JWST's MIRI Dark Engineering template, available in the Astronomer’s Proposal Tool (APT), is used for calibration observations for the MIRI instrument.  

Introduction

These parameters are required to obtain Dark observations. Note that this type of observation is expected to be obtained as a parallel to normal science observations.

Test patterns will be executed during commissioning in a period when the temperature is in a range such that the MIRI wheels cannot be moved. Trying to move them will result in a failure of the related Commissioning activity.

To prevent the mechanism from moving, the following special requirements are added automatically when a Test Pattern is selected.

• EXPOSE ONLY - NO MECHANISM COMMANDING
• SPECIAL COMMANDING Expose Only (a SPECIAL COMMANDING requirement with the included command "Expose Only.")

Note that while it is critical that these special requirements be present, if they are removed APT does not provide an error or warning message.

Note for developers. If a PARALLEL special requirement is not present, give a warning. When a TEST PATTERN is selected, add a NO MECHANISM COMMANDING special requirement and a SPECIAL COMMANDING special requirement with text "Expose Only."

The MIRI Dark template consists of the following parameters:

General Information  

 The following parameters are generic to all templates, and are not discussed in this article: Observation Number, Observation Label, Observations Comments, and Special Requirements.

Detector

DETECTOR [DETECTOR] = IMAGER, MRS, ALL

This parameter specifies the detector array(s) on which data will be collected. If IMAGER is selected, data is collected on the single IMAGER detector array.  If the selection is MRS, data is collected on both of the IFU detector arrays.  When the selection is ALL, data is collected from all three detector arrays.

Note for developers: The following tables show what should be displayed in the GUI, along with the appropriate commanding name for the database, for each value of DETECTOR.

Test Pattern

MIRI detector "test patterns" are almost like real exposures, with the main difference being that the science pixels are fed known values generated by the Focal Plane Electronics (FPE) instead of the pixels being sampled. The patterns are allowed for the three MIRI Detectors: two MRS, plus the IMAGER.

TEST PATTERN [TEST_PATTERN] = NONE (default), COLUMNS, ROWS, FRAMES, ALL

This field specifies the the test pattern to use.

If TEST PATTERN = COLUMNS all the pixels in Column 1 are given the value of 1, all the pixels in Column 2 are given the value of 2 and so on up to 258.

If TEST PATTERN = ROWS all the pixels in Row 1 are given the value of 1, all the pixels in Row 2 are given the value of 2 and so on up to 1024.

If TEST PATTERN = FRAMES all the pixels have the same value in the first frame and that value is the number of frames (which is Groups/Integration) requested. In the next frame all the pixels have the same value again, but that value is one less than the number of frame requested and so on down to 1.

If TEST PATTERN = ALL Output 1 has COLUMNS, Output 2 has ROWS, Output 3 has FRAMES, and Output 4 has all pixels set to 0 as the reference channel. Note that for the first three modes, the same data is sent to each of the 5 outputs.

The default value of NONE is used for regular calibration exposures.  If another value is selected, a test pattern image will be generated.

Imager Subarray

IMAGER SUBARRAY [SUBARRAY] = FULL, BRIGHTSKY, SUB256, SUB128, SUB64, SLITLESSPRISM, MASK1550, MASK1140, MASK1065, MASKLYOT

This parameter specifies the region of the detector that is to be read out; see Table 1 for details. Note that this parameter is only valid for DETECTOR=IMAGER or DETECTOR=ALL.

The value of SUBARRAY for the MRS detectors will always be FULL and will be set to that value by the scripts.

Table 1. Subarrays for MIRI Dark

Note for developers: users can specify one or more combinations of the parameters below for DARK.

Exposure Specification 

For each exposure, specify the READOUT PATTERN, NUMBER OF GROUPS/INTEGRATION, NUMBER OF INTEGRATIONS/EXPOSURE, and NUMBER OF EXPOSURES/DITHER.

Readout Pattern 

READOUT PATTERN [READOUT PATTERN] =  FASTR1, FASTR100, SLOWR1, FAST, SLOW, FASTGRPAVG

This field specifies the readout pattern to be used to obtain the data.

FASTR100 is allowed only when SUBARRAY=SUB64

SLOW and SLOWR1 are allowed only when SUBARRAY=FULL

Number of Groups/Integration

NUMBER OF GROUPS/INTEGRATION [NGROUPS] specifies the number of groups in an integration on the detector.

 MIRI integration duration may not be greater than 2000 seconds. Integration time = (Frame time * NUMBER OF GROUPS/INTEGRATION). Frame time is a property of the selected READOUT PATTERN. For more information, see MIRI Detector Readout Overview.

Note to developer: Maximum MIRI integration duration is specified in the PRD as max_integration_duration_miri  in the observing_limitations table.

Table 2. Allowed values for NUMBER OF GROUPS/INTEGRATION

Number of Integrations/Exposure

 NUMBER OF INTEGRATIONS/EXPOSURE [NINTS] specifies the number of times the integration is repeated on the detector.

Number of Exposures/Dither

NUMBER OF EXPOSURES/DITHER [NEXP] specifies the number of times the dark exposure is to be repeated. The default value is 1. If TEST PATTERN is not NONE, then the NUMBER OF EXPOSURES/DITHER must be 1.

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