GPS Measurements Research Articles

Design of a Lightweight Autonomous Robotic Phenotyping System for Turfgrass

High-throughput field inspection and phenotyping are among the most promising applications for agricultural robotics. We present an autonomous, lightweight robotic system for turfgrass phenotyping applications. The robot is built on two integrated bikebot platform with high-clearance and low soil compaction. To improve the motion control accuracy, an invariant extended Kalman filter is built with fusion of GPS and inertial measurement unit for outdoor localization and navigation. Multiple cameras are used for multi-modal imaging collections. Preliminary experiment results show that the localization accuracy is at the centimeter level and the path-following error is less than 0.5 m most time for various reference trajectories in the feld. The robot design and autonomous navigation demonstrates the feasibility for turfgrass inspection application.

Hazard assessment and hydrodynamic, morphodynamic, and hydrological response to Hurricane Gamma and Hurricane Delta on the northern Yucatán Peninsula

Abstract. Barrier islands in tropical regions are prone to coastal flooding and erosion during hurricane events. The Yucatán coast, characterized by karstic geology and the presence of barrier islands, was impacted by Hurricane Gamma and Hurricane Delta in October 2020. Inner shelf, coastal, and inland observations were acquired simultaneously near a coastal community (Sisal, Yucatán) located within 150 km of the hurricanes' tracks. In the study area, Gamma moved slowly and induced heavy rain, mixing in the shelf sea, and strong winds (>20 m s−1). Similar wind and wave conditions were observed during the passage of Hurricane Delta; however, a higher storm surge was measured due to wind setup and the drop (<1000 mbar) in atmospheric pressure. Beach morphology changes, based on GPS measurements conducted before and after the passage of the storms, show alongshore gradients ascribed to the presence of coastal structures and macrophyte wracks on the beach face. Urban flooding occurred mainly on the back barrier associated with heavy inland rain and the coastal aquifer's confinement, preventing rapid infiltration. Two different modeling systems, aimed at providing coastal flooding early warning and coastal hazard assessment, presented difficulties in forecasting the coastal hydrodynamic response during these seaward-traveling events, regardless of the grid resolution, which might be ascribed to a lack of terrestrial processes and uncertainties in the bathymetry and boundary conditions. Compound flooding plays an important role in this region and must be incorporated in future modeling efforts.

Return of the Atacama deep Slow Slip Event: The 5-year recurrence confirmed by continuous GPS

Four years ago, using survey GPS measurements, the first deep slow slip event (SSE) was detected in Chile (near Copiapó, Atacama region), unrelated to any major earthquake. It was located between 40 and 60 km depth on the subduction interface, lasted approximately 18 months (2014–2016.5) and reached an equivalent magnitude of Mw 6.9. The single permanent station operating in the region between 2002 and 2015 revealed that similar events had occurred at least twice before around 2006 and 2010, suggesting a 5-year repeat time. In anticipation of the next event expected for 2020, we densified the existing continuous GNSS network in the region with 5 new stations in early 2019. Here we show that the SSE occurred in 2020 as expected with the 5 year recurrence time. The event started around March 2020 and developed during 6 months, before it was perturbed by the 2020 Atacama seismic sequence that occurred nearby. During those initial 6 months, the 2020 event had the same characteristics as the 2014 SSE. It occurred in the same area and at the same depth, repeating a similar pattern of surface deformation. Before the occurrence of the nearby seismic sequence of September 2020, it had reached a third of the total amplitude of the 2014 SSE which had lasted three times longer. Whether the 2020 SSE was aborted when the nearby seismic sequence occurred or continued in the background is unknown but this will be resolved with longer times series.

Robust Map Merging Method for Collaborative LiDAR-based SLAM Using GPS Sensor

Typical lidar-based mappings need to cover the entire environment alone, which often leads to long build cycles and large computational resource requirements. Collaborative simultaneous localization and mapping have been applied to explore large and complex scenarios. However, merging local maps from multiple robots remains a challenge. It is crucial for Collaborative SLAM to identify overlapping areas and obtain the transformation matrix for map merging. To this end, this paper proposes a map merging method for collaborative lidar-based SLAM based on GPS measurements and improved Iterative Closest Point (ICP). We add a GPS sensor to the traditional robot configuration and use a simplified model to convert latitude and longitude data into plane coordinate data. According to Euclidean geometry, we determine the overlapping regions scanned by robots and calculate the initial pose transformation matrix between different robots. Based on the traditional ICP algorithm, KD-tree and normal vectors are used to register point clouds in overlapping regions accurately. The transformation matrix obtained by precise registration is used to rotate and translate the source local point cloud, so as to obtain the global point cloud map. In the real-world experiment, the initial transformation matrix is successfully obtained based on GPS measurements, which provides a good initial pose for the ICP algorithm. Compared with the ICP algorithm, the time consumption and RMSE of the improved ICP algorithm are reduced by 26.3% and 7.94%, respectively. Experimental results demonstrate that the proposed method can achieve accurate and efficient map fusion for multi-robot collaborative SLAM.

A long-term charge/discharge cycle at Mt. Etna volcano revealed through absolute gravity and GPS measurements

We present results of repeated absolute gravity and GPS measurements, carried out at Mt. Etna volcano between 2009 and 2018. Absolute gravity measurements are rarely performed along arrays of stations on active volcanoes and, through our unprecedented dataset, we highlight the possibilities of this method to track underground mass changes over long time-scales. Analysis of the residual absolute gravity data and ground deformation reveals a cycle of gravity increase and uplift during 2009 to 2011, followed by gravity decrease and subsidence during 2011 to 2014. Data inversion points to a common mass and pressure source, lying beneath the summit area of the volcano, at depth of ~ 5 km b.s.l. The bulk volume change inferred by the inversion of the deformation data can account for only a small portion of the mass change needed to explain the correspondent gravity variations. We propose that the observed relationship between gravity and vertical deformation was mostly due to the compressibility of the magma in the inferred reservoir, which, in turn, was enhanced by the presence of exsolved gas. Overall, the gravity and deformation data we present reveal a cycle of magma recharge (2009–2011) and discharge (2011–2014) to/from the inferred storage zone. During the recharge phase only degassing occurred from the summit craters of Mt. Etna. During the following phase of discharge, the magma lost from the reservoir at ~ 5 km b.s.l. fed the exceptional phase of volcanic activity during 2011–2014, when tens of lava fountaining episodes took place.

Cloud-Assisted Collaborative Road Information Discovery With Gaussian Process: Application to Road Profile Estimation

There is an increasing popularity in exploiting modern vehicles as mobile sensors to obtain important road information such as potholes, black ice and road profile. Availability of such information has been identified as a key enabler for next-generation vehicles with enhanced safety, efficiency, and comfort. However, existing road information discovery approaches have been predominately performed in a single-vehicle setting, which is inevitably susceptible to vehicle model uncertainty and measurement errors. To overcome these limitations, this paper presents a novel cloud-assisted collaborative estimation framework that can utilize multiple heterogeneous vehicles to iteratively enhance estimation performance. Specifically, each vehicle combines its onboard measurements with a cloud-based Gaussian process (GP), crowdsourced from prior participating vehicles as “pseudo-measurements”, into a local estimator to refine the estimation. The resultant local onboard estimation is then sent back to the cloud to update the GP, where we utilize a noisy input GP (NIGP) method to explicitly handle uncertain GPS measurements. We employ the proposed framework to the application of collaborative road profile estimation. Promising results on extensive simulations and hardware-in-the-loop experiments show that the proposed collaborative estimation can significantly enhance estimation and iteratively improve the performance from vehicle to vehicle, despite vehicle heterogeneity, model uncertainty, and measurement noises.

Spatially varying crustal stress along the Zagros seismic belt inferred from earthquake focal mechanisms

We determine the stress field of the Zagros fold-and-thrust belt (ZFTB) in the collisional zone between the Arabian and Iranian plates. Using 898 mainshock focal mechanisms, which occurred along the belt between 1956 and 2021, we calculate stress at 32 locations. The results reveal that the crustal stress in the Zagros belt is heterogeneous with variations in the orientation of SHmax as well as in the stress ratio. The interpolation of the Simpson's index Aϕ points to three distinct domains: northern, central and southern, which are characterized by wrench, compressional, and wrench-compressional to compressional tectonic regimes, respectively. Tectonic stress in the study area is characterized by a horizontal to sub-horizontal maximum compression axis in the ∼NE-SW to ∼NNW-SSE direction. The GPS measurements of the strain tensor and the SHmax direction inferred from the stress inversion indicate that both the deformation pattern and the seismicity along the ZFTB zone are primarily affected by convergence of the Arabian and Iranian plates.

Elastic interaction between Mauna Loa and Kīlauea evidenced by independent component analysis

The contrasting dynamics between Mauna Loa and Kīlauea have been studied over the last 100 years from multiple viewpoints. The fact that dynamic changes of one volcano trigger a dynamic response of the other volcano indicates a connection may exist. Petrological works show a direct relationship between the magmatic systems of these two volcanoes is not possible. We analysed DInSAR data and GPS measurements of ground deformation patterns associated with the activity of Mauna Loa and Kīlauea volcanoes. The DInSAR SBAS dataset spans the interval between 2003 and 2010, and was acquired along ascending and descending orbits of the ENVISAT (ESA) satellite under different look angles. Of the 10 tracks that cover the Big Island (Hawai‘i), 4 cover both volcanic edifices. Using GPS measurements, we computed the areal strain on 15 triplets of stations for Kīlauea volcano and 11 for Mauna Loa volcano. DInSAR data was analysed by applying Independent Component Analysis (ICA) to decompose the time-varying ground deformation pattern of both volcanoes. The results revealed anticorrelated ground deformation behaviour of the main calderas of Mauna Loa and Kīlauea, meaning that the opposite response is seen in the ground deformation of one volcano with respect to the other. At the same time, Kīlauea exhibits a more complex pattern, with an additional component, which appears not to be correlated with the dynamics of Mauna Loa. The GPS areal strain time series support these findings. To corroborate and help interpret the results, we performed inverse modelling of the observed ground deformation pattern using analytical source models. The results indicate that the ground deformation of Mauna Loa is associated with a dike-shaped source located at 6.2 km depth. In comparison, the anticorrelated ground deformation of Kīlauea is associated with a volumetric source at 1.2 km depth. This excludes a hydraulic connection as a possible mechanism to explain the anticorrelated behaviour; instead, we postulate a stress-transfer mechanism. To support this hypothesis, we performed a 3D numerical modelling of stress and strain fields in the study area, determining the elastic interaction of each source over the others. The most relevant finding is that the Mauna Loa shallow plumbing system can affect the shallowest magmatic reservoir of Kīlauea, while the opposite scenario is unlikely. Conversely, the second independent component observed at Kīlauea is associated to a sill-shaped source located at a depth of 3.5 km, which is less affected by this interaction process.

High-resolution bathymetries and shorelines for the Great Lakes of the White Nile basin

HRBS-GLWNB 2020 presents the first open-source and high-resolution bathymetry, shoreline, and water level data for Lakes Victoria, Albert, Edward, and George in East Africa. For each Lake, these data have three primary products collected for this project. The bathymetric datasets were created from approximately 18 million acoustic soundings. Over 8,200 km of shorelines are delineated across the three lakes from high-resolution satellite systems and uncrewed aerial vehicles. Finally, these data are tied together by creating lake surface elevation models collected from GPS and altimeter measures. The data repository includes additional derived products, including surface areas, water volumes, shoreline lengths, lake elevation levels, and geodetic information. These data can be used to make allocation decisions regarding the freshwater resources within Africa, manage food resources on which many tens of millions of people rely, and help preserve the region’s endemic biodiversity. Finally, as these data are tied to globally consistent geodetic models, they can be used in future global and regional climate change models.

Present-day fault kinematic around the eastern Himalayan Syntaxis and probable viscoelastic relaxation perturbation following the 1950 Mw 8.7 Assam earthquake

Strike-slip and tensile/dip-slip rates around the EHS region from the elastic block model. • An elastic block model was constructed to analyze the fault slip rates and regional kinematic around the Eastern Himalayan Syntaxis (EHS). • The postseismic viscoelastic relaxation effects caused by the 1950 Assam Mw 8.7 earthquake is still significant even after 65 years. • The interseismic slip rate across the eastern Himalaya derived from pure elastic solution may be overestimated if ignoring the viscoelastic relaxation effects. The Eastern Himalayan Syntaxis (EHS) played important role in accommodating the intracontinental deformation and material flow in southeastern Tibet. Quantifying the regional kinematics around the EHS is critical for understanding the deformation mechanism of the Tibetan Plateau. In this study, we compiled all available GPS measurements and constructed an elastic block model to analyze the fault kinematics around the EHS. The results suggest that the deformation characteristics around the EHS can be well explained by a linear spherical block model that considers the intra-block homogeneous strain. The fault slip rates from the block model agree well with the late Quaternary slip rates, suggesting that the GPS-derived slip rates can generally represent the long-term slip rates. However, some relatively large residuals, especially in the frontal EHS region, are still detectable, suggesting that various other factors, such as the postseismic viscoelastic relaxation, may also influence the deformation. We simulated the postseismic viscoelastic relaxation deformation caused by the 1950 Mw 8.7 Assam earthquake endured as the largest intracontinental earthquake ever recorded. The results indicate significant postseismic viscoelastic deformation due to the Assam earthquake even after 65 years. The interseismic convergence rates across the Mishmi thrust and the Arunachal Himalaya derived from pure elastic solution may be overestimated if ignoring the viscoelastic relaxation effects. The spatial variations of convergence rates across the central and eastern Himalayas could be partly related to the transient deformation following great Himalayan earthquakes.

Seasonal heavy precipitation sensitivity to moisture corrections in the western Mediterranean across resolutions

The controlling role of atmospheric water vapour for heavy precipitation leading to extreme events has been widely demonstrated, along with the existing gap of adequate moisture observations and the frequent biases present in model simulations concerning this fundamental variable. In this study, we profit from a state-of-the-art dense network of GPS measurements over Europe retrieving a homogenized GPS-derived Zenith Total Delay (GPS-ZTD) data set up to 10 min of temporal resolution, to assess the seasonal sensitivity of convection-related processes and heavy precipitation modelling to atmospheric humidity corrections. For this purpose, we perform nudging experiments with the COSMO-CLM model at two spatial resolutions, 7 km (parameterized convection) and 2.8 km (explicitly resolved convection) covering the autumn period of 2012, when the Special Observation Period (SOP) 1 of the Hydrological Cycle in the Mediterranean Experiment (HyMeX) program took place in the Western Mediterranean, which is our area of interest.The benefits and disadvantages of GPS-ZTD nudging and resulting moisture corrections are disentangled. The impact on high-resolution parameterized versus convection-permitting simulations is compared. A process-understanding methodology and a local-to-regional approach are used. Our results show a beneficial impact on the seasonal scale at both model grid spacings improving the representation of the chain of processes leading to heavy precipitation, contrary to the non-systematic improvement at the event and sub-event scales. The correction of atmospheric moisture entails a reduction of about 10% in the total column water vapour and corrections on single locations up to 10 mm counteracting the model wet bias across scales. The location, structure, and amount of total precipitation are positively affected. Particularly, the combination of high-resolution atmospheric humidity observations and fine convection-permitting simulations shows great potential for correction of the precipitation daily cycle, key for accurate precipitation modelling. The difference in the density of local and upstream observational networks and the lack of information on the vertical stratification of moisture are identified weaknesses, which could be determinants in obtaining more accurate corrections on seasonal to sub-seasonal scales after assimilation strategies.

Variations of distance and accelerometry-based GPS measures and their influence on body composition in professional women soccer players

External intensity quantification and body composition assessments across the season allow soccer coaches to adjust the intensity during training sessions, thereby avoiding excessive fatigue and helping players maximize their physical fitness status during matches. Thus, the aims of this study were (1) to describe variations in external intensity periods of distance and accelerometry-based measures across the early and mid-competitive phases and (2) to analyze whether the intensity variations influenced body composition across the 2019/20 competitive season. Ten players from a Portuguese BPI Ligue team (professional league) participated in this study. The participants completed ≥80% of 57 training sessions and 13 matches. The athletes were assessed in three phases (before the start of the season, after 2 months, and after 4 months) for the following variables: body fat mass, soft lean mass, fat-free mass, intracellular water, extracellular water, total body water, and phase angle (50 kHz) through bioelectrical impedance analysis (InBody S10). A 10-Hz GPS device (PlayerTek) was used to collect distance and accelerometry-based measures, which included total distance, high-speed running distance, sprint distance, acceleration, deceleration, and player load. Repeated-measures analysis of covariance (ANCOVA) with GPS-derived measures as covariates or repeated-measures analysis of variance (ANOVA) was used to compare the three moments of assessment. Although the patterns of variables’ responses were not the same as the season progressed, the values of body fat mass, fat-free mass, intracellular water, extracellular water, total body water, ratios of ECW/TBW, ECW/ICW, and phase angle improved. Variations in external intensity measures seem to influence the body composition variables across the season. These results may indicate good adaptations to the training and conditioning strategies managed by the coach and technical staff.

Current motion and deformation of the Nazca Plate: new constraints from GPS measurements

SUMMARYWe use new GPS data to determine an updated Euler pole describing the present-day motion of the oceanic Nazca Plate. Our solution includes continuous GPS (cGPS) measurements at Malpelo Island offshore Colombia, two sites in the Galapagos archipelago, Easter Island and Salas y Gomez Island in the western part of the plate and Robinson Crusoe Island offshore Chile. A careful analysis of geodetic time-series reveals that (1) previous estimates using former cGPS site EISL are biased by several millimetres per year eastward due to station malfunctioning (2) north velocity component of cGPS site GLPS at Santa Cruz Island in the Galapagos is impacted by volcanic deformation at the 1–2 mm yr–1 level, probably caused by the recurrent volcanic activity of the Sierra Negra volcano. In addition, we find shortening at ∼1 mm yr–1 between Easter Island (cGPS ISPA) and Salas y Gomez Island (cGPS ILSG), consistent with the elastic deformation induced by rapid opening at the East Pacific rise. cGPS site at Robinson Crusoe Island shows ∼4–5 mm yr–1 abnormally fast East velocity induced by the visco-elastic relaxation following the Maule Mw 8.8 2010 earthquake. Using this information, we determine a new Euler pole (longitude: –90.93°E, latitude 56.19°N, 0.588 deg Myr–1) describing the present-day Nazca–South America Plate motion, using five sites (Malpelo Island, two sites in the Galapagos archipelago, Easter Island and Salas y Gomez Island). The proposed Euler pole provides a weighted root mean square (wrms) of residual velocities of 0.6 mm yr–1, slightly higher than usually observed for other major tectonic plates and accounting for the uncertainty of potential volcanic–tectonic deformation. Our model predicts a maximum convergence rate at 65.5 ± 0.8 mm yr–1 at latitude ∼30°S along the Chile trench, decreasing to 50.8 ± 0.7 mm yr–1 in northern Colombia and 64.5 ± 0.9 mm yr–1 in southern Chile (1σ confidence level). Comparison with the geological models NUVEL1A and MORVEL indicates constant decrease since 3.16 Ma of opening rate along the Nazca–Antarctic Plate boundary spreading centres at ∼1 cm yr–1 per Myr. Combined with the ITRF2014 pole for the Pacific and Antarctic plates, our derived Euler pole predicts closure at the ∼1 mm yr–1 level for Pacific–Antarctic–Nazca Plate circuit. However, combining our results with MORVEL estimates for the Cocos Plate, the non-closure of the Pacific–Cocos–Nazca Plate circuit is 9.7 ± 1.6 mm yr–1, 30 per cent lower than the 14 ± 5 mm yr–1 reported in MORVEL model, but still significant. A small (∼1.5 mm yr–1) velocity residual at Malpelo Island neither supports the hypothesis of an independent Malpelo microplate offshore Colombia nor large scale internal deformation induced by thermal contraction. Our solution rather suggests that non-closure of the Pacific–Cocos–Nazca Plate circuit arises from the determination of the Cocos Plate motion in MORVEL, an hypothesis further supported by the large discrepancy between MORVEL’s prediction and the observed GPS velocity observed at Cocos Islands (cGPS ISCO).

Development Status and Service Performance Preliminary Analysis for BDSBAS

The BeiDou global navigation satellite system (BDS-3) provides positioning, navigation and timing services for global users, moreover, it provides BDS satellite-based augmentation system (BDSBAS) single-frequency (SF) and dual-frequency multi-constellation (DFMC) services for users in China and its surrounding areas. The BDSBAS SF service is in accordance with Radio Technical Commission for Aeronautics (RTCA) standard protocol (RTCA MOPS) and augment GPS constellation, while the BDSBAS DFMC service is in line with SBAS L5 DFMC standard protocol and is aimed at supporting any combination of BDS/GPS/Galileo/GLONASS constellations, including only a single constellation operation. We introduced the development status of the BDSBAS system, including the system architecture and navigation user algorithms. Based on the GPS measurements, the accuracy, integrity and availability of the BDSBAS SF service were evaluated, and with the BDS measurements, the accuracy of the BDSBAS DFMC service was preliminarily analyzed. The integrity and availability of the BDSBAS DFMC service will be discussed in future work as some of the DFMC integrity parameters are still under discussion for optimization. The results show that, for BDSBAS SF service, the horizontal and vertical position accuracy were about 1.0 m and 2.0 m (95%), respectively, which were improved by 39% and 33%, respectively, compared with the GPS SF position accuracy. For BDSBAS DFMC service, the horizontal and vertical position accuracy were about 0.6 m and 1.2 m (95%), respectively, which were improved by about 25% and 20% compared with the BDS dual-frequency position accuracy. No system integrity risk event was detected during the testing period for BDSBAS SF service. The average availability of the BDSBAS SF service was about 98% which was mainly affected by the availability of ionospheric grid delay corrections.

Patch-Like Reduction (PLR): A SAR Offset Tracking amplitude filter for deformation monitoring

As complementary to Synthetic Aperture Radar (SAR) Differential Interferometry (DInSAR), SAR Offset Tracking (OT) is an efficient tool for large ground deformation monitoring in situations when DInSAR cannot work. However, SAR images are affected by speckle noise and some strong point-like scatters which can cause what is known as Patch Like (PL), a kind of errors that can be seen as homogeneous patches of almost constant deformation in the results. These errors are clearly visible in the results as non-consistent deformations along time, but they are difficult to detect with the traditional metrics that evaluate the cross-correlation results, like the Signal to Noise Ratio (SNR). This paper addresses this problem and proposes a simple amplitude filter to reduce PL named as Patch Like Reduction (PLR). The main idea is to find a sensor and scene independent threshold to remove the high amplitude pixels prone to cause PL. Five different SAR data sets and in-field GPS measurements are used to determine the optimal threshold and evaluate the performance of the proposed method. The results show that PL effects can be reduced with the proposed amplitude filter. The processing parameters of the improved OT processing chain are optimized as well to preserve the results resolution as much as possible. • The causes of Patch Like errors in Offset Tracking results have been investigated. • An amplitude filter (PLR) has been proposed to reduce PLs. • The filter threshold is automatically defined from images amplitude distributions. • The filter improves OT results by reducing the changes of PL appearance. • Template sizes and tapering windows have been optimized in terms of resolution.

Small baselines techniques of time series InSAR to monitor and predict land subsidence causing flood vulnerability in Sidoarjo, Indonesia

Floods are the most common sort of natural disaster that occurs when a body of water overflows and submerges on dry terrain. Several regions in Sidoarjo District, East Java such as Kedungbanteng and Banjarasri Village, have experienced floods with varying heights since 2018 due to heavy rainfall in the areas. According to the Meteorological, Climatological, and Geophysical Agency (BMKG), rainfall intensity in these areas reach 100 mm/day. Furthermore, the physical environment in both areas shows land subsidence that causes a change in the flow pattern, which triggers its occurrence. This research incorporated different small baseline techniques of InSAR time series analysis and used GPS measurement to evaluate and monitor the land subsidence in both areas. The reseachers used Sentinel-1 SAR data both from ascending and descending for the period between 2017 and 2021. The results showed significant subsidence value by up to −200 mm/year both in Kedungbanteng and Banjarasri Village, and GPS observation also confirmed approximately −3.2 cm of subsidence value during 2 months of sampling observations. Using the neural network analysis, the reseachers predicted the time series displacement for one year and showed that a continuous trend of deformation still existed.

Low-Cost Attitude Estimation Using GPS/IMU Fusion Aided by Land Vehicle Model Constraints and Gravity-Based Angles

This paper details a method to improve accuracy of the land vehicle attitude estimation. It employs the vehicle model constraints to enhance the integration of GPS and a low-cost MEMS inertial measurement unit (MIMU) (GPS/MIMU). To improve the yaw angle estimation, we propose a lateral velocity constraint (LVC) aided method based on the observability analysis for the integrated fusion system. The theoretical analysis indicates that the yaw angle will be directly observed if LVC is augmented into the GPS/MIMU fusion algorithm. Furthermore, for LVC/MIMU system without GPS, the roll angle is always well estimated regardless of whether the vehicle is moving or stationary, and, surprisingly, the pitch angle can also be relatively accurately estimated if the vehicle is moving. Thus, when GPS is unavailable, the LVC/MIMU fusion is proposed by replacing the GPS measurement with the virtual measurement LVC. It is an encouraging improvement since the accumulating errors induced by gyro bias can be suppressed using MIMU alone. Moreover, to overcome the shortage that the pitch angle is not observed if the vehicle is stationary, we propose to fuse the gyros with gravity-based angles by Kalman filtering if the vehicle is detected motionless based on a switching rule. The experimental results compare favorably to theoretical analysis, showing that the proposed method can effectively improve the accuracy for land vehicle attitude estimation.

Importance of continuous monitoring GPS permanent station at Multi-Parametric Geophysical Observatory (MPGO), IMPHAL, Manipur (India)

GPS measurements are precise enough to allow a determination of tectonic motion within a few years. This can be made using a network of permanent stations, dynamically defined, using an inertial reference frame that moves with the geo-center. Comparing the position of these points over time, it’s possible to compute the velocity and direction of the plate motion. The goal of this work is to describe the hypothetical tectonic motion using a network of GPS permanent stations located approximately in the center of Imphal Valley. We report data processing results of GPS measurements of crustal deformation at Imphal, Manipur. The results suggest that the site of Imphal valley is not located on the Indian plate. The site is actually located on the Burma plate. Keywords: GPS, Crustal deformation, Imphal Valley, MPGO.

An investigation of a new artificial neural network-based TEC model using ground-based GPS and COSMIC-2 measurements over low latitudes

Mapping the ionosphere over low-latitude regions with a high accuracy is a challenging task due to the complex nature of the ionospheric structure. In this study, the artificial neural network (ANN) technique was used to investigate the determination of the total electron content (TEC) in low latitude regions using measurements from 187 ground-based International global navigation satellite system (GNSS) Service (IGS) stations and the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC-2) mission in the period from 1 October 2019 to 30 September 2021. To reduce the systematic discrepancies between the space-borne and ground-based observational systems, the ANN technique was also utilized to calibrate the COSMIC-2 derived TECs to the ground level. The RMSE of the calibrated COSMIC-2 TECs was 1.78 TECU. This, in comparison with the RMSE value of 4.10 TECU for the uncalibrated COSMIC-2 TECs, demonstrated 57% improvement. It is found that the performance of the new model was strongly associated with the value of TEC and low-latitude ionospheric structure, such as the equatorial ionization anomaly (EIA). Compared with the IRI-2016 model, the Technical University of Catalonia (UPC) rapid global ionospheric maps (GIMs) (UQRG), the Center for Orbit Determination in Europe (CODE) final GIMs (CODG), and the Chinese Academy of Sciences (CAS) final GIMs (CASG), the new model outperformed the IRI-2016 model and was competitive with the GIMs. All results suggest that the new model developed using both ground-based and space-borne measurements together with the ANN technique can model the ionospheric structure, such as the EIA. Therefore, the new model developed may become a good reference for the studies of the structure and variation of the ionosphere over low latitudes.

Validating ATLAS: A regional‐scale high‐throughput tracking system

Abstract Fine‐scale tracking of animal movement is important to understand the proximate mechanisms of animal behaviour. The reverse‐GPS system—ATLAS—uses inexpensive (~€25), lightweight (<1 g) and low‐power (~0.4 mJ/transmission) tags. Six systems are now operational worldwide and have successfully tracked over 50 species in various landscape types. The growing use of ATLAS to track animal movement motivates further refinement of best‐practice application and an assessment of its accuracy. Here, we test the accuracy and precision of the largest ATLAS system, located in the Dutch Wadden Sea, using concurrent GPS measurements as a reference. This large‐scale ATLAS system consists of 26 receivers and covers 1,326 km2 of intertidal region, with almost no physical obstacles for radio signals, providing a useful baseline for other systems. We compared ATLAS and GPS location estimates for a route (mobile test) and 16 fixed locations (stationary test) on the Griend mudflat. Precision was estimated using standard deviation during the stationary tests. We also give examples of tracked red knots Calidris canutus islandica to illustrate the use of the system in tracking small shorebirds (~120 g). ATLAS‐derived location estimates differed from GPS by a median of 4.2 m (stationary test) and 5.7 m (mobile test). Signals that were collected by more receiver stations were more accurate, although even three‐receiver localisations were comparable with GPS localisations (~10 m difference). Receivers that detected 90% of the 1 Hz transmissions from our test tag were within 5 km of their furthest detection but height of both receiver and tag seemed to influence detection distance. The test tag (1 Hz) had a fix rate of >90% at 15 of 16 stationary sites. Tags on birds (1/6 Hz) on the Griend mudflat had a mean fix rate of 51%, yielding an average sampling rate of 0.085 Hz. Fix rates were higher in more central parts of the receiver array. ATLAS provides accurate, regional‐scale tracking with which hundreds of relatively small‐bodied species can be tracked simultaneously for long periods of time. Future ATLAS users should consider the height of receivers, their spatial arrangement, density and the movement modes of their study species (e.g. ground‐dwelling or flying).