Availability of observing capabilities in cycle 16-19

 

During this long-term cycle, we will start using the new Telescope Manager Specification System (TMSS) for specification and scheduling of LOFAR observations.  Development will continue during Cycles 16 and 17 to deliver additional functionality. Therefore, during Cycle 16, a limited set of functionality will be available.

The capabilities of the telescope are split into three categories: available functionality during Cycle 16, additional functionality available in Cycles 17-19, and functionality that is not offered (Cycles 16-19). The content of this list will be revised for next single cycle proposal calls, based on the progress of the TMSS development. The capabilities are presented in the following table and described in more detail in the text following the table. It is followed by a section describing dynamic scheduling, which is new in Cycle 16, and a section regarding the construction of a windfarm near the LOFAR core.

It is important that you check the details regarding specification and scheduling such that you are sure that your observing campaign can be executed. The details can be found below the table and on the separate web pages. Long-term projects requiring functionality that will only become available in Cycles 17-19 should adjust their observing setups for Cycle 16 so as to match the available functionality in that Cycle.

If you are unclear about the available functionality for your proposal, please contact Science Data Center Operations through the JIRA helpdesk [link]. For more detailed information about the observing modes, please follow this [link].

 

 

 Functionality in Cycle 16

Additional functionality in Cycles 17-19

Not offered in Cycles 16-19(1)

Number of beams

- Up to 8

 

 

Number of subbands

- Up to 488

 

 

Antenna modes

- LBA_OUTER

- LBA_SPARSE_EVEN(2)

- HBA_DUAL

- HBA_DUAL_INNER

- HBA_ONE

- HBA_ZERO

 

- LBA_INNER

- HBA_JOINED

Filters

- 10-90 MHz

- 30-90 MHz

- 110-190 MHz

 

- 170-230 MHz

- 210-250 MHz

Interferometric observing strategies

- Book-ended calibrator

- Parallel calibrator

- LST distributed imaging(3)

- Single target observation

- Additional calibrator to book-ended strategy

- Parallel observations(3)

- Interleaved

- Lucky imaging

Interferometric pipelines

- Preprocessing pipeline

- Demixing up to two sources

 

- Long baseline pipeline

- Standard imaging pipeline

Beamformed observing modes

- Multi-TAB

- Pulsar timing (complex voltage)

- Fly's eye

 

 

Beamformed pipelines

- Pulsar Pipeline (PulP)

 

- Dynamic spectrum pipeline(3)

 

 

Advanced and expert observing functionality

- Rapid Response mode

- Transient Buffer Board

- AARTFAAC

- Single station use in local mode during ILT time

- Ingest of raw data from only one dataproduct of beamformed + imaging observation

- Simultaneous beamformed + imaging(3)

- Simultaneous beamformed + imaging, additional mode with parallel observations(3)

- Manual changes in the system

- Projects requiring continuous availability of telescope time(4)

Scheduling constraints

- Day/Night/Avoid Twilight

- Minimum elevation

- Offset from transit

- Specific time

- Simple, independent cadence (e.g. Monthly)

- Windfarm standstill time(5)

- More complicated cadences (e.g. day 1,2,5,10)

 

- Inter-observational constraints(3)

- Orbital constraints(6)

 

(1) Some functionality may become available in future single cycle proposal calls
(2) LBA_SPARSE_EVEN is offered in a shared risk mode. Details about the perofmance are available here

(3) See explanation below
(4) Because of extensive test time, projects requiring guaranteed continuous availability of telescope functionality (e.g., for observations in every week throughout the cycle) will not be granted.
(5) The dynamic scheduler in cycle 16 will not be able to handle stand-still time from the windmills, standstill time cannot be an absolute requirement for a project.
(6) Orbital constraints for binary systems are not modelled in the dynamic scheduler in cycle 16. The proposers should specify all available windows when requesting observations requiring a certain phase of a (binary) system. 

Additional details on available functionality for Cycle 16 and the long-term period (Cycles 16-19):

 

Cycle 16

The HBA interferometric mode:
Free selection of subbands within the 110-190 MHz range, total bandwidth of up to 96 MHz, divided over up to 8 beams.
Pipeline: Preprocessing pipeline, demixing up to two sources
Antennaset: HBA_DUAL, HBA_DUAL_INNER, HBA_ONE, HBA_ZERO
Co-observing: We recommend users to co-observe with the LOFAR Two-metre Sky Survey (LoTSS) [link], if possible.
NOTE: The calibrator(s) will inherit the observing setup (e.g. antennaset, instrument filter, subband list, etc.) of the specified target observation.

 

The LBA interferometric mode:
Free selection of subbands within the 10-90 MHz range, total bandwidth of up to 96 MHz, divided over up to 8 beams.
Observing strategy: One or multiple targets in parallel with a calibrator.
Pipeline: Preprocessing pipeline, demixing up to two sources
Antennaset: LBA_OUTER, LBA_SPARSE_EVEN
Co-observing: We recommend users to co-observe with the LBA survey project [link], if possible.
NOTE: The calibrator(s) will inherit the observing setup (e.g. antennaset, instrument filter, subband list, etc.) of the specified target observation.

 

The Pulsar Timing mode:
Complex voltage beamformed observation with a pipeline producing folded pulsar profiles for known pulsars. Available in the frequency range 10-90 MHz and 110-190 MHz.
Antennaset: HBA_DUAL, HBA_DUAL_INNER, LBA_OUTER,  LBA_SPARSE_EVEN
Pipeline: Pulsar Pipeline for pulsar folding and/or to convert data to 8-bit



The Pulsar Search mode:
A beamformed observation with multiple tied-array beams in combination with incoherent array beams, in accordance to known limits [link]. Free selection of subbands in the frequency range 10-90 MHz and 110-190 MHz.
Antennaset: HBA_DUAL, HBA_DUAL_INNER, LBA_OUTER,  LBA_SPARSE_EVEN
Pipeline: Pulsar Pipeline to convert data and to fold known pulsars

 

Transient Buffer Board raw voltage mode:
Direct storage of data from individual antennas.

 

The Rapid Response mode (Fast ToO) [link]:
An observation triggered automatically, within 5 minutes of the request. Observations are requested through a file uploaded by the user based on default templates available in the system. Four Templates are available: for an LBA imaging (target  + parallel calibrator), HBA imaging (target + calibrator), HBA imaging (7 targets + calibrator) and beamformed (complex voltage) mode. Note that any testing of the new system may require the responsive telescope mode to be unavailable during part of the cycle.
NOTE: The calibrator(s) will inherit the observing setup (e.g. antennaset, instrument filter, subband list, etc.) of the specified target observation.

 

The Fly's eye mode:
A beamformed observation with each station recorded separately, but pointing in the same direction.
Antennaset: HBA_DUAL, HBA_DUAL_INNER, LBA_OUTER
Pipeline: Pulsar pipeline, and Dynamic spectrum pipeline starting from Cycle 17

 

LST distributed imaging (observing strategy):
In LBA, we have observed using 1 hour scans, spread over 3 non-continuous LST ranges. The LST offset window can be used to specify this. For each observation, the LST offset windows should be specified in the proposal. An LST offset window is specified as [start time, stop time] relative to transit. Please allow for 30 minutes extra when specifying the window, e.g., [-4 hr,-2.5hr] for a 1 hour observation.

 

Simultaneous beamformed + imaging observations
A few specific setups are available for simultaneous beamformed + imaging observations, see [link]

 

International Stations used in local mode during ILT time
It is possible to propose for International Station use in local mode during ILT time, if arrangements have been made with the International Station owners regarding the observing and processing of the data.

 

Additional functionality offered in Cycles 17-19:

Also, the following capabilities are offered from Cycle 17 onwards:

  • Observing strategies: Add or remove a calibrator from the default HBA strategy, interleaved observations
  • The Dynamic spectrum pipeline (Execution in Cycle 16 is not generally offered. However, if your project is strongly dependent on this functionality, we advise you to get in contact with SDCO to investigate possibilities.)
  • Advanced solar observing, using various parallel observations

 

Not offered in Cycles 16-19:

  • Antennasets: LBA_INNER, HBA_JOINED
  • The high frequency filters: 170-230 MHz, 210-250 MHz
  • The Long baseline pipeline
  • The Standard imaging pipeline
  • Observing and processing setups that require editing of specifications outside of TMSS (e.g. COBALT correlator override)
  • Projects requiring guaranteed continuous availability of telescope functionality (e.g. observations every week throughout the cycle)
  • Parallel observations - multiple observations that run simultaneously using different stations.

This list will be revised in later single cycle proposal calls.

 

 

Important considerations about dynamic scheduling

TMSS will dynamically schedule observations. All observing templates will be prepared before the start of the cycle and entered in the scheduling queue. They will then be scheduled automatically based on the constraints and the priority of the observations. The priority is set by scientific ranking, A/B queue and the target list ordering in the proposal.

Inter-observational constraints: Observations whose execution time depends on the schedule of other projects in the same cycle cannot be handled properly by the dynamic scheduler in Cycle 16 (e.g. a request to run an observation two days after another one). Proposers that have specific needs in this regard are advised to contact the SDCO group to further discuss options for Cycle 16. An exception to this is regularly repeated observations, e.g., monthly observations.

If your observations should be performed following specific scheduling constraints, as usual you should clarify these in the appropriate field in the proposal. The requested constraints will be evaluated by the technical review panel.

Note that the following defaults are used:

  • Minimum target elevation: 30 degrees
  • Minimum calibrator elevation: 30 degrees 

We aim to observe around transit. The typical transit offset tolerance is set to 1 hour. It is possible to observe off-transit, e.g. for the LST distributed imaging observing strategy, by providing a relative allowed start and end time compared to transit. Please allow half an hour flexibility in this case. As an example, we can specify that this 1 hour observation should run between -4.0 and -2.5 hours compared to transit.

In addition to requesting strictly day time or night time observing, it is also possible to request avoiding sunrise and sunset. There is a special category for low-RFI observations at night, where reflections from planes are lowered.

In general, the dynamic scheduler will pick the start time of the observations. However, observing at a specific start time or at an allowed range of start times can be specified, for simultaneous observing with other instruments.

Since the dynamic scheduler in Cycle 16 will not be able to handle standstill time from the windmills, standstill time cannot be an absolute requirement for a project, and will not be guaranteed to any project. However, if the proposal clearly argues the benefit from windmill standstill time, this might be accommodated on a best effort basis.

 

 

Additonal information over Windmill Impact

PRESENCE:

Over the course of 2020 and 2021 a windfarm is being constructed, consisting of 45 turbines along several rows extending 3-7 km roughly eastward from the LOFAR Core area.

CONSTRUCTION PHASE:

The construction work itself will, from time to time, lead to RFI, but the magnitude and extent is unpredictable (at the time of the Cycle 16 proposal call). Consultation with the windfarm operators is set up with the aim to restrict RFI impact.

RFI EMITTED:

In accordance with conditions laid down in the co-existence covenant between the windfarm operators and ASTRON, the turbines have been specially designed to limit their electromagnetic emissions on the LOFAR Core in the relevant frequency bands ("RFI"). Significant adaptations to the standard design have led to substantial improvements.

A measurement campaign on the fully operational test turbine has confirmed that there is no excess RFI emitted above the ceiling agreed in the covenant. That limit can be globally summarised in astronomical terms as leading to less than 10% increase above the thermal noise in an image from a 4-hour integration (LBA or HBA). Note that long-baseline imaging will be largely unaffected, because the noise is not correlated.

It is likely that in some frequency ranges, the actual RFI emitted by the windfarm will be below that ceiling, but the measurement campaign was not designed to yield reliable measurements below the agreed upper limit.

Adherence to the limit will be actively monitored when the windfarm is operational; in case of transgression, the windfarm operators have the obligation to solve the issue.

 

RFI REFLECTED:

The measurement campaign on the test turbine has confirmed prior expectations of increased RFI from external sources reflected by the windfarm onto LOFAR. The most important impact has been measured in the band 174-230 MHz, which has Europe-wide frequency allocations for Digital Audio Broadcasting. DAB broadcasters close to LOFAR stations are known sources of RFI already; with the windfarm, DAB broadcasters from a wider area will impact the LOFAR Core. A few narrow bands are unaffected in this frequency range, and certain types of broad-band science may still be possible; proposers should contact ASTRON staff for advice in advance. Current information indicates that the HBA below 174 MHz is also largely free of RFI by reflection.

TURBINE STANDSTILL TIME

As part of the covenant conditions, the operators will put their turbines into "EMC Shutdown Mode" for at least 600 hours per year, during low-wind conditions. All electrical equipment will be off, the turbines will be parked and not turning.

 

The measurement campaign has not been designed to yield reliable measurements below the agreed emission upper limit. Arguments suggest that standstill may yield a 10-15 dB reduction of RFI emitted, but only upper limits have been measured to date. Users interested in deep observing (several tens of hours or more in a field), are encouraged to contact ASTRON well ahead of the proposal deadline, to explore setting up a shared-risk project, in which their exposure time could be carefully built up with the dual goals of gradually yielding science, and eventually measuring the practical noise levels in standstill conditions. The science validity and allocation of such a project will be subject to ILT-PC review. It could be considered to carry out such a project throughout the windfarm building phase.

During standstill time, reflection RFI will be stationary, because the turbines do not turn. Transient and pulsar projects may therefore benefit particularly from standstill time.

Proposers should include careful argumentation why their project would greatly benefit from standstill time. Most standstill time slots will come at unpredictable moments, each lasting 24 hours only. It may be possible to schedule at short notice observations requiring standstill RFI conditions at any LST during these time slots, although this cannot be guaranteed. Since the dynamic scheduler in Cycle 16 will not be able to handle standstill time from the windmills, standstill time cannot be an absolute requirement for a project, and will not be guaranteed to any project. Instead, earmarking for eligibility will be conferred to scientifically highly ranked projects that clearly argue their benefit from windfarm standstill time.

Design: Kuenst.    Development: Dripl.    © 2021 ASTRON