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Our aims within the LSKSP are not only to provide
publicly available radio images and catalogues of the sky but also to increase our understanding of the detected sources through a coordinated scientific exploitation of the images and auxiliary data.
To date, with this approach, the LOFAR surveys have facilitated numerous scientific studies\footnote{https://lofar-surveys.org/publications.html} in core areas of radio astronomy such as the physics of active galactic nuclei, particle acceleration in galaxy clusters, large scale structure and star formation.
Furthermore, the breadth of scientific studies continues to expand to include topics ranging from cosmological studies (\citealt{Siewert_2020}) through to pulsars (\citealt{Tan_2018}), supernovae remnants (\citealt{Arias_2019}) and even exoplanets (\citealt{Vedantham_2020}). Meanwhile, valuable synergies are being established such as those with the LOFAR Magnetism Key Science Project\footnote{https://lofar-mksp.org/}, APERTIF imaging surveys, Extended Baryon Oscillation Spectroscopic Survey (eBOSS; \citealt{Dawson_2016}), extended ROentgen Survey with an Imaging Telescope Array (eROSITA; \citealt{Predehl_2021}) and the William Herschel Telescope Enhanced Area Velocity Explorer survey of LOFAR selected sources (WEAVE-LOFAR; \citealt{Smith_2016}) which are each enabling new scientific studies (e.g. \citealt{Ghirardini_2021}, \citealt{Morganti_2021}, \citealt{OSullivan_2020}, \citealt{Wolf_2021}). Finally, the LOFAR surveys are also having a large technical impact with studies of calibration and imaging techniques (e.g. \citealt{deGasperin_2019}, \citealt{Tasse_2021} and \citealt{vanWeeren_2021}, \citealt{Morabito_prep} and \citealt{Sweijen_2022}), efficient distributed processing
(\citealt{Drabent_2019} and \citealt{Mechev_2019}), photometric
redshift estimators (\citealt{Duncan_2019}) and automated source classification
(e.g. \citealt{Mostert_2021} and \citealt{Mingo_2019}). Excitingly, despite all
of these advances, the LOFAR surveys data still retain vast, and largely untapped, potential. For example, 96\% of existing LoTSS observations have been conducted with the full international LOFAR telescope which now includes 14 stations outside of the Netherlands and are archived at high (1\,s) time and frequency (12.1875\,kHz) resolution. Presently, due to resource limitations and ongoing technical developments, during regular LoTSS processing we significantly average the data and remove the international stations. We thus do not yet fully realise the higher sensitivity sub-arcsecond wide-field imaging (e.g. \citealt{Morabito_prep}, \citealt{Sweijen_2022}), source variability (e.g. \citealt{Vedantham_2020,callingham2021}) and spectral line (see e.g. \citealt{Emig_2020}, \citealt{Salas_2019}) capabilities of the data.

In this publication we present our second LoTSS data release (LoTSS-DR2) and a characterisation of the associated images. This builds significantly upon our previous work by making use of our enhanced direction dependent calibration and imaging processing pipeline (see \citealt{Tasse_2021}) as well as improved processing efficiency and automation (see e.g. \citealt{Drabent_2019} and \citealt{Mechev_2019}).
These improvements enable us to present images spanning 5,634 square degrees (27\%) of the Northern sky, and a catalogue containing 4,396,228 radio sources -- the largest catalogue of radio sources released to date. In addition to radio continuum catalogues and images at multiple resolutions, we also release polarisation images and calibrated $uv$-datasets. All data products associated with this release have the Digital Object Identifier (DOI) 10.25606/SURF.LoTSS-DR2 and are available via the collaboration's webpage\footnote{\url{https://www.lofar-surveys.org/}}, the ASTRON Virtual Observatory\footnote{\url{https://vo.astron.nl}} and the SURF Data Repository\footnote{\url{https://repository.surfsara.nl/}}.