Understanding Data Files
JWST data files are FITS files with unique names that map to the original proposal, observation, visit, and instrument and detector used. Their particular format depends on the stage of the JWST Data Reduction Pipeline where these were created.
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 an understanding of JWST FITS files, Advanced Scientific Data Format (ASDF) files, and JSON files. FITS format files contain the science data pixels, ASDF files contain the world coordinate system information, and the JSON files contain information regarding the way the science data is associated.
JWST data are FITS format files generated by the Data Management System (DMS) via the Science Data Processing (SDP) and the Calibration Pipeline. The telemetry data from the Recorded Science Data files that are received by DMS, is in the same binary format as stored on the JWST Solid State Recorder (SSR). These files will come in 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).
The corresponding transformation from the detector positions to a world coordinate frame (ICRS and wavelength) for the science data are provided via distortion and spectral models stored in ASDF format extensions to the FITS file.