The operations of the Herschel Space Observatory are conducted in a decentralised manner. As can be seen in Figure 10, the Ground Segment comprises the following elements:
A Herschel Science Centre (HSC), provided by ESA, located at ESAC, Madrid. The HSC, supported by the NASA Herschel Science Center (NHSC), located at IPAC, acts as the point of interface to the science community and the outside world in general. The HSC is supported by the Herschel Science Team, for the maximisation of the scientific return of the mission, and by the Herschel Observing Time Allocation Committee (HOTAC) for the selection of observing proposals.
Three dedicated Instrument Control Centres (ICCs), one for each instrument, provided by the respective PI. Each ICC is responsible for enabling the operation and for the calibration of its instrument.
A Mission Operations Centre (MOC), provided by ESA, located at ESOC, Darmstadt, which is responsible for the execution of all in-orbit operations.
The Herschel Science Centre provides the information required for the submission of proposals in the Herschel Space Observatory Web site ( http://herschel.esac.esa.int), in collaboration with the ICCs. Astronomers are requested to register to access the services of the observatory, which includes the capability of submitting proposals, access to the helpdesk and retrieval of observational data from the Herschel Archive.
Proposal entering and submission is done through the HSpot tool (see Section 7.1, “Introduction to HSpot”), the Herschel Observation Planning Software. A scientific proposal contains at least an AOR, or Astronomical Observation Request. Each AOR is based on an AOT, or Astronomical Observation Template, which is a pre-defined observing mode, characterised by an instrument configuration and way of operation that have been optimised for the execution of a particular type of observation (see Section 7, “Observing with Herschel”). An AOR is generated when the proposer provides the parameters required for the selected AOT, and is equivalent to the term "observation" used in this document.
A proposal submitted through HSpot is stored in the Herschel Space Observatory database. The proposer, and co-proposers selected by the principal investigator, are allowed to retrieve, modify and upload their proposal(s) until the closing date of the AO. At that time, the database is closed to HSpot, and the HSC distributes the stored proposals to the HOTAC panels. Proposers can check the status of their proposal(s) in relation to the HOTAC review in the Proposal status Web page ( http://herschel.esac.esa.int). During the review process, the HSC provides support to the HOTAC and, on request, assesses the technical feasibility of the observations. In addition, a systematic technical feasibility assessment is carried out on all accepted proposals.
The period of proposal submission before the HOTAC review is called Phase-1. After the HOTAC review results are public, proposal submission Phase-2 starts. In this period, observers are allowed to refine their accepted proposals, modify them following the HOTAC guidelines, and use updated AOTs and the latest available observatory knowledge. Please see the "Herschel Space Observatory Call for Proposals: Policies and Procedures" document for a definition of proposal submission Phase-1 and Phase-2, and for the policies on proposal modifications. The end of proposal submission Phase-2 results in a consolidated database of accepted proposals and its corresponding AORs.
The database of accepted observations defines the observatory schedule. The HSC will carry out a careful study of the observation database to define a long-term mission plan that will accommodate all constraints and will maximise the scientific return. Following the agreed long term mission plan, short term observing schedules, together with the corresponding instrument commands, will be produced with the Mission Planning System at the HSC, and transferred to the Mission Operations Centre (MOC), at ESOC. The MOC will add the satellite commands and produce the final detailed mission timeline that will be uplinked to the spacecraft.
The basic time unit for the mission planning is the Operational Day, or OD. It is defined as the interval of time between the start of two consecutive DTCPs. The DTCP, or Daily TeleCommunication Period, is the time interval when the spacecraft antenna will be pointed to the Earth to receive telecommands and send the recorded telemetry. The duration of an OD will normally be about 24 hours, but it will depend on the availability and detailed schedule of the New Norcia Ground Station, which is shared with other ESA missions. The operational constraints of the Herschel instruments determine that only observations with a certain instrument sub-system are schedule in a single OD. For instrument sub-systems that require cooler recycling, only observations of that particular sub-system (e.g. PACS photometer) will be scheduled in two consecutive ODs.
The satellite will execute autonomously the mission timeline that has been uplinked during the DTCP. The observational data will be stored on board, and downlinked to the New Norcia Ground Station (which is backed-up by the Cebreros Ground Station) during the next DTCP. In this period, which lasts approximately 3 hours, the status of the satellite will be monitored and operational or emergency procedures will be applied when necessary. In addition, the mission timeline with the commands to be executed during the next OD will be uplinked. The downlinked satellite telemetry will be transferred from the ground station to the MOC, where it will be consolidated and be made available to the HSC. The HSC will routinely retrieve the consolidated telemetry and auxiliary data from the MOC, and ingest them in the HSC database.
All Herschel telemetry and auxiliary data will be automatically processed at the HSC with the Standard Product Generation software (SPG), to produce the observational data products. The following four levels of Herschel data products are defined:
Level-0 data product: Raw telemetry data as measured by the instrument, minimally manipulated and ingested as Data Frames into the mission data base/archive.
Level-1 data product: Detector readouts calibrated and converted to physical units, in principle instrument and observatory independent. It is expected that level-1 data processing can be performed without human intervention.
Level- 2 data product: Level-1 data further processed to such a level that scientific analysis can be performed. For optimal results many of the processing steps involved to generate level-2 data may require human interaction, based both on instrument understanding as well as understanding of the scientific aims of the observation. These data products are at a publishable quality level and should be suitable for VO access.
Level-3 data product: These are the publishable science products where level-2 data products are used as input. These products are not only from the specific instrument, but are usually combined with theoretical models, other observations, laboratory data, catalogues, etc. Their formats should be VO compatible and these data products should be suitable for VO access.
While the generation of level-0 and level-1 data products will be automatic, proper quality level-2 and level-3 data products may require interactive processing. It is expected that the degree of human intervention necessary to generate these products will decrease with time as the knowledge of the instruments' behaviour increases during the mission. This is the same as saying that the quality of the automatically generated product will be progressively enhanced. However, in many cases it will not be possible to discard interactive processing, especially in the derivation of level-3 data products.
In addition to these observational products, calibration, auxiliary and quality control products will be provided. For more information on the Herschel products, please see the corresponding Instrument Observer User's Manual. In the next future, the Herschel Products Definitions document and the Herschel Data User's Manual document will contain detailed descriptions of all Herschel data.
Herschel data products will be stored in the Herschel Archive. By using the Herschel Archive Browser, astronomers will be able to search, browse, select and retrieve data products according to the observations proprietary rights. The Herschel Archive will also act as a repository of highly processed data products provided by the astronomical community. When requesting observational data from the Herschel archive, the user will be offered as options:
(i) to retrieve directly the stored products,
(ii) to request re-processing with the latest SPG version, and
(iii) to perform On-Demand processing of the selected observations. In the latter, the user customises the standard product generation by choosing values for given parameters that will depend on the type of observation (e.g. low flux observation data processing).
In addition to standard products, a Herschel Observer Interactive Analysis package will be offered to the astronomical community to interactively reduce the Herschel data (starting from level-0, -1 or -2 products), and to perform science analysis. The Herschel Interactive Analysis package does not require commercial licenses and is built to be platform-independent. The distribution will include source of software, calibration data and documentation. In addition, the astronomer will be able to develop and integrate his/her own data processing algorithms within the system.
Observation quality control is an important responsibility of the HSC. Its main purpose is to ensure that the observations have been correctly executed, that their observational data meet the established requirements, and that they can be processed error free. It is important to note that the HSC will not assess systematically the scientific validity of individual observations, but will concentrate on their execution and the data processing aspects.
In combination with the SPG processing, the observational data will be run through the Quality Control Pipeline (QCP). An HSC operator will visually inspect all Herschel observations and will proceed according to agreed observatory procedures. For certain types of problems, the operator will request the assistance of the instrument and satellite specialists at the HSC, ICCs or MOC, who will investigate the reason for the anomaly, assess its impact on the quality of the observational data and determine possible implications for the ground segment. In severe cases, observations may be flagged as "bad" in the database, and made available for re-scheduling. For every observation, quality information will be gathered in a "quality control report summary" product, that will be available in the Herschel Archive in addition to the observational data. The report will contain both the automatically generated quality control data and the conclusions of the problem analysis by the experts, when applicable. Items that will be included in the report are: MOC spacecraft and operations information, on-board observation execution anomalies (instrument or satellite related), telemetry gaps, pointing issues, space weather events, instrument specific warnings (e.g., high glitch rate), and data processing problems.
The calibration and cross-calibration of the Herschel instruments is the responsibility of the observatory, in particular of the ICCs and the HSC. The pointing calibration is the responsibility of the HSC and the MOC. Therefore, the preparation and scheduling of calibration observations is an exclusive duty of these groups. The calibration data required for the reduction and analysis of the Herschel observations will be provided to the astronomer in the form of products in the Herschel Archive, and will be integrated in the Data Processing software (SPG, QCP, IA).
Calibration and engineering observations will be the main components of the schedule during the Commissioning and Performance Verification phases. Their aim will be to achieve the necessary understanding of the instruments and spacecraft, and attain the required calibration and pointing accuracies to ensure a proper execution and data reduction of the science observations during the Science Demonstration and Routine phases. In the routine phase, it is expected that up to 15% of the available observatory time will be used for calibration. Calibration observations may be based on non-AOT observing modes defined by the instrument specialists at the ICCs and HSC, but in general they will be defined using the AOTs available to the community for science observations. Calibration observations are in principle public. However, if a calibration observation is a duplicate of a scientific observation (see the document "Herschel Space Observatory Call for Proposals: Policies and Procedures" for a definition of "duplication"), the corresponding proprietary rights will apply.