Working with JWST data requires an understanding of the JWST data products and the steps in the JWST Science Calibration Pipeline that produces them.

See also: Getting Started with JWST Data, Understanding JWST Data Files, File Header Contents
Software documentation outside JDox: File Naming Conventions, Data Product Types, Science Product Structures and Extensions, Data File Associations, JWST Data Products Information

Science data products

JWST science data products can be divided into 4 main types, depending on the stages of processing of the file and the how these relate to other exposures:

• Uncalibrated products are from single exposures.
• Products of stage 1 are also from single exposures.
  
• Data products from single or multiple exposures produced during stage 2 of the JWST science calibration pipeline.
• Data products that result from the combination and/or association of the single exposures into a single integrated product in stage 3 of the JWST Science Calibration Pipeline.

Within the 2 categories that include multiple exposures, there are different ways in which a set or subset of exposures are combined, and each of these have a unique association. More information about the JWST data products and how these relate to the different type of data and calibration steps can be found in the software documentation.

Uncalibrated data

Uncalibrated data are generated by the the Science Data Processing (SDP) system from telemetry data. These are input to the stage 1 of the calibration pipeline. These come from single exposures and are usually contained within a single FITS file. However, when the raw data volume for an individual exposure is large enough, like for time-series observations, the uncalibrated data are broken into multiple segments less than 2GB each, so as to keep total file sizes to a reasonable level. These exposures usually include "segNNN" in the file names, where NNN is 1-indexed and always includes any leading zeros.

Stage 1 data products

Stage 1 data products from single exposures can be science or non-science products. Science products include files generated by intermediate steps, like count rate data, or the final product generated by this stage. Some of this data are generated by default and can be retrieved from MAST, while others are optional products that can be generated by reprocessing the data yourself; check the example Jupyter notebooks to learn how to run the pipeline. Non-science products can be calibration data products, like dark exposures, that use the same steps used to in stage 1 for JWST science data. These also could be auxiliary products that provide relevant information about the data, such as charge trap state data.

Stage 2 data products

Stage 2 data products depend on the observing mode and these can be generated from a single exposure or from the combination of more than one exposure. The number and type of products generated will vary for imaging, spectroscopy, and TSO data. For spectroscopy data it will also depend on how the observation was planned. When observations include background exposures, the background-subtracted data is also produced by default. Information about what data should be combined is captured in stage 2 association files. In this stage, users have the option to produce an on-the-fly constructed flat for NIRSpec data.

Stage 3 data products

Stage 3 data products result from the combination of stage 2 exposures into a single integrated product in stage 3 of the JWST science calibration pipeline. The type and number of data products of this stage vary with the type of observation, but each of these corresponds to a unique association. The information about which data will be combined is captured in association files.

For more information about associations refer to the association overview article.