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Curzi, Giacomo, Dario Modenini y Paolo Tortora. "Large Constellations of Small Satellites: A Survey of Near Future Challenges and Missions". Aerospace 7, n.º 9 (7 de septiembre de 2020): 133. http://dx.doi.org/10.3390/aerospace7090133.
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Constellations of satellites are being proposed in large numbers; most of them are expected to be in orbit within the next decade. They will provide communication to unserved and underserved communities, enable global monitoring of Earth and enhance space observation. Mostly enabled by technology miniaturization, satellite constellations require a coordinated effort to face the technological limits in spacecraft operations and space traffic. At the moment in fact, no cost-effective infrastructure is available to withstand coordinated flight of large fleets of satellites. In order for large constellations to be sustainable, there is the need to efficiently integrate and use them in the current space framework. This review paper provides an overview of the available experience in constellation operations and statistical trends about upcoming constellations at the moment of writing. It highlights also the tools most often proposed in the analyzed works to overcome constellation management issues, such as applications of machine learning/artificial intelligence and resource/infrastructure sharing. As such, it is intended to be a useful resource for both identifying emerging trends in satellite constellations, and enabling technologies still requiring substantial development efforts.
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Kocifaj, M., F. Kundracik, J. C. Barentine y S. Bará. "The proliferation of space objects is a rapidly increasing source of artificial night sky brightness". Monthly Notices of the Royal Astronomical Society: Letters 504, n.º 1 (29 de marzo de 2021): L40—L44. http://dx.doi.org/10.1093/mnrasl/slab030.
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ABSTRACT The population of artificial satellites and space debris orbiting the Earth imposes non-negligible constraints on both space operations and ground-based optical and radio astronomy. The ongoing deployment of several satellite ‘mega-constellations’ in the 2020s represents an additional threat that raises significant concerns. The expected severity of its unwanted consequences is still under study, including radio interference and information loss by satellite streaks appearing in science images. In this Letter, we report a new skyglow effect produced by space objects: increased night sky brightness caused by sunlight reflected and scattered by that large set of orbiting bodies whose direct radiance is a diffuse component when observed with the naked eye or with low angular resolution photometric instruments. According to our preliminary estimates, the zenith luminance of this additional light pollution source may have already reached ∼20 $\mu$cd m−2, which amounts to an approximately 10 per cent increase over the brightness of the night sky determined by natural sources of light. This is the critical limit adopted in 1979 by the International Astronomical Union for the light pollution level not to be exceeded at the sites of astronomical observatories.
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Sampaio, J. C., A. G. S. Neto, S. S. Fernandes, R. Vilhena de Moraes y M. O. Terra. "Artificial satellites orbits in 2:1 resonance: GPS constellation". Acta Astronautica 81, n.º 2 (diciembre de 2012): 623–34. http://dx.doi.org/10.1016/j.actaastro.2012.08.025.
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Zhang, Pengfei. "Research on satellite selection algorithm in ship positioning based on both geometry and geometric dilution of precision contribution". International Journal of Advanced Robotic Systems 16, n.º 1 (1 de enero de 2019): 172988141983024. http://dx.doi.org/10.1177/1729881419830246.
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With the networking of four Global Navigation Satellite Systems, the combination of multi-constellation applications has become an inevitable trend, and there will be more and more visible satellites that can be participated in ship positioning. However, the computational complexity increases sharply, which greatly improves the load capacity of the receiver’s data processor and reduces the output frequency of the positioning result. To achieve the balance between positioning accuracy and computational complexity, a new fast satellite selection algorithm based on both of geometry and geometric dilution of precision contribution is proposed. Firstly, this article analyzes the geometry characteristics of the least visible satellites has minimum geometric dilution of precision that meet the positioning requirements and makes clear the layout of their elevation angles and azimuth angles. In addition, it derives the relationship of geometric dilution of precision and the visible satellites layout and gets geometric dilution of precision contribution of each satellite. Finally, based on the observation data of JFNG tracking station of the Multi-Global Navigation Satellite System (GNSS) Experiment trial network, the positioning error and the elapsed time of GPS/Beidou Satellite Navigation System and GPS/Beidou Satellite Navigation System/Russian Global Orbiting Navigation Satellite System (GLOANSS) are compared. Simulation results show that the algorithm solves the problem that there are a lot of matrix multiplications and matrix inversions in the traditional satellite selection algorithm, and the new algorithm can reduce computational complexity and increase receiver processing speed.
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Bonnet, Grégory y Catherine Tessier. "Evaluation d'un système multirobot. Cas d'une constellation de satellites". Revue d'intelligence artificielle 23, n.º 5-6 (10 de noviembre de 2009): 565–92. http://dx.doi.org/10.3166/ria.23.565-592.
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Schetter, Thomas, Mark Campbell y Derek Surka. "Multiple agent-based autonomy for satellite constellations". Artificial Intelligence 145, n.º 1-2 (abril de 2003): 147–80. http://dx.doi.org/10.1016/s0004-3702(02)00382-x.
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Walczak, Ken, Geza Gyuk, Andrew Kruger, Enoch Byers y Sigi Huerta. "NITESat: A High Resolution, Full-Color, Light Pollution Imaging Satellite Mission". International Journal of Sustainable Lighting 19, n.º 1 (28 de junio de 2017): 48–55. http://dx.doi.org/10.26607/ijsl.v19i1.68.
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The NITESat (Night Imaging and Tracking Experiment Satellite) mission is a 2U CubeSat satellite designed for nighttime Earth imaging to quantify and characterize light pollution across the Midwestern United States. It is accompanied and supported by an array of ground-based light pollution observing stations called GONet (Ground Observing Network). NITESat is a pilot mission testing the potential for a simple and inexpensive (<$500,000) satellite to deliver high-resolution, three-color regional data of artificial light at night. In addition, GONet will form the core of an educational outreach program by establishing an array of all-sky monitors covering the imaging region of the satellite with 20+ full sky light pollution citizen-operated stations. This will provide synchronized data coinciding with the NITESat overpasses as well as providing near continuous night sky quality monitoring. If the initial mission is a success, the potential exists to expand the program into a low cost constellation of satellites capable of delivering global coverage. NITESat is being designed, built and will be operated by the Far Horizons program at the Adler Planetarium in Chicago, Illinois. Far Horizons is a student and volunteer centered program offering hands-on engineering and scientific research opportunities for education.
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Zhu, Li Li y Yi Feng Duan. "Research on the Resource Allocation Model for the Satellite Constellation Communication System". Advanced Materials Research 121-122 (junio de 2010): 669–77. http://dx.doi.org/10.4028/www.scientific.net/amr.121-122.669.
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Satellite constellation, emerging as a new paradigm for next-generation communicating, enables large-scale application of the geographically and spatially distributed heterogeneous resources for solving problems in science, engineering, and military affairs. The resource allocation in such a large-scale distributed environment is a complex task. Due to the factors that trigger the deployment of resources in satellite constellation communication system, the artificial immune theory is applied to resource allocation field to propose the task-oriented common mathematic model about resource allocation of communication system, which is aimed at the purpose of improving the effectiveness of resource allocation and is based on the 2 important indicators that are communication task’s effectiveness factors and the degree of satisfaction in the communication system. As the immune system has characteristics of self-adaptive, self-learning and self-organization, an immune allocation algorithm that fuzzy processing time is presented by applying the immune theory to resource allocation. Simulation results show that these methods are feasible and efficient in solving the problems of resource allocation for satellite constellation communication system, and the research on this object is a meaningful exploring.
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Yalcin, I., S. Kocaman, S. Saunier y C. Albinet. "RADIOMETRIC QUALITY ASSESSMENT FOR MAXAR HD IMAGERY". International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLIII-B3-2021 (29 de junio de 2021): 797–804. http://dx.doi.org/10.5194/isprs-archives-xliii-b3-2021-797-2021.
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Abstract. The requirement for very high-resolution satellite imagery by different applications has been increasing continuously. Several commercial and government-supported missions provide sub-meter spatial resolutions from optical sensors aboard Earth Observation (EO) satellites. The MAXAR satellite constellation acquires images with up to 30 cm Ground Sampling Distances (GSDs); and the High-Definition (HD) image production technology developed by MAXAR doubles the resolution by using artificial intelligence methods. Although the spatial resolution is one of the most important image quality metrics, several other factors indicated by diverse radiometric and geometric characteristics may circumscribe the usability of data in different projects. As part of mandatory activities of European Space Agency (ESA), Earthnet Programme provides a framework for integrating Third-Party Missions into the overall EO strategy and promotes the international use of the data. The Earthnet Data Assessment Pilot (EDAP) project aims at assessing the quality and the suitability of TPMs, and provides a communication platform between mission providers to ensure the coherence of the systems. In this study, the radiometric quality of the MAXAR HD products was evaluated within the EDAP project framework by using several General Image-Quality Equation (GIQE) metrics, visual inspections, and comparative assessments with orthophotos obtained from an Unmanned Aerial Vehicle (UAV) platform and with the original (non-HD) orthophotos with 30 cm resolutions. The results show that the spatial resolution improvements are observable in urban areas, where sharp edges are present. However, blurring and color noise patterns also occured in the HD images.
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Vasilyev, Roman, Artem Setov, Vladimir Frolov, Konstantin Ratovsky, Aleksandr Beletsky, Aleksey Oinats, Yury Yasyukevich y Andrey Medvedev. "Modern heating facility for research into the mid-latitude ionosphere". Solnechno-Zemnaya Fizika 6, n.º 2 (27 de junio de 2020): 61–78. http://dx.doi.org/10.12737/szf-62202005.
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The development of new devices for research in physics of the upper atmosphere and near-Earth space, which can be used to carry out controlled experiments on the modification of the ionosphere by powerful short-wave radiation, is an urgent task of modern solar-terrestrial physics, space weather, operation of satellite constellations in near-Earth space, radio communications, and radar. The paper describes a modern heating facility, created within the framework of the National Heliogeophysical Complex of the Russian Academy of Sciences. We review the tasks facing the heater, discuss its main technical characteristics, and describe the capability of the observational infrastructure surrounding the heating facility. The paper justifies the long-term benefits of the development of a heating facility at middle latitudes of Eastern Siberia, which can radiate in a frequency range 2.5–6.0 MHz with an effective power of the order of several hundred megawatts. It is important that the heater will be surrounded by such multifunctional instruments as the modern incoherent scatter radar, mesostratospheric lidar, observational systems that can provide a wide range of possibilities for diagnosing artificial plasma disturbances and artificial airglow structures.
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Vasilyev, Roman, Artem Setov, Vladimir Frolov, Konstantin Ratovsky, Aleksandr Beletsky, Aleksey Oinats, Yury Yasyukevich y Andrey Medvedev. "Modern heating facility for research into the mid-latitude ionosphere". Solar-Terrestrial Physics 6, n.º 2 (27 de junio de 2020): 49–62. http://dx.doi.org/10.12737/stp-62202005.
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The development of new devices for research in physics of the upper atmosphere and near-Earth space, which can be used to carry out controlled experiments on the modification of the ionosphere by powerful short-wave radiation, is an urgent task of modern solar-terrestrial physics, space weather, operation of satellite constellations in near-Earth space, radio communications, and radar. The paper describes a modern heating facility, created within the framework of the National Heliogeophysical Complex of the Russian Academy of Sciences. We review the tasks facing the heater, discuss its main technical characteristics, and describe the capability of the observational infrastructure surrounding the heating facility. The paper justifies the long-term benefits of the development of a heating facility at middle latitudes of Eastern Siberia, which can radiate in a frequency range 2.5–6.0 MHz with an effective power of the order of several hundred megawatts. It is important that the heater will be surrounded by such multifunctional instruments as the modern incoherent scatter radar, mesostratospheric lidar, observational systems that can provide a wide range of possibilities for diagnosing artificial plasma disturbances and artificial airglow structures.
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Brunet, P. M., P. Lassalle, S. Baillarin, B. Vallet, A. Le Bris, G. Romeyer, G. Le Besnerais et al. "AI4GEO: A DATA INTELLIGENCE PLATFORM FOR 3D GEOSPATIAL MAPPING". International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLIII-B2-2021 (28 de junio de 2021): 817–23. http://dx.doi.org/10.5194/isprs-archives-xliii-b2-2021-817-2021.
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Abstract. The availability of 3D Geospatial information is a key issue for many expanding sectors such as autonomous vehicles, business intelligence and urban planning. Its production is now possible thanks to the abundance of available data (Earth observation satellite constellations, insitu data, …) but manual interventions are still needed to guarantee a high level of quality, which prevents mass production. New artificial intelligence and big data technologies adapted to 3D imagery can help to remove these obstacles. The AI4GEO project aims at developing an automatic solution for producing 3D geospatial information and new added-value services. This paper will first introduce AI4GEO initiative, context and overall objectives. It will then present the current status of the project and in particular it will focus on the innovative platform put in place to handle big 3D datasets for analytics needs and it will present the first results of 3D semantic segmentations and associated perspectives.
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Li, Zhijiang, Haonan Zhu, Chunxia Zhou, Liqin Cao, Yanfei Zhong, Tao Zeng y Jianqiang Liu. "A Color Consistency Processing Method for HY-1C Images of Antarctica". Remote Sensing 12, n.º 7 (3 de abril de 2020): 1143. http://dx.doi.org/10.3390/rs12071143.
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The HY-1C satellite, as part of China’s optical satellite constellation for global ocean monitoring, monitors the ocean and coastal environment by the three broad visible bands of the Coastal Zone Imager (CZI) instrument. However, as a result of the sensor instrument noise, the atmospheric environment during imaging, and the shooting angle, the satellite images often show uneven illumination and inconsistent color between neighboring images. In this paper, according to the characteristics of the HY-1C CZI instrument, we propose a color consistency processing framework for coastal zone images of Antarctica. First of all, the high-frequency and low-frequency information of the image is separated by a statistical filter with simple clustering. The uneven lighting is then replaced by artificial lighting, which is globally uniform. Finally, the color difference between images is corrected by a color transfer method. In order to evaluate the color consistency results quantitatively, a new quantitative evaluation method is proposed. The experimental results for the coastal zone images of Antarctica show that the new processing framework can effectively eliminate the unevenness in the lighting and color. The mosaic results show a good performance in consistent lighting and tones, and the lack of visible mosaic lines proves the effectiveness of the proposed method. The quantitative evaluation analysis confirms the superiority of the proposed method over the Wallis method.
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SEKERA, Jakub y Andrej NOVÁK. "The future of data communication in Aviation 4.0 environment". INCAS BULLETIN 13, n.º 3 (4 de septiembre de 2021): 165–78. http://dx.doi.org/10.13111/2066-8201.2021.13.3.14.
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Currently experienced the dawn of the Aviation 4.0 era is transforming the contemporary technological environment, throughout the whole aeronautical industry, by creating cyber-physical systems. Following the evolutionary path, incorporating advanced automated and first autonomy systems, the applications involved are becoming increasingly data- oriented. The need for progressive data analytics, massive adoption and operation of IoT devices, delivering advanced monitoring and machine learning opportunities, building the core structure for artificial intelligence, will put a significant pressure on data communication and connectivity itself. In the near future, the problems may especially arise in datalink used in civil aviation. This research paper briefly studies the contemporary systems used for datalink, determines dominant aspects of Aviation 4.0 and their overall impact on the performance requirements of the data communications network, and proposes the possible solution to the problematics, with newly emerging LEO satellite mega-constellations providing Internet connectivity. The conclusion of this paper highlights the requirements for future data communication systems and determines whether the existing and proposed datalink subnetwork technologies are capable of meeting the demands established by Aviation 4.0.
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Douglas, Alyson y Tristan L'Ecuyer. "Quantifying variations in shortwave aerosol–cloud–radiation interactions using local meteorology and cloud state constraints". Atmospheric Chemistry and Physics 19, n.º 9 (13 de mayo de 2019): 6251–68. http://dx.doi.org/10.5194/acp-19-6251-2019.
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Abstract. While many studies have tried to quantify the sign and the magnitude of the warm marine cloud response to aerosol loading, both remain uncertain, owing to the multitude of factors that modulate microphysical and thermodynamic processes within the cloud. Constraining aerosol–cloud interactions using the local meteorology and cloud liquid water may offer a way to account for covarying influences, potentially increasing our confidence in observational estimates of warm cloud indirect effects. A total of 4 years of collocated satellite observations from the NASA A-Train constellation, combined with reanalysis from MERRA-2, are used to partition marine warm clouds into regimes based on stability, the free atmospheric relative humidity, and liquid water path. Organizing the sizable number of satellite observations into regimes is shown to minimize the covariance between the environment or liquid water path and the indirect effect. Controlling for local meteorology and cloud state mitigates artificial signals and reveals substantial variance in both the sign and magnitude of the cloud radiative response, including regions where clouds become systematically darker with increased aerosol concentration in dry, unstable environments. A darkening effect is evident even under the most stringent of constraints. These results suggest it is not meaningful to report a single global sensitivity of cloud radiative effect to aerosol. To the contrary, we find the sensitivity can range from −0.46 to 0.11 Wm−2 ln(AI)−1 regionally.
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Mol Lous, M., E. Weenk, M. A. Kenworthy, K. Zwintz y R. Kuschnig. "A search for transiting planets in the β Pictoris system". Astronomy & Astrophysics 615 (julio de 2018): A145. http://dx.doi.org/10.1051/0004-6361/201731941.
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Context. Transiting exoplanets provide an opportunity for the characterization of their atmospheres, and finding the brightest star in the sky with a transiting planet enables high signal-to-noise ratio observations. The Kepler satellite has detected over 365 multiple transiting exoplanet systems, a large fraction of which have nearly coplanar orbits. If one planet is seen to transit the star, then it is likely that other planets in the system will transit the star too. The bright (V = 3.86) star β Pictoris is a nearby young star with a debris disk and gas giant exoplanet, β Pictoris b, in a multi-decade orbit around it. Both the planet’s orbit and disk are almost edge-on to our line of sight. Aims. We carry out a search for any transiting planets in the β Pictoris system with orbits of less than 30 days that are coplanar with the planet β Pictoris b. Methods. We search for a planetary transit using data from the BRITE-Constellation nanosatellite BRITE-Heweliusz, analyzing the photometry using the Box-Fitting Least Squares Algorithm (BLS). The sensitivity of the method is verified by injection of artificial planetary transit signals using the Bad-Ass Transit Model cAlculatioN (BATMAN) code. Results. No planet was found in the BRITE-Constellation data set. We rule out planets larger than 0.6 RJ for periods of less than 5 days, larger than 0.75 RJ for periods of less than 10 days, and larger than 1.05 RJ for periods of less than 20 days.
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Senyurek, Volkan, Fangni Lei, Dylan Boyd, Mehmet Kurum, Ali Cafer Gurbuz y Robert Moorhead. "Machine Learning-Based CYGNSS Soil Moisture Estimates over ISMN sites in CONUS". Remote Sensing 12, n.º 7 (5 de abril de 2020): 1168. http://dx.doi.org/10.3390/rs12071168.
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Soil moisture (SM) derived from satellite-based remote sensing measurements plays a vital role for understanding Earth’s land and near-surface atmosphere interactions. Bistatic Global Navigation Satellite System (GNSS) Reflectometry (GNSS-R) has emerged in recent years as a new domain of microwave remote sensing with great potential for SM retrievals, particularly at high spatio-temporal resolutions. In this work, a machine learning (ML)-based framework is presented for obtaining SM data products over the International Soil Moisture Network (ISMN) sites in the Continental United States (CONUS) by leveraging spaceborne GNSS-R observations provided by NASA’s Cyclone GNSS (CYGNSS) constellation alongside remotely sensed geophysical data products. Three widely-used ML approaches—artificial neural network (ANN), random forest (RF), and support vector machine (SVM)—are compared and analyzed for the SM retrieval through utilizing multiple validation strategies. Specifically, using a 5-fold cross-validation method, overall RMSE values of 0.052, 0.061, and 0.065 cm3/cm3 are achieved for the RF, ANN, and SVM techniques, respectively. In addition, both a site-independent and a year-based validation techniques demonstrate satisfactory accuracy of the proposed ML model, suggesting that this SM approach can be generalized in space and time domains. Moreover, the achieved accuracy can be further improved when the model is trained and tested over individual SM networks as opposed to combining all available SM networks. Additionally, factors including soil type and land cover are analyzed with respect to their impacts on the accuracy of SM retrievals. Overall, the results demonstrated here indicate that the proposed technique can confidently provide SM estimates over lightly-vegetated areas with vegetation water content (VWC) less than 5 kg/m2 and relatively low spatial heterogeneity.
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Li, Wang, Dongsheng Zhao, Changyong He, Andong Hu y Kefei Zhang. "Advanced Machine Learning Optimized by The Genetic Algorithm in Ionospheric Models Using Long-Term Multi-Instrument Observations". Remote Sensing 12, n.º 5 (7 de marzo de 2020): 866. http://dx.doi.org/10.3390/rs12050866.
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The ionospheric delay is of paramount importance to radio communication, satellite navigation and positioning. It is necessary to predict high-accuracy ionospheric peak parameters for single frequency receivers. In this study, the state-of-the-art artificial neural network (ANN) technique optimized by the genetic algorithm is used to develop global ionospheric models for predicting foF2 and hmF2. The models are based on long-term multiple measurements including ionospheric peak frequency model (GIPFM) and global ionospheric peak height model (GIPHM). Predictions of the GIPFM and GIPHM are compared with the International Reference Ionosphere (IRI) model in 2009 and 2013 respectively. This comparison shows that the root-mean-square errors (RMSEs) of GIPFM are 0.82 MHz and 0.71 MHz in 2013 and 2009, respectively. This result is about 20%–35% lower than that of IRI. Additionally, the corresponding hmF2 median errors of GIPHM are 20% to 30% smaller than that of IRI. Furthermore, the ANN models present a good capability to capture the global or regional ionospheric spatial-temporal characteristics, e.g., the equatorial ionization anomaly and Weddell Sea anomaly. The study shows that the ANN-based model has a better agreement to reference value than the IRI model, not only along the Greenwich meridian, but also on a global scale. The approach proposed in this study has the potential to be a new three-dimensional electron density model combined with the inclusion of the upcoming Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC-2) data.
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Kalantari, Ashkan y Erik G. Larsson. "Statistical test for GNSS spoofing attack detection by using multiple receivers on a rigid body". EURASIP Journal on Advances in Signal Processing 2020, n.º 1 (26 de febrero de 2020). http://dx.doi.org/10.1186/s13634-020-0663-z.
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AbstractGlobal navigation satellite systems (GNSS) are being the target of various jamming, spoofing, and meaconing attacks. This paper proposes a new statistical test for the presence of multiple spoofers based on range measurements observed by a plurality of receivers located on a rigid body platform. The relative positions of the receivers are known, but the location and orientation of the platform are unknown. The test is based on the generalized likelihood ratio test (GLRT) paradigm and essentially performs a consistency check between the set of observed range measurements and known information about the satellite topology and the geometry of the receiver constellation. Optimal spoofing locations and optimal artificial time delays (as induced by the spoofers) are also determined.Exact evaluation of the GLRT requires the maximum-likelihood estimates of all parameters, which proves difficult. Instead, approximations based on iterative algorithms and the squared-range least squares algorithm are derived. The accuracy of these approximations is benchmarked against Cramér-Rao lower bounds.Numerical examples demonstrate the effectiveness of the proposed algorithm and show that increasing the number of GNSS receivers makes the attack easier to detect. We also show that using multiple GNSS receivers limits the availability of optimal attack positions.
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Stolle, C., I. Michaelis, C. Xiong, M. Rother, Th Usbeck, Y. Yamazaki, J. Rauberg y K. Styp-Rekowski. "Observing Earth’s magnetic environment with the GRACE-FO mission". Earth, Planets and Space 73, n.º 1 (15 de febrero de 2021). http://dx.doi.org/10.1186/s40623-021-01364-w.
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AbstractThe Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission carries magnetometers that are dedicated to enhance the satellite’s navigation. After appropriate calibration and characterisation of artificial magnetic disturbances, these observations are valuable assets to characterise the natural variability of Earth’s magnetic field. We describe the data pre-processing, the calibration, and characterisation strategy against a high-precision magnetic field model applied to the GRACE-FO magnetic data. During times of geomagnetic quiet conditions, the mean residual to the magnetic model is around 1 nT with standard deviations below 10 nT. The mean difference to data of ESA’s Swarm mission, which is dedicated to monitor the Earth’s magnetic field, is mainly within ± 10 nT during conjunctions. The performance of GRACE-FO magnetic data is further discussed on selected scientific examples. During a magnetic storm event in August 2018, GRACE-FO reveals the local time dependence of the magnetospheric ring current signature, which is in good agreement with results from a network of ground magnetic observations. Also, derived field-aligned currents (FACs) are applied to monitor auroral FACs that compare well in amplitude and statistical behaviour for local time, hemisphere, and solar wind conditions to approved earlier findings from other missions including Swarm. On a case event, it is demonstrated that the dual-satellite constellation of GRACE-FO is most suitable to derive the persistence of auroral FACs with scale lengths of 180 km or longer. Due to a relatively larger noise level compared to dedicated magnetic missions, GRACE-FO is especially suitable for high-amplitude event studies. However, GRACE-FO is also sensitive to ionospheric signatures even below the noise level within statistical approaches. The combination with data of dedicated magnetic field missions and other missions carrying non-dedicated magnetometers greatly enhances related scientific perspectives.
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Zajdel, Radosław, Krzysztof Sośnica, Grzegorz Bury, Rolf Dach, Lars Prange y Kamil Kazmierski. "Sub-daily polar motion from GPS, GLONASS, and Galileo". Journal of Geodesy 95, n.º 1 (23 de diciembre de 2020). http://dx.doi.org/10.1007/s00190-020-01453-w.
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AbstractWe derive an empirical model of the sub-daily polar motion (PM) based on the multi-GNSS processing incorporating GPS, GLONASS, and Galileo observations. The sub-daily PM model is based on 3-year multi-GNSS solutions with a 2 h temporal resolution. Firstly, we discuss differences in sub-daily PM estimates delivered from individual GNSS constellations, including GPS, GLONASS, Galileo, and the combined multi-GNSS solutions. Secondly, we evaluate the consistency between the GNSS-based estimates of the sub-daily PM with three independent models, i.e., the model recommended in the International Earth Rotation and Reference Systems Service (IERS) 2010 Conventions, the Desai–Sibois model, and the Gipson model. The sub-daily PM estimates, which are derived from system-specific solutions, are inherently affected by artificial non-tidal signals. These signals arise mainly from the resonance between the Earth rotation period and the satellite revolution period. We found strong spurious signals in GLONASS-based and Galileo-based results with amplitudes up to 30 µas. The combined multi-GNSS solution delivers the best estimates and the best consistency of the sub-daily PM with external geophysical and empirical models. Moreover, the impact of the non-tidal spurious signals in the frequency domain diminishes in the multi-GNSS combination. After the recovery of the tidal coefficients for 38 tides, we infer better consistency of the GNSS-based empirical models with the new Desai–Sibois model than the model recommended in the IERS 2010 Conventions. The consistency with the Desai–Sibois model, in terms of the inter-quartile ranges of tidal amplitude differences, reaches the level of 1.6, 5.7, 6.3, 2.2 µas for the prograde diurnal tidal terms and 1.2/2.1, 2.3/6.0, 2.6/5.5, 2.1/5.1 µas for prograde/retrograde semi-diurnal tidal terms, for the combined multi-GNSS, GPS, GLONASS, and Galileo solutions, respectively.