JWST Observation Duplication Checking

Users are responsible for checking their proposed observations for potential duplications against accepted or previously executed observations, and either removing the duplication or explaining any such potential duplications in their science proposals.

On this page

See also: Identifying Potential JWST Duplicate Observations and JWST Duplication policy
Relevant Links outside of JDox: MAST Data Discovery Portal and JWST Program ID Look-up GUI

As part of maximizing the science return of JWST, unnecessary duplication of observations needs to be avoided. Proposed observations that duplicate or potentially duplicate existing or planned observations must be scientifically justified by the proposer. The JWST Duplication Policy defines what constitutes a duplication.

Duplication checking prior to submission is the proposer's responsibility. Any duplications or potential duplications (for programs where the details are not known up front) must be discussed and/or justified in the text of the proposal. Failure to do so may result in the rejection of the proposed observation even after proposal acceptance. For accepted proposals, STScI will perform a detailed duplication check to catch and remove any duplications within the current pool of accepted proposals.

Pre-submission checking

See also:  Identifying Potential JWST Duplicate Observations, and JWST Duplication Policy
Relevant Links outside of JDox: Summary listings of accepted GTO Program Information and ERS Program Information including links to the public APT files.

To avoid unintentional duplications, proposers will be required to check their proposed observations against those already approved (both in the queue and previously observed).  As JWST observations are obtained and archived, all observations are placed into the Mikulski Archive for Space Telescopes (MAST), forming the basis for duplication checking.

Note: You may want to perform this duplication checking step prior to going through the effort of entering and validating your own APT proposal, to avoid the potential of finding out after the fact that your observations had already been proposed. If there is a scientific justification for a duplication, such as a time-variable source or need for higher signal to noise than in the previously approved JWST observations, you can still request it but you should provide a justification for it in your science proposal text.

Target duplication checks

The MAST Data Discovery Portal will assist you in making checks for potential duplications, allowing you to quickly see whether your proposed targets appear in any previously approved JWST observations. For large target lists, consider using the MAST API functionality.  Details are provided in the article Identifying Potential JWST Duplicate ObservationsIf no previously planned JWST observations are indicated by your check in MAST, no further checking is required. This MAST target check may also identify data from HST and other missions that you may find useful.

Observation duplication checks

Words in bold are GUI menus/
panels or data software packages; 
bold italics are buttons in GUI
tools or package parameters.

Targets are not protected, but rather observations of targets with a particular instrument, instrument mode, and requested S/N are protected against unjustified duplications. However, the MAST Portal does not provide all the information needed for duplication checking, in particular for accepted observations that have yet to execute. Hence, you will need to inspect the APT files from any accepted JWST programs indicated in MAST to assess the details on the instrument configuration(s) and exposure times being requested to determine if a duplication exists.   

There are several ways to view the details in accepted JWST programs:

  1. Peruse the lists of program IDs and titles for ERSGTO, and prior accepted GO programs. Clicking on a program ID will take you to a program information page with links to a "public PDF" file and the program's APT file.

  2. Alternatively, enter an accepted program ID number in the JWST Program Information tool to get the program information.

  3. The APT files for accepted programs can be loaded directly into an APT session. In APT, go to the top File pull-down menu, select Retrieve from STScI → Retrieve using Proposal IDand enter the program ID in the box. 

To assess if your proposed observation is a likely duplication, open the APT file and check the instrument mode, filters/gratings, dithers, and total exposure time, as well as any other details relevant to the mode you are proposing. If desired, display relevant observations in Aladin to see the full dither pattern or mosaic being proposed.

If any duplications with your planned observations are identified, either justify the need for new data or adjust your proposed observing plan to avoid the duplication.

Some cases will be complicated enough that you can only discuss that a potential duplication exists. A prime example is NIRSpec MSA observations, where the specific objects for observation are not selected until a final MSA configuration is determined for the accepted program.  Therefore, specific duplications may be unknowable at proposal time. See the JWST Duplication Policy for details.


Post-acceptance checking

Once a proposal is accepted, one of the first steps in proposal processing is a duplication check performed by STScI staff. Their software not only checks for duplications against previous and planned observations, but also checks the pool of accepted programs in a given cycle to catch any new or unintended potential duplications.  STScI will contact affected PIs to resolve any such duplications if they occur. 

Notable updates
    Updates for Cycle 2 and beyond.

  • Removed duplications with JWST Duplication Policy article.

    Article streamlined by removing redundancy and duplicate linking.
Originally published