Location (town, country): LOFAR has its central core situated in Exloo, the Netherlands. There are several stations distributed over the North Eastern part of the Netherlands and 14 international stations, 1 in Ireland, 1 in the UK, 1 in France, 6 in Germany, 3 in Poland, 1 in Sweden and 1 in Latvia.

Web site: https://www.astron.nl/index.php/telescopes/lofar

Description of the infrastructure:

The LOFAR radio telescope is dedicated to low frequency (10-250MHz) radio astronomical observations, which can be strongly affected by the ionosphere. A typical observing mode is its use as an interferometer to make detailed images of astronomical radio sources. To make the sharpest images, the observations must be calibrated for ionospheric effects, a process which in itself results in information on the ionospheric structure distorting the incoming radio signals, including calculations of the differential Total Electron Content and Faraday rotation of the signal due to the geomagnetic field (Mevius et al., 2016, https://doi.org/10.1002/2016RS006028; De Gasperin et al., 2018, https://doi.org/10.1051/0004-6361/201833012). In uncalibrated snapshot images of the radio sky, individual sources may appear displaced from the default positions due to refraction through the ionosphere. Although still an area for research, assessment of this displacement in all-sky images containing many individual radio sources could result in all-sky maps of any Traveling Ionospheric Disturbances or other activity present (similar to research using the Murchison Widefield Array in western Australia, e.g., Loi et al., 2015, http://dx.doi.org/10.1002/2015RS005711).

Furthermore, single-station observations of compact radio sources allow wide bandwidth scintillation measurements of the ionosphere, which both reveal ionospheric detail unavailable to discrete-frequency observations from GNSS, and act as a low-frequency complement to them (Fallows et al., 2020, https://arxiv.org/abs/2003.04013). Combining scintillation measurements of several nearby stations also gives a unique picture of the dynamics of small-scale structures in the ionosphere. Single LOFAR stations can furthermore be operated as all-sky monitors for, e.g., radar experiments.

Services currently offered by the infrastructure:

LOFAR is an open access scientific facility to which anyone can apply for time through standard scientific proposal procedures. Data are stored in a long-term archive and typically made

public after one year. This archive already contains scintillation data from several years of ad-hoc observations. Training in the specification of observations suitable for ionospheric research purposes and the analysis of LOFAR data will be offered, alongside advise on how to apply for observing time and getting access to existing data. Since 2000, 1604 papers are published in peer review journals and conference publications based on LOFAR data.

New areas opening to users:

  • Analysis of unique data on small scale disturbances and their dynamics;
  • Assessment of any association with large-scale structures (e.g., TIDs) detected and modeled by other instruments.
  • Potential for passive radar experiments.