1. NIRCam Readout Pattern Considerations
For readout patterns with the same Nframes+Nskip (e.g. Bright1 and Bright2),
the pattern with the smaller number of Nframes provides better cosmic ray rejection
The pattern with the small number of Nskip provides better readout performance and therefore more sensitivity
For more information, see Robberto 2010 JWST-STScI-2128 “NIRCam Point Source SNR vs. Filter, Source Brightness and Readout Combinations”

2. “Highest SNR” NIRCam Readout Pattern
From Robberto 2010 JWST-STScI-2100 “NIRCam Optimal Readout II: General Case (Including Photon Noise)”

3. NIRISS Readout Patterns
NISRAPID Nskip = 0 Nframe = 1 tframe = sec Min(Ngroup) = 1* Max(Ngroup) = 30 NIS Nframe = 4 Max(Ngroup) = 200 *not recommended

4. MIRI Readout Patterns
FASTMODE Nskip = 0 Nframe = Ngroup tframe = sec SLOWMODE* tframe = sec *not recommended for imaging and not allowed for subarrays The MIRI team recommends a minimum of 5 groups per integration for good calibration

5. NIRCam Subarrays Full Field uses 4 amplifiers, Subarray uses 1
Subarrays are only taken on module B
For imaging subarrays, only SCA B3 for SW
Subarrays have same size in pixels on SW and LW
SW and LW subarrays have the same center on the sky
There are
Point Source subarrays
Extended Source subarray
All point source subarrays will be on B3
B3 is the fundamental detector for flux calibration, extend to other detectors using LMC
From M. Robberto

6. NIRCam Subarrays
The subarrays are designed to provide for sources that are 2, 4, 6 magnitudes brighter than allowed by the full array

7. DIRBE All-Sky Maps

8. JWST Backgrounds A – Zodiacal Light Scattered (5500 K)
B – Zodiacal Light Emission (270 K)
C – Observatory Straylight (133.8 K)
D – Observatory Straylight (71.0 K)
E – Observatory Straylight (62.0 K)
F – Observatory Straylight (51.7 K)
Glasse et al. (2015)

9. Gain in bright source limit
MIRI Subarrays
Enables observations of bright sources. For example, observations of the telescope background at F2550W will saturate the imager in one FULL frame time
Subarray
Frame time [sec]
Gain in bright source limit
FULL
2.775
1.00
BRIGHTSKY
0.865
3.21
SUB256
0.300
9.25
SUB128
0.119
23.32
SUB64
0.085
32.65
MASKLYOT
0.324
8.56
MASK1550
0.240
11.56
MASK1140
MASK1065
SLITLESSPRISM
0.159
17.45
From A. Glasse

10. NIRCam Point Source Sensitivity
Extra-wide, wide, medium, and narrow filters are labeled in normal, bold, and italic text, respectively each with progressively thicker bars.
Calculated assuming 1000 sec exposures, a flat source spectra in nJy, and zodiacal light at 1.2 times the minimum. More precise sensitivity estimates may obtained using acquired from the Exposure Time Calculator (ETC).

11. NIRCam Saturation Limits
Saturation, in magnitudes, in Vega K-band for a solar type G2V star in 21.4 sec (based on 2 readouts of the full detector), filling pixel wells to 80% capacity. Brighter saturation limits may be achieved by using subarrays to reduce the exposure time, and/or using time series observations with the weak lenses or grism.

12. NIRCam and NIRISS Sensitivities
S/N = 10 in 10 ks
NIRISS
Filter
nJy
m(Vega)
F090W
11.28
28.28
F115W
11.22
28.06
F140M
14.80
27.43
F150W
9.19
27.83
F158M
12.88
27.39
F200W
7.81
27.54
F277W
6.63
27.09
F356W
6.89
26.56
F380M
18.74
24.34
F430M
28.32
24.65
F444W
12.29
25.49
F480M
36.85
24.14
NIRCam SW advantages: (1) lower read noise (2) smaller pixels for resolving background for zodiacal light
Filter widths are shown as horizontal bars. NIRISS advantages (1) All reflective optics (NIRCam dichroic absorbs) (2) Better Quantum Yield effects
NIRCam F115W  13.2 nJy NIRISS   F150W  11.2 nJy

13. MIRI Sensitivity and Saturation Limits
These sensitivity limits (below) apply to faint sources observed with the FULL imager field of view.
They assume a photometric aperture of radius, rphot = 0.42 (l / 10 mm) (Note: The full width at half maximum intensity (FWHM) of the point spread function (PSF) is dFWHM = 0.32 (l / 10 mm).
Filter Name
Wave-length
Band-width
Sensitivity S/N = 10 in 10,000 second on-chip integration.
Saturation Limit (Fbright)
Point Source
Extended Source
Extended Source* µm
microJansky
microJansky arcsec-2
milliJansky
milliJansky arcsec-2
F560W
5.6
1.2
0.16
0.89 13
140
F770W
7.7
2.2
0.25
0.77 7 75
F1000W
10.0
2.0
0.54
0.99 15
103
F1130W
11.3
0.7
1.35
1.89 68
366
F1280W
12.8
2.4
0.84
0.88 27
113
F1500W
15.0
3.0
1.39
1.11 36
110
F1800W
18.0
3.46
1.9 65
138
F2100W
21.0
5.0
7.09
2.9 66
F2550W
25.5
4.0
26.2
7.3
195
206
From A. Glasse

14. Observing Overheads
Offset times (within mosaics or dither patterns) will depend on the size of the offset with larger offsets requiring more time
Offsets larger than 20”-80”, depending on ecliptic latitude, will require a guide star acquisition. Guide star acquisitions are longer than simple offsets. Mosaics and the NIRCam FULL dither patterns will require guide star acquisitions.
APT will be used to estimate overheads. The version of APT to be released in Fall 2017 will include accurate Cycle 1 overheads times.
APT has a grayed out box that will give the exact visiting splitting distance for an observation

15. Mosaicking versus Dithering
Mosaic patterns (for any instrument) are intended for covering larger areas of the sky than a single field of view.
Fundamental operational difference between Dither and Mosaic:
Dithers: all spatial positions in a pattern are imaged through the same filter before making a filter change.
Mosaics: all filters in an observation (and all dithers) are executed before moving to the next mosaic point.
Thus, dithers with large patterns and large step sizes can incur significant overheads due to spacecraft maneuvers.
This must be balanced against lifetime limitations on filter wheel rotations.
From G. Kriss

16. From M. Perrin

17. Example: NIRCam Mosaic
Orion bar is broken up into 3 parts to improve the schedulability
Long rectangles constrain the orientation of the telescope tighly
Since there is typically +/-5 degree flexibility in orient at a time, breaking up into square pieces helps
In cycle 2, may have a tool that designs mosaick intellgently based on when the target is observed
From M. Robberto

18. Observability Constraints
Snapshot from the schedulability tool from Chris Stark showing that in this configuration the orion bar observations can be made over the entire visibility window
From M. Robberto

19. Coordinated Parallels
Available Cycle 1:
NIRCam Imaging and MIRI Imaging
NIRCam Imaging and NIRISS WFSS
MIRI Imaging and NIRISS WFSS
NIRCam Imaging and NIRISS Imaging

20. Coordinated Parallel Dither Patterns: NIRCam + MIRI
Have to deal with differences in SI-to-SI orientations and pixel scales
E.g.: MIRI is offset by degrees w.r.t. NIRCam (as of CV3)
Dither patterns generally keep pixel phases “ideal” to within 0.05 pixel for parallel SI
Exception: MIRI at λ > 12 μm (well-sampled anyway)
Dither patterns involving MIRI customized for each filter, with offsets >= 3 × (FWHMPSF)
Otherwise typically “Small”, “Medium”, and “Large” dither offsets being offered
From P. Goudfrooij

21. NIRCam Detector Performance
CDS noise
CDS noise
Effective
noise
Effective
noise
NIRCam readout noise performance generally better than requirements
Noise levels at long times a little higher than expected because of 1/f noise
NIRCam team working on how to remove 1/f noise
From M. Robberto

22. MIRI Detector Performance
The MIRIM detector has great cosmetics (<300 dead, hot or noisy pixels in the science field).
MIRI’s PSF is well described at long wavelengths by the JWST’s diffraction profile.
At short wavelengths (F560W, F770W filters) a cruciform pattern appears, at a level comparable to the telescope diffraction spikes. Identified with scattering in the detector.
A model has been developed using PSF and out-of-field straylight test data which predicts that 22% of the point source light at F560W is scattered into the cross (11% for F770W).
CV2 F560W image of OSIM IR LED
Model JWST diffraction limited PSF
Model MIRI PSF, including scattering.
From A. Glasse