Overview of Herschel Observing


The Herschel Space Observatory (aka Herschel) is an ESA facility available for the worldwide astronomical community. Herschel is designed to provide 3 years of routine science operations. The observing time consists of Guaranteed Time (GT) and Open Time (OT), the fraction GT is 32%, the remainder is OT. The GT is owned by contributors to the Herschel mission, mainly the science payload consortia. The OT will be awarded in a standard competitive proposal procedure in response to Announcements of Opportunity (AO) issued by the Herschel Science Centre (HSC) managed by the Herschel Project Scientist on behalf of the Director of Science and Robotic Exploration.

Announcements of Opportunity

The initial Announcement of Opportunity (AO) process for Herschel observing time took place in February 2007 to February 2008, and concerned 'Key Programme' (KP) proposals only. By coincidence it resulted in exactly the same number of KP guaranteed time (GT) and open time (OT) programmes; in both cases 21 programmes have been awarded observing time. The contents of these programmes are briefly described under Key Programmes where also links (where available) to their own dedicated websites are provided. The KPGT and KPOT programmes represent approximately 5500 hours of observing time each.

The first in-flight AO process (AO-1) took place in February to December 2010, and comprised guaranteed and open time phases, labelled GT1 and OT1. The contents of the approved observing programmes are briefly described under GT1 programmes and OT1 programmes where also links (where available) to their own dedicated websites are provided. There are 33 GT1 observing programmes representing about 555 hours and 241 OT1 observing programmes representing almost 6600 hours of observing time. OT1 observing time was awarded as priority 1 (almost 5000 hours) and priority 2 time.

The second in-flight AO cycle (AO-2) will also consist of an initial guaranteed time phase (GT2), followed by an open time (OT2) phase. GT2 will be released on 7 April 2011 with proposal submission deadline on 12 May 2011, while OT2 has been be released on 9 June 2011 with proposal submission deadline on 15 September 2011. AO-2 is the last Herschel AO cycle for observing time proposals. For more information use the buttons under "Herschel Announcement of Opportunity (AO-2)" on the left.


In connection with the OT1 process a number of questions regarding Herschel scheduling have arisen. The purpose of this section is to provide an overview of how the scheduling is performed, in particular with respect to priorities between different 'categories' of observations.

The top priority for Herschel scheduling is scheduling efficiency, or in other words, 'helium economy'. The output of the mission planning are schedules that utilise the available observing time in the most efficient fashion. Scheduling 'cycles' contain sequences of instrument usage, adhering to various constraints, and reflecting the nature and amounts of observations available for scheduling for the part of the sky currently visible. There are no specified priority differences between the various Key Programmes (KPs), however, the GT KPs have been available for a longer time and have a higher average completion percentage than the OT KPs do.

It is worth commenting at this point that there are large differences between the completion levels between different KPs. This is true for the GT as well as (and in particular) for the OT KPs. However, it is possible to provide a rational explanation in each case. Generally spectroscopy is lagging photometry, although it is worth to point out that despite the fact that the HIFI instrument was unavailable for about half a year, on the average HIFI completion levels are not lagging those of PACS and SPIRE.

In the spring of 2010 the GT1 observations became available for scheduling, and as of December 2010 the OT1 observing programmes are gradually becoming available for scheduling. A number GT1 observations have been executed, and the very first OT1 observations have been scheduled for execution in December 2010. However, for some months into 2011 the emphasis will remain on the KPs.

In addition to the top priority of producing efficient schedules, there is a second mission planning priority, observations belonging to an earlier AO have priority over observations from a later AO. This is true also within an AO, the GT observations have priority over OT observations in the same AO (but not over OT from an earlier AO). Thus, as examples, the KPs have priority over GT1/OT1, GT1 over OT1, but OT1 has priority over (yet to be assigned) GT2. However, these priorities will not be allowed to interfere with efficient scheduling which always has top priority. What this means is that OT1 execution will be slow in early 2011, but it also means that occasionally OT1 observations will be carried out.

Execution Status

Information about the actual current execution status of the various programmes is provided in the Latest News 'Status summary' section. This information is regularly updated, and the applicable date is provided.

Proprietary time

The basic rules for regarding proprietary time come from the Herschel 'Science Management Plan' (SMP) and have been reproduced in the 'Policies and Procedures' document in each AO.

The basic rule is that: 'All observations (GT and OT, KP and non-KP) observed in the first year of the routine science phase will have proprietary times of 12 months, while for all observations observed later, the proprietary time will be 6 months, with a simple 'bridging scheme'. The proprietary time applies to each observation individually, counted from the day when the data are available to the initial data owner.'

It has recently been decided that 'the first year of routine science phase' started on 15 December 2009 for all PACS, SPIRE, and SPIRE/PACS parallel mode observations, and on 15 April 2010 for all HIFI observations. The 'bridging scheme' referred to is a simple linear interpolation ensuring that observation2, carried out later than observation1, is not becoming public earlier than observation1.

What this means in terms of dates is the following. For non-HIFI observations carried out:

  • on 14 December 2010 or earlier, the proprietary time is 12 months
  • on 15 June 2011 or later, the proprietary time is 6 months
  • from 15 December 2010 to 14 June 2011, will become public at the same time as observations carried out on 15 June 2011.

For HIFI observations carried out:

  • on 14 April 2011 or earlier, the proprietary time is 12 months
  • on 15 October 2011 or later, the proprietary time is 6 months
  • from 15 April to 14 October 2011, will become public at the same time as observations carried out on 15 October 2011.


The basic rule applies to individual observations (AORs), neither to targets, fields, sets of spectral lines, or the like, nor to observing programmes: 'The proprietary time applies to each observation individually, counted from the day when the data are made available to the initial data owner.'

These rules were written well before the launch of Herschel, and at the time it was prudent to allow for the unknown: 'However, a scheme will be put in place whereby the Herschel Project Scientist and the HOTAC Chair in consultation can grant additional proprietary time to certain large programmes, in order to prevent the release of improperly or inhomogeneously calibrated or processed data.'

A couple of requests have been submitted for proprietary time extensions on the basis of this part of the rules. It is clear that such requests cannot be viewed in isolation, a policy is required to ensure fairness and correctness, anticipating also possible additional future requests.

As a starting point it is necessary to recall that the rules were written the way they were to deliberately 'force' the maximum number of observations into the public domain as early as possible. This is the explicitly intended situation! To deviate would require extraordinary circumstances, where it could be argued that it is necessary to deviate from the letter of the SMP in order to preserve its spirit.

On the basis of discussions in the Herschel Science Team and with the HOTAC chair it has been decided that with the current knowledge of the in-flight performance of Herschel this 'escape route' is no longer applicable. Hence, the proprietary time rules will be strictly applied per observation as was the originally stated intention.