Availability of observing capabilities in cycle 14-17

During this long term cycle, development will take place towards a new specification and scheduling system. When ready, this system will be put in production, but with an initial limited set of functionality. To streamline operations during this period, limited functionality is offered in this proposal call.

 

The current capabilities of the telescope are split into three categories: available functionality during the long term (Cycle 14-17), additional functionality available during cycle 14, and functionality that is no longer offered (Cycle 14-17). These are presented in the following table and described in more details in the text following the table.

 

In case of any unclarity regarding available functionality for your proposal, please contact SOS through the JIRA helpdesk [link]. For more detailed information about the observing modes, please follow this [link]

 

 

Long term and cycle 14

Additional functionality in cycle 14

Not offered in cycles 14-17

Number of beams

Up to 8

 

 

Number of subbands

Up to 488

 

 

Antenna modes

- LBA_OUTER

- HBA_DUAL

- HBA_DUAL_INNER

 

- LBA_INNER

- HBA_JOINED

- HBA_ONE

- HBA_ZERO

Filters

- 10-90 MHz

- 30-90 MHz

- 110-190 MHz

 

- 170-230 MHz

- 210-250 MHz

Interferometric observing strategies

- Book-ended calibrator

- Parallel calibrator

- Interleaved observations

- 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

 

Advanced and expert observing functionality

- Rapid Responsive mode

- Transient Buffer Board

- Simultaneous beamformed + imaging

- Advanced solar observing

- AARTFAAC

- Single station use in local mode under ILT time

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

- Manual changes in the system

- Projects requiring continuous availability of the telescope*

*Because of extensive test time, projects requiring guaranteed continuous availability of telescope functionality (e.g., for observations in every week throughout the cycle) cannot be granted.

 

 

Available functionality for the Long Term (Cycle 14-17):

The HBA interferometric mode:

Free selection of subbands within the 110-190 MHz range up to 96 MHz total, divided over up  8 beams.

Observing strategy: Calibrator – Observation – Calibrator

Pipeline: Preprocessing pipeline, demixing up to two sources

Antennaset: HBA_DUAL, HBA_DUAL_INNER

 

The LBA interferometric mode:

Free selection of subbands within the 10-90 MHz range up to 96 MHz total, 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

 

The Pulsar Timing mode:

Complex voltage beamformed observation with a pipeline producing folded pulsar profiles for known pulsars. Available in frequency range 10-90 MHz and 110-190 MHz

Antennaset: HBA_DUAL, HBA_DUAL_INNER, LBA_OUTER

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 frequency range 10-90 MHz and 110-190 MHz.

Antennaset: HBA_DUAL, HBA_DUAL_INNER, LBA_OUTER

Pipeline: Pulsar Pipeline to convert data and to fold known pulsars

 

Transient Buffer Board raw voltage mode:

Direct storage of data from individual antenna’s.

 

The Responsive Telescope mode [link]:

An automatically started observation, within 5 minutes of the request. Observations are requested by an XML file upload by the user following one of three default templates for a beamformed mode, an LBA imaging mode and an HBA imaging mode. Note that necessary testing of the new system may require the responsive telescope to be off during part of the time in the cycle.

 

 

Additional functionality offered in cycle 14.

One additional observing mode is offered in cycle 14:

 

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, dynamic spectrum pipeline

 

Also, the following capabilities are offered in the single cycle:

  • Advanced observing strategies: interleaved observations, lucky imaging
  • Simultaneous beamformed + imaging observations within known limits [link]
  • The dynamic spectrum pipeline
  • AARTFAAC piggybacking allowed
  • Advanced solar observing, usin, e.g., various parallel observations
  • International stations used in local mode under ILT time

Not offered for cycle 14-17:

  • Antennasets: LBA_INNER, HBA_JOINED, HBA_ONE, HBA_ZERO
  • The high frequency filters: 170-230 MHz, 210-250 MHz
  • The Long Baseline pipeline
  • The Standard Imaging Pipeline [this was already obsolete]
  • Ingest of raw data from only one data product of beamformed + imaging observations
  • Observations requiring manual changes in the system [OTDB, COBALT]
  • Projects requiring guaranteed continuous availability of telescope functionality (e.g., for observations in every week throughout the cycle)


Additional information over Windmill Impact

 

PRESENCE:

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

 

CONSTRUCTION PHASE:

The first turbine, used initially for testing, is operational now. Further general infrastructure preparations for the full windfarm will take place in early 2020. Turbine construction will start in the second half of 2020; turbines will be taken into operation one-by-one, with the windfarm scheduled for completion in 2021.

 

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 14 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 Radio Observatory 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 the Radio Observatory well ahead of the proposal deadline, to explore setting up a shared-risks 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 from standstill time.

 

Proposers may include careful argumentation why their project would greatly benefit from standstill time. However, most standstill time slots will come at unpredictable moments, each lasting 6-12 hours only. The Radio Observatory does not have dynamic scheduling in place yet. Thus, 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 both clearly argue their benefit from windfarm standstill time, and can also be flexibly scheduled in appropriate blocks. 
Design: Kuenst.    Development: Dripl.    © 2020 ASTRON