Per Høeg

• Spogli, Luca; Jin, Yaqi; Urbář, Jaroslav; Wood, Alan G.; Donegan-Lawley, Elizabeth E. & Clausen, Lasse [Show all 20 contributors for this article] (2024). Statistical models of the variability of plasma in the topside ionosphere: 2. Performance assessment. Journal of Space Weather and Space Climate. 14. doi: 10.1051/swsc/2024003. Full text in Research Archive Show summary

  Statistical models of the variability of plasma in the topside ionosphere based on the Swarm data have been developed in the “Swarm Variability of Ionospheric Plasma” (Swarm-VIP) project within the European Space Agency’s Swarm+4D-Ionosphere framework. The models can predict the electron density, its gradients for three horizontal spatial scales – 20, 50 and 100 km – along the North-South direction and the level of the density fluctuations. Despite being developed by leveraging on Swarm data, the models provide predictions that are independent of these data, having a global coverage, fed by various parameters and proxies of the helio-geophysical conditions. Those features make the Swarm-VIP models useful for various purposes, which include the possible support for already available ionospheric models and proxy of the effect of ionospheric irregularities of the medium scales that affect the signals emitted by Global Navigation Satellite Systems (GNSS). The formulation, optimisation and validation of the Swarm-VIP models are reported in Paper 1 (Wood et al. 2024. J Space Weather Space Clim. in press). This paper describes the performance assessment of the models, by addressing their capability to reproduce the known climatological variability of the modelled quantities, and the ionospheric weather as depicted by ground-based GNSS, as a proxy for the ionospheric effect on GNSS signals. Additionally, we demonstrate that, under certain conditions, the model can better reproduce the ionospheric variability than a physics-based model, namely the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM).

• Wood, Alan G.; Donegan-Lawley, Elizabeth E.; Clausen, Lasse; Spogli, Luca; Urbář, Jaroslav & Jin, Yaqi [Show all 20 contributors for this article] (2024). Statistical models of the variability of plasma in the topside ionosphere: 1. Development and optimisation. Journal of Space Weather and Space Climate. 14. doi: 10.1051/swsc/2024002. Full text in Research Archive Show summary

  This work presents statistical models of the variability of plasma in the topside ionosphere based on observations made by the European Space Agency’s (ESA) Swarm satellites. The models were developed in the “Swarm Variability of Ionospheric Plasma” (Swarm-VIP) project within the European Space Agency’s Swarm+4D-Ionosphere framework. The configuration of the Swarm satellites, their near-polar orbits and the data products developed, enable studies of the spatial variability of the ionosphere at multiple scale sizes. The statistical modelling technique of Generalised Linear Modelling (GLM) was used to create models of both the electron density and measures of the variability of the plasma structures at horizontal spatial scales between 20 km and 100 km. Despite being developed using the Swarm data, the models provide predictions that are independent of these data. Separate models were created for low, middle, auroral and polar latitudes. The models make predictions based on heliogeophysical variables, which act as proxies for the solar and geomagnetic processes. The first and most significant term in the majority of the models was a proxy for solar activity. The most common second term varied with the latitudinal region. This was the Solar Zenith Angle (SZA) in the polar region, a measure of latitude in the auroral region, solar time in the mid-latitude region and a measure of latitude in the equatorial region. Other, less significant terms in the models covered a range of proxies for the solar wind, geomagnetic activity and location. In this paper, the formulation, optimisation and evaluation of these models are discussed. The models show very little bias, with a mean error of zero to two decimal places in 14 out of 20 cases. The models capture some, but not all, of the trends present in the data, with Pearson correlation coefficients of up to 0.75 between the observations and the model predictions. The models also capture some, but not all, of the variability of the ionospheric plasma, as indicated by the precision, which ranged between 0.20 and 0.83. The addition of the thermospheric density as an explanatory variable in the models improved the precision in the polar and auroral regions. It is suggested that, if the thermosphere could be observed at a higher spatial resolution, then even more of the variability of the plasma structures could be captured by statistical models. The formulation and optimisation of the models are presented in this paper. The capability of the model in reproducing the expected climatological features of the topside ionosphere, in supporting GNSS-based ionospheric observations and the performance of the model against the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM), are provided in a companion paper (Spogli L et al. 2024. J Space Weather Space Clim https://doi.org/10.1051/swsc/2024003).

• Høeg, Per & Carlström, Anders (2023). Sea Surface Roughness Determination from Grazing Angle GPS Ocean Observations and Scatterometry Simulations. Remote Sensing. 15(15). doi: 10.3390/rs15153794. Full text in Research Archive Show summary

  Measurements of grazing angle GNSS-R ocean reflections combined with meteorological troposphere data are used for retrieval of ocean wave heights and surface roughness parameters. The observational results are compared to multiphase screen simulations for the same atmosphere conditions. The retrieved data from observations and simulations give equal results within the error bounds of the methods. The obtained ocean mean wave-heights are almost proportional to the square of the wind speed when applying a first-order approximation model to the high-wave-number part of the measured GNSS-R power spectra. The spectral variances from the measurements link directly to the ocean surface roughness, which is also verified by the performed multiple phase-screen wave propagation simulations. Thus, grazing angle GNSS-R techniques are an efficient method for determining the ocean state and the conditions in the boundary layer of the troposphere.

• Jin, Yaqi; Clausen, Lasse; Miloch, Wojciech Jacek; Høeg, Per; Jarmołowski, Wojciech & Wielgosz, Pawel [Show all 13 contributors for this article] (2022). Climatology and modeling of ionospheric irregularities over Greenland based on empirical orthogonal function method. Journal of Space Weather and Space Climate. 12(23). doi: 10.1051/swsc/2022022. Full text in Research Archive Show summary

  This paper addresses the long-term climatology (over two solar cycles) of total electron content (TEC) irregularities from a polar cap station (Thule) using the rate of change of the TEC index (ROTI). The climatology reveals variabilities over different time scales, i.e., solar cycle, seasonal, and diurnal variations. These variations in different time scales can be explained by different drivers/contributors. The solar activity (represented by the solar radiation index F10.7P) dominates the longest time scale variations. The seasonal variations are controlled by the interplay of the energy input into the polar cap ionosphere and the solar illumination that damps the amplitude of ionospheric irregularities. The diurnal variations (with respect to local time) are controlled by the relative location of the station with respect to the auroral oval. We further decompose the climatology of ionospheric irregularities using the empirical orthogonal function (EOF) method. The first four EOFs could reflect the majority (99.49%) of the total data variability. A climatological model of ionospheric irregularities is developed by fitting the EOF coefficients using three geophysical proxies (namely, F10.7P, Bt, and Dst). The data-model comparison shows satisfactory results with a high Pearson correlation coefficient and adequate errors. Additionally, we modeled the historical ROTI during the modern grand maximum dating back to 1965 and made the prediction during solar cycle 25. In such a way, we can directly compare the climatic variations of the ROTI activity across six solar cycles.

• Paziewski, Jacek; Høeg, Per; Sieradzki, Rafal; Jin, Yaqi; Jarmolowski, Wojciech & Hoque, M. Mainul [Show all 12 contributors for this article] (2022). The implications of ionospheric disturbances for precise GNSS positioning in Greenland. Journal of Space Weather and Space Climate. 12. doi: 10.1051/swsc/2022029. Full text in Research Archive Show summary

  Ionospheric irregularities impair Global Navigation Satellite System (GNSS) signals and, in turn, affect the performance of GNSS positioning. Such effects are especially evident at low and high latitudes, which are currently gaining the attention of research and industry sectors. This study evaluates the impact of ionospheric irregularities on GNSS positioning in Greenland. We assess the performance of positioning methods that meet the demands of a wide range of users. In particular, we address the needs of the users of mass-market single-frequency receivers and those who require a solution of high precision provided by geodetic dual-frequency receivers. We take advantage of the datasets collected during three ionospheric storms: the St. Patrick’s Day storm of March 17, 2015, the storm on June 22, 2015, and another on August 25–26, 2018. We discover a significant impact of the ionospheric disturbances on the ambiguity resolution performance and the accuracy of the float solution in Real Time Kinematics (RTK) positioning. Next, assessing the single-frequency ionosphere-free Precise Point Positioning (PPP), we demonstrate that the model is generally unaffected by ionospheric disturbances. Hence, the model is predestined for the application by the users of single-frequency receivers in the areas of frequent ionospheric disturbances. Finally, based on the observation analyses, we reveal that phase signals on the L2 frequency band are more prone to cycle slips induced by ionospheric irregularities than those transmitted on the L1. Such signal properties explain a noticeable decline in the dual-frequency RTK performance during the ionospherically disturbed period and merely no effect for the single-frequency ionosphere-free PPP model.

• Kotova, Daria; Jin, Yaqi; Spogli, Luca; Wood, Alan G.; Urbar, Jaroslav & Rawling, James T. [Show all 11 contributors for this article] (2022). Electron density fluctuations from Swarm as a proxy for ground-based scintillation data: A statistical perspective. Advances in Space Research. ISSN 0273-1177. doi: 10.1016/j.asr.2022.11.042. Full text in Research Archive Show summary

  The Swarm satellite mission has been used for numerous studies of the ionosphere. Here we use a global product, based on electron density measurements from Swarm that characterises ionospheric variability. The IPIR (Ionospheric Plasma IRregularities product) provides characteristics of plasma irregularities in terms of their amplitudes, gradients and spatial scales and assigns them to geomagnetic regions. Ionospheric irregularities and fluctuations are often the cause of errors in position, navigation, and timing (PNT) based on the Global Navigation Satellite Systems (GNSS), in which signals pass through the ionosphere. The IPIR dataset also provides an indication, in the form of a numerical value index (IPIR index), of the severity of irregularities affecting the integrity of trans-ionospheric radio signals and hence, the accuracy of GNSS positioning. We analysed datasets from Swarm A and ground-based scintillation receivers. Time intervals (when Swarm A passes over the field of view of the ground-based GPS receiver) are compared to ground-based scintillation data, collecting an azimuthal selection of the GNSS data relevant to the Swarm satellite overpass. We provide validations of the IPIR product against the ground-based measurements from 23 ground-based receivers, focusing on GPS TEC and scintillation data in low-latitude, auroral and polar regions, and in different longitudinal sectors. We have determined the median, mean, maximum and standard deviation of the parameter values for both datasets and each conjunction point. We found a weak correlation of the intensity of both phase and amplitude scintillation with the IPIR index.

• Urbar, Jaroslav; Spogli, Luca; Cicone, Antonio; Clausen, Lasse; Jin, Yaqi & Wood, Alan G. [Show all 11 contributors for this article] (2022). Multi-scale response of the high-latitude topside ionosphere to geospace forcing. Advances in Space Research. ISSN 0273-1177. doi: 10.1016/j.asr.2022.06.045. Full text in Research Archive Show summary

  We investigate the response of the topside ionosphere, auroral and polar sectors, to the forcing of the geospace during September 2017. Specifically, we aim at characterizing such a response in terms of the involved spatial scales and of their intensification during the different auroral and polar cap activity conditions experienced in the selected month, that is characterized by severe geomagnetic storm conditions. For our purposes, we leverage on and compare various in situ plasma density data products provided by the Swarm constellation of the European Space Agency (ESA). The spatio-temporal variability of the involved scales in the plasma density observation is featured through the application of the Fast Iterative Filtering (FIF) signal decomposition technique and, for the first time in the ionospheric field, of a FIF-derived dynamical spectrum called “IMFogram”. The instantaneous time-frequency representation provided through the IMFogram illustrates the time development of the multi-scale processes with spatial and temporal resolutions higher than those obtained with traditional signal processing techniques. To demonstrate this, the IMFogram is tested against Fast Fourier and Continuous Wavelet Transforms. With our fine characterization, we highlight how scale cascading and intensification processes in the plasma density observations follow the ionospheric currents activity, as depicted through the auroral activity and polar cap indices, and through the field-aligned currents data product provided by Swarm.

• Wood, Alan G.; Alfonsi, Lucilla; Clausen, Lasse; Jin, Yaqi; Spogli, Luca & Urbář, Jaroslav [Show all 19 contributors for this article] (2022). Variability of Ionospheric Plasma: Results from the ESA Swarm Mission. Space Science Reviews. ISSN 0038-6308. 218(6). doi: 10.1007/s11214-022-00916-0. Full text in Research Archive Show summary

  Abstract Swarm is the first European Space Agency (ESA) constellation mission for Earth Observation. Three identical Swarm satellites were launched into near-polar orbits on 22 November 2013. Each satellite hosts a range of instruments, including a Langmuir probe, GPS receivers, and magnetometers, from which the ionospheric plasma can be sampled and current systems inferred. In March 2018, the CASSIOPE/e-POP mission was formally integrated into the Swarm mission through ESA’s Earthnet Third Party Mission Programme. Collectively the instruments on the Swarm satellites enable detailed studies of ionospheric plasma, together with the variability of this plasma in space and in time. This allows the driving processes to be determined and understood. The purpose of this paper is to review ionospheric results from the first seven years of the Swarm mission and to discuss scientific challenges for future work in this field.

• Monte-Moreno, Enric; Hernández-Pajares, Manuel; Yang, Heng; Garcia, Rigo Alberto; Jin, Yaqi & Høeg, Per [Show all 13 contributors for this article] (2021). Method for Forecasting Ionospheric Electron Content Fluctuations Based on the Optical Flow Algorithm. IEEE Transactions on Geoscience and Remote Sensing. ISSN 0196-2892. doi: 10.1109/TGRS.2021.3126888. Full text in Research Archive
• Fragner, H; Dielacher, A; Moritsch, M; Zangerl, F; Beck, P & Koudelka, O [Show all 16 contributors for this article] (2019). Recycling GPS signals and radiation monitoring: the two payloads onboard PRETTY. Proceedings of SPIE, the International Society for Optical Engineering. ISSN 0277-786X. 11131. doi: 10.1117/12.2530806. Full text in Research Archive
• Cardellach, E; Wickert, J; Baggen, Rens; Benito, Javier; Camps, Adriano & Catarino, Nuno [Show all 36 contributors for this article] (2018). GNSS Transpolar Earth Reflectometry exploriNg System (G-TERN): Mission Concept. IEEE Access. 6, p. 13980–14018. doi: 10.1109/ACCESS.2018.2814072. Full text in Research Archive
• Durgonics, T; Komjathy, A; Verkhoglyadova, O; Shume, EB; Benzon, H-H von & Mannucci, AJ [Show all 9 contributors for this article] (2017). Multiinstrument observations of a geomagnetic storm and its effects on the Arctic ionosphere: A case study of the 19 February 2014 storm. Radio Science. ISSN 0048-6604. 52, p. 146–165. doi: 10.1002/2016RS006106. Full text in Research Archive Show summary

  We present a multiinstrumented approach for the analysis of the Arctic ionosphere during the 19 February 2014 highly complex, multiphase geomagnetic storm, which had the largest impact on the disturbance storm-time index that year. The geomagnetic storm was the result of two powerful Earth-directed coronal mass ejections (CMEs). It produced a strong long lasting negative storm phase over Greenland with a dominant energy input in the polar cap. We employed global navigation satellite system (GNSS) networks, geomagnetic observatories, and a specific ionosonde station in Greenland. We complemented the approach with spaceborne measurements in order to map the state and variability of the Arctic ionosphere. In situ observations from the Canadian CASSIOPE (CAScade, Smallsat and IOnospheric Polar Explorer) satellite's ion mass spectrometer were used to derive ion flow data from the polar cap topside ionosphere during the event. Our research specifically found that (1) thermospheric O/N2 measurements demonstrated significantly lower values over the Greenland sector than prior to the storm time. (2) An increased ion flow in the topside ionosphere was observed during the negative storm phase. (3) Negative storm phase was a direct consequence of energy input into the polar cap. (4) Polar patch formation was significantly decreased during the negative storm phase. This paper addresses the physical processes that can be responsible for this ionospheric storm development in the northern high latitudes. We conclude that ionospheric heating due to the CME's energy input caused changes in the polar atmosphere resulting in Ne upwelling, which was the major factor in high-latitude ionosphere dynamics for this storm. This research was originally published in Radio Science. © 2017 Wiley

• Høeg, P; Nielsen, TS & Olsen, A (2017). Copenhagen ITS: Forsøg med wifi-baseret positionering på H.C. Andersens Boulevard. Trafik & Veje. ISSN 1903-7384. 94(8), p. 39–42. Full text in Research Archive Show summary

  I samarbejde med Københavns Kommune afprøvede CITS konsortiet potentialet i WiFi-baseret positionering med en forsøgsstrækning på H.C. Andersens Boulevard i vintermånederne 2014-2015. WiFipositioneringen giver et nyt datagrundlag for trafik- og bylivsundersøgelser, herunder f.eks. et grundlag for at følge både ophold og trafik med fokus på retning og bevægelse/hastighed. Udviklingsbehovet knytter sig til, hvilken præcision det er muligt at opnå, samt hvad der er den ”optimale” efterbehandling af data for at understøtte analyser.

• Benzon, Hans-Henrik; Høeg, Per & Durgonics, Tibor (2016). Analysis of satellite-based navigation signal reflectometry: Simulations and observations. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. ISSN 1939-1404. 9(10), p. 4879–4883. doi: 10.1109/JSTARS.2015.2510667. Full text in Research Archive
• Benzon, Hans-Henrik & Høeg, Per (2016). Wave optics-based LEO-LEO radio occultation retrieval. Radio Science. ISSN 0048-6604. 51, p. 589–602. doi: 10.1002/2015RS005852. Full text in Research Archive Show summary

  This paper describes the theory for performing retrieval of radio occultations that use probing frequencies in the XK and KM band. Normally, radio occultations use frequencies in the L band, and GPS satellites are used as the transmitting source, and the occultation signals are received by a GPS receiver on board a Low Earth Orbit (LEO) satellite. The technique is based on the Doppler shift imposed, by the atmosphere, on the signal emitted from the GPS satellite. Two LEO satellites are assumed in the occultations discussed in this paper, and the retrieval is also dependent on the decrease in the signal amplitude caused by atmospheric absorption. The radio wave transmitter is placed on one of these satellites, while the receiver is placed on the other LEO satellite. One of the drawbacks of normal GPS‐based radio occultations is that external information is needed to calculate some of the atmospheric products such as the correct water vapor content in the atmosphere. These limitations can be overcome when a proper selected range of high‐frequency waves are used to probe the atmosphere. Probing frequencies close to the absorption line of water vapor have been included, thus allowing the retrieval of the water vapor content. Selecting the correct probing frequencies would make it possible to retrieve other information such as the content of ozone. The retrieval is performed through a number of processing steps which are based on the Full Spectrum Inversion (FSI) technique. The retrieval chain is therefore a wave optics‐based retrieval chain, and it is therefore possible to process measurements that include multipath. In this paper simulated LEO to LEO radio occultations based on five different frequencies are used. The five frequencies are placed in the XK or KM frequency band. This new wave optics‐based retrieval chain is used on a number of examples, and the retrieved atmospheric parameters are compared to the parameters from a global European Centre for Medium‐Range Weather Forecasts analysis model. This model is used in a forward propagator that simulates the electromagnetic field amplitudes and phases at the receiver on board the LEO satellite. LEO‐LEO cross‐link radio occultations using high frequencies are a relatively new technique, and the possibilities and advantages of the technique still need to be investigated. The retrieval of this type of radio occultations is considerably more complicated than standard GPS to LEO radio occultations, because the attenuation of the probing radio waves is used in the retrieval and the atmospheric parameters are found using a least squares solver. The best algorithms and the number of probing frequencies that is economically viable must also be determined. This paper intends to answer some of these questions using end‐to‐end simulations. © 2016 American Geophysical Union

• Wickert, Jens; Cardellach, Estel; Martín-Neira, Manuel; Bandeiras, Jorge; Bertino, Laurent & Andersen, Ole B [Show all 31 contributors for this article] (2016). GEROS-ISS: GNSS reflectometry, radio occultation and scatterometry onboard the International Space Station. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. ISSN 1939-1404. 9(10), p. 4552–4581. doi: 10.1109/JSTARS.2016.2614428. Full text in Research Archive

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• Miloch, Wojciech Jacek; Alfonsi, Lucilla; Spogli, Luca; Urbar, Jaroslav; Cesaroni, Claudio & Cicone, Antonio [Show all 15 contributors for this article] (2022). Swarm – VIP: Variability of Ionospheric Plasma studied and modelled based on data from the Swarm satellites. Full text in Research Archive
• Jin, Yaqi; Miloch, Wojciech Jacek; Alfonsi, Lucilla; Spogli, Luca; Urbar, Jaroslav & Cesaroni, Claudio [Show all 13 contributors for this article] (2022). Variability of Ionospheric Plasma studied and modelled based on data from the Swarm satellites. Full text in Research Archive
• Kotova, Daria; Jin, Yaqi; Spogli, Luca; Wood, Alan G.; Urbar, Jaroslav & Rawlings, James T. [Show all 11 contributors for this article] (2022). Electron density fluctuations from Swarm as a proxy for ground-based scintillation data: A statistical perspective. Full text in Research Archive
• Kotova, Daria; Jin, Yaqi; Spogli, Luca; Wood, Alan G.; Alfonsi, Lucilla & Urbar, Jaroslav [Show all 9 contributors for this article] (2022). Comparison Of Electron Density Fluctuations From Swarm Satellites With The Ground-based Scintillation Data: A Statistical Perspective. Full text in Research Archive Show summary

  The Swarm satellite mission is actively used to conduct various studies of the ionosphere, focusing on such aspects as the electric and magnetic fields or plasma temperature, structuring and irregularities. The mission is a constellation of three satellites that were launched in November 2013 and have been collecting data continuously since then. We use a global product based on the Swarm satellite measurements that characterizes ionospheric irregularities and fluctuations. The IPIR (Ionospheric Plasma IRregularities product) provides in-situ characteristics of plasma density structures in the ionosphere, of plasma irregularities in terms of their amplitudes, gradients and spatial scales and assigns them to geomagnetic regions. Ionospheric irregularities and fluctuations are often the cause increases the error in position, velocity, time determination based on Global Navigation Satellite Systems (GNSS), which signals pass through the ionosphere. The IPIR provides an indication, in the form of a numerical value index, on severity of irregularities for the integrity of trans-ionospheric radio signals and hence the accuracy of GNSS precise positioning. This work demonstrates that data from the Swarm satellite's flyby height can be used as a proxy for ground-based scintillation data. We compare two datasets from Swarm satellites (with 1-second resolution) and from groundbased scintillation receivers (with 1-minute resolution). To consider the measured parameters for the same area, we find time intervals when the Swarm satellites pass over the field of view of the ground-based Global Positioning System (GPS) receiver. A geometry with an elevation angle of 30° above the receiver was used to calculate these passes. We also performed an azimuthal selection of the GNSS data according to Swarm satellite fly. We used only those GPS satellites that flew near the position of the Swarm satellite in azimuth sector ±10°. We provide validations of the IPIR product against the ground-based measurements, focusing on GPS TEC and scintillation data in low and high-latitudes regions in different longitudinal sectors. We calculate median, mean, maximum and standard deviation values for parameters for both dataset for each conjunction point (for each GPS satellite and Swarm). We observe a weak trend of stronger scintillations with an increasing IPIR index, where the IPIR index presents a product of amplitudes and temporal variations in plasma densities.

• Miloch, Wojciech Jacek; Alfonsi, Lucilla; Spogli, Luca; Urbar, Jaroslav; Cesaroni, C & Cicone, Antonio [Show all 14 contributors for this article] (2021). Variability of ionosphere studied and modelled based on data from the Swarm satellites. Full text in Research Archive
• Dielacher, Andreas; Fragner, Heinz; Moritsch, Michael; Wickert, Jens; Koudelka, Otto & Høeg, Per [Show all 12 contributors for this article] (2020). First field-test results of iGNSS-R instrument of the PRETTY payload. Full text in Research Archive
• Miloch, Wojciech Jacek; Alfonsi, Lucilla; Spogli, Luca; Wood, Alan; Sahtahmassebi, Golnaz & Clausen, Lasse [Show all 10 contributors for this article] (2020). Variability of Ionospheric Plasma Based on Swarm Satellite Data. Full text in Research Archive
• Wickert, J; Fragner, H; Cardellach, E; Høeg, Per; Beck, P & Dielacher, A [Show all 12 contributors for this article] (2019). PRETTY: CubeSat for precise altimetry using navigation satellites. Full text in Research Archive
• Dielacher, A; Fragner, H; Koudelka, O; Beck, P; Wickert, J & Cardellach, E [Show all 7 contributors for this article] (2019). The ESA Passive REflectomeTry and DosimeTrY (PRETTY) mission. Full text in Research Archive
• Høeg, Per & Durgonics, Tibor (2019). A new index for polar cap solar EUV irradiance for forecasting strong and extreme solar events. Full text in Research Archive
• Mannucci, Anthony J.; Berger, Thomas; Bortnik, Jacob; Cherniak, Iurii; Gulyaeva, Tamara & Høeg, Per [Show all 18 contributors for this article] (2019). Chapman Conference on Scientific Challenges Pertaining to Space Weather Forecasting Including Extremes: Recommendations for the Community. Full text in Research Archive
• Høeg, Per & Durgonics, Tibor (2018). Cross-validation of TEC map products from IGS and ESA SWE during quiet and disturbed conditions. Full text in Research Archive
• Durgonics, Tibor; Høeg, Per & Vennerstrøm, Susanne (2018). Multi-instrument observations of solar EUV irradiance induced ionospheric variations in the Arctic polar cap. Full text in Research Archive
• Høeg, Per (2018). 4DSpace - Research Activities. Full text in Research Archive
• Høeg, Per & Durgonics, Tibor (2018). Polar cap patch signatures during geomagnetic disturbed conditions. Full text in Research Archive
• Høeg, Per & Durgonics, Tibor (2018). Influence of polar cap patch scintillations on GNSS receiver performance during geomagnetic disturbed conditions. Full text in Research Archive
• Fragner, H; Dielacher, A; Zangerl, F; Koudelka, O; Høeg, P & Beck, P [Show all 7 contributors for this article] (2017). PRETTY: Grazing altimetry measurements based on the interferometric method. Full text in Research Archive
• Høeg, Per (2017). Cross-validation of TEC maps from ESA Ionosphere Expert Service Centre. Full text in Research Archive
• Høeg, Per (2017). Space weather and signatures of polar cap patches. Full text in Research Archive
• Høeg, Per (2017). Disruption of GNSS - Time for Backup. Full text in Research Archive
• Wickert, Jens; Andersen, OB; Bandeiras, J; Bertino, Laurent; Cardellach, Estel & Camps, Adriano [Show all 25 contributors for this article] (2016). Innovative sea surface monitoring with GNSS-Reflectometry aboard ISS: Overview and recent results from GEROS-ISS. Full text in Research Archive

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