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Legend has it that a strange orb sometimes seen hovering over the railroad tracks in the remote area around Summerville, South Carolina, is a lantern borne by a ghost whose husband lost his head in a train accident.

Gravitationally induced deformation of the receiving unit of radio telescopes used for Very Long Baseline Interferometry (VLBI) distorts the observations and biases the deduced products. As this deformation ac...

Abstract

Spoofing detection is an essential process in global navigation satellite system anti-spoofing. Signal quality monitoring (SQM) methods have been widely studied as simple and effective means to detect spoofing. However, the disadvantages of the existing SQM methods, such as long alarm times and low detection rates, necessitate the study of new methods. Therefore, to address these challenges, this paper proposes a novel SQM method based on a long short-term memory-detect (LSTM-Detect) model with a strong capacity for sequential signal processing. In particular, this method evaluates the distortion of the autocorrelation function (ACF) by the trained LSTM-Detect model for spoofing detection. The simulation results demonstrate that the LSTM-Detect model can detect a wide range of spoofing signals, varying in signal power advantages, code phase differences, and carrier phase differences. In the Texas Spoofing Test Battery datasets 2–6, the detection rate exceeds 98.5%, with an alarm time of less than 5 ms. Compared with five existing SQM methods, the LSTM-Detect model exhibits a more comprehensive spoofing detection performance.

Abstract

Low-cost (LC) Global Navigation Satellite System (GNSS) receivers are argued as an alternative solution to geodetic GNSS counterparts for different applications. Single-frequency low-cost (SF-LC) GNSS receivers have been in the market for many years while their inability to acquire GNSS observations in second frequency limited their use. A few years ago, dual-frequency low-cost (DF-LC) GNSS receivers with enhanced capabilities entered the mass market, considering the advancements they have been tested and evaluated by many researchers. Lastly, multi-frequency low-cost (MF-LC) GNSS receivers become available. With the ability to track more satellite signals, these GNSS receivers are expected to obtain better overall performance. This review article aims to analyze recent advances and applications of LC GNSS receivers. To provide answers to the research question relevant articles were selected and analyzed. From the reviewed articles, it was concluded that the performance of SF-LC and DF-LC GNSS receivers is comparable to that of geodetic counterparts only in open-sky conditions. However, in adverse conditions, the differences become more highlighted. In such environments, SF and DF-LC GNSS receivers face challenges not only with positioning quality but also with their proper work. Limited studies on MF-LC receivers have reported comparable observations and positioning performance to geodetic GNSS receivers. Despite drawbacks, LC GNSS receivers have been successfully applied in surveying, mapping, geodetic monitoring, precision agriculture, navigation, atmosphere monitoring, Earth surface monitoring, and other fields.

Nature Geoscience, Published online: 23 January 2025; doi:10.1038/s41561-024-01635-7

Coral bleaching and mortality are substantially overestimated in most model projections that are based on Degree Heating Months instead of Degree Heating Weeks, calling into question results generated using Degree Heating Months.

Nature Geoscience, Published online: 23 January 2025; doi:10.1038/s41561-024-01630-y

Upper-crustal magma bodies are present beneath most Cascade Range volcanoes, indicating that large volumes of melt can persist at shallow depth through eruption cycles, according to systematic seismic imaging.

We have developed two novel axial anisotropic inversion codes for magnetotelluric (MT) data: a full axial inversion and a decoupled axial inversion. Both codes are based on the data space Gauss–Newton inversio...

The magnitude 7.9 Bonin Islands earthquake sequence in May 2015, which ruptured deep within the earth near the base of the upper mantle, did not include an aftershock that extended to record depths into the lower mantle, according to a study appearing in The Seismic Record.

A new study shows biochar to be far more effective at long-term carbon storage than previously thought. The study reveals critical flaws in the models used by the IPCC and European climate policymakers.

Scientists at the University of Lausanne (UNIL) have used AI to massively speed up computer calculations and simulate the last ice cover in the Alps. Much more in line with field observations, the new results show that the ice was thinner than in previous models. This innovative method opens the door to countless new simulations and predictions linked to climate upheavals. The research is published in Nature Communications.

When glaciers and ice sheets melt, they can destabilize slopes and reactivate faults, which in turn can trigger landslides and reshape the surface of Earth over long periods of time. Researchers can monitor some locations in real time to determine which combinations of factors lead to landslides, but understanding what triggered landslides thousands of years ago is more difficult.

Deeply hidden in Earth's mantle there are two huge "islands" the size of a continent. New research from Utrecht University shows that these regions are not only hotter than the surrounding graveyard of cold sunken tectonic plates, but also that they must be ancient: at least half a billion years old, perhaps even older.

The Great Salt Lake, the largest saltwater lake in the Western Hemisphere, reached historic low levels in 2022, raising economic, ecological and public health concerns for Utah.

Author(s): Swati Swagatika Mishra, Sudeep Bhattacharjee, and Pascal Brault

Atmospheric pressure helium plasmas are investigated through molecular dynamics simulations at room temperature (300 K) for various ionization fractions (χi=10−1−10−5) in the strongly coupled regime (ion coupling parameter, Γi∼1−10) employing Coulomb and Yukawa interaction potentials. The role of el…

[Phys. Rev. E 111, 015208] Published Wed Jan 22, 2025

Author(s): B. Clavier, D. Zarzoso, D. del-Castillo-Negrete, and E. Frénod

Generative artificial intelligence methods are employed for the first time to construct a surrogate model for plasma turbulence that enables long-time transport simulations. The proposed GAIT (Generative Artificial Intelligence Turbulence) model is based on the coupling of a convolutional variationa…

[Phys. Rev. E 111, L013202] Published Wed Jan 22, 2025

SummaryMagneto-Coriolis (MC) modes in Earth’s fluid core involve oscillations sustained by the combined effect of the Lorentz and Coriolis forces. Here, we investigate the properties of MC modes that involve purely axisymmetric flow, which we term axiMC modes. We provide a basic description of the wave dynamics of these modes, and simple predictions for the expected scalings of their frequency ω, decay rate λ, and quality factor Q based on a uniform ambient magnetic field. In particular, Q scales with the Elsasser number Λ, which depends on the square of the r.m.s. strength of the azimuthally averaged meridional field. When Λ > 1, Q > 1 and axiMC modes may be excited; when Λ ≪ 1, Q ≪ 1 and axiMC modes revert to quasi-free magnetic decay modes. We present computations of axiMC modes in an inviscid, electrically conducting sphere for two idealized ambient magnetic field configurations, a uniform axial field and an axial poloidal field. We show that a flow gradient in the axial direction is a key property of axiMC modes. For the uniform axial field, ω, λ and Q follow the scalings expected for a uniform field. For the axial poloidal field, the structure of the modes changes substantially when Λ ≳ 1, becoming more concentrated in regions of lower field strength. The combination of this structural change and advection of field lines by flow significantly increases λ, resulting in a Q that remains close to 1 even at high Λ. For a magnetic field strength inside the Earth’s core of a few mT, the gravest axiMC modes are expected to have periods in the range of one thousand to a few thousand years and a Q not substantially above 1. AxiMC modes may be connected to a part of the observed millennial changes in Earth’s magnetic field, may exchange axial angular momentum with the mantle, and hence may also explain a part of the observed millennial changes in length of day.

SummaryMulti-channel analysis of surface wave (MASW) is a non-destructive technique to characterize the sub-surface using the dispersive nature of Rayleigh waves. Field dispersion curves are inverted to predict the shear wave velocity structure of the ground and pavement profile. Adjusting the dynamic properties of the initially assumed soil profile necessitates information regarding the dominant sensitive layers. Therefore, a swift and accurate computation of the Jacobian of phase velocity is essential to generate an appropriate shear wave velocity profile and accelerate the inversion process. This is especially crucial for the 2D MASW survey, which requires hundreds of 1D inversions to create a high resolution 2D profile. Available numerical methods are computationally expensive and often suffer from instabilities for highly sensitive layers. The existing analytical methods involve mathematical complexities and require rigorous treatment. Furthermore, they are time-consuming and often found to be marginally faster than the numerical methods. Based on the fast delta matrix algorithm, the paper presents a new efficient analytical formulation of the Jacobian matrix of modal phase velocities concerning the layer parameters. The proposed algorithm leverages the simpler and fewer matrix elements of the fast delta matrix, thus significantly reducing the number of mathematical operations required. Additionally, it reduces the algorithm's cost by factorizing non-zero elements, thereby markedly reducing the computational time. Five different types of synthetic earth models are adopted from the published literature to validate the accuracy and efficacy of the newly developed algorithm. The presented work will significantly benefit the practicing engineers and geophysicists in processing field MASW test data.

Publication date: 15 January 2025

Source: Advances in Space Research, Volume 75, Issue 2

Author(s): Dachen Peng, Kai Shao, Defeng Gu, Houzhe Zhang, Zhiyong Huang, Bin Yi, Jubo Zhu

Publication date: 15 January 2025

Source: Advances in Space Research, Volume 75, Issue 2

Author(s): A.K. de Almeida, T. Vaillant, L.B.T. Santos, D. Maia