The first two Medium Earth Orbit (MEO) satellites of the third generation of BeiDou satellite navigation System (BDS-3) were successfully launched on November 5, 2017. This historical launch starts ...the new era of the global navigation satellite system of BeiDou. Before the first two satellites of BDS-3, a demonstration system for BDS-3 with five satellites, including two Inclined Geosynchronous Orbit satellites (IGSO) and three MEO satellites, was established between 2015 and 2016 for testing the new payloads, new designed signals and new techniques. In the demonstration system, the new S frequency signal and satellite hydrogen clock as well as inter-satellite link (ISL) based on Ka-band signals with time-division multiple addresses (TDMA) were tested. This paper mainly analyzes the performances of the demonstration system, including the signalto- noise ratios, pseudorange errors and the multipath errors of the civilian signals of BDS-3. The qualities of signals in space, time synchronization and timing precision were tested as well. Most of the performances were compared with those of the regional BeiDou satellite navigation system (BDS-2). At last, the performances of positioning, navigation and timing (PNT) of the future BeiDou global system (BDS-3) were evaluated based on the signal quality of the present demonstration satellite system.
The National Aeronautics and Space Administration Global‐scale Observations of the Limb and Disk ultraviolet spectrograph has been imaging the equatorial ionization anomaly (EIA), regions of the ...ionosphere with enhanced electron density north and south of the magnetic equator, since October 2018. The initial 3 months of observations was during solar minimum conditions, and they included observations in December solstice of unanticipated variability and depleted regions. Depletions are seen on most nights, in contrast to expectations from previous space‐based observations. The variety of scales and morphologies also pose challenges to understanding of the EIA. Abrupt changes in the EIA location, which could be related to in situ measurements of large‐scale depletion regions, are observed on some nights. Such synoptic‐scale disruptions have not been previously identified.
Plain Language Summary
In this study, ultraviolet images of emissions from the Earth's nighttime ionosphere were examined to determine the location of the equatorial ionization anomaly, regions of enhanced ionization that result in bands of nighttime airglow emission that typically appear parallel to the magnetic equator near +15° and −15° magnetic latitude. We found that gaps in the anomaly are observed much more frequently in these observations than in previous space‐based observations. These gaps, sometimes referred to as ionospheric bubbles or depletions, are important because they are associated with ionospheric changes that can cause disruptions in communications and satellite navigation that depend on satellites, such as GPS. The location of the anomaly was also observed to vary significantly, by as much as 15°, from the typical latitudes. The observed level of variability seen during the unusually quiet geomagnetic conditions during which the observations occurred suggests that accurate predictions of the location and variability of the equatorial ionization anomaly requires significant advances in understanding the causes of this variability.
Key Points
During geomagnetically quiet solar minimum conditions, significant temporal and spatial variability is observed in the equatorial ionosphere
At solar minimum, depleted ionospheric regions are observed on most nights, at varying longitudes, and with evident meridional symmetry
Synoptic‐scale disruptions of the ionization crests are seen on several nights, possibly associated with large‐scale plasma instabilities
The article discusses the using of the rubidium - 87 quantum frequency standard for satellite navigation systems. A method for improving the parameters of the microwave excitation signal to enhance ...the short-term and long-term stability of the standard is proposed. The results of experimental studies are presented.
In this work, we present a case history relative to ground penetrating radar measurements performed close to the Roman amphitheatre of Lecce, Italy. We have performed a classical data elaboration ...with focusing of the data and slicing putting into evidence hidden details of the structure of the monument. It will be shown that the interpretation of the ground penetrating radar data is meaningfully helped by the consultation of ancient documents, which makes the final result multidisciplinary. Finally, we have georeferenced the data matching the shape of the depth slices with the shape of the investigated roads. In fact, we did not have at disposal any differential global satellite navigation systems. Indeed, this can be a method exploitable in cases when satellite data are not available, either because the area is shadowed or because the user does not have a differential global satellite navigation system. The proposed geographical matching is achieved by means of the matching between the shape of the slices and those of the physical obstacles present in the field. Therefore, it is essentially based on a continuous of points, and so it is probably more precise than a method based on the only vertexes. In particular, the proposed procedure does not require any deformation of the shape of the slice.
Overview of BDS III new signals Lu, Mingquan; Li, Wenyi; Yao, Zheng ...
Navigation (Washington),
Spring 2019, Letnik:
66, Številka:
1
Journal Article
Recenzirano
With the completion of the experimental and regional phases, China's BeiDou Navigation Satellite System (BDS) is being speedily expanded to a global and multifunctional satellite navigation system, ...BDS III. Confronted with challenges such as limited frequency resources and diversified user requirements, new signals with novel modulation techniques are adopted in BDS III. In addition to the legacy B1I and B3I signals, new open service signals, B1C and B2a/B2b, as well as some new authorized service signals, will be broadcast by BDS III satellites. Among them, B1C and B2a are compatible and interoperable with GPS and Galileo. The modulation techniques and the detailed signal structures of B1C and B2a are introduced in this paper, along with analysis of the initial in‐orbit test results of the new signals.
GNSS Spoofing and Detection Psiaki, Mark L.; Humphreys, Todd E.
Proceedings of the IEEE,
2016-June, 2016-6-00, 20160601, Letnik:
104, Številka:
6
Journal Article
Recenzirano
Global navigation satellite signals can be spoofed by false signals, but special receivers can provide defenses against such attacks. The development of good spoofing defenses requires an ...understanding of the possible attack modes of a spoofer and the properties of those modes that can be exploited for defense purposes. Sets of attack methods and defense methods are described in detail. An attack/defense matrix is developed that documents which defense techniques are effective against the various attack techniques. Recommendations are generated to improve the offerings of commercial off-the-shelf receivers from the current situation, a complete lack of spoofing defenses, to a situation in which various levels of defense are present, some that add significant security for relatively little additional cost and others that add more security at costs that start to become appreciable.
Nudge, not sludge Thaler, Richard H
Science (American Association for the Advancement of Science),
08/2018, Letnik:
361, Številka:
6401
Journal Article
Recenzirano
Odprti dostop
For some, the world is becoming increasingly complicated in that there are ever greater responsibilities, from selecting health insurance to figuring out how much to save for retirement. Ten years ...ago, my friend (and Harvard law professor) Cass Sunstein and I published a book called Nudge: Improving Decisions About Health, Wealth, and Happiness that offered a simple idea. By improving the environment in which people choose—what we call the “choice architecture”—they can make wiser choices without restricting any options. The Global Positioning System (GPS) technology on smartphones is an example. You decide where you want to go, the app offers possible routes, and you are free to decline the advice if you decide to take a detour. Sunstein and I stressed that the goal of a conscientious choice architect is to help people make better choices “as judged by themselves.” But what about activities that are essentially nudging for evil? This “sludge” just mucks things up and makes wise decision-making and prosocial activity more difficult.
Human activity and related land use change are the primary cause of accelerated soil erosion, which has substantial implications for nutrient and carbon cycling, land productivity and in turn, ...worldwide socio-economic conditions. Here we present an unprecedentedly high resolution (250 × 250 m) global potential soil erosion model, using a combination of remote sensing, GIS modelling and census data. We challenge the previous annual soil erosion reference values as our estimate, of 35.9 Pg yr
of soil eroded in 2012, is at least two times lower. Moreover, we estimate the spatial and temporal effects of land use change between 2001 and 2012 and the potential offset of the global application of conservation practices. Our findings indicate a potential overall increase in global soil erosion driven by cropland expansion. The greatest increases are predicted to occur in Sub-Saharan Africa, South America and Southeast Asia. The least developed economies have been found to experience the highest estimates of soil erosion rates.
Abstract
In radar signal processing, radar target parameter estimation is one of the important tasks of radar target detection. Multipath effect is one of the main error sources of satellite ...navigation system. In the existing research, the method based on maximum likelihood estimation criterion is considered as the best multipath suppression technology, but its calculation is particularly complicated when there are multiple signals and the number of paths is unknown. This paper mainly studies the application of sparse representation theory in radar target parameter estimation, taking Doppler frequency estimation as an example. The sparse model of Doppler frequency estimation is established, and the frequency estimation is carried out by the classical greedy iterative reconstruction algorithm, and high resolution is obtained. In this paper, a variable step-size fitting algorithm is adopted, which is simple and practical, has little computation, is independent of multipath number, is easy to realize and is easy for real-time signal processing.
PDF
