A cycle slip fixing method with GPS + GLONASS observations in real-time kinematic PPP

A key limitation of precise point positioning (PPP) is the long convergence time, which requires about 30 min under normal conditions. Frequent cycle slips or data gaps in real-time operation force repeated re-convergence. Repairing cycle slips with GPS data alone in severely blocked environments is difficult. Adding GLONASS data can supply redundant observations, but adds the difficulty of having to deal with differing wavelengths. We propose a single-difference between epoch (SDBE) method to integrate GPS and GLONASS for cycle slip fixing. The inter-system bias can be eliminated by SDBE, thus only one receiver clock parameter is needed for both systems. The inter-frequency bias of GLONASS satellites also cancels in the SDBE, so cycle slips are preserved as integers, and the LAMBDA method is adopted to search for cycle slips. Data from 7 days of 20 globally distributed IGS sites were selected to test the proposed cycle slip fixing procedure with artificial blocking of the signal; cycle slips were introduced for all un-blocked satellites at each epoch. For a 30-s sampling interval, the average success rate of fixing can be improved from 73 to 98 % by adding GLONASS. Even for a 180-s sampling interval, GPS + GLONASS can achieve a success rate of 81 %. A real-time kinematic PPP experiment was also performed, and the results show that using GPS + GLONASS can achieve continuous high-accuracy real-time PPP without re-convergence.     

Floor positioning method indoors with smartphone’s barometer

ABSTRACT

This paper presents an indoor floor positioning method with the smartphone’s barometer for the purpose of solving the problem of low availability and high environmental dependence of the traditional floor positioning technology. First, an initial floor position algorithm with the “entering” detection algorithm has been obtained. Second, the user’s going upstairs or downstairs activities are identified by the characteristics of the air pressure fluctuation. Third, the moving distance in the vertical direction and the floor change during going upstairs or downstairs are estimated to obtain the accurate floor position. In order to solve the problem of the floor misjudgment from different mobile phone’s barometers, this paper calculates the pressure data from the different cell phones, and effectively reduce the errors of the air pressure estimating the elevation which is caused by the heterogeneity of the mobile phones. The experiment results show that the average correct rate of the floor identification is more than 85% for three types of the cell phones while reducing environmental dependence and improving availability. Further, this paper compares and analyzes the three common floor location methods – the WLAN Floor Location (WFL) method based on the fingerprint, the Neural Network Floor Location (NFL) methods, and the Magnetic Floor Location (MFL) method with our method. The experiment results achieve 94.2% correct rate of the floor identification with Huawei mate10 Pro mobile phone.     

Improvement of GPS/acoustic seafloor positioning precision through controlling the ship’s track line

The precision of GPS/acoustic seafloor positioning was improved by introducing a hull-mounted onboard system in March 2008, which allows us to conduct acoustic ranging measurements with the vessel sailing along the pre-determined track lines, while the early system before 2008 could only adopt the uncontrollable drifting observation. The continuity of the positioning results due to the transition was first confirmed through the comparison between results from sailing and drifting observations conducted in parallel. Using the data acquired for about 3 years since 2008, the repeatability of the determined position for the sailing observation was evaluated to be about 2 cm in root mean squares in the horizontal component, significantly better than that for the early drifting observation. The improvement of positioning precision probably resulted from the improvement of geometric distribution of acoustic ranging data by controlling the track lines. It was also shown that the sailing observation allows to obtain reliable results with a smaller amount of data. Comparison between the results in different sea regions suggests that positioning precision is better in the region along the Nankai Trough than in the region along the Japan Trench, probably because of the complicated acoustic velocity structure of seawater often observed in the latter. Furthermore, the precision of height determination was also improved, which leads us to expect that vertical crustal movement will be detectable in the future through accumulation of data as well as further technology development.     

Assessment of GPS + Galileo and multi-frequency Galileo single-epoch precise positioning with network corrections

Several processing strategies that use dual-frequency GPS-only solution, multi-frequency Galileo-only solution, and finally tightly combined dual-frequency GPS + Galileo solution were tested and analyzed for their applicability to single-epoch long-range precise positioning. In particular, a multi-system GPS + Galileo solution was compared to GPS double-frequency solution as well as to Galileo double-, triple-, and quadruple-frequency solutions. Also, the performance of the strategies was analyzed under clear-sky and obstructed satellite visibility in both single-baseline and multi-baseline modes. The results indicate that tightly combined GPS + Galileo instantaneous positioning has a clear advantage over single-system solutions and provides an accurate and reliable solution. It was also confirmed that application of multi-frequency observations in case of Galileo system has an advantage over a dual-frequency solution.     

Computation of GPS P1–P2 Differential Code Biases with JASON-2

GPS Differential Code Biases (DCBs) computation is usually based on ground networks of permanent stations. The drawback of the classical methods is the need for the ionospheric delay so that any error in this quantity will map into the solution. Nowadays, many low-orbiting satellites are equipped with GPS receivers which are initially used for precise orbitography. Considering spacecrafts at an altitude above the ionosphere, the ionized contribution comes from the plasmasphere, which is less variable in time and space. Based on GPS data collected onboard JASON-2 spacecraft, we present a methodology which computes in the same adjustment the satellite and receiver DCBs in addition to the plasmaspheric vertical total electron content (VTEC) above the satellite, the average satellite bias being set to zero. Results show that GPS satellite DCB solutions are very close to those of the IGS analysis centers using ground measurements. However, the receiver DCB and VTEC are closely correlated, and their value remains sensitive to the choice of the plasmaspheric parametrization.     

Spatiotemporal filtering of regional GNSS network’s position time series with missing data using principle component analysis

The existing spatiotemporal analysis methods suppose that the involved time series are complete and have the same data interval. However missing data inevitably occur in the position time series of Global Navigation Satellite Systems networks for many reasons. In this paper, we develop a modified principal component analysis to extract the Common Mode Error (CME) from the incomplete position time series. The principle of the proposed method is that a time series can be reproduced from its principle components. The method is equivalent to the method of Dong et al. (J Geophys Res 111:3405–3421, 2006) in case of no missing data in the time series and to the extended ‘stacking’ approach under the assumption of a uniformly spatial response. The new method is first applied to extract the CME from the position time series of the Crustal Movement Observation Network of China (CMONOC) over the period of 1999–2009 where the missing data occur in all stations with the different gaps. The results show that the CMEs are significant in CMONOC. The size of the first principle components for the North, East and Up coordinates are as large as 40, 41 and 37 % of total principle components and their spatial responses are not uniform. The minimum amplitudes of the first eigenvectors are only 41, 15 and 29 % for the North, East and Up coordinate components, respectively. The extracted CMEs of our method are close to the data filling method, and the Root Mean Squared error (RMS) values computed from the differences of maximum CMEs between two methods are only 0.31, 0.52 and 1.55 mm for North, East and Up coordinates, respectively. The RMS of the position time series is greatly reduced after filtering out the CMEs. The accuracies of the reconstructed missing data using the two methods are also comparable. To further comprehensively test the efficiency of our method, the repeated experiments are then carried out by randomly deleting different percentages of data at some stations. The results show that the CMEs can be extracted with high accuracy at the non missing-data epochs. And at the missing-data epochs, the accuracy of extracted CMEs has a strong dependence on the number of stations with missing data.     

Correction on Effect of Earth’s Oblateness in Inversion of GPS Occultation Data

IntroductionRadio occultation technique was firstly appliedin the astronomic research in the 18th century .It has developed greatly by the scientists in JetPropulsion Laboratory (JPL) and Stanford Uni-versity since the 1960’s and widely usedin manymissions for planets exploration, which providedus with i mportant information about the at mos-phere of these planets[1]. In 1965 , it wasbrought forward by Fischbach that this tech-nique can be used in the research of the Earth’sat mosphere[2…     

Correction on effect of Earth’s oblateness in inversion of GPS occultation data

By using observed CHAMP orbit ephemeredes and MSISE-90 dry air model and regarding the earth as a sphere and an ellipsoid respectively, phase delays are simulated and the simulated data are retrieved under different schemes. The comparison between the inverted temperature profiles and the model temperature profiles shows that by inverting observed data, we will get temperature results with large errors if the effect of Earth’s oblateness is omitted. The correction method is proved to be effective because the temperature errors decreased obviously with this method.     

Signal, orbit and attitude analysis of Japan’s first QZSS satellite Michibiki

Results are presented for Michibiki, the first satellite of Japan’s Quasi-Zenith Satellite System. Measurements for the analysis have been collected with five GNSS tracking stations in the service area of QZSS, which track five of the six signals transmitted by the satellite. The analysis discusses the carrier-to-noise density ratio as measured by the receiver for the different signals. Pseudorange noise and multipath are evaluated with dual-frequency and triple-frequency combinations. QZSS uses two separate antennas for signal transmission, which allows the determination of the yaw orientation of the spacecraft. Yaw angle estimation results for an attitude mode switch from yaw-steering to orbit-normal orientation are presented. Estimates of differential code biases between QZSS and GPS observations are shown in the analysis of the orbit determination results for Michibiki. The estimated orbits are compared with the broadcast ephemerides, and their accuracy is assessed with overlap comparisons.     

CODE’s five-system orbit and clock solution—the challenges of multi-GNSS data analysis

This article describes the processing strategy and the validation results of CODE’s MGEX (COM) orbit and satellite clock solution, including the satellite systems GPS, GLONASS, Galileo, BeiDou, and QZSS. The validation with orbit misclosures and SLR residuals shows that the orbits of the new systems Galileo, BeiDou, and QZSS are affected by modelling deficiencies with impact on the orbit scale (e.g., antenna calibration, Earth albedo, and transmitter antenna thrust). Another weakness is the attitude and solar radiation pressure (SRP) modelling of satellites moving in the orbit normal mode—which is not yet correctly considered in the COM solution. Due to these issues, we consider the current state COM solution as preliminary. We, however, use the long-time series of COM products for identifying the challenges and for the assessment of model-improvements. The latter is demonstrated on the example of the solar radiation pressure (SRP) model, which has been replaced by a more generalized model. The SLR validation shows that the new SRP model significantly improves the orbit determination of Galileo and QZSS satellites at times when the satellite’s attitude is maintained by yaw-steering. The impact of this orbit improvement is also visible in the estimated satellite clocks—demonstrating the potential use of the new generation satellite clocks for orbit validation. Finally, we point out further challenges and open issues affecting multi-GNSS data processing that deserves dedicated studies.     

Discriminating lava flows of different age within Nyamuragira’s volcanic field using spectral mixture analysis

In this study, linear spectral mixture analysis (LSMA) is used to characterize the spectral heterogeneity of lava flows from Nyamuragira volcano, Democratic Republic of Congo, where vegetation and lava are the two main land covers. In order to estimate fractions of vegetation and lava through satellite remote sensing, we made use of 30 m resolution Landsat Enhanced Thematic Mapper Plus (ETM+) and Advanced Land Imager (ALI) imagery. 2 m Pleiades data was used for validation. From the results, we conclude that (1) LSMA is capable of characterizing volcanic fields and discriminating between different types of lava surfaces; (2) three lava endmembers can be identified as lava of old, intermediate and young age, corresponding to different stages in lichen growth and chemical weathering; (3) a strong relationship is observed between vegetation fraction and lava age, where vegetation at Nyamuragira starts to significantly colonize lava flows ∼15 years after eruption and occupies over 50% of the lava surfaces ∼40 years after eruption. Our study demonstrates the capability of spectral unmixing to characterize lava surfaces and vegetation colonization over time, which is particularly useful for poorly known volcanoes or those not accessible for physical or political reasons.     

Exploring the spatiotemporal behavior of Helsinki’s housing prices with fractal geometry and co-integration

Fractal geometry and co-integration are combined for exploring spatial morphological aspects of quarterly dwelling prices in Helsinki’s region from 1977 to 2011. Curves of fractal scaling behavior are first employed to measure the fractal dimensions of high- and low-price/m² spatial clusters at multiple scales. Subsequently, the fractal dimensions at indicative neighborhood and citywide scales are modeled with vector error correction specifications. The results identify long-run joint equilibria between the fractal geometries of high- and low-price/m² clusters at both spatial scales. High-price/m² clusters exhibit consistently higher fractal dimensions than their low-value counterparts at the neighborhood scale, while this long-run relation is reversed at the citywide scale. Short-run disequilibria and subsequent adjustments are also scale sensitive. The fractal geometry of high-price/m² clusters leads the dynamics at the neighborhood scale, while low-price/m² clusters lead at the citywide scale. The system’s responses to exogenous shocks take longer time to stabilize at the neighborhood scale compared to the citywide scale, but in both scales the non-stationary nature of fractal behavior is evident. These elements indicate that a closer look on spatial economic behavior at more than one spatial and temporal scale at a time can reveal non-trivial information in the context of urban research and policy analysis.     

‘I’ve got my Sat Nav,it’s alright’: Users’ Attitudes towards,and Engagements with,Technologies of Navigation

The use of qualitative research techniques in a largely quantitative cartographic domain is opening up myriad ways to explore users’ engagements technologies of navigation. This study draws on young UK-based students’ real words and life experiences as they engage with Satellite Navigation and other wayfinding technologies during first-time visits to new places to reflect on the nature of the changing relationships between self, navigational object, space and place.     

Secular changes in Earth’s shape and surface mass loading derived from combinations of reprocessed global GPS networks

The changing distribution of surface mass (oceans, atmospheric pressure, continental water storage, groundwater, lakes, snow and ice) causes detectable changes in the shape of the solid Earth, on time scales ranging from hours to millennia. Transient changes in the Earth’s shape can, regardless of cause, be readily separated from steady secular variation in surface mass loading, but other secular changes due to plate tectonics and glacial isostatic adjustment (GIA) cannot. We estimate secular station velocities from almost 11 years of high quality combined GPS position solutions (GPS weeks 1,000–1,570) submitted as part of the first international global navigation satellite system service reprocessing campaign. Individual station velocities are estimated as a linear fit, paying careful attention to outliers and offsets. We remove a suite of a priori GIA models, each with an associated set of plate tectonic Euler vectors estimated by us; the latter are shown to be insensitive to the a priori GIA model. From the coordinate time series residuals after removing the GIA models and corresponding plate tectonic velocities, we use mass-conserving continental basis functions to estimate surface mass loading including the secular term. The different GIA models lead to significant differences in the estimates of loading in selected regions. Although our loading estimates are broadly comparable with independent estimates from other satellite missions, their range highlights the need for better, more robust GIA models that incorporate 3D Earth structure and accurately represent 3D surface displacements.     

Analysis of the influential factors for changes to land use in China’s Xingwen Global Geopark against a tourism development background

This study employs geographic information system software to explore the influences of elevation, slope, the river system, traffic arteries and the central development zone on the land-use changes in Shihai between 1995 and 2010. Data were drawn from statistics from the first two remote sensing investigations of land use in the town of Shihai in China’s Xingwen Global Geopark and its digital elevation model data. An analysis of the relationships between changes in land use was performed using relevant models, including a comprehensive land-use dynamic degree model, a single land-use dynamic degree model and a comprehensive index model for the extent of land use. The results suggest that a combination of natural and human factors influenced the changes in Shihai’s land use during the time from 1995 to 2010. First, elevation and slope exerted environmental resistance. Specifically, as elevation or slope increased, the extent of change in land use decreased, despite local policies that have reduced the extent of this resistance. Second, the river system influenced land use such that, as distance from the river increased, changes in land use decreased and then increased, suggesting that the river has a resistant as well as propulsive influence. Third, traffic arteries and the central development zone created an environmental motivation to the changes in Shihai’s land use; specifically, the evolving tourism industry results in increasing numbers of tourist trails and roads and continually expanding Geopark services’ infrastructure. Thus, relatively more dramatic changes are experienced in the Geopark’s proximate land use than in its surroundings.     

On the equivalence of spherical splines with least-squares collocation and Stokes’s formula for regional geoid computation

This work is an investigation of three methods for regional geoid computation: Stokes’s formula, least-squares collocation (LSC), and spherical radial base functions (RBFs) using the spline kernel (SK). It is a first attempt to compare the three methods theoretically and numerically in a unified framework. While Stokes integration and LSC may be regarded as classic methods for regional geoid computation, RBFs may still be regarded as a modern approach. All methods are theoretically equal when applied globally, and we therefore expect them to give comparable results in regional applications. However, it has been shown by de Min (Bull Géod 69:223–232, 1995. doi: 10.1007/BF00806734) that the equivalence of Stokes’s formula and LSC does not hold in regional applications without modifying the cross-covariance function. In order to make all methods comparable in regional applications, the corresponding modification has been introduced also in the SK. Ultimately, we present numerical examples comparing Stokes’s formula, LSC, and SKs in a closed-loop environment using synthetic noise-free data, to verify their equivalence. All agree on the millimeter level.