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Mauna Loa on the Island of Hawaiʻi erupted on 27 November 2022, the first eruption since 1984, which marked the culmination of decades-long period of non-eruptive unrest and relative quiescence. We briefly describe the evolution of the USGS Hawaiian Volcano Observatory's geodetic monitoring network at Mauna Loa and show patterns of deformation as measured by Global Navigation Satellite Systems (GNSS), interferometric synthetic aperture radar (InSAR), and borehole tilt. We highlight the long-term buildup and the imminent pre-eruptive geodetic signals, including subtle changes observed in early 2021 that suggested a potential eruption. We then describe the significant ramp up of activity in September 2022 that provided strong evidence of likely impending eruptive activity. Of particular importance are the first borehole tilt excursions related to magma movement measured at Mauna Loa's summit, which began in 2021 and were accompanied by increased rates of seismicity. In addition to describing the evolution of surface displacements, we also model the co-eruption deformation, which can be fit by dike-like opening that matches the geometry of the surface eruptive fissures. [ABSTRACT FROM AUTHOR]

The ionosphere plays a critical role in radio wave propagation, impacting satellite-based communication and navigation systems. This study evaluates near-real-time ionosphere maps (NRTIMs) derived from dual-frequency Global Positioning System (GPS) observations and validates them against established ionosphere models. Using dual-frequency Global Navigation Satellite System (GNSS) technology, the research mitigates ionospheric errors by measuring phase delays at L1 and L2 frequencies. Global ionosphere maps (GIMs) generated by the International GNSS Service (IGS) provide essential ionospheric corrections. Our approach combines accurate GPS observations with regional modeling to enhance GNSS positioning accuracy. The results demonstrate the effectiveness of the developed MATLAB algorithm in estimating ionospheric delays, showing strong convergence with GIMs. The results show a significant convergence between the Regional Ionosphere Modeling of RIM, IGS (Final Ionosphere Product), IGU (Ultra Rapid Ionosphere Product), and IGR (Rapid Ionosphere Product), as the highest average values during the 77th DOY of winter 2020 at the CPVG station were 14.753 TECU for RIM and 14.736, 14.7373 and 14.731 TECU at the CPVG station for IGS, IGU, and IGR while the average was for RIM, IGS, IGU, and IGR are respectively lower, with the lowest average values during the 190th DOY of autumn 2020 at station IZMI with a value of 3.5472 TECU for RIM, 3.5541, 3.5421 and 3.5624 TECU at IZMI station for IGS, IGU, and IGR respectively. By achieving strong agreement with existing GIMs and providing high-frequency results, the algorithm improves the reliability of GPS systems by effectively monitoring envelope disturbances. Ionic and dilute. [ABSTRACT FROM AUTHOR]

As low‐cost global navigation satellite systems receiver and antenna become increasingly prevalent for water vapour monitoring, precise millimetre‐level characterisation of instrument biases is crucial for maintaining measurement accuracy and reliability. This study examines the impact of phase centre variation (PCV) corrections on zenith wet delay (ZWD) accuracy in precise point positioning (PPP) solutions using low‐cost systems. The results show that PCV corrections significantly improve ZWD estimation, reducing bias and RMS by 66% and 31% in ambiguity float PPP, and by 71% and 38% in ambiguity fixed PPP. In addition, integer ambiguity resolution offers no significant improvement in ZWD accuracy without PCV correction. When PCV corrections and ambiguity fixing are applied, low‐cost receivers demonstrate ZWD estimates comparable to those of high‐precision geodetic receivers, with a deviation of 0.2 mm and an RMS of 2 mm. However, variations in signal tracking and multipath suppression can still influence ambiguity fixing rates, resulting in slightly lower performance for low‐cost receivers compared to their high‐precision counterparts. The study concludes that deploying low‐cost receivers with calibrated antennas offers a cost‐effective approach to increasing the spatial resolution of atmospheric water vapour measurements, thereby enhancing weather monitoring and early warning systems, particularly for localised extreme weather events. [ABSTRACT FROM AUTHOR]

In this study, the concept of multichannel signal tracking, previously discussed in the Global Navigation Satellite System literature, is expanded towards next-generation satellite navigation paradigms by leveraging multiple narrowband signals that are synchronously transmitted from the same satellite. This approach achieves a performance comparable to that of signals transmitted over larger bandwidths while effectively reallocating frequency resources to enhance the capacity of a wideband communication channel. This methodology can be applied to orthogonal signals, independently from their respective modulations and regardless of whether they are transmitted over different carrier frequencies or occupy the same bandwidth. The resulting architecture is tested in modern positioning, navigation and timing (PNT) scenarios, addressing in particular, the forthcoming low earth orbit (LEO) PNT paradigm to broad the technique’s applicability also towards potential piggybacked services hosted by broadband megaconstellations (e.g. Kuiper, Starlink). The applicability domain of the signal tracking architecture is explored through a parametric analysis, assessing the performance under different combined conditions such as transmission bands, multichannel combination modes, Doppler profiles, and propagation conditions. This technique has shown large performance improvements with respect to conventional single channel processing, yielding code estimation error reductions above 90% in almost all the tested conditions.

Attempts to understand wildlife population dynamics and implement management practices benefit from understanding animal behavior traits. In Alaska, USA, grizzly bear (Ursus arctos) behavior is important to understand because the species is an apex predator, exerts top-down population effects, and is a cornerstone species across complex landscapes. Our objectives were to examine how environmental and anthropogenic factors affect behavior patterns in grizzly bears in south-central Alaska. We hypothesized that, for a given sex, the time spent by bears resting, foraging, and traveling are similar and show consistent seasonal shifts as resource availability changes throughout their nondenning season. Additionally, we hypothesized that males spend more time traveling than do females because of differences in home range sizes, metabolic needs, and the rearing of cubs associated with females. We used a hidden Markov model (HMM) to test our hypotheses and examine how various dynamic, static, and temporal variables affected bear (n = 12) behavior during the summers of 2021–2022. Males spent the most time foraging and the least time resting while females spent the most time resting and the least time foraging. These patterns shifted as the summer progressed with increases in traveling and foraging and decreases in resting for both sexes. Bears were found to be most likely in a resting state at hotter temperatures and more likely to be traveling at colder temperatures. Additionally, bear behaviors deviated depending on elevation, whereby bears were foraging at higher elevations and resting or traveling at lower elevations. Our findings indicate that male–female differences in behavior are seasonally dependent, being similar in autumn and opposite during the postdenning period. In addition, we see evidence that changes in environmental conditions, such as warming, can have direct effects on behavior. Further studies should explore how future environmental and anthropogenic factors such as predicted changes in climate and increases in land-use changes can affect bear behavior and subsequent demographic effects. [ABSTRACT FROM AUTHOR]

The Rose Canyon fault is the southern extension of the larger Newport-Inglewood-Rose Canyon fault system, which represents a major structural boundary in the Inner Continental Borderland (ICB) offshore of southern California. Ten to fifteen percent of total plate boundary motion in southern California is thought to be accommodated by the faults of the ICB, but the exact distribution of slip is uncertain. With an onshore segment, the Rose Canyon fault offers an opportunity to measure the slip rate using traditional geodetic methods. In this study, we use Global Positioning System (GPS) surface velocities from a combined campaign and continuous GPS network to constrain elastic models of the Rose Canyon fault. We then compare the observed surface velocities with proposed conceptual models of regional fault connections that facilitate the transfer of slip into the Rose Canyon fault to assess how well the observations are explained by the models. The results of elastic half-space models suggest that the Rose Canyon fault may be slipping toward the higher end of geologic estimates, with the preferred model indicating a slip rate of 2.4 ± 0.5 mm/yr. Although limited in terms of near-fault benchmarks, we find an improved model fit using an asymmetrical elastic half-space model and a higher slip rate, suggesting a potential rheological contrast across the Rose Canyon fault, similar to observations from the northern Newport-Inglewood fault segments. Observed GPS surface velocities, background seismicity, and gravity anomalies south of San Diego Bay point toward a more easterly trace for the Rose Canyon fault, suggesting a possible connection with the San Miguel-Vallecitos fault system. Such a connection could increase the potential rupture lengths of future earthquakes and have important consequences for regional seismic hazards. [ABSTRACT FROM AUTHOR]

New requirements for quantum frequency standards have emerged due to the evolving demands of global navigation satellite systems and the advancements in deep space exploration technologies. One of the quantum frequency standards that meets the new requirements is the quantum frequency standard on mercury-199 ions, which is currently one of the most promising frequency standards. We have presented a comprehensive review of current research on the quantum frequency standard on mercury-199 ions in several countries, including the USA, Russia, the European Union, and China. We have compared and analyzed the characteristics of different developments of the quantum frequency standard on mercury-199 ions. The main differences between them are the ion traps and the mercury-202 light sources. In addition, we have analyzed the Allan deviation of the quantum frequency standard on mercury-199 ions developed by different countries, and the results showed that the long-term stability (105 s) of the USA and Chinese data is an order of magnitude higher than the Russian and European Union data. [ABSTRACT FROM AUTHOR]

This work presents a summary of the continuous non-stop (hereinafter 24/7) real-time measurement and warning system for EUV solar activity, which is based on worldwide multifrequency Global Navigation Satellite Systems (GNSS) observations. The system relies on continuous tracking of the intensity of expected global patterns in the Earth's ionosphere's free electron distribution, which are associated with solar flares. The paper includes a discussion on the foundations of GNSS Solar Astronomy, along with details on its real-time implementation that began in 2011. Furthermore, a summary of the corresponding validation is provided, comparing it to external and direct solar EUV flux measurements obtained from SOHO-SEM. Finally, there will be a brief mention of the ongoing efforts to extend this technique to detect huge extra-solar sources. [ABSTRACT FROM AUTHOR]

We consider the issues of calibration of the transmission coefficient of an antenna system of the ground station used for monitoring of the energy characteristics of signals from global navigation satellite systems. We present the most commonly used method intended for calibration according to the solar radio-emission of the transmission coefficient of large-aperture reflector antenna systems used as basic in the construction of ground control stations. We describe the advantages and disadvantages of the method of calibration according to the radio-emission. To eliminate the disadvantages of calibration based on solar radio-emission (the limited range of working elevation angles and the necessity of using third-party data on the spectral intensity of solar radio-emission), it is proposed to consider an alternative approach, namely, the calibration based on the use of an artificial source of radio-emission placed on board of an unmanned aerial vehicle. The specific features of this approach, namely, the necessity of operation in the near-field zone of the investigated antenna system and the motion of an artificial source of radio-emission in a plane parallel to the aperture plane of the antenna system, are indicated. We develop a block diagram of the payload of an unmanned aerial vehicle for measuring in the near-field zone of the analyzed antenna system. We present the results of investigations of the characteristics of a payload signal generator of an unmanned aerial vehicle. We propose a solution, which eliminates the error in specifying the output power of the signal generator (the difference between the nominal and actual signal power) according to the results of measurement. The necessity of using a control signal power meter and a bandpass filter as components of the payload is demonstrated. A system for monitoring of the output power of signal generator is designed. The components of the payload satisfying the restrictions imposed on the weight and size characteristics are selected. The possibility of remote connection of an operator to the payload equipment of an unmanned aerial vehicle is realized. We also describe the prospects of subsequent development of the payload model. [ABSTRACT FROM AUTHOR]

Based on the broadcast ephemeris of a global navigation satellite system (GNSS) uploaded from the ground, an orbital-based terrestrial reference frame (TRF) can be produced in consistence with the ground-based TRF. High-precision inter-satellite link (ISL) ranging technology makes satellite autonomous orbit determination (AOD) possible. Therefore, if the broadcast ephemeris cannot be uploaded, the GNSS satellites can independently maintain the accuracy of the orbital-based TRF. In this paper, orbital-based TRF realized by the autonomous orbit determination (AOD) based on BDS-3 ISL measurements is compared with the ITRF2014. The accuracy of the orbital-based TRF realized by the AOD is evaluated. The comparison between the AOD orbits and the post-processed precise orbits over 60 days via the 7 parameters Helmert transformation shows that the maximum differences of the three-axis translation between the orbital-based TRF and ITRF2014 are 1.25 m, 1.32 m and 0.47 m, and the maximum difference of the scale is 6.2 ppb. The differences of the three-axis rotation parameters between the orbital-based TRF and ITRF2014 are related to whether the orientation correction method is applied. Since the long-term orbit prediction (OP) generated by the orbit dynamics models can predict the right ascension of the ascending node (RAAN) and the inclination accurately in Geocentric Celestial Reference System (GCRS), in the orientation correction method, the long-term OP is used as the reference to constrain the rotation differences. If the orientation correction method is not applied, the maximum differences of the three-axis rotation parameters are 65.0 mas, 77.1 mas, 122.5 mas; however, if the orientation correction method is applied, the maximum differences of the three-axis rotation parameters are reduced to 32.5 mas, 46.9 mas and 67.1 mas. Part of the residual rotation differences are caused by the prediction errors of the rapid Earth rotation parameters (ERPs) from International Earth Rotation and Reference Systems Service (IERS) bulletin A. Over 60 days, the differences between the rapid ERPs from IERS bulletin A and the final estimated ERPs from IERS bulletin B are equal to 2.56 mas, 15.03 mas and 84.12 mas in X, Y, Z axis, respectively. The influence of the orbit prediction accuracy on the orbit-based TRF based on the AOD method is also analyzed. If precise satellite orbits with an accuracy of 0.10 m are applied as long-term orbit prediction, the accuracy of the orbital TRF is improved significantly. During 60 days, the maximum differences of the three-axis translation are reduced to 0.10 m, 0.10 m, and 0.12 m, the maximum differences of the three-axis rotation are reduced to 3.03 mas, 3.47 mas, and 4.94 mas, and the maximum difference of the scale is reduced to 1–2 ppb. [ABSTRACT FROM AUTHOR]

Objectives. The problem of developing an algorithm for estimating the absolute total electron content of the ionosphere from dual-frequency phase and range satellite measurements for a single receiving station of global navigation satellite systems is being solved.Methods. To obtain an estimate the phase measurement data are corrected using digital signal processing methods, well known total electron content formulas for phase and range measurements are applied and combined, and also the differential code bias of the receiving station is estimated using the least squares method.Results. It is shown that the total electron content calculated from phase measurements provides high accuracy, but up to an unknown constant, but the content calculated from range measurements allows one to obtain the absolute value, but with a large noise component and differential code bias of a satellite and receiver equipment. An algorithm for estimating the absolute total electron content of the ionosphere has been developed, its description and diagram are given. The algorithm was used to estimate the total electronic content within six months of observations, and the average error of the resulting estimate was calculated.Conclusion. The developed algorithm can be used to estimate the absolute total electron content of the ionosphere for a single receiving station of global navigation satellite systems. In contrast to theoretically known formulas for phase and range measurements, this article contains information about adjusting phase measurements and estimating the differential code delay of receiving station. Further research may be related to the adaptive selection of parameters and testing of the algorithm for working with nanosatellites of the CubeSat format.

With the continuous development of global navigation satellite systems (GNSS) modernization, the code bias presented in the form of observation-specific biases (OSB) is more flexible and effective when processing modern multi-frequency and multi-GNSS signals, and therefore widely accepted by the GNSS community. However, the newly reported signal distortion biases (SDB) are ignored in the existing OSB estimation methods, which may affect the reliability of the final OSB estimation. In addition, the existing studies about SDB estimation are independent of OSB estimation, and thus a set of SDB products is generated independent of OSB products, which undoubtedly brings more complicated correction operations to GNSS users. In view of it, this study proposes an approach to code OSB estimation for multi-frequency and multi-GNSS arbitrary signals by reparameterization, which considers the SDB parameter. The aim of this study is to generate a set of code OSB products that take into account SDB parameters for the GNSS users to use. Due to considering the influence of SDB on raw code observations, the OSB estimation obtained by the proposed method is related to specific satellite-receiver pairs, which makes it different from the traditional OSB estimation methods. To achieve this, an extended model for multi-frequency and multi-GNSS arbitrary signal is first established based on the undifferenced and uncombined model, in which the SDB parameter is taken into account by re-parameterization. Based on the proposed model, three types of code bias that contain the OSB information can be obtained for the subsequent OSB estimation. Then, the three types of code bias in the first step are used as virtual observations for multi-frequency and multi-GNSS arbitrary signal OSB estimation through a two-step method. The proposed method is validated with a whole month of real measured data from 418 stations in MGEX and GA CORS to generate OSBs for GPS, GLONASS, and Galileo. The comparison between the estimated OSBs and the OSB products from CAS indicates the reliability of the proposed method. Besides, all types of OSB for four receiver groups are generated based on the proposed method to analyze the relationship between OSB and receiver groups. Results indicate that the estimated OSBs are related to receiver groups, and specific differences exist between different satellites and GNSS signals. It also proves that the OSB estimation is biased by the inconsistencies of the deviation in different receiver groups, which is more obvious for GLONASS. [ABSTRACT FROM AUTHOR]

The article develops a methodology for analyzing the noise immunity of satellite communication systems under small-scale disturbances of the ionosphere, taking into account the possibility of general and time-selective fading of received signals Differential Phase Shift Keying. The refined dependences of the intervals of time and space correlation of fading in the transionospheric radio channel on the parameters of transmitted signals and the state of the ionosphere are obtained. The analytical dependence of the probability of erroneous reception of signals with Differential Phase Shift Keying on the average signal-to-noise ratio at the receiver input, the frequency-time parameters of the signals and the characteristics of small-scale ionospheric inhomogeneities was obtained.

The miniaturisation and decrease of price are amongst the main current trends in the area of Global Navigation Satellite Systems (GNSS) receivers. Besides standalone receivers also receivers incorporated into Android devices can provide raw GNSS measurements thus enabling much wider options, formerly restricted to devices of much higher price. The article describes two datasets. The first was collected using a Xiaomi Mi 8 smartphone with and without application of a simple ground plane. In the second we compared a smartphone receiver (Google Pixel 5) with a standalone low-cost receiver (u-Blox ZED F9P). In both cases the datasets consist of multiple measurement sessions, also considering the conditions where the reception of GNSS signals was obstructed by trees’ canopy. The datasets are focused on repeatability (multiple measurements), influence of external conditions (canopy and foliage state) and the devices used.

The time evolution of the total number of free electrons in the Earth's ionosphere, i.e., the Global Electron Content (GEC), during more than two solar cycles is analyzed in this work. The GEC time series has been extracted from the Global Ionospheric Maps (GIMs) of Vertical Total Electron Content (VTEC) estimated by UPC-IonSAT with TOMION-v1 software from global GPS measurements since the end of 1996. A dual-layer voxel-based tomographic model solved with a forward Kalman scalar filter, from dual-frequency carrier GPS data only, provides the so-called UQRG GIM after VTEC kriging interpolation, with a resolution of 15 min in time, 5° in longitude and 2.5° in latitude. UQRG is one of the best behaving GIMs in the International GNSS Service (IGS).In this context, the potential application of the GEC spectrum evolution as a potential space weather index is discussed and demonstrated. [ABSTRACT FROM AUTHOR]

This article presents a robust methodology for long-term offshore structural health monitoring (SHM) using the Global Navigation Satellite Systems (GNSS). The methodology relies on recently developed regional reference frames and single-receiver phase-ambiguity-fixed Precise Point Positioning techniques. The stable Gulf of Mexico Reference Frame 2020 (GOM20) provides a robust and consistent reference system for long-term offshore SHM in the Gulf of Mexico (GOM). Continuous GNSS observations (DEV1, 2010–2020) on a fixed platform in the Eugene Island 330 oil field are used to illustrate the methodology. The platform was installed in 1982 in 82-m water about 130 km away from the Mississippi Delta coastline. The major monitoring items include horizontal movements, seafloor subsidence, structure submergence, and seasonal oscillations. The stand-alone GNSS monitoring achieves 3- to 4-mm root-mean-square accuracy in the horizontal direction and 7 mm in the vertical direction for daily positions in the GOM region. According to this study, the GNSS antenna (DEV1) has moved 6 cm toward the northeast with respect to GOM20 since 2010; the ongoing structure submergence rate in the Eugene Island 330 oil field area is approximately 15 mm/year, a combination of seafloor subsidence (12 mm/year) and sea-level rise (2.6 mm/year) with respect to GOM20. The submergence in the future 40 years (2021–2060) would be greater than 0.6 m, likely between 0.8 and 1.0 m, but is unlikely to exceed 1.3 m. The peak-to-trough amplitudes of the seasonal movements at the top of the platform are below 5 mm in all three directions, comparable with the seasonal movements recorded by onshore GNSS in the Louisiana coastal region. The methodology introduced in this article can be applied to SHM in other offshore regions where stable regional reference frames are available. [ABSTRACT FROM AUTHOR]

The article develops a methodology for analyzing the noise immunity of satellite communication systems under small-scale disturbances of the ionosphere, taking into account the possibility of general and time-selective fading of received signals Differential Phase Shift Keying. The refined dependences of the intervals of time and space correlation of fading in the transionospheric radio channel on the parameters of transmitted signals and the state of the ionosphere are obtained. The analytical dependence of the probability of erroneous reception of signals with Differential Phase Shift Keying on the average signal-to-noise ratio at the receiver input, the frequency-time parameters of the signals and the characteristics of small-scale ionospheric inhomogeneities was obtained. [ABSTRACT FROM AUTHOR]

Many common discriminators used for code tracking of global navigation satellite system (GNSS) signals are ratios of quadratic forms of the correlation outputs. Here we derive a general expression for the gain of this type of discriminator and show that it depends on the effective carrier-to-noise ratio. We then evaluate this expression for several different code discriminators and GNSS signals, including GPS C/A-code, P-code, L1C, and M-code, Galileo E1 OS, GLONASS L1OF and L2OF, and BeiDou B1I and B2I. We also determine how noise and interference saturate the discriminator (i.e., make its output less sensitive to changes in the input) and the resulting effect on loop bandwidth. The discriminator gains described in this paper compensate for the saturation and ensure that loop bandwidth and code tracking performance can be accurately predicted and controlled over a critical range of effective carrier-to-noise ratios. [ABSTRACT FROM AUTHOR]

The fore-arc of the southern Cascadia subduction zone (CSZ), north of the Mendocino triple junction (MTJ), is home to a network of Quaternary-active crustal faults that accumulate strain due to the interaction of the North American, Juan de Fuca (Gorda), and Pacific plates. These faults, including the Little Salmon and Mad River fault (LSF and MRF) zones, are located near the most populated parts of California's north coast and show paleoseismic evidence for three slip events of several-meter scale in the past 1700 yr. However, the geodetic slip rates of these faults are poorly constrained. In this work, we analyze a new compilation of interseismic geodetic velocities from Global Navigation Satellite Systems, leveling, and tide gauge data near the MTJ to constrain present-day slip deficit rates on upper-plate faults and coupling on the megathrust. We construct Green's functions for interseismic slip deficit for discrete faults embedded in an elastic plate overlying a viscoelastic mantle. We then use a constrained least-squares inversion to determine best-fitting slip rates on the major faults and investigate slip rate trade-offs between faults. Results indicate that the LSF and MRF systems together accumulate 4-5 mm/yr of reverse-slip deficit, although their separate slip rates cannot be determined independently. Modeling of the horizontal and vertical velocities suggests that the southernmost CSZ is coupled interseismically to deeper than 25 km depth. We also find that 6-17 mm/yr of right-lateral slip deficit extends north of the MTJ and into the southern Cascadia fore-arc. These results reinforce the notion that both the southernmost Cascadia megathrust and the smaller fore-arc faults above it contribute to regional seismic hazard. [ABSTRACT FROM AUTHOR]

The susceptibility of global navigation satellite systems (GNSSs) to interference significantly limits the possibility of their use. From the standpoint of possible consequences, the most dangerous interference is the so-called spoofing. Simultaneously, in most cases of GNSS use, an inertial navigation system (INS) or an attitude and heading reference system (AHRS) is also present on the board of mobile objects. In this regard, the research goal is to assess the possibility of detecting GNSS spoofing in inertial satellite navigation systems. This paper examines the method for detecting GNSS spoofing by combining a pair of commercially available GNSS receivers and antennas with an INS or AHRS. The method is based on a comparison of the double differences of GNSS carrier phase measurements performed by receivers under conditions of resolved integer ambiguity and the values of the range double differences predicted using an INS. GNSS carrier phase integer ambiguity can be resolved using a strapdown inertial navigation system (SINS) or AHRS data. The mathematical model of GNSS phase difference measurements and the SINS-predicted satellite range differences model are given. The proposed algorithm calculates the moving average of the residuals between the SINS-predicted satellite range double differences and the measured GNSS carrier phase double differences. The primary criterion for spoofing detection is the specified threshold excess of the moving average of the double difference residuals. Experimental studies are performed using simulation and hardware-in-the-loop simulation. The experimental results allow us to evaluate the efficiency of the proposed approach and estimate the potential characteristics of the spoofing detection algorithm based on it. [ABSTRACT FROM AUTHOR]

In the early April 2021, the tropical cyclone Seroja was formed over the Savu Sea in the southeastern Indonesia. Seroja provided a unique opportunity to observe a tropical cyclone over the Indonesian region using ground-based global navigation satellite systems (GNSS) observations. Precipitable water vapor (PWV) from several permanent GNSS stations in the region was utilized to detect Seroja. From in situ meteorological observations, we found that surface pressure values dropped by more than 14 hPa during Seroja, relative humidity increased, and temperature was reduced. PWV at two nearest stations showed an upward trend (around 70 mm at its peak) during the formation of the cyclone, then dropped immediately (less than 20 mm). After Seroja, the mean PWV was lower (56 mm before and 39 mm after), whereas the standard deviation was higher (5–6 mm before and 9 mm after). We also compared hourly PWV with precipitation from the global satellite mapping of precipitation (GSMaP). Before Seroja, some precipitation events occurred, followed by heavy rains that lasted for several days when the cyclone was passing. After Seroja had passed, both PWV and precipitation dropped significantly. However, while PWV values after Seroja were fluctuating, no rain occurred. We then investigated the water vapor budget to understand the change of PWV over time. We found that precipitation and the divergence of moisture flux played an important role in the change of PWV over time. Heavy precipitation during Seroja resulted in a drop in PWV, although the negative divergence provided a bit of offset. After Seroja had passed, no precipitation occurred, and the change of PWV could be attributed mainly to the moisture divergence. The lagged correlation between PWV and precipitation was determined using moving average over the time series. The highest correlation was found 1–2 days before the event with moving average periods of 7 and 10 days. [ABSTRACT FROM AUTHOR]

Abstract Aiming at the problem that the traditional inter-system double-difference model is not suitable for non-overlapping signal frequencies, we propose a new inter-system double-difference model with single difference ambiguity estimation, which can be applied for both overlapping and non-overlapping signal frequencies. The single difference ambiguities of all satellites and Differential Inter-System Biases (DISB) are first estimated, and the intra-system double difference ambiguities, which have integer characteristics, are then fixed. After the ambiguities are successfully fixed, high-precision coordinates and DISB can be obtained with a constructed transformation matrix. The model effectively avoids the DISB parameter filtering discontinuity caused by the reference satellite transformation and the low precision of the reference satellite single difference ambiguity calculated with the code. A zero-baseline using multiple types of receivers is selected to verify the stability of the estimated DISB. Three baselines with different lengths are selected to assess the positioning performance of the model. The ionospheric-fixed and ionospheric-float models are used for short and medium-long baselines, respectively. The results show that the Differential Inter-System Code Biases (DISCB) and Differential Inter-System Phase Biases (DISPB) have good stability regardless of the receivers type and the signal frequency used and can be calibrated to enhance the strength of the positioning model. The positioning results with three baselines of different lengths show that the proposed inter-system double-difference model can improve the positioning accuracy by 6–22% compared with the intra-system double-difference model which selects the reference satellite independently for each system. The Time to First Fix (TTFF) of the two medium-long baselines is reduced by 30% and 29%, respectively.

The aspects of monitoring the energy characteristics of radio navigation signals of the global navigation satellite system (GLONASS) have been considered. It has been noted that the power of the incoming radio navigation signal in the lower atmosphere depends on the parameters of the onboard antenna system of the navigation spacecraft, primarily, on the shape of the antenna amplitude pattern. The amplitude pattern of the onboard antenna of the spacecraft has a complex shape, and in order to compensate for changes in the power of the radio navigation signal due to the navigation spacecraft moving away from (or approaching) the signal user, the shape of the amplitude pattern should be axisymmetric, i.e., resembling a figure of revolution. Based on regular monitoring of the energy characteristics of the GLONASS radio navigation signals, the shapes of the amplitude patterns of the onboard antenna feed systems of the spacecraft from the orbital group have been evaluated. As a result, asymmetry in the amplitude patterns of some spacecraft has been detected. It has been shown that the asymmetry of the amplitude pattern leads to a dependence of the power of the incoming radio navigation signal on the spacecraft aspect angle, i.e., the position of the spacecraft emitting antenna system relative to the signal user. The probable cause of such asymmetry has been identified as the gradual aging of the active devices in the antenna feed path. The obtained results indicate the need for regular and prompt monitoring of the energy characteristics of radio navigation signals in the lower atmosphere. The observed effect of asymmetry in the amplitude patterns should be taken into account when developing spacecraft antenna feed systems. [ABSTRACT FROM AUTHOR]

The need for precise orbit determination (POD) has grown significantly due to the increased amount of space-based activities taking place at an accelerating pace. Accurate POD positively contributes to achieving the requirements of Low-Earth Orbit (LEO) satellite missions, including improved tracking, reliability and continuity. This research aims to systematically analyze the LEO–POD in four aspects: (i) data sources used; (ii) POD technique implemented; (iii) validation method applied; (iv) accuracy level obtained. We also present the most used GNSS systems, satellite missions, processing procedures and ephemeris. The review includes studies on LEO–POD algorithms/methods and software published in the last two decades (2000–2021). To this end, 137 primary studies relevant to achieving the objective of this research were identified. After the investigation of these primary studies, it was found that several types of POD techniques have been employed in the POD of LEO satellites, with a clear trend observed for techniques using reduced-dynamic model, least-squares solvers, dual-frequency signals with undifferenced phase and code observations in post-processing mode. This review provides an understanding of the various POD techniques, dataset utilized, validation techniques, and accuracy level of LEO satellites, which have interest to developers of small satellites, new researchers and practitioners. [ABSTRACT FROM AUTHOR]

Currently, the developers of global navigation satellite systems (GNSS) are making significant efforts to solve a number of fundamental problems. However, ignorimg by researchers the entire set of nonequilibrium physical and chemical processes occurring in the ionosphere, which affect the propagation of satellite signals, often does not allow to have a progress in their solution. In this paper, we discuss the main chemical reactions that occur in the lower ionosphere of the Earth with the participation of the Rydberg states of O2, N2, and NO molecules. An explanation of the physical reason for the time delay of the satellite signal, leading to errors in GNSS positioning, is given. A quantum approach is proposed, through which the transition from the traditional idea of the propagation of radio waves to the movement of the corresponding photons is carried out. In this case, the effective delay time in resonant photon scattering is determined by the characteristic lifetime of the intermediate autoionization states of vibrationally excited Rydberg complexes. The value of the lifetime is defined by the presence of a strong nonadiabatic coupling of the electronic and nuclear motions in the intermediate states of the complex, which does not depend on the strength of the external field created by the GNSS transmitter. [ABSTRACT FROM AUTHOR]

Motion analysis using wearable sensors is an essential research topic with broad mathematical foundations and applications in various areas, including engineering, robotics, and neurology. This paper presents the use of the global navigation satellite system (GNSS) for detecting and recording the position of a moving body, along with signals from additional sensors, for monitoring of physical activity and analyzing heart rate dynamics during running on route segments of different slopes and speeds. This method provides an alternative to the heart monitoring on the treadmill ergometer in the cardiology laboratory. The proposed computational methodology involves digital data preprocessing, time synchronization, and data resampling to enable their correlation, feature extraction both in time and frequency domains, and classification. The datasets include signals acquired during ten experimental runs in the selected area. The motion patterns detection involves segmenting the signals by analysing the GNSS data, evaluating the patterns, and classifying the motion signals under different terrain conditions. This classification method compares neural networks, support vector machine, Bayesian, and $k$ -nearest neighbour methods. The highest accuracy of 93.3 % was achieved by using combined features and a two-layer neural network for classification into three classes with different slopes. The proposed method and graphical user interface demonstrate the efficiency of multi-channel and multi-dimensional signal processing with applications in rehabilitation, fitness movement monitoring, neurology, cardiology, engineering, and robotic systems.

This study investigated the nonlinear changes in the vertical motion of 411 GNSS reference stations situated in mainland China and assessed the influence of the environmental load on their vertical displacement. The researchers evaluated the effect of environmental load by calculating the change in annual cycle amplitude before and after its removal, focusing on its impact across regions with distinct foundation types. The results demonstrate that removing the environmental load led to a considerable reduction of approximately 50.25% in the annual cycle amplitude of vertical motion for GNSS reference stations in mainland China. This reduction in amplitude improved the positioning accuracy of the stations, with the highest WRMS reduction being 2.72 mm and an average reduction of 1.03 mm. The most significant impact was observed in the southwestern, northern, and northwestern regions, where the amplitude experienced a notable decrease. Conversely, the southeastern region exhibited a corresponding increase in amplitude. This article innovatively explored the effects of environmental loads on diverse foundation types. When categorizing GNSS reference stations based on their foundation type, namely, bedrock, 18 m soil layer, and 4–8 m soil layer stations, this study found that removing the environmental load resulted in reductions in annual cycle amplitudes of 49.37%, 59.61%, and 46.48%, respectively. These findings indicate that 18 m soil layer stations were more susceptible to environmental load-induced vertical motion. In conclusion, the impact of the environmental load was crucial when analyzing the vertical motion of GNSS reference stations in mainland China, as it was essential for establishing a high-precision coordinate reference framework and studying the tectonic structure of the region. [ABSTRACT FROM AUTHOR]

Aiming at the problem that the traditional inter-system double-difference model is not suitable for non-overlapping signal frequencies, we propose a new inter-system double-difference model with single difference ambiguity estimation, which can be applied for both overlapping and non-overlapping signal frequencies. The single difference ambiguities of all satellites and Differential Inter-System Biases (DISB) are first estimated, and the intra-system double difference ambiguities, which have integer characteristics, are then fixed. After the ambiguities are successfully fixed, high-precision coordinates and DISB can be obtained with a constructed transformation matrix. The model effectively avoids the DISB parameter filtering discontinuity caused by the reference satellite transformation and the low precision of the reference satellite single difference ambiguity calculated with the code. A zero-baseline using multiple types of receivers is selected to verify the stability of the estimated DISB. Three baselines with different lengths are selected to assess the positioning performance of the model. The ionospheric-fixed and ionospheric-float models are used for short and medium-long baselines, respectively. The results show that the Differential Inter-System Code Biases (DISCB) and Differential Inter-System Phase Biases (DISPB) have good stability regardless of the receivers type and the signal frequency used and can be calibrated to enhance the strength of the positioning model. The positioning results with three baselines of different lengths show that the proposed inter-system double-difference model can improve the positioning accuracy by 6–22% compared with the intra-system double-difference model which selects the reference satellite independently for each system. The Time to First Fix (TTFF) of the two medium-long baselines is reduced by 30% and 29%, respectively. [ABSTRACT FROM AUTHOR]

Context and background In Ghana the predominant method for performing cadastral surveys is through the use of Global Navigation Satellite Systems (GNSS) static surveys and to a lesser extent Total Stations. This work investigates the use of Unmanned Aerial Vehicles (UAV) for performing cadastral surveys and investigate the effects of varying sensor types, flying height, image overlap and number of ground control points in the acquisition of imagery for producing acceptable cadastral maps for use in Ghana. Goal and Objectives: The main aim of this study is therefore to assess some defining parameters for the use of UAV surveys for cadastral mapping and hence suggest some guidelines for the geomatic community in Ghana. The objectives of this work are as follows: i. To determine in generic terms UAV types that are appropriate for cadastral mapping in Ghana ii. To identify some threshold flight parameters necessary for obtaining desirable accuracies for cadastral mapping from UAV data iii. To investigate the optimal number of ground control points necessary for accurate cadastral mapping work .Methodology: A quantitative method was adopted where two sources of primary data were used. The control dataset was obtained by using static GNSS methods to obtain the boundary coordinates of the 20-acre study area. This control data was compared to 20 different data sets of boundary coordinates obtained from UAV imagery resulting from a permutation of different UAV types, varying flight heights, forward/side overlap and number of GCP’s used for georefencing. Results: Optimal results were achieved when georeferenced with 8 Ground Control Points (GCP's) with average Root Mean Square Error (RMSEX)and RMSEY values of 1.383 ft and 1.034 ft respectively. There was no marked improvement in increasing GCP's to 12 thus a minimum of 1 GCP per 2.5 acres is suggested for georeferencing to achieve the ± 3 feet required tolerance stipulated by Surveying and Mapping Division of Ghana. The results suggest that UAV’s with sensor resolutions of 12 mega-pixels (MP) or greater are suitable and that a minimum forward lap of 70% is adequate for obtaining imagery suitable for cadastral mapping.

Global navigation satellite systems (GNSS) provide a great data source about the ionosphere state. These data can be used for testing ionosphere models. We studied the performance of nine ionospheric models (Klobuchar, NeQuickG, BDGIM, GLONASS, IRI-2016, IRI-2012, IRI-Plas, NeQuick2, and GEMTEC) both in the total electron content (TEC) domain—i.e., how precise the models calculate TEC—and in the positioning error domain—i.e., how the models improve single frequency positioning. The whole data set covers 20 years (2000–2020) from 13 GNSS stations, but the main analysis involves data during 2014–2020 when calculations are available from all the models. We used single-frequency positioning without ionospheric correction and with correction via global ionospheric maps (IGSG) data as expected limits for errors. Improvements against noncorrected solution were as follows: GIM IGSG—22.0%, BDGIM—15.3%, NeQuick2—13.8%, GEMTEC, NeQuickG and IRI-2016—13.3%, Klobuchar—13.2%, IRI-2012—11.6%, IRI-Plas—8.0%, GLONASS—7.3%. TEC bias and mean absolute TEC errors for the models are as follows: GEMTEC—−0.3 and 2.4 TECU, BDGIM—−0.7 and 2.9 TECU, NeQuick2—−1.2 and 3.5 TECU, IRI-2012—−1.5 and 3.2 TECU, NeQuickG—−1.5 and 3.5 TECU, IRI-2016—−1.8 and 3.2 TECU, Klobuchar—1.2 and 4.9 TECU, GLONASS—−1.9 and 4.8 TECU, and IRI-Plas—3.1 and 4.2 TECU. While TEC and positioning domains differ, new-generation operational models (BDGIM and NeQuickG) could overperform or at least be at the same level as classical empirical models. [ABSTRACT FROM AUTHOR]

The use of global navigation satellite systems (GNSS) technology within the fields of ecology and biology has increased over recent years. With Global Positioning System, GLObalnaya NAvigatsionnaya Sputnikovaya Sistema, Galileo, and BeiDou systems fully deployed, >140 navigation satellites are currently available for navigation and high precision positioning applications. The technological improvements in GNSS devices, mainly due to the multi‐frequency capability, reduce signal acquisition time and increase the reliability, the continuity, and the accuracy of the estimated position, especially in complex environments like forests or areas with a steep topography. This study aims to test experimentally the influence of multi‐constellation multi‐frequency modules on the performance of the GNSS collars used to monitor wildlife. We applied static and kinematic tests designed to assess and compare the performance of GNSS collars equipped with a single‐frequency versus a multi‐frequency chipset. We evaluated the availability and continuity of solutions, number of satellites used, dilution of precision, precision, accuracy, and repeatability of these quality parameters for GNSS devices in southeastern Spain from February 2021 to June 2022. The results confirmed that the multi‐constellation multi‐frequency GNSS collar showed a stable and good performance in terms of the number of satellites used (>10), horizontal dilution of precision (<1.3), fix success rate (100%), mean location error (<1.5 m), and circular error probability (CEP), which was better by approximately one order of magnitude than the single‐frequency collar (1–10 m). The use of reliable and accurate GNSS devices will expand our knowledge of animal behavior and the interactions between species. Multi‐frequency GNSS collars allow collection of accurate locations, providing fine‐scale information about animal behavior (e.g., feeding strategies, competition for resources), whereas the single‐frequency GNSS collars can used for broad‐scale studies (e.g., home ranges, habitat use). [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) is vital for ensuring the service safety of aging bridges. As one of the most advanced sensing techniques, Global Navigation Satellite Systems (GNSS) could capture massive spatiotemporal information for effective bridge structural health monitoring (BSHM). Unfortunately, GNSS measurements often contain outliers due to various factors (e.g., severe weather conditions, multipath effects, etc.). All such outliers could jeopardize the accuracy and reliability of BSHM significantly. Previous studies have examined the feasibility of integrating the conventional multi-rate Kalman filter (MKF) with an adaptive algorithm in the data processing processes to ensure BSHM accuracy. However, frequent parameter adjustments are still needed in tedious data processing processes. This study proposed an outlier detection method using a Nelder-Mead simplex robust multi-rate Kalman filter (RMKF) for supporting trustworthy BSHM using GNSS and accelerometer. In the end, the authors have validated the proposed method using the monitoring data collected at the Wilford Bridge in the UK. Results showed that the accuracy of the total dynamic vibration displacement time series has been improved by 21% compared with the results using the conventional MKF approach. The authors envision that the proposed method will shed light on reliable and explainable data processing policy and trustworthy BSHM. [ABSTRACT FROM AUTHOR]

ESA's Swarm constellation entered in a "overfly" configuration in the period between September and October 2021, when the longitudinal distance between the lower pair and the upper satellite was at its minimum since the launch of the spacecrafts. In addition, the local time of the nighttime tracks was favorable to detect and study the morphology of post‐sunset equatorial plasma bubbles (EPBs). In this study, we focus on the Swarm overfly occurring between 00:41 UT and 00:59 UT on 30 September 2021, which covered one of the most densely instrumented regions for the study of the ionospheric irregularities embedded in the EPBs: the South American sector. By exploiting the use of ground‐based receivers of Global Navigation Satellite System (GNSS) signals in combination with the Swarm plasma density measurements, we study the irregularities in the EPB formed at ∼60°W and investigate the different scales of the irregularities and the cascading processes along the magnetic flux tubes. We also highlight how diffusion along the magnetic field lines occurs simultaneously with the plasma uplift, contributing then to the correct interpretation of the EPB evolution and decay process. The precious overfly conditions also allow the introduction of ionosphere‐related quantities, evaluated across the tracks at satellite altitudes enlarging the possibilities given by the same quantities already available along the tracks. Such opportunity envisages the possibility to proxy the impact of EPBs on GNSS signals with Low‐Earth Orbit satellite data provided by future missions specifically dedicated to the characterization of the near‐Earth environment and ionospheric studies. Plain Language Summary: Ionospheric Equatorial Plasma Bubbles (EPBs) are the most dangerous threat to radio‐wave propagation in the frequencies from HF, used for telecommunications, to L‐band, emitted by Global Navigation Satellite Systems (GNSS). Such bubbles form in the post‐sunset hours at equatorial latitudes and their occurrence is still a challenge for the scientific community, in terms of capability to model their triggering mechanisms, formation, growth and decay. On 30 September 2021, a precious occasion occurred. The 3 satellites constituting the ESA's Swarm constellation—a set of three satellites, two orbiting at 440 km and flying in pairs and one at 510 km—entered in a "overfly" configuration over Brazil. In other words, the lower pair and the upper satellite flew in a narrow longitudinal band and in one of the most densely instrumented regions in terms of ground‐based GNSS receiver. This translated into the possibility to step into a single EPB. We exploited this configuration and the ground‐based measurements to provide an unprecedented reconstruction of a plasma bubble and to introduce new measurements that can be used by future satellite missions to provide insights on the most dangerous natural hazard to radio waves. Key Points: Swarm overfly allowed offers an unprecedented possibility to investigate the features of a single plasma bubble at different altitudesScales of the irregularities and their cascading processes along the magnetic flux tubes are identifiedIonosphere‐related quantities, evaluated across the tracks at different satellite altitudes, are introduced [ABSTRACT FROM AUTHOR]

We propose an optimized Structure-from-Motion (SfM) Multi-View Stereopsis (MVS) workflow, based on minimizing different errors and inaccuracies of historical aerial photograph series (1945, 1979, 1984, and 2008 surveys), prior to generation of elevation-calibrated historical Digital Surface Models (hDSM) at 1 m resolution. We applied LiDAR techniques on Airborne Laser Scanning (ALS) point clouds (Spanish PNOA LiDAR flights of 2014 and 2019) for comparison and validation purposes. Implementation of these products in multi-temporal analysis requires quality control due to the diversity of sources and technologies involved. To accomplish this, (i) we used the Mean Absolute Error (MAE) between GNSS-Validation Points and the elevations observed by DSM-ALS to evaluate the elevation accuracy of DSM-ALS generated with the LAScatalog processing engine; (ii) optimization of the SfM sparse clouds in the georeferencing step was evaluated by calculating the Root Mean Square Error (RMSE) between the Check Points extracted from DSM-ALS and the predicted elevations per sparse cloud; (iii) the MVS clouds were evaluated by calculating the MAE between ALS-Validation Points and the predicted elevations per MVS cloud; iv) the accuracy of the resulting historical SfM-MVS DSMs were assessed using the MAE between ALS-Validation Points and the observed elevations per historical DSM; and (v) we implemented a calibration method based on a linear correction to reduce the elevation discrepancies between historical DSMs and the DSM-ALS 2019 reference elevations. This optimized workflow can generate high-resolution (1 m pixel size) hDSMs with reasonable accuracy: MAE in z ranges from 0.41 m (2008 DSM) to 5.21 m (1945 DSM). Overall, hDSMs generated using historical images have great potential for geo-environmental processes monitoring in different ecosystems and, in some cases (i.e., sufficient image overlapping and quality), being an acceptable replacement for LiDAR data when it is not available. [ABSTRACT FROM AUTHOR]

Caves are open ecosystems with natural microbiota, and they are generally stable if environmental conditions are stable. Some have rock art, which is generally characterized as fragile, especially when the equilibrium conditions of the hypogeum are changed. This article shows how high-resolution microphotogrammetry, supported by other geomatic techniques, allows the objective and quantifiable control of the alterations suffered by the pigment and its variation over time regarding earlier campaigns. This method, applied periodically, makes it possible to prevent and/or detect possible alterations at an early stage and improve the conditions of the conservation of the cave.

The susceptibility of global navigation satellite systems (GNSSs) to interference significantly limits the possibility of their use. From the standpoint of possible consequences, the most dangerous interference is the so-called spoofing. Simultaneously, in most cases of GNSS use, an inertial navigation system (INS) or an attitude and heading reference system (AHRS) is also present on the board of mobile objects. In this regard, the research goal is to assess the possibility of detecting GNSS spoofing in inertial satellite navigation systems. This paper examines the method for detecting GNSS spoofing by combining a pair of commercially available GNSS receivers and antennas with an INS or AHRS. The method is based on a comparison of the double differences of GNSS carrier phase measurements performed by receivers under conditions of resolved integer ambiguity and the values of the range double differences predicted using an INS. GNSS carrier phase integer ambiguity can be resolved using a strapdown inertial navigation system (SINS) or AHRS data. The mathematical model of GNSS phase difference measurements and the SINS-predicted satellite range differences model are given. The proposed algorithm calculates the moving average of the residuals between the SINS-predicted satellite range double differences and the measured GNSS carrier phase double differences. The primary criterion for spoofing detection is the specified threshold excess of the moving average of the double difference residuals. Experimental studies are performed using simulation and hardware-in-the-loop simulation. The experimental results allow us to evaluate the efficiency of the proposed approach and estimate the potential characteristics of the spoofing detection algorithm based on it.

Abstract ESA's Swarm constellation entered in a “overfly” configuration in the period between September and October 2021, when the longitudinal distance between the lower pair and the upper satellite was at its minimum since the launch of the spacecrafts. In addition, the local time of the nighttime tracks was favorable to detect and study the morphology of post‐sunset equatorial plasma bubbles (EPBs). In this study, we focus on the Swarm overfly occurring between 00:41 UT and 00:59 UT on 30 September 2021, which covered one of the most densely instrumented regions for the study of the ionospheric irregularities embedded in the EPBs: the South American sector. By exploiting the use of ground‐based receivers of Global Navigation Satellite System (GNSS) signals in combination with the Swarm plasma density measurements, we study the irregularities in the EPB formed at ∼60°W and investigate the different scales of the irregularities and the cascading processes along the magnetic flux tubes. We also highlight how diffusion along the magnetic field lines occurs simultaneously with the plasma uplift, contributing then to the correct interpretation of the EPB evolution and decay process. The precious overfly conditions also allow the introduction of ionosphere‐related quantities, evaluated across the tracks at satellite altitudes enlarging the possibilities given by the same quantities already available along the tracks. Such opportunity envisages the possibility to proxy the impact of EPBs on GNSS signals with Low‐Earth Orbit satellite data provided by future missions specifically dedicated to the characterization of the near‐Earth environment and ionospheric studies.

Rock art offers traces of our most remote past and was made with mineral and organic substances in shelters, walls, or the ceilings of caves. As it is notably fragile, it is fortunate that some instances remain intact—but a variety of natural and anthropogenic factors can lead to its disappearance. Therefore, as a valuable cultural heritage, rock art requires special conservation and protection measures. Geomatic remote-sensing technologies such as 3D terrestrial laser scanning (3DTLS), drone flight, and ground-penetrating radar (GPR) allow us to generate exhaustive documentation of caves and their environment in 2D, 2.5D, and 3D. However, only its combined use with 3D geographic information systems (GIS) lets us generate new cave maps with details such as overlying layer thickness, sinkholes, fractures, joints, and detachments that also more precisely reveal interior–exterior interconnections and gaseous exchange; i.e., the state of senescence of the karst that houses the cave. Information of this kind is of great value for the research, management, conservation, monitoring, and dissemination of cave art. [ABSTRACT FROM AUTHOR]

Navigation is often regarded as one of the most-exciting use cases for Augmented Reality (AR). Current AR Head-Mounted Displays (HMDs) are rather bulky and cumbersome to use and, therefore, do not offer a satisfactory user experience for the mass market yet. However, the latest-generation smartphones offer AR capabilities out of the box, with sometimes even pre-installed apps. Apple's framework ARKit is available on iOS devices, free to use for developers. Android similarly features a counterpart, ARCore. Both systems work well for small spatially confined applications, but lack global positional awareness. This is a direct result of one limitation in current mobile technology. Global Navigation Satellite Systems (GNSSs) are relatively inaccurate and often cannot work indoors due to the restriction of the signal to penetrate through solid objects, such as walls. In this paper, we present the Pedestrian Augmented Reality Navigator (PAReNt) iOS app as a solution to this problem. The app implements a data fusion technique to increase accuracy in global positioning and showcases AR navigation as one use case for the improved data. ARKit provides data about the smartphone's motion, which is fused with GNSS data and a Bluetooth indoor positioning system via a Kalman Filter (KF). Four different KFs with different underlying models have been implemented and independently evaluated to find the best filter. The evaluation measures the app's accuracy against a ground truth under controlled circumstances. Two main testing methods were introduced and applied to determine which KF works best. Depending on the evaluation method, this novel approach improved the accuracy by 57% (when GPS and AR were used) or 32% (when Bluetooth and AR were used) over the raw sensor data. [ABSTRACT FROM AUTHOR]

This paper presents a novel technique to estimate DCBs from GPS transmitters and receivers on-board Low Earth Orbit (LEO) satellites. The technique consists of obtaining the DCBs as residuals from the difference between the ionospheric combination of the code and the associated ionospheric delay. The ionospheric delay is computed with TOMION, a background-model-free ionospheric tomographic technique based on dual-frequency GPS carrier phase data only, and solved with a Kalman filter. Thus, DCBs are also estimated epoch-wise from the LEO Precise Orbit Determination (POD) GPS receiver as a secondary product. The results for GPS satellite DCBs, obtained exclusively from the three MetOp LEO POD GPS receivers over four consecutive weeks, are in full agreement (i.e., at the level of a few tenths of ns) with those reported independently with other techniques from hundreds of ground-based receivers exclusively, by JPL and CODE analysis centers. [ABSTRACT FROM AUTHOR]

The paper analyzes the development of strapdown inertial airborne gravimeters, which have significant advantages over gyrostabilized gravimeters in terms of size, power consumption and cost and substantially expand the capabilities of gravity survey. Technical solutions are described that make implementation of strapdown airborne gravimeters possible. The trends in their development are discussed, including integration of data from strapdown and gyrostabilized gravimeters. [ABSTRACT FROM AUTHOR]