All JWST data shares a basic data structure with slight variations that depend on the observing mode or instrument used. Being able to work with JWST data requires understanding of JWST FITS files and Advanced Scientific Data Format (ASDF) files, which contain the world coordinate system information.
JWST data are FITS format files generated in the Data Management System (DMS) by the Science Data Processing (SDP) and the Calibration Pipeline. The telemetry data from the Recorded Science Data files is received by DMS is in the same binary format as stored on the JWST Solid State Recorder (SSR). These files will come into compressed packets that will be read by SDP to extract science data and relevant detector and exposure information.
The initial FITS header will contain keywords required by the FITS standard and keywords required for identification, naming of the files, data structure definition, and for the correct calibration of the science data by the calibration pipeline. These keywords are populated with telemetry packet headers and Science Image headers; proposal, planning, and scheduling information; spacecraft position; time conversions; pointing information; and select engineering parameters (JWST-STScI-002111).
JWST data products can be divided in two main types of data; data products from single exposures produced during stages 1 (also known as Level 2a) and 2 (Level 2b) of the calibration pipeline and data products that result from the combination of these exposures into a single one produced with stage 3 (also known as Level 3). These products can be easily told apart by their File Naming Conventions and Data Products or their Header Keywords and Relationships to the proposal from where these originated. Within associations the exposure level data are combined into what we call level 3 or level 4. There are different ways in which a set or subset of exposures are combined, each of these corresponding to a unique association. However, not only the data that will be combined will be part of an association. When considered necessary, an association will also include data that needs to be kept together for calibration purposes or post-calibration analysis by experienced observers.