
The number of standard calibration cycles of data needed to achieve the target S/N is:
| Target S/N Cycles | |||
|---|---|---|---|
| Mode | 24 | 70 | 160 |
| Compact Source | 50 | 100 | 250 |
| Large Source | 25 | 100 | 63 |
| Compact Source Super-Resolution | - | 100 | - |
| Large Source Super-Resolution | - | - | - |
| SED Mode | - | 34/chop | - |
| Scan Map, Fast | 100 | 200 | 500 |
| Scan Map, Medium | 100 | 200 | 500 |
| Scan Map, Slop | 100 | 200 | 500 |
We already have a number of Flats/Illumination Corrections scheduled in IOC/SV which can be used to create the necessary calibration files. They are:
| Calibration Cycles by Task | |||
|---|---|---|---|
| Task | Name | Cycles | # Repeats |
| MIPS-299 | SED Slit Illumination Function | 4 | 8 |
| MIPS-305 | 24 um Flat - detailed, Scan AOR | 30 | 1 |
| MIPS-306 | 70 um Flat - detailed, Scan AOR | 30 | 1 |
| MIPS-307 | 160 um Flat - detailed, Scan AOR | 30 | 1 |
| MIPS-313 | 70 um NF Illumination Correction | 6 | 11 |
| MIPS-914 | 24 um Flat - routine, Scan AOR | 4 | 8 |
| MIPS-915 | 70 um Flat - routine, Scan AOR | 4 | 8 |
| MIPS-916 | 160 um Flat - routine, Scan AOR | 4 | 8 |
| MIPS-917 | 24 um Flat - routine, Phot AOR | 4 | 13 |
| MIPS-918 | 70 um Flat - routine, Phot AOR | 9 | 5 |
| MIPS-919 | 160 um Flat - routine, Phot AOR | 9 | 5 |
The combination of all of these tasks gives the currently scheduled number of cycles of data useful for creating flats/illumination corrections. Remembering that scan map observations give all three arrays simultaneously, the sums are (excluding campaign D1 where the telescope emissions were too high):
| Already Scheduled Cycles | |||
|---|---|---|---|
| Mode | 24 | 70 | 160 |
| Compact Source | 52 | 45 | 45 |
| Large Source | 0 | 0 | 0 |
| Compact Source Super-Resolution | - | 66 | - |
| Large Source Super-Resolution | - | - | - |
| SED Mode | - | 32 (0,+2 chops) | - |
| Scan Map, Fast | 186 | 186 | 186 |
| Scan Map, Medium | 0 | 0 | 0 |
| Scan Map, Slop | 0 | 0 | 0 |
This leads us to the number of needed cycles of data (approximately):
| Needed Cycles | |||
|---|---|---|---|
| Mode | 24 | 70 | 160 |
| Compact Source | 0 | 55 | 195 |
| Large Source | 25 | 100 | 63 |
| Compact Source Super-Resolution | - | 34 | - |
| Large Source Super-Resolution | - | - | - |
| SED Mode | - | 34 (+1,+3 chops) | - |
| Scan Map, Fast | 0 | 14 | 314 |
| Scan Map, Medium | 100 | 200 | 500 |
| Scan Map, Slop | 100 | 200 | 500 |
Finally, the tasks and time needed to achieve our target S/N in all modes is (accounting for the fact that scan gives us all three arrays at once):
| Calibration Cycles by Task | |||
|---|---|---|---|
| Task | Name | # Repeats | Clock Time [min] |
| MIPS-299 | SED Slit Illumination Function +1 Chop | 8 | 166 |
| MIPS-299 | SED Slit Illumination Function +3 Chop | 8 | 166 |
| MIPS-313 | 70 um NF Illumination Correction | 6 | 133 |
| MIPS-914 | 24 um Flat - routine, Scan AOR - Medium | 14 | 252 |
| MIPS-914 | 24 um Flat - routine, Scan AOR - Slow | 5 | 228 |
| MIPS-915 | 70 um Flat - routine, Scan AOR | 4 | 57 |
| MIPS-915 | 70 um Flat - routine, Scan AOR - Medium | 14 | 252 |
| MIPS-915 | 70 um Flat - routine, Scan AOR - Slow | 5 | 228 |
| MIPS-916 | 160 um Flat - routine, Scan AOR | 75 | 1071 |
| MIPS-916 | 160 um Flat - routine, Scan AOR - Medium | 43 | 773 |
| MIPS-916 | 160 um Flat - routine, Scan AOR - Slow | 15 | 684 |
| MIPS-917 | 24 um Flat - routine, Phot AOR - Large Source | 6 | 95 |
| MIPS-918 | 70 um Flat - routine, Phot AOR | 6 | 146 |
| MIPS-918 | 70 um Flat - routine, Phot AOR - Large Source | 22 | 339 |
| MIPS-919 | 160 um Flat - routine, Phot AOR | 22 | 532 |
| MIPS-919 | 160 um Flat - routine, Phot AOR - Large Source | 7 | 394 |
| Total = | 5856 min = 97.5 hours | ||
| Total (24 & 70 only) = | 2062 min = 34.4 hours | ||
Where the medium scan AOR is 1 degree with 7 cycles and the slow scan AOR is 0.5 degree and 20 cycles.