Ionospheric Conditions Research Articles

Identifying spurious cycle slips based on iterative filtering under disturbed ionospheric conditions for undifferenced GNSS observations

The TurboEdit method is widely used to detect cycle slips on the global navigation satellite system (GNSS) carrier-phase measurements. However, it leads to an increasing number of false alarms in detecting cycle slips under disturbed ionospheric conditions. Besides, once the method detects a cycle slip at one satellite, it treats dual frequencies with cycle slips rather than at one frequency. Considering these two challenges, we developed a solution-based iterative filter detection method to reduce the number of spurious cycle slip detection under disturbed ionospheric conditions. The method initially assumes that there is no cycle slip at each frequency. We then estimate the solutions without cycle slips. A decision of exiting cycle slips is made by examining and comparing the two results solutions with or without cycle slips in terms of usable satellites, ambiguities, and residuals. The uncombined precise point positioning (PPP) during disturbed ionospheric conditions on 17 March 2015 at high latitude was studied to validate the proposed method. Results showed that the detected number of spurious cycle slips was reduced significantly. With fewer marked cycle slips, more stable and smoother positioning performance was achieved when fewer ambiguity parameters were reinitialized.

Joule heating in the mid-latitude ionosphere by high power HF radio waves

We present an estimation of the heating rate due to Joule heating in the F region of the ionosphere as a result of its interaction with high-power HF O-mode radio waves transmitted by a ground-based antenna. We refer to experiments conducted at Platteville, Colorado in the 70’s, i.e., at a mid-latitude ionosphere, as the ionospheric conditions and experimental facility parameters are well known. Analytical expressions for the electric field of the HF wave, ionospheric electric conductivity and heating rate are inserted into the calculations. The subsequent spatial and temporal changes in electron and ion temperatures were estimated. The results show that the electron temperatures demonstrate an increase of 115% above their unperturbed values and the ion temperatures demonstrate a corresponding increase of 13%.

Polarization Characteristics of a Single Mode Radio Wave Traversing Through the Ionosphere: A Unique Observation From the RRI on ePOP/SWARM‐E

AbstractThe polarization characteristics of radio waves traversing the ionosphere can be determined using the cross‐dipole antennas of Radio Receiver Instrument (RRI) onboard the Enhanced Polar Outflow Probe payload on the CAScade, Smallsat, and Ionospheric Polar Explorer/Swarm‐E satellite. Numerous coordinated ground‐RRI transionospheric propagation experiments have been executed, with the present study using transmitted radio waves from a High Frequency (HF) ground transmitter located in Ottawa, Canada (45.41°N, 75.55°W). Most of these experiments have shown the HF radio waves to propagate with both magnetoionic propagation modes, the O‐ and X‐modes, combined. However, the coordinated ground‐RRI experiment on 12 May 2017 showed only one magnetoionic propagation mode. The observed polarization state had a stable orientation angle, but the ellipticity angle changed from −19° to linear (0°) and finally 30° within a latitude span of 15°. A detailed investigation using magnetoionic ray trace modeling and ground‐based ionogram observations revealed that the HF transmitted frequency and ionospheric conditions were such that only the O‐mode radio waves reached the satellite for the entire pass. This distinct observation is a unique opportunity to examine the radio wave polarization state during a transionospheric propagation of only O‐mode waves.

Systematic study of ionospheric scintillation over the indian low-latitudes during low solar activity conditions

A systematic study of ionospheric scintillation at the low-latitudes, especially around the Equatorial Ionization Anomaly (EIA) and the magnetic equator, is essential in understanding the dynamics of ionospheric variation and related physical processes. Our study involves NavIC S4C observations over Indore and Hyderabad. Additionally, GPS S4C observations over Indore were analyzed, under disturbed as well as quiet time ionospheric conditions from September 2017 through 2019, falling in the declining phase of the solar cycle 24. The S4C observations were further analyzed using proxy parameters: ROT and ROTI. These results have been obtained from three satellites of the NavIC constellation (PRNs 2, 5, and 6). The onset times of scintillations were observed to be around 19:30 LT (h) and 20:30 LT (h) for Hyderabad and Indore respectively, while the S4C peak values occurred between 22:00 LT (h) and 23:00 LT (h). The reliability of NavIC was evaluated using scattering coefficients that revealed a good correlation across the pair of signals during quiet time ionospheric conditions. The observations clearly show that the amplitude scintillation of the NavIC signal follows the Nakagami-m distribution along with the α-μ distribution as a depiction of the deep power fades caused by scintillation on these signals. This paper shows the impact of such systematic studies near these locations for the first time, in improving the understanding of the dynamic nature of low-latitude ionosphere under low solar activity conditions.

Bayesian data analysis for sky-averaged 21-cm experiments in the presence of ionospheric effects

ABSTRACT The ionosphere introduces chromatic distortions on low frequency radio waves, and thus poses a hurdle for 21-cm cosmology. In this paper, we introduce time-varying chromatic ionospheric effects on simulated antenna temperature data of a global 21-cm data analysis pipeline, and try to detect the injected global signal. We demonstrate that given turbulent ionospheric conditions, more than 5 per cent error in our knowledge of the ionospheric parameters could lead to comparatively low evidence and high root-mean-square error (RMSE), suggesting a false or null detection. When using a constant antenna beam for cases that include data at different times, the significance of the detection lowers as the number of time samples increases. It is also shown that for observations that include data at different times, readjusting beam configurations according to the time-varying ionospheric conditions should greatly improve the significance of a detection, yielding higher evidences and lower RMSE, and that it is a necessary procedure for a successful detection when the ionospheric conditions are not ideal.

High Frequency Land Backscatter Coefficients Over Northern Australia and the Effects of Various Surface Properties

Over-the-horizon radars (OTHRs) utilize the refractive properties of the ionosphere to illuminate targets beyond the Earth’s horizon. Consequently, the performance of this type of radar is highly dependent on the ionosphere. Reliable models of the radar ground backscatter are required to accurately assess the ionospheric propagation conditions and, thus, the expected performance of OTHRs. The ground backscatter coefficient characterizes the amount of radiation scattered back from a surface toward a receiver per unit area. While the backscatter coefficient of the sea is well understood and may be calculated from theory if the sea state is known, the backscatter coefficient of land at high frequencies is not well understood. To calculate the land backscatter coefficients over Northern Australia, a methodology that compares observed backscatter ionograms to those synthesized using high-frequency (HF) radio wave ray-tracing techniques through model ionospheres was developed. Maps of the backscatter coefficients across Northern Australia were produced. The effects of surface properties, including topography, soil moisture, and vegetation cover on the backscatter coefficients, were investigated. A weak positive correlation between the backscatter coefficient and the soil moisture and surface roughness was observed; however, it was found that the vegetation had the largest effect on the backscatter coefficient.

Model evaluation of accuracy of obtaining total electron content by the method of spaced reception of low Earth orbit satellite signals

A model-based technique to estimate the accuracy of the ionospheric total electron content (TEC) based on the data from spaced receivers of low Earth orbit satellite signals has been suggested. That allows us to estimate the total electron content errors for both quiet ionosphere conditions and under the presence of a plasma ring. To estimate the error, the dynamic model of the electron concentration of the Earth's ionosphere has been used. For the selected input parameters (day of the year, time of day, etc.), a model two-dimensional electron density distribution has been calculated using this model. When calculating this two-dimensional distribution of the electron density, changes have been made that transformed it into a distribution that most closely matches the real ionosphere, for example, the presence of a plasma ring, a trough, etc. Using the obtained distribution, some model quantities (differential phase and total electron content) have been calculated. Then they are used for model estimation of errors in the calculation of the TEC by the spaced reception method. For quite conditions in the ionosphere, the relative error of determining the initial phase constant does not exceed 3 %, and in the case of the plasma ring - 13 %. For the vertical total electron content, the relative error in quite conditions does not exceed 7 %, and in the case of a plasma ring - 60 %. Large values of the relative error are in areas of sharp change of the vertical total electron content.

Generalized Rayleigh‐Taylor Instability: Ion Inertia, Acceleration Forces, and E Region Drivers

AbstractA linear theory of the generalized Rayleigh‐Taylor instability (GRTI) is derived which includes ion inertia and acceleration forces, as well as E region drivers: the zonal neutral wind and plasma drift. This is in contrast to the F region drivers (aside from gravity): the meridional neutral wind and the meridional/vertical plasma drifts. Both a local theory and a flux‐tube integrated theory are presented with application to the onset of ionosphere irregularities associated with equatorial spread F. Inertia and acceleration forces do not affect the growth rate of the GRTI for nominal ionospheric conditions, but the E region zonal drifts can significantly increase or decrease the growth rate of the GRTI in the equatorial and mid‐latitude ionosphere depending on their direction.

Advances in Ionospheric Space Weather by Using FORMOSAT-7/COSMIC-2 GNSS Radio Occultations

This paper provides an overview of the contributions of the space-based global navigation satellite system (GNSS) radio occultation (RO) measurements from the FORMOSAT-7/COSMIC2 (F7/C2) mission in advancing our understanding of ionospheric plasma physics in the purview of space weather. The global positioning system (GPS) occultation experiment (GOX) onboard FORMOSAT-3/COSMIC (F3/C), with more than four and half million ionospheric RO soundings during April 2006–May 2020, offered a unique three-dimensional (3D) perspective to examine the global electron density distribution and unravel the underlying physical processes. The current F7/C2 carries TGRS (Tri-GNSS radio occultation system) has tracked more than 4000 RO profiles within ±35° latitudes per day since 25 June 2019. Taking advantage of the larger number of low-latitude soundings, the F7/C2 TGRS observations were used here to examine the 3D electron density structures and electrodynamics of the equatorial ionization anomaly, plasma depletion bays, and four-peaked patterns, as well as the S4 index of GNSS signal scintillations in the equatorial and low-latitude ionosphere, which have been previously investigated by using F3/C measurements. The results demonstrated that the denser low-latitude soundings enable the construction of monthly global electron density maps as well the altitude-latitude profiles with higher spatial and temporal resolution windows, and revealed longitudinal and seasonal characteristics in greater detail. The enhanced F7/C2 RO observations were further applied by the Central Weather Bureau/Space Weather Operation Office (CWB/SWOO) in Taiwan and the National Oceanic and Atmospheric Administration/Space Weather Prediction Center (NOAA/SWPC) in the United States to specify the ionospheric conditions for issuing alerts and warnings for positioning, navigation, and communication customers. A brief description of the two models is also provided.

Multiple E-Region Radar Propagation Modes Measured by the VHF SIMONe Norway System During Active Ionospheric Conditions

Multiple propagation modes between different bistatic radar links were measured during the operations of a very high frequency (VHF) 32.55 MHz radar system in northern Norway. The Spread Spectrum Interferometric Multistatic meteor radar Observing Network (SIMONe) Norway system detected meteor trails, direct transmitter to receiver signal propagation, over-the-horizon signal propagation from the SIMONe Germany system, ground and/or sea scatter, and ionospheric scatter on 27 August 2021 between 16:30–20:00 UT. These simultaneous detections were during an active ionospheric period with multiple occurrences of energetic charged particle precipitation. The SIMONe systems used continuous-wave (CW) pseudo-random phase modulated transmit signals and interferometry to make it possible to isolate each of these propagation modes and examine their characteristics. Different multistatic links at three receiver locations were analyzed, providing multistatic measurements of the regions with spatial and temporal resolutions on the order of 1.5 km and 2 s. The analysis techniques are described, with characteristics of the radar signal presented for each propagation mode and multistatic link. This study serves to highlight the capabilities of the SIMONe Norway system to research multiple aspects of ionospheric phenomena, specifically in the lower thermosphere-mesosphere boundary region.

A contribution to real-time space weather monitoring based on scintillation observations and IoT

The ionosphere is a region of plasma in altitudes extending up to 1000 km. Over low latitudes, steep depletions in the ionospheric density, commonly referred to as equatorial plasma bubbles, are generated after sunset as a result of plasma instabilities. Large variations in the index of refraction associated with these plasma bubbles affect the amplitude and phase of trans-ionopsheric radio signals used for communication, remote sensing and navigation, causing the so-called ionospheric scintillation. Therefore, better understanding of the ionospheric conditions is important for various applications. Unfortunately, real-time ionospheric monitoring systems have been limited, in most cases, by the cost and distribution of adequate sensors. In this work, we present and discuss an internet-of-things (IoT) system composed of a mobile application that acquires data from a network of low-cost scintillation monitors (ScintPi) capable of detecting the occurrence of ionospheric irregularities. The system, referred to as Ionik2, provides real-time information about ionospheric scintillation. A mobile app named ScintApp provides time-series of scintillation indices (S4) and spatial distribution of scintillation using Google Maps. ScintApp also has post-processing capability allowing database queries. Finally, ScintApp is based on a native mobile smartphone application for Android operating systems. Here, we present initial results obtained with an interim prototype distribution of ScintPi monitors. We compare the information provided by ScintApp with observations made by independent instrumentation that have been widely used for ionospheric studies but do not provide real-time data. The results proof the concept of a system capable of providing realt-time information about scintillation events associated with equatorial plasma bubbles.

A Comparison of the Barrick and Backscatter Ionogram Methods of Calculating Sea Surface Backscatter Coefficients

An understanding of land and sea surface backscatter coefficients at high frequencies (HF) is required to accurately assess ionospheric propagation conditions for over-the-horizon radar. In this paper, two methods of calculating sea surface backscatter coefficients are compared. The first method is a theoretical method developed by Barrick in 1972, which treats the sea as a slightly rough surface defined by a wave height spectrum and uses a perturbation approach. The second method compares the difference between observed and modelled backscatter ionograms in which all other losses are accounted for to obtain a measurement of the sea surface backscatter coefficient. Similar trends and values for the sea surface backscatter coefficients from each method were found despite the many models and assumptions required for both these methods. However, it was noted that there was a larger range of values for the sea surface backscatter coefficients when the Barrick method was used.

An Optima Combination Method of Three-Frequency Real-Time Cycle Slip Detection for Non-Normal Ionospheric Variation Data

Linear combinations of triple-frequency help improve the performance of cycle slip detection for high-precision positioning using a single receiver; however, the position can be easily misjudged under ionospheric scintillation conditions or low sampling rates. We propose a method, which is developed specially for the datasets under ionospheric scintillation conditions or low sampling rates, to detect the triple-frequency cycle slips in real-time based on optimal linear combination coefficients and ionospheric range delay. Detection formulas are derived from the triple-frequency geometry-free code-phase combination, and ionospheric range delay is estimated by the wide lane combination. In addition, the principle used to select an optimal linear phase combination coefficient is derived, and the optimal linear coefficient suitable under high ionospheric activity conditions is provided. Finally, the data collected from self-build stations JYPS and NQ01 are used to test the performance of the method. The results demonstrate that the improved method can be used to detect all combinations of cycle slips in real-time, even under conditions of ionospheric scintillation or a sampling period exceeding 10 s.

Investigating GNSS PPP\u2013RTK with external ionospheric constraints

Real-Time Kinematic Precise Point Positioning (PPP–RTK) is inextricably linked to external ionospheric information. The PPP–RTK performances vary much with the accuracy of ionospheric information, which is derived from different network scales, given different prior variances, and obtained under different disturbed ionospheric conditions. This study investigates the relationships between the PPP–RTK performances, in terms of precision and convergence time, and the accuracy of external ionospheric information. The statistical results show that The Time to First Fix (TTFF) for the PPP–RTK constrained by Global Ionosphere Map (PPP–RTK-GIM) is about 8–10 min, improved by 20%–50% as compared with that for PPP Ambiguity Resolution (PPP-AR) whose TTFF is about 13–16 min. Additionally, the TTFF of PPP–RTK is 4.4 min, 5.2 min, and 6.8 min, respectively, when constrained by the external ionospheric information derived from different network scales, e.g. small-, medium-, and large-scale networks, respectively. To analyze the influences of the optimal prior variances of external ionospheric delay on the PPP–RTK results, the errors of 0.5 Total Electron Content Unit (TECU), 1 TECU, 3 TECU, and 5 TECU are added to the initial ionospheric delays, respectively. The corresponding convergence time of PPP–RTK is less than 1 min, about 3, 5, and 6 min, respectively. After adding the errors, the ionospheric information with a small variance leads to a long convergence time and that with a larger variance leads to the same convergence time as that of PPP-AR. Only when an optimal prior variance is determined for the ionospheric delay in PPP–RTK model, the convergence time for PPP–RTK can be shorten greatly. The impact of Travelling Ionospheric Disturbance (TID) on the PPP–RTK performances is further studied with simulation. It is found that the TIDs increase the errors of ionospheric corrections, thus affecting the convergence time, positioning accuracy, and reliability of PPP–RTK.

Assessment of the performance of GPS/Galileo PPP-RTK convergence using ionospheric corrections from networks with different scales

The rapid convergence of precise point positioning real-time kinematics (PPP-RTK) with centimeter-level accuracy is of utmost importance for many applications. One way of accelerating this convergence is to explore the use of ionospheric models and multiple global navigation satellite system (GNSS) observations, e.g., Global Positioning System (GPS) and Galileo Satellite Navigation System (Galileo) observations. Because the temporal and spatial variations of the ionosphere are significant, convergence analysis of PPP-RTK should be investigated in networks with different scales, especially networks with large differences in their scales. This study describes the convergence performance of PPP-RTK using GPS/Galileo observations derived from networks with different scales under medium ionospheric conditions. Slant ionospheric corrections were first estimated from the reference network and then imported as virtual observations to enhance the convergence performance of PPP-RTK at the user interface. The results show that for the 165-km reference site spacing, the portions of single-differenced (SD) ionospheric residuals within 0.3 total electron content units (TECU) were 85.2% and 81.7% for the GPS and Galileo observations, respectively. Considering the 90th percentile of horizontal position errors, the PPP-RTK convergence time within the network with 165-km spacing was shortened from 2.5 min for GPS-only observations to 2.0 min for integrated GPS + Galileo observations. For the network of about 50 km, the proportions of the SD ionospheric residuals of the GPS and Galileo constellation within 0.3 TECU were 95.9% and 82.8%, respectively. The PPP-RTK convergence time of the 90th percentile horizontal positioning errors based on GPS-only observations was 2.0 min but 1.5 min based on integrated GPS + Galileo observations. Using GPS and Galileo observations, the convergence time could be reduced by 25% for the network with 50-km spacing. Our results suggest that the convergence time of PPP-RTK depends on the scale of the reference network and becomes shorter as the scale of the network decreases. Compared with the GPS-only PPP-RTK, the GPS/Galileo PPP-RTK could shorten the convergence time further.Graphical

Forecast of the Global TEC by Nearest Neighbour Technique

We propose a method for Global Ionospheric Maps of Total Electron Content forecasting using the Nearest Neighbour method. The assumption is that in a database of global ionosphere maps spanning more than two solar cycles, one can select a set of past observations that have similar geomagnetic conditions to those of the current map. The assumption is that the current ionospheric condition can be expressed by a linear combination of conditions seen in the past. The average of these maps leads to common geomagnetic components being preserved and those not shared by several maps being reduced. The method is based on searching the historical database for the dates of the maps closest to the current map and using as a prediction the maps in the database that correspond to time shifts on the prediction horizons. In contrast to other methods of machine learning, the implementation only requires a distance computation and does not need a previous step of model training and adjustment for each prediction horizon. It also provides confidence intervals for the forecast. The method has been analyzed for two full years (2015 and 2018), for selected days of 2015 and 2018, i.e., two storm days and two non-storm days and the performance of the system has been compared with CODE (24- and 48-h forecast horizons).

Ionospheric Science: An Example of the Importance of Diversity in Approaches to Scientific Research

This paper discusses the strategic importance of contemporary ionospheric science. It outlines some key features of the evolution of the science from the first practical experiments in the 1920s through to the diverse inter-disciplinary science of today. This science includes fundamental studies of partially ionised plasmas and of the complex systems that arise when those plasmas are coupled to neutral atmospheres and magnetospheres. However, the science also has great potential to deliver societal benefits if the science can be refined to obtain a deep physical understanding of ionospheric phenomena and that understanding is then transitioned into use by operational services such as forecasts of ionospheric conditions. Thus, ionospheric science is now very similar in form to other environment sciences and, the same as them, needs to be positioned in a diverse scientific culture that supports the full range of science research, including not only curiosity-driven studies, but also targeted research to deepen our physical understanding to a level that is sufficient to enable a transition to operational services. That diversity also includes support for that transition and also facilitates feedback from operations teams to researchers. Such feedback can be a powerful stimulus for future research.

Investigating the impact of the latitudinal velocity profile on nonlinear gradient drift instability development in the subauroral ionosphere

Subauroral polarization streams (SAPS) are regions in the subauroral ionosphere with lower plasma density and large westward flow driven by a poleward electric field. Density irregularities have been observed in the SAPS region; these irregularities can negatively impact radio signals by causing phase and amplitude fluctuations. Previous work identified the gradient drift instability (GDI) as a generation mechanism of such ionospheric irregularities in SAPS and investigated the impact of the velocity profile on the GDI development. The turbulence spectra of the GDI are important to understand as they can provide insight into spatial scales associated with the turbulent evolution that may impact radio propagation. We hypothesize that the background electric field, through the neutral wind, and the nature of the velocity shear have an impact on the power laws from the turbulence spectra. A 2D fluid model is used to investigate the turbulence spectra of GDI in SAPS with a fixed background density profile and different latitudinal velocity profiles. Data from Super Dual Auroral Radar Network (SuperDARN) radar and Global Positioning System (GPS) provide the background ionospheric conditions. The neutral wind direction is chosen to be in the equatorward direction, which is in line with typical observations; however, this can be used to modify the electric field to consider new possibilities in the SAPS region. The angle of the electric field is manifested through the combination of the background velocity profile ( drift) and the neutral wind. The turbulence spectra of cases with no velocity profile and with different neutral wind directions are analyzed. The impact of velocity shear is studied by translating the velocity shear location relative to the density gradient. Numerical spectral analysis results are presented and compared to recent experimental observations. Results of spectral slopes of GDI simulations with no background velocity ( drift) were found to be and for the normalized density and the perturbed electric potential, respectively. Spectral slopes for simulations with different velocity shear locations were found to follow power laws of and for the normalized density and perturbed electric potential (inside SAPS region), respectively.

Artificial Neural Network-Based Ionospheric Delay Correction Method for Satellite-Based Augmentation Systems

Ionospheric delay is a critical error source in Global Navigation Satellite Systems (GNSSs) and a principal aspect of Satellite Based Augmentation System (SBAS) corrections. Grid Ionospheric Vertical Delays (GIVDs) are derived from the delays on Ionosphere Pierce Points (IPPs), which are observed by SBAS reference stations. SBAS master stations calculate ionospheric delay corrections by several methods, such as planar fit or Kriging. However, when there are not enough IPPs around an Ionosphere Grid Point (IGP) or the IPPs are unevenly distributed, the fitting accuracy of planar fit or Kriging is unsatisfactory. Moreover, the integrity bounds of Grid Ionospheric Vertical Errors (GIVEs) are overly conservative. Since Artificial Neural Networks (ANNs) are widely used in ionospheric research due to their self-adaptation, parallelism, non-linearity, robustness, and learnability, the ANN method for GIVD and GIVE derivation is proposed in this article. Networks are separately trained for IGPs, and five years of historical data are applied on network training. Principal Component Analysis (PCA) is applied for dimensionality reduction of geomagnetic and solar indices, which is employed as a network input feature. Furthermore, the GIVE algorithm of the ANN method is derived based on the distribution of the residual random variable. Finally, experiments are conducted on 12 IGPs over the East China region. Under normal ionospheric conditions, compared with the planar fit and Kriging methods, the residual reduction of the ANN method is approximately 15%. The ANN method fits the ionospheric delay residual error better. The percentage of GIVE availability under 2.7 m increases at least 25 points in comparison to Kriging. Under disturbed conditions, due to a lack of training samples, the ANN method is incompetent compared with planar fit or Kriging.

Sub-arcsecond imaging with the International LOFAR Telescope

The International LOFAR Telescope is an interferometer with stations spread across Europe. With baselines of up to ~2000 km, LOFAR has the unique capability of achieving sub-arcsecond resolution at frequencies below 200 MHz. However, it is technically and logistically challenging to process LOFAR data at this resolution. To date only a handful of publications have exploited this capability. Here we present a calibration strategy that builds on previous high-resolution work with LOFAR. It is implemented in a pipeline using mostly dedicated LOFAR software tools and the same processing framework as the LOFAR Two-metre Sky Survey (LoTSS). We give an overview of the calibration strategy and discuss the special challenges inherent to enacting high-resolution imaging with LOFAR, and describe the pipeline, which is publicly available, in detail. We demonstrate the calibration strategy by using the pipeline on P205+55, a typical LoTSS pointing with an 8 h observation and 13 international stations. We perform in-field delay calibration, solution referencing to other calibrators in the field, self-calibration of these calibrators, and imaging of example directions of interest in the field. We find that for this specific field and these ionospheric conditions, dispersive delay solutions can be transferred between calibrators up to ~1.5° away, while phase solution transferral works well over ~1°. We also demonstrate a check of the astrometry and flux density scale with the in-field delay calibrator source. Imaging in 17 directions, we find the restoring beam is typically ~0.3′′ ×0.2′′ although this varies slightly over the entire 5 deg2field of view. We find we can achieve ~80–300 μJy bm−1image rms noise, which is dependent on the distance from the phase centre; typical values are ~90 μJy bm−1for the 8 h observation with 48 MHz of bandwidth. Seventy percent of processed sources are detected, and from this we estimate that we should be able to image roughly 900 sources per LoTSS pointing. This equates to ~ 3 million sources in the northern sky, which LoTSS will entirely cover in the next several years. Future optimisation of the calibration strategy for efficient post-processing of LoTSS at high resolution makes this estimate a lower limit.