scholarly journals GARPOS: Analysis Software for the GNSS‐A Seafloor Positioning With Simultaneous Estimation of Sound Speed Structure

2020 ◽  
Vol 8 ◽  
Author(s):  
Shun-ichi Watanabe ◽  
Tadashi Ishikawa ◽  
Yusuke Yokota ◽  
Yuto Nakamura
Keyword(s):  
Sound Speed ◽  
Empirical Bayes ◽  
Information Criterion ◽  
Satellite System ◽  
Observation Equation ◽  
Simultaneous Estimation ◽  
Acoustic Ranging ◽  
Observation Network ◽  
Sound Speed Structure ◽  
Global Navigation Satellite

Global Navigation Satellite System–Acoustic ranging combined seafloor geodetic technique (GNSS-A) has extended the geodetic observation network into the ocean. The key issue for analyzing the GNSS-A data is how to correct the effect of sound speed variation in the seawater. We constructed a generalized observation equation and developed a method to directly extract the gradient sound speed structure by introducing appropriate statistical properties in the observation equation, especially the data correlation term. In the proposed scheme, we calculate the posterior probability based on the empirical Bayes approach using the Akaike’s Bayesian Information Criterion for model selection. This approach enabled us to suppress the overfitting of sound speed variables and thus to extract simpler sound speed field and stable seafloor positions from the GNSS-A dataset. The proposed procedure is implemented in the Python-based software “GARPOS” (GNSS-Acoustic Ranging combined POsitioning Solver).

scholarly journals An Integrated Positioning and Attitude Determination System for Immersed Tunnel Elements: A Simulation Study

Sensors ◽  
2020 ◽  
Vol 20 (24) ◽  
pp. 7296
Author(s):  
Guanqing Li ◽  
Lasse Klingbeil ◽  
Florian Zimmermann ◽  
Shengxiang Huang ◽  
Heiner Kuhlmann
Keyword(s):  
Sound Speed ◽  
Attitude Determination ◽  
Satellite System ◽  
Sufficient Accuracy ◽  
Navigation Satellite ◽  
Accuracy Analysis ◽  
Absolute Position ◽  
Immersed Tunnel ◽  
Determination System ◽  
Global Navigation Satellite

Immersed tunnel elements need to be exactly controlled during their immersion process. Position and attitude of the element should be determined quickly and accurately to navigate the element from the holding area to the final location in the tunnel trench. In this paper, a newly-developed positioning and attitude determination system, integrating a 3-antenna Global Navigation Satellite System (GNSS) system, an inclinometer and a range-measurement system, is presented. The system is designed to provide the absolute position of both ends of the element with sufficient accuracy in real time. Special attention in the accuracy analysis is paid to the influence of GNSS multipath error and sound speed profile. Simulations are conducted to illustrate the performance of the system in different scenarios. If both elements are very close, the accuracies of the system are higher than 0.02 m in the directions perpendicular to and along the tunnel axis.

scholarly journals Signal Extraction from GNSS Position Time Series Using Weighted Wavelet Analysis

2020 ◽  
Vol 12 (6) ◽  
pp. 992 ◽  
Author(s):  
Kunpu Ji ◽  
Yunzhong Shen ◽  
Fengwei Wang
Keyword(s):  
Time Series ◽  
Wavelet Analysis ◽  
Satellite System ◽  
Signal Extraction ◽  
Average Error ◽  
North East ◽  
Observation Network ◽  
Position Time Series ◽  
Global Navigation Satellite ◽  
Gnss Position Time Series

The daily position time series derived by Global Navigation Satellite System (GNSS) contain nonlinear signals which are suitably extracted by using wavelet analysis. Considering formal errors are also provided in daily GNSS solutions, a weighted wavelet analysis is proposed in this contribution where the weight factors are constructed via the formal errors. The proposed approach is applied to process the position time series of 27 permanent stations from the Crustal Movement Observation Network of China (CMONOC), compared to traditional wavelet analysis. The results show that the proposed approach can extract more exact signals than traditional wavelet analysis, with the average error reductions are 13.24%, 13.53% and 9.35% in north, east and up coordinate components, respectively. The results from 500 simulations indicate that the signals extracted by proposed approach are closer to true signals than the traditional wavelet analysis.

scholarly journals A satellite-based method for modeling ionospheric slant TEC from GNSS observations: algorithm and validation

GPS Solutions ◽  
2021 ◽  
Vol 26 (1) ◽  
Author(s):  
Wen Li ◽  
Zishen Li ◽  
Ningbo Wang ◽  
Ang Liu ◽  
Kai Zhou ◽  
...  
Keyword(s):  
Mapping Function ◽  
Satellite System ◽  
Ionospheric Delay ◽  
Electron Content ◽  
Observation Data ◽  
Total Electron ◽  
Observation Network ◽  
Different Seasons ◽  
Global Navigation Satellite ◽  
Validation Tests

AbstractTotal Electron Content (TEC) modeling is critical for Global Navigation Satellite System (GNSS) users to mitigate ionospheric delay errors. The mapping function is usually used for Vertical TEC ionospheric correction models for slant and vertical TEC conversion. But the mapping function cannot characterize TEC variation in different azimuths between the user and satellites. The ionospheric modeling error resulting from the mapping function tends to be bigger in middle and low latitudes. Therefore, a new algorithm for ionospheric Slant TEC (STEC) modeling with Satellite-based Ionospheric Model (SIM) is proposed in this contribution. Validation tests are carried out with GNSS observation data from the Crustal Movement Observation Network of China during different solar activities and in different seasons. The performance of SIM is compared with that of several commonly-used Global Ionospheric Map (GIM) and Regional Ionospheric Map (RIM) products. The results show that the STEC bias and STD of SIM are within 1.0 TECU and about 2.0 TECU, respectively, and SIM can correct over 90% STEC RMS errors, outperforming the GIM and RIM products. Consequently, the SIM algorithm can be a new option for high-accuracy ionospheric delay correction in regional and local GNSS networks.

scholarly journals Development of a kinematic GNSS-Acoustic positioning method based on a state-space model

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Fumiaki Tomita ◽  
Motoyuki Kido ◽  
Chie Honsho ◽  
Ryo Matsui
Keyword(s):  
Observational Data ◽  
Sound Speed ◽  
New Method ◽  
Superior Performance ◽  
Acoustic Ranging ◽  
Vertical Displacements ◽  
Positioning Method ◽  
Acoustic Array ◽  
Sound Speed Structure ◽  
Acoustic Positioning

Abstract GNSS-A (combination of Global Navigation Satellite System and Acoustic ranging) observations have provided important geophysical results, typically based on static GNSS-Acoustic positioning methods. Recently, continuous GNSS-Acoustic observations using a moored buoy have been attempted. Precise kinematic GNSS-Acoustic positioning is essential for these approaches. In this study, we developed a new kinematic GNSS-A positioning method using the extended Kalman filter (EKF). As for the observation model, parameters expressing underwater sound speed structure [nadir total delay (NTD) and underwater delay gradients] are defined in a similar manner to the satellite geodetic positioning. We then investigated the performance of the new method using both the synthetic and observational data. We also investigated the utility of a GNSS-Acoustic array geometry composed of multi-angled transponders for detection of vertical displacements. The synthetic tests successfully demonstrated that (1) the EKF-based GNSS-Acoustic positioning method can resolve the GNSS-Acoustic array displacements, as well as NTDs and underwater delay gradients, more precisely than those estimated by the conventional kinematic positioning methods and (2) precise detection of vertical displacements can be achieved using multi-angled transponders and EKF-based GNSS-Acoustic positioning. Analyses of the observational data also demonstrated superior performance of the EKF-based GNSS-Acoustic positioning method, when assuming a laterally stratified sound speed structure. Further, we found three superior aspects to the EKF-based array positioning method when using observational data: (1) robustness of the solutions when some transponders fail to respond, (2) precise detection for an abrupt vertical displacement, and (3) applicability to real-time positioning when sampling interval of the acoustic ranging is shorter than 30 min. The precision of the detection of abrupt steps, such as those caused by coseismic slips, is ~ 5 cm (1σ) using this method, an improvement on the precision of ~ 10 cm of conventional methods. Using the observational data, the underwater delay gradients and the horizontal array displacements could not be accurately solved even using the new method. This suggests that short-wavelength spatial heterogeneity exists in the actual ocean sound speed structure, which cannot be approximated using a simple horizontally graded sound speed structure.

scholarly journals Solving the Multilateration Problem without Iteration

Geomatics ◽  
2021 ◽  
Vol 1 (3) ◽  
pp. 324-334
Author(s):  
Thomas H. Meyer ◽  
Ahmed F. Elaksher
Keyword(s):  
Three Dimensional ◽  
Satellite System ◽  
Simultaneous Equations ◽  
Observation Equation ◽  
Atmospheric Refraction ◽  
Land Surveying ◽  
Global Navigation Satellite ◽  
Gnss Data ◽  
Radio Beacon ◽  
Taylor’S Series

The process of positioning, using only distances from control stations, is called trilateration (or multilateration if the problem is over-determined). The observation equation is Pythagoras’s formula, in terms of the summed squares of coordinate differences and, thus, is nonlinear. There is one observation equation for each control station, at a minimum, which produces a system of simultaneous equations to solve. Over-determined nonlinear systems of simultaneous equations are typically solved using iterative least squares after forming the system as a truncated Taylor’s series, omitting the nonlinear terms. This paper provides a linearization of the observation equation that is not a truncated infinite series—it is exact—and, thus, is solved exactly, with full rigor, without iteration and, thus, without the need of first providing approximate coordinates to seed the iteration. However, there is a cost of requiring an additional observation beyond that required by the non-linear approach. The examples and terminology come from terrestrial land surveying, but the method is fully general: it works for, say, radio beacon positioning, as well. The approach can use slope distances directly, which avoids the possible errors introduced by atmospheric refraction into the zenith-angle observations needed to provide horizontal distances. The formulas are derived for two- and three-dimensional cases and illustrated with an example using total-station and global navigation satellite system (GNSS) data.

Consistent Estimation of Strain Rate Fields from GNSS Velocity Data Using Basis Function Expansion with ABIC

2021 ◽  
Author(s):  
Tomohisa Okazaki ◽  
Yukitoshi Fukahata ◽  
Takuya Nishimura
Keyword(s):  
Strain Rate ◽  
Basis Function ◽  
Crustal Deformation ◽  
Information Criterion ◽  
Satellite System ◽  
Simple Formulation ◽  
Function Expansion ◽  
Global Navigation Satellite ◽  
Gnss Data ◽  
Strain Rate Field

Abstract Present day crustal displacement rates can be accurately observed at stations of global navigation satellite system (GNSS), and crustal deformation has been investigated by estimating strain-rate fields from discrete GNSS data. The method proposed by Shen et al. (J Geophys Res 101:27957–27980, 1996) offers a simple formulation for simultaneously estimating smooth velocity and strain-rate fields, and it has contributed to clarify crustal deformation fields in many regions all over the world. However, in this paper, we point out three theoretical disadvantages of the method: mathematical inconsistency between estimated velocity and strain-rate fields, inability to objectively determine the optimal value of a hyperparameter that controls smoothness, and inaccurate estimation of uncertainty. As an alternative, we propose a method of basis function expansion with Akaike's Bayesian information criterion (ABIC), which overcomes the above difficulties. Application of the two methods to GNSS data in Japan reveals that the inconsistency in the method of Shen et al. is generally insignificant, but could be serious in regions with sparser observation stations such as in islet areas. More importantly, the method of basis function expansion with ABIC shows a significantly better performance than the method of Shen et al. in terms of the trade-off curve between the residual of fitting and the roughness of velocity field. The estimated strain-rate field with the basis function expansion clearly exhibits a low strain-rate zone in the forearc from the southern Tohoku district to central Japan. We also find that the Ou Backbone Range has several contractive spots around active volcanoes and that these locations well correspond to the subsidence areas detected by InSAR after the 2011 Tohoku-oki earthquake. Thus, the method of basis function expansion with ABIC would serve as an effective tool for estimating strain-rate fields from GNSS data.

scholarly journals Optimal Transponder Array and Survey Line Configurations for GNSS-A Observation Evaluated by Numerical Simulation

2021 ◽  
Vol 9 ◽  
Author(s):  
Yuto Nakamura ◽  
Yusuke Yokota ◽  
Tadashi Ishikawa ◽  
Shun-ichi Watanabe
Keyword(s):  
Numerical Experiments ◽  
Satellite System ◽  
Observation Time ◽  
Array Size ◽  
Observation System ◽  
Positioning Accuracy ◽  
Combination Technique ◽  
Acoustic Ranging ◽  
Survey Line ◽  
Global Navigation Satellite

The Global Navigation Satellite System-Acoustic ranging combination technique (GNSS-A) has enabled us to measure seafloor crustal deformation in the precision of centimeters, leading to numerous discoveries of subseafloor tectonic phenomena. The moving observation conducted by our research group allows us to measure both the horizontal and vertical absolute positions of a reference point on the seafloor. However, the observation frequency of our GNSS-A observation system is still insufficient to observe short-term phenomena. This paper focused on the possibility to reduce the observation time per a seafloor site by shrinking the seafloor transponder array size and the survey line radius, which were empirically defined to be equal to the seafloor site depth in the early research. We evaluated the effects of changing these sizes on the GNSS-A positioning accuracy by conducting a series of numerical experiments. The results of the numerical experiments indicated that for a seafloor site with a depth of 3,000 m, the positioning accuracy is rapidly degraded as the transponder array size and the survey line radius are reduced to less than 3,000 m. Additional experiments done for transponder array sizes and survey line radii around 2,000–4,000 m revealed that shrinking the survey line radius has a dominant effect on the decrease in positioning accuracy. Thus, shrinking the transponder array size and the survey line radius is not a suitable option for reducing observation time, and the empirically defined observation configurations are concluded to be quite optimal when regarding both the positioning accuracy and the observation time.

A TOA/AOA Underwater Acoustic Positioning System Based on the Equivalent Sound Speed

2018 ◽  
Vol 71 (6) ◽  
pp. 1431-1440 ◽  
Author(s):  
Mingzhen Xin ◽  
Fanlin Yang ◽  
Faxing Wang ◽  
Bo Shi ◽  
Kai Zhang ◽  
...  
Keyword(s):  
Sound Speed ◽  
Target Position ◽  
Incident Beam ◽  
Satellite System ◽  
Time Of Arrival ◽  
Beam Angle ◽  
Unknown Parameters ◽  
Underwater Positioning ◽  
Global Navigation Satellite ◽  
Better Than

High-precision underwater positioning must eliminate the influence of refraction artefacts. Since a Time Of Arrival - Global Navigation Satellite System Intelligent Buoys (TOA-GIB) system does not measure incident beam angles, common refraction correction methods cannot be directly used for refraction artefacts. An Equivalent Sound Speed (ESS) iteration method is proposed and is based on the transformation relations between depth, the ESS gradient and the incident beam angle. On this basis, a TOA/AOA-GIB system without a real-time Sound Speed Profile (SSP) is proposed to estimate the target position and the ESS gradient as unknown parameters. The results from a simulation experiment show that the positioning accuracy of a TOA/AOA-GIB system is better than 0·07% of water depth when the accuracy of the incident beam angle is 0·1°.

Sign in / Sign up

Export Citation Format

Share Document