JWST Data Calibration Considerations
The JWST calibration program is charged with obtaining the necessary reference files used by the JWST Science Calibration Pipeline to remove instrumental signatures and produce data products that are absolutely calibrated.
Ongoing calibration
Aspects of the JWST calibration plan will be executed throughout
normal operations. Expect periodic updates to calibration reference files
and reprocess your data as needed.
Please refer to JWST Calibration Pipeline Caveats for more information.
On this page
See also: JWST Data Absolute Astrometric Calibration, JWST Data Absolute Flux Calibration, JWST Data Absolute Wavelength Calibration, JWST Data Calibration Reference Files
Absolute calibration
The requirements for the JWST absolute flux, wavelength, and position calibration are given in the tables below. At this point, we expect to meet all these requirements. The planned calibration programs are sufficient to meet or exceed these requirements.
Flux
Table 1 lists the requirements for absolute flux calibration, which vary by instrument and observation mode. For the details of targets, etc. see the article on JWST Data Absolute Flux Calibration. Note that the needed flux prediction accuracy on the targets exceeds those listed in the table as there are other terms involved beyond the prediction accuracy (aperture correction accuracy, stability, etc.).
Table 1. Absolute flux requirements
Instrument | Imaging | Coronagraphy | Spectroscopy† |
|---|---|---|---|
NIRCam | 5% | 5% | 10%‡ |
NIRSpec | N/A | N/A | 10% |
NIRISS | 5% | N/A | 10%‡ |
MIRI | 5% | 15% | 15% |
† For sources observed through slits, the value is for well-centered observations.
‡ Not a formal requirement, by analogy with NIRSpec spectroscopy.
Wavelength
The requirements for absolute wavelength calibration vary by instrument. They are listed in Table 2. For the details of targets, etc., see the JWST Data Absolute Wavelength Calibration article. Note that the needed wavelength prediction accuracy on the targets exceeds those listed in the table as there are other terms involved beyond the prediction accuracy (aperture centering accuracy, stability, etc.).
Table 2. Absolute wavelength requirements
Instrument | Accuracy |
|---|---|
NIRCam | 10%* |
NIRSpec | 12.5% |
NIRISS | 10% |
MIRI | 10% |
* Not a formal requirement, by analogy with NIRISS spectroscopy.
Position (astrometry)
The requirement for absolute position (astrometric) calibration is 5 mas. Specifically, the 5 mas refers to the uncertainty in the observatory field distortion correction within any instrument and the guider. For details see the article titled JWST Data Absolute Astrometric Calibration.
JWST calibration programs
The JWST calibration programs provide a set of deliverables needed to remove instrumental signatures and calibrate the JWST observations. The main deliverables from the calibration program are reference files for the science calibration pipeline. Data from these calibration programs are used in combination with any similar observations taken during JWST commissioning to produce the highest quality reference files.
Example deliverables
- Darks
- Bad pixel maps
- Read noise measurements
- Flat fields (both pixel and illumination versions)
- Linearity corrections
- Persistence characterization
- PSF images and characterization
- Astrometric solutions (including distortion characterization)
- Wavelength calibration
- Line spread function characterization (for the spectrographs)
- Absolute (spectro)photometric calibration
- Relative throughput of NIRSpec apertures
- NIRSpec MSA shutter contrast and failed shutter maps
- NIRISS WFSS spectral traces