Flattening a Lumpy Sky
Models of the Effects of Cirrus and Sources on MIPS Flat/IC Quality:
Flattening a Lumpy Sky
John Stansberry, Chad Engelbracht, Herve Dole (MIPS)
April 8, 2002
Models of MIPS sky (H. Dole et al., 2002)
Note: Cirrus amplitude in these models is overestimated by a factor
of ~5 (Sept. 5, 02). The models will be recomputed soon, and the conclusions
of this study revised as needed. The new modeling can also take advantage
of the higher-fidelity data simulation capability of Chad's scripts.
24um
70um
160um
Source Counts in Models
ISM and Zodi for Models and SSC Flat Regions
24um:
70um:
160um:
Making Flats/ICS :: SCAN vs. PHOTOMETRY AOTs (scaled +- 5%)
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SCAN AOT |
PHOTOMETRY AOT |
24um: 40 DCEs |
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70um, 40 DCEs: |
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160um, 40 DCEs: (scaled +- 15%) |
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Statistical Quality of Flats vs. #DCEs in the Flat
24um:
70um:
160um:
160um : Troublesome!
160um Flat/IC Appearance vs. # DCEs (scaled +- 15%)
40 DCEs
90 DCEs
250 DCEs
490 DCEs
Preliminary Conclusions:
- ISM and sources do impact # frames needed to construct a good flat.
- 24um: need only ~40 DCEs to do better than 0.5% RMS.
- 70um: need ~200 DCEs to do better than 0.5% RMS.
- 160um: need ~500 DCEs to approach 1% RMS.
- MIPS flats will have structure due to rigid dither/scan observing patterns
- Co-addition of many flats will eventually smooth them out.
- By combining all Flat/IC observations from IOC, we will obtain very good
calibration frames, except perhaps at 160um.
To Do:
- Visualization of photometry mode image sampling needed for verification of models.
- 70um dither used for all bands - particularly bad at 160um.
- Prepare model fields w/ correct absolute ISM/Zodi/Source brightnesses?