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Spitzer Observing Rules

2         Duplicate Observations

In order to ensure the most efficient use of the Spitzer Space Telescope, proposed observations that duplicate those already executed or approved for execution (and therefore in the Science Operations Database) are not permitted without the explicit approval of the SSC Director, or designee.  Archival data should be used whenever possible to accomplish the science goals of any proposed investigation.

2.1       Definitions

Given the large number of Spitzer observations annually (> 20,000), it is important to define quantitative thresholds which permit automated checking of AORs to identify candidates for duplication. Two or more observations are considered to be potential duplicates when, for a given channel, the following criteria are met.


1.      The integration time per pixel for each observation agrees to within a factor of four (corresponding to a factor of ~two in sensitivity). 


2.      The areas on the sky covered by two proposed imaging observations overlap by more than 25% of either of the fields/areas being compared. Note that for very large programs, an area overlap of less than 25% could still translate into a significant amount of Spitzer observing time.  Observations with area overlaps less than 25%, but greater than 10 hours of observing time, will receive additional scrutiny by the SSC and may be disallowed by the SSC Director.


Note that a lengthy observation within the same observing proposal may be segmented into multiple AORs because of operational constraints, and that the series of component observations are not deemed to be duplicates.


Newly proposed observations that are identified to be potential duplicates must be approved by the SSC Director.  Approval will be contingent on a legitimate scientific justification for carrying out the new observations.  Examples of observations that may be approved include: synoptic observations of time-variable phenomena and second-epoch (or later) observations searching for transient phenomena.  Another example includes a large-area survey, where excising (“cutting out”) a small area to avoid overlap with a previously cataloged observation is so inefficient that it increases the observing time for the affected observation.  Finally, a proposed observation resulting from an evolution of the Spitzer AOTs and which leads to a demonstrably better observation strategy for a particular science goal will be considered for approval.


If a new candidate observation is less sensitive than a previously accepted observation and if it meets the area overlap criterion above, it will always be considered a duplicate since the science objective of the new program can be achieved using the deeper observation.


2.2       Procedures

It is the responsibility of any investigator to avoid proposing duplicate observations, apart from the exclusions listed in this sub-section.  Each Call for Proposals is accompanied by a comprehensive list of targets and AORs previously approved (§3.2).  All previously approved and executed observations can also be queried using Leopard, the SSC Archive software. Any newly proposed AOR meeting the criteria listed in §2.1 would be deemed a potential duplicate observation.


It is the responsibility of Principal Investigators of existing approved programs to check the Reserved Observations Catalog released after each completed proposal cycle to determine if any newly approved observations are duplications of any part of their program(s).  The SSC should be alerted if any duplications are found.


One exception to the duplicate observation policy described in §2.1 is the case where a series of observations of the same target are intended to search for time-variable phenomena.  In this case, a single observation of the same area of the sky will not disallow the time-series observations.  On the other hand, if the time-series observations occur before the single observation, it may disallow the single observation (since the objectives of the single observation could be achieved by using data from the time-series observations).


Previously accepted observations (i.e., AORs already entered into the Science Operations Database, or SODB) will always take priority over newly proposed observations.  A new or modified AOR that is found to be a duplicate of an existing AOR cannot be entered into the SODB without special permission granted by the SSC Director.  To be granted this dispensation, the investigator who stands to lose a proposed duplicate observation must file a request to the Director, describing why the AOR already entered in the SODB cannot be utilized in the proposed investigation.  Basing a request solely on the time lag associated with gaining access to data from an existing AOR (whose observation may not yet have been executed and whose data may not enter the public domain until proprietary rights expire) will be insufficient, unless such a delay will significantly compromise the timing and integrity of the proposed investigation.  [Affected investigators can always contact the Principal Investigator of the original AOR to seek access to the required data.]


Investigators must describe their observations unambiguously by completing AORs. In general, the TAC shall not recommend observations that duplicate approved observations from a previous Cycle. The final program for a Cycle recommended by the TAC and approved by the SSC Director may include programs with intra-Cycle duplications.  These observations will in general be executed by the SSC as approved.


The SSC Director shall have final authority to either allow or disallow duplicate observations.