Navigation Files Research Articles

Concurrent 15. Presentation for: INPEX-led Ichthys Joint Venture – developing a dynamic adjustment area to identify, time, duration and potential exposure periods related to a 2D seismic survey offshore Western Australia

Presented on Wednesday 18 May: Session 15 The oil and gas industry is striving for effective consultation between titleholders and commercial fishing stakeholders. Recent developments in cross-industry consultation have resulted in frameworks to provide an adjustment (compensation) claim process, where short-term displacement of fishers and reduction of catch coincident and following marine seismic survey activities may occur. 3D seismic surveys are undertaken more intensively, in geographically smaller areas and shorter time periods. This allows for discreet areas and periods to be defined for the applicability of a claim when fishing catch rates or displacement may occur. By contrast, 2D seismic surveys can be undertaken at regional scales with long sail line transects. These result in a survey vessel being active in an area of potential acoustic influence for infrequent and short periods of time, thus making justification for claims, for loss of catch or displacement, over the full survey area and full acquisition period challenging. To address this challenge a novel approach was developed to determine a dynamic area, based on where and when a survey vessel was operating the seismic source. INPEX utilised the 10 nautical miles (nm) × 10 nm geospatial grid data set provided by Department of Primary Industries Resources and Development, for commercial fishers to report catch effort. The methodology used modified navigation files, to determine the frequency, duration and number of times a fishing block was intersected during the survey. The resulting data provided an ‘adjustment area’ and ‘exposure date’ which could then be referred to as a basis for claim. To access the presentation click the link on the right. To read the full paper click here

INPEX-led Ichthys Joint Venture – developing a dynamic adjustment area to identify, time, duration and potential exposure periods related to a 2D seismic survey offshore Western Australia

The oil and gas industry is striving for effective consultation between titleholders and commercial fishing stakeholders. Recent developments in cross-industry consultation have resulted in frameworks to provide an adjustment (compensation) claim process, where short-term displacement of fishers and reduction of catch coincident and following marine seismic survey activities may occur. 3D seismic surveys are undertaken more intensively, in geographically smaller areas and shorter time periods. This allows for discreet areas and periods to be defined for the applicability of a claim when fishing catch rates or displacement may occur. By contrast, 2D seismic surveys can be undertaken at regional scales with long sail line transects. These result in a survey vessel being active in an area of potential acoustic influence for infrequent and short periods of time, thus making justification for claims, for loss of catch or displacement, over the full survey area and full acquisition period challenging. To address this challenge a novel approach was developed to determine a dynamic area, based on where and when a survey vessel was operating the seismic source. INPEX utilised the 10 nautical miles (nm) × 10 nm geospatial grid data set provided by Department of Primary Industries Resources and Development, for commercial fishers to report catch effort. The methodology used modified navigation files, to determine the frequency, duration and number of times a fishing block was intersected during the survey. The resulting data provided an ‘adjustment area’ and ‘exposure date’ which could then be referred to as a basis for claim.

Distribution of clock correction and ephemeris parameters in broadcast navigation messages

The distribution of clock correction and ephemeris (CCE) parameters in navigation messages broadcast by operational satellite vehicles (SVs) of the Global Navigation Satellite System (GNSS) is studied. For this purpose, two evaluation metrics are proposed, namely atypical navigation message structures and time to complete CCE sets (TTCS). The evaluation metrics are used to analyze three and a half years of operational Galileo F/NAV and GPS LNAV messages. The study considers arbitrary and healthy-only signal-in-space (SIS) health statuses. The frequently used receiver independent exchange format (RINEX) navigation files are shown to not provide sufficient information to determine the CCE parameters transmitted at every time instance. Due to the identified limitations, binary navigation data collected by a worldwide network of monitoring stations are used for the analysis. During operations, the maximum of the TTCS metric is shown to be impacted by the issue of data (IOD) update periods and structures with mismatched IOD parameters, potentially introducing an additional delay to the time to first fix (TTFF). The message timing requirements of dual-frequency multi-constellation (DFMC) satellite-based augmentation system (SBAS) are shown to be in line with the minimum times needed to obtain multiple complete Galileo F/NAV and GPS LNAV CCE sets.

Galileo L10 Satellites: Orbit, Clock and Signal-in-Space Performance Analysis.

The tenth launch (L10) of the European Global Navigation Satellite System Galileo filled in all orbital slots in the constellation. The launch carried four Galileo satellites and took place in July 2018. The satellites were declared operational in February 2019. In this study, we report on the performance of the Galileo L10 satellites in terms of orbital inclination and repeat period parameters, broadcast satellite clocks and signal in space (SiS) performance indicators. We used all available broadcast navigation data from the IGS consolidated navigation files. These satellites have not been reported in the previous studies. First, the orbital inclination (°) and repeat period ( s) for all four satellites are within the nominal values. The data analysis reveals also 13.5-, 27-, 177- and 354-days periodic signals. Second, the broadcast satellite clocks show different correction magnitude due to different trends in the bias component. One clock switch and several other minor correction jumps have occurred since the satellites were declared operational. Short-term discontinuities are within ±1 ps/s, whereas clock accuracy values are constantly below 0.20 m (root-mean-square—rms). Finally, the SiS performance has been very high in terms of availability and accuracy. Monthly SiS availability has been constantly above the target value of 87% and much higher in 2020 as compared to 2019. Monthly SiS accuracy has been below 0.20 m (95th percentile) and below 0.40 m (99th percentile). The performance figures depend on the content and quality of the consolidated navigation files as well as the precise reference products. Nevertheless, these levels of accuracy are well below the 7 m threshold (95th percentile) specified in the Galileo service definition document.

2019-333-FA_sol: Digital Chirp Subbottom Profile Start of Line Data Collected During USGS Field Activity Number 2019-333-FA Offshore of the Rockaway Peninsula, New York, September–October 2019

From September 27 through October 5, 2019, researchers from the U.S. Geological Survey (USGS) conducted a geophysical survey to investigate shoreface morphology and geology near the Rockaway Peninsula, New York. The Coastal Sediment Availability and Flux project objectives include understanding the morphologic evolution of the barrier island system on a variety of time scales (months to centuries) and resolving storm-related impacts, post-storm beach response, and recovery. This publication serves as an archive of high-resolution chirp subbottom trace data, survey trackline map, navigation files, geographic information system (GIS) data, and formal Federal Geographic Data Committee (FGDC) Content Standard for Digital Geospatial Metadata (CSDGM). Processed subbottom profile images are also provided. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y revision 0 format (Barry and others, 1975). In addition to this data release, the SEG-Y files can be downloaded from the USGS Coastal and Marine Geoscience Data System (CMGDS) at, https://cmgds.marine.usgs.gov. Bathymetry and backscatter data were also collected during this survey and are available in Stalk and others (2020).

Galileo Broadcast Ephemeris and Clock Errors Analysis: 1 January 2017 to 31 July 2020.

A preliminary analysis of Galileo F/NAV broadcast Clock and Ephemeris is performed in this paper with 43 months of data. Using consolidated Galileo Receiver Independent Exchange (RINEX) navigation files, automated navigation data monitoring is applied from 1 January 2017 to 31 July 2020 to detect and verify potential faults in the satellite broadcast navigation data. Based on these observation results, the Galileo Signal-in-Space is assessed, and the probability of satellite failure is estimated. The Galileo nominal ranging accuracy is also characterized. Results for GPS satellites are included in the paper to compare Galileo performances with a consolidated constellation. Although this study is limited by the short observation period available, the analysis over the last three-year window shows promising results with = 3.2 × 10−6/sat, which is below the value of 1 × 10−5 stated by the Galileo commitments.

Python software tools for GNSS interferometric reflectometry (GNSS-IR)

Global Navigation Satellite System (GNSS) interferometric reflectometry, also known as the GNSS-IR, uses data from geodetic-quality GNSS antennas to extract information about the environment surrounding the antenna. Soil moisture monitoring is one of the most important applications of the GNSS-IR technique. This manuscript presents the main ideas and implementation decisions needed to write the Python code for software tools that transform RINEX format observation and navigation files into an appropriate format for GNSS-IR (which includes the SNR observations and the azimuth and elevation of the satellites) and to determine the reflection height and the adjusted phase and amplitude values of the interferometric wave for each individual satellite track. The main goal of the manuscript is to share the software with the scientific community to introduce new users to the GNSS-IR technique.

GPS: User Position Calculation Including Advanced Troposphere Delay Modeling

Objective of this project is to analyze and mitigate troposphere delays induced in GPS signals, which can result in very large position errors while estimating user position. The standard models currently present do not take into account all the various set of parameters or elements of the troposphere that can cause a significant delay. This project also includes study of troposphere propagation delays that improve the understanding of GPS signal propagation through the troposphere during irregular conditions. This characteristic is very important as it can play crucial role in real time surveying, navigation, precision farming and positioning for emergency services. Due to the tropical nature of the Indian climate the troposphere delay can be observed significantly in India sub-continent. In order to accurately estimate delay troposphere in real time conditions is taken into account, which are provided by the Indian meteorological department, by their automatic weather surveillance systems. GPS data for stations in India is obtained from CORS data for Bangalore, from where we obtain the observation and navigation files used in the calculations. Obtained data is processed and run through various algorithms like least squares satellite position calculation, error mitigation and ray tracing algorithms to mitigate troposphere and better estimate user position. Apart from these algorithms this project also includes a study on various concepts/formulas that help in using the forecasted real time data to be used in snell’s law to estimate delay as part of ray tracing techniques. All the code development in this project is done using MATLAB by math works and GUI is developed for an easier interface. For analysis purposes the data is analyzed with and without the advanced mitigation techniques to show the improvement in position estimation using advanced troposphere mitigation techniques.

Six-Year BDS-2 Broadcast Navigation Message Analysis from 2013 to 2018: Availability, Anomaly, and SIS UREs Assessment.

The second-generation of the Beidou Navigation Satellite System (BDS-2) has been officially providing positioning, navigation, and timing (PNT) services within the Asia–Pacific region for six years, starting from 2013. A comprehensive analysis of BDS-2 satellite broadcast navigation message performance during the past six years is highly demanded, not only for the regional service but also for the global service announced in December 2018. Therefore, this study focuses on the performance assessment of six-year BDS-2 broadcast navigation messages from 2013 to 2018 in three aspects: Message availability, anomaly detection, and signal-in-space user range errors (SIS UREs). Firstly, our results, based on International GNSS service (IGS) Multi-GNSS Experiment (MGEX) navigation files, indicate that the BDS-2 Geosynchronous Earth Orbit (GEO) and Inclined Geosynchronous Satellite Orbit (IGSO) satellites have >98.51% broadcast navigation message availability, and the Medium Earth Orbit (MEO) satellites has a ~90.03% availability. Secondly, the comparison between broadcast navigation messages and IGS precise products reveals that the User Range Accuracy Index (URAI) contained in the broadcast message could not reflect satellite performance correctly. Another satellite status indicator, space vehicle (SV) health, can only partially detect a satellite anomaly. The anomaly detection result using IGS precise products for reference shows 20241 anomalies out of 651038 broadcast navigation messages within six years. Finally, compared with the IGSO and MEO satellites, the orbit qualities of GEO satellites are significantly worse due to their large along-track orbit error. The clock performance of all satellites are at the comparable level. The satellite orbit type (GEO/IGSO/MEO) does not impact the orbit-only URE, global-average URE, and worst-case URE.

NavIC receiver clock offsets estimation with common view master clock method

The current manuscript proposes a new methodology for receiver clock offset estimation in IRNSS (Indian Regional Navigation Satellite System) which is also known as NavIC (Navigation Indian Constellation). This new methodology has been designed by clubbing the master clock concept with the traditional common view time transfer method and therefore it has been named as Common View Master Clock Method (CVMCM). The proposed methodology is intended to share the reference time uniformly and precisely across all the receiver clocks of IRNSS. The IRNSS receivers equipped at IRIMS (IRNSS Range and Integrity Monitoring Stations) acquire IRNSS satellite signals and generate code and carrier phase measurements on L5 and S frequencies. For ease of convenience, this range measurements and broadcast navigation messages are converted to standard RINEX (Receiver Independent Exchange) format in the form of RINEX observation files and RINEX navigation files respectively. As IRNWT1 (IRNSS Network Time Facility Bangalore) has been directly fetched to IRIMS Bangalore we have chosen IRIMS Bangalore as the master (reference) station. This is followed by time offset estimation of all IRIMS with respect to IRIMS Bangalore using the CVMCM method. This proposed methodology reduces all the error sources in IRNSS signals and produces very accurate time offsets results for all IRIMS. This helps in maintaining IRNSS reference time very precisely across all IRIMS with a proper time steering, thereby revamping the process of time synchronization in NavIC. Analyses were performed which establishes the stability and credibility of our results. In the process, it also corrects almost all the error sources in NavIC signals.

Anomaly analysis of 18 years of newly merged GPS ephemeris from four IGS data centers

The merged GPS navigation files from the International GNSS Service (IGS) data centers, i.e., the Crustal Dynamics Data Information System (CDDIS), the Bundesamt fur Kartographie und Geodasie (BKG), the Scripps Institution of Oceanography (SIO), and the Institut Geographique National (IGN) are occasionally contaminated by anomalies and inconsistent user range accuracy (URA). This contamination impairs the performance assessment of GPS service, especially the system integrity. We remerged these files starting Day of Year (DOY) 1, 2000 using all available navigation data files from IGS stations. To effectively get the upper bound URA, a frequency-dependent pattern recognition method was developed. In addition, a comprehensive comparison between the navigation data remerged by us and those provided by the four IGS data centers was performed. The compared results revealed that TGD and Issue of Data Clock (IODC) were the dominating anomalies in the merged navigation data from CDDIS and SIO for the first several years after 2000, and M0, Ω0, ω, and af0 were the dominant anomalies in the merged data from IGN. In addition to a number of missing records, many records with incorrect PRN (pseudo-random noise number), identifying a GPS satellite, were found in files from the IGS data centers. Although the number of anomalies in the merged files from CDDIS has continued to decrease in recent years, they have not disappeared and would affect system-level assessment and scientific applications to a certain extent. The results also revealed that our remerged files were more complete, clean, compact and consistent, making them more suitable for GPS system performance assessment and related research studies. Moreover, those data are now openly available.

Soft Tissue Envelope Preserving Technique for Computer Navigated Total Knee Arthroplasty

Objectives:Current techniques in Total Knee Arthroplasty(TKA) are utilitarian in that all patients are recommended to have the same alignment of neutral mechanical axis. It has been well established that the population has a varied natural alignment with less than 20% of patients naturally neutral. The ability to predictably individualise alignment for patients is hypothesised to result in greater patient satisfaction. This technique aims to modify mechanical axis technique to consider an individual’s soft tissue constraints.Methods:Soft Tissue Envelope Preserving (STEP) is an operative technique for performing TKA that utilises the soft tissue data obtained intra-operatively from computer navigation registration to determine the optimal alignment to provide balanced positioning of implants without the need for soft tissue releases. Hence balance is achieved through bone cuts rather than altering the patient’s soft tissue balance. The technique will be described in detail.Results:The last 100 patients performed with complete data sets including navigation files and both pre-op and one year post operative outcome measures were reviewed. The spread of overall alignments and bony resections have been compiled with no outliers outside 5 degrees of neutral. The clinical results were comparable with other series and patient satisfaction of greater than 90% was reported. There were no MCL or LCL releases performed. Ilio-tibial band partial releases were the only reported soft tissue releases made.Conclusions:This technique is a safe and effective method of performing TKA with good short term outcomes. It minimises the use of soft tissue releases by utilising the patient’s own soft tissue envelope to balance the knee whilst maintaining the basic principles of a measured resection mechanical axis technique. It has resulted in excellent patient satisfaction in the short term.

Combining GPS and GLONASS in all-in-view for time transfer

GPS code measurements have been used for three decades for remote clock comparison, also called Time Transfer. Initially based on a technique using common-view (CV) single-frequency measurements, GPS time transfer now mostly uses dual-frequency measurements from geodetic receivers processed in all-in-view (AV). With the completion of the GLONASS constellation, it has been possible to readily use it in the CV single-frequency mode, providing results similar to GPS for short-distance time links. However GLONASS results are not readily equivalent to GPS in the dual-frequency AV mode, necessary for any moderate- to long-distance link, and this paper shows how to achieve this. We first present the GLONASS upgrade of the R2CGGTTS software, a tool to provide dual-frequency measurements in a format dedicated to time transfer named CGGTTS (Common GPS GLONASS Time Transfer Standard). The GLONASS navigation files are used to determine satellite clocks and positions, and dual-frequency pseudorange measurements are linearly combined to compute the CGGTTS results in a similar way as for GPS. In a second part, we present the combination of GPS and GLONASS into one unique time transfer solution based on AV. The results are first corrected using precise satellite orbit and clock products delivered by the IGS analysis centre ESOC, and characterized by the same reference for the GPS and GLONASS satellite clocks. Then, the need to introduce satellite-dependent hardware delays in GLONASS results is emphasized, and a procedure is proposed for their determination. The time transfer solutions obtained for GPS-only and GPS+GLONASS are then compared. The combination of GPS and GLONASS results in AV provides a time transfer solution having the same quality as GPS only. Furthermore, comparisons show that even when increasing the number of observations in CV thanks to the combination of the two constellations, the AV remains superior to the CV solution in terms of noise and short term stability, especially for long baselines.

Antenna Phase Center Variations Corrections in Processing of Gps Observations with Use of Commercial Software

It is well known that magnitude of antenna phase center variations (PCV) can reach several centimeters. Unfortunately part of commercial GPS post-processing software does not include corrections related to antenna PCV. This paper presents a proposal of a subroutine which introduces PCV corrections to code and phase observations basing on ANTEX file and RINEX observations and navigation files. This approach has been tested using GPS data collected at four measurement points. Three different types of antenna were used in observations. Observation processing was done with Ashtech Solutions and TopconTools software. The results of calculations show, that the proposed subroutine can be successfully used in commercial software which does not include such correction algorithms. The subroutine can also serve to verify antenna PCV corrections algorithms in commercial software where there is often no possibility of looking into applied algorithms.