File Naming Schemes

Exposure file names

The names of the exposure level data (stage 0 to 2) are constructed with information from the science header of the exposure, allowing users to map it to the observation in their corresponding APT files. The FITS file naming scheme for Stage 0, 1, and 2 “exposure-based” products is:



  • ppppp: program ID number

  • ooo: observation number

  • vvv: visit number

  • gg: visit group

  • s: parallel sequence ID (1=prime, 2-5=parallel)

  • aa: activity number (base 36)

  • eeeee: exposure number

  • segNNN: the text “seg” followed by a three-digit segment number (optional)

  • detector: detector name (e.g. ‘nrca1’, ‘nrcblong’, ‘mirimage’)

  • prodType: product type identifier (e.g. ‘uncal’, ‘rate’, ‘cal’)

An example Stage 1 product FITS file name is:


Stage 3 file names

In this stage, the calibration pipeline uses the association information to identify the relationship between exposures that are to be combined by design to form a single product. These data products result from the combination of multiple exposures like dithers or mosaics.

The format for the file name of a Stage 3 association product has all alphabetic characters in lower case, underscores are only used to delineate between major fields, and dashes can be used as separators for optional fields. Just as for Stage 2, the suffix distinguishes the different file products of Stage 3 of the calibration pipeline.

The FITS file naming scheme for Stage 3 “source-based” products is as follows, where items in parentheses are optional:

jw<ppppp>-<AC_ID>_[<”t”TargID | “s”SourceID>](-<”epoch”X>)_<instr>_<optElements>(-<subarray>)_<prodType>(-<ACT_ID>).fits


  • ppppp: Program ID number

  • AC_ID: Association candidate ID

  • TargID: 3-digit Target ID (either TargID or SourceID must be present)

  • SourceID: 5-digit Source ID

  • epochX: The text “epoch” followed by a single digit epoch number (optional)

  • instr: Science instrument name (e.g. ‘nircam’, ‘miri’)

  • optElements: A single or hyphen-separated list of optical elements (e.g. filter, grating)

  • subarray: Subarray name (optional)

  • prodType: Product type identifier (e.g. ‘i2d’, ‘s3d’, ‘x1d’)

  • ACT_ID: 2-digit activity ID (optional)

An example Stage 3 product FITS file name is:


Optional Components

A number of components are optional, all either proposal-dependent or data-specific. The general cases where an optional component may appear are as follows:

TargID vs SourceID

For single-target modes, this is the target identifier as defined in the APT proposal.

For multi-object modes, such as NIRSpec MOS, this will be the slit ID for each object.


If a proposal has specified that observations be performed in multiple epochs, this will be the epoch id.


Present for all instruments/observing modes that allow subarray specification.


Present when associations are dependent on being unique across visit activities. Currently, only Wavefront Sensing & Control (WFS&C) coarse and fine phasing are activity-dependent.

Segmented Products

When the raw data volume for an individual exposure is determined to be large enough to result in Stage 2 products greater than 2 GB in size, all Stage 0-2 products for the exposure are broken into multiple segments, so as to keep total file sizes to a reasonable level. This is often the case with Time Series Observations (TSO), where individual exposures can have thousands of integrations. The detector data are broken along integration boundaries (never within an integration) and stored in “segmented” products. The segments are identified by the “segNNN” field in exposure-based file names, where NNN is 1-indexed and always includes any leading zeros.

Segmented products contain extra keywords located in their primary headers that help to identify the segments and the contents of each segment. The following segment-related keywords are used:

  • EXSEGNUM: The segment number of the current product

  • EXSEGTOT: The total number of segments

  • INTSTART: The starting integration number of the data in this segment

  • INTEND: The ending integration number of the data in this segment

All of the Stage 1 and Stage 2 calibration pipelines will process each segment independently, creating the full set of intermediate and calibrated products for each segment. The calibrated data for all segments is then combined by one of the Stage 3 pipelines into a source-based Stage 3 product.