Data Processing and Calibration Files

The JWST calibration program will obtain the necessary reference files used by the pipeline to remove instrumental signatures and produce data products that are absolutely calibrated. 

Introduction

See also: Absolute Astrometric CalibrationAbsolute Flux CalibrationAbsolute Wavelength CalibrationAll Calibration Reference Files

The overall goal of the JWST pipeline is to produce data products that minimize instrumental signatures and are absolutely calibrated in physical units. This is done through the use of extensive ground-test data and on-orbit observations.


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

The requirements for absolute flux calibration vary by instrument and observation mode. They are listed in Table 1. For the details of targets, etc. see the Absolute Flux Calibration article. 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

Spectroscopy1

NIRCam

5%

5%

10%2

NIRSpec

N/A

N/A

10%

NIRISS

5%

N/A

10%2 

MIRI

5%

15%

15%

1 For sources observed through slits, the value is for well centered observations. 

2  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 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
(resolution element)

NIRCam

10%1

NIRSpec

12.5%

NIRISS

10%

MIRI

10%

1  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 Absolute Astrometric Calibration.


Cycle 1 calibration programs

The instrument cycle 1 calibration programs will provide a set of deliverables needed to remove instrumental signatures and calibrate the JWST observations. Revisions to these programs are in progress with updates expected near the end of 2017. 

The main deliverables from the calibration program are reference files for the pipeline.

The cycle 1 calibration program will be used in combination with any similar observations taken during the 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


References

JWST technical documents


Last updated

Published August 7, 2017