MIRI Target Acquisition

The JWST Mid-Infrared Instrument (MIRI) provides target acquisition capabilities for the low-resolution spectroscopy, medium-resolution spectroscopy, and coronagraphic imaging modes.

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Overview of MIRI target acquisitions

Parent page: MIRI Operations

Target acquisition (TA) is a procedure that centroids a source and places it accurately within an aperture, region of interest (ROI), or subarray. The filters available for MIRI TA are F560W, F1000W, F1500W, and FND. TA procedures are discussed in the context of the observatory in memos and reports by Gordon & Meixner (2008), Meixner et al. (2006), Nelan et al. (2005), and Meixner et al. (2004).  

TA procedures within the Astronomer's Proposal Tool (APT) are available for:

FASTGRPAVG detector readout capability

See alsoUnderstanding Exposure Times

Individual target acquisition groups need to be stored in onboard memory to be processed by the target acquisition algorithm.  Since onboard memory can only store the equivalent of 10 full frame groups of MIRI data at a time, target acquisition in un-grouped FAST mode is limited to a maximum exposure time that might be shorter than desired by the user.  

For MIRI target acquisition only, the following FASTGRPAVG modes are available to users to allow for longer exposure times. This is done by averaging a given number of MIRI frames together in the ISIM FPAP (Focal Plane Array Processor) as a group.

Readout mode      (as offered in APT)

#averaged     MIRI frames

Group time (FULL array)

Group time (Slitlessprism subarray)

Group Time (MaskLyot subarray)

Group Time (4QPM subarrays)
FASTGRPAVG411.10 s0.64 s1.30 s0.96 s
FASTGRPAVG8822.20 s1.27 s2.59 s1.92 s
FASTGRPAVG161644.40 s2.54 s5.18 s3.84 s
FASTGRPAVG323288.80 s5.09 s10.37 s7.67 s
FASTGRPAVG6464177.60 s10.18 s20.74 s15.34 s


Gordon, K. & Meixner, M., 2008, JWST-STScI-001407 (PDF)

Mid-InfraRed Instrument (MIRI) Target Acquisition Strategies and Use Cases 

Gordon, K., 2008, JWST-STScI-001347 (PDF)
Mid-Infrared Instrument (MIRI) Low Resolution Target Acquisition for Faint Sources

Meixner, M. et al., 2004, STScI-JWST-TM-2004-0018A 

Mid-Infrared Instrument (MIRI) Target Acquisition Requirements and Strategies

 Nelan, E. et al., 2005, STScI-JWST-R-2005-0001
JWST Science Instrument Target Acquisition Concepts



Latest updates


Added links for LRS slit and Slitless TA