Science topic

Global Navigation Satellite System - Science topic

A satellite navigation or SAT NAV system is a system of satellites that provide autonomous geo-spatial positioning with global coverage. A satellite navigation system with global coverage may be termed a global navigation satellite system or GNSS. Global coverage for each system is generally achieved by a satellite constellation of 20–30 medium Earth orbit (MEO) satellites spread between several orbital planes. The actual systems vary, but use orbit inclinations of >50° and orbital periods of roughly twelve hours (at an altitude of about 20,000 kilometres (12,000 mi)).
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I have downloaded the 7 days GNSS observation data from one of the UNAVCO listed CORS station. So there are 7 different 24h files for each day for the same CORS station. Can I perform PPP in RTKLIB using all 7 days 24h files at the same time? If so how can I do that?
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#### Basic Approach
When setting the path to the PPP datasets:
-obs
-brdm
-sp3
-clk
you may use any of the following parsers (these are general keywords):
##########################################################
%Y ==> yyyy : four-digit year (2000-2099)
%y ==> yy : two-digit year (00-99)
%m ==> mm : month (01-12)
%d ==> dd : day of month (01-31)
%h ==> hh : hours (00-23)
%H ==> a : hour code (a-x)
%M ==> mm : minutes (00-59)
%n ==> ddd : day of year (DOY, 001-366)
%W ==> wwww : gps week (0001-9999)
%D ==> d : day of gps week (0-6)
%N ==> d : sequence number (0- )
%s ==> ssss : station name (lower-case)
%S ==> SSSS : station name (upper-case)
%r ==> rrrr : station name
##########################################################
For example, for your task, you may set the DOY for multi-day processing or the station name for multi-station processing.
Note: Remember to list the station names in the processing
scheme.
For example:
-karo
-mzuz
-ctpm
-vwzm
-...
#### Advanced Approach
You may write a program to call the following:
-PPP configuration file
-rnx2rtkp
The processing program may be written in
-Bash
-Python
-Julia
-...
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I am currently working on GNSS Spoofing as my master's thesis and working on GPS signal generation using MATLAB.
I wanted to know whether it is possible to use MATLAB for generating a complete signal of 5 satellites or not?
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Thank you so much for your kind responses. I have completed my Masters thesis and got an A grade on my thesis too. :)
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Inside RTKPOST software, there is various positioning modes available. Among, three are: PPP Static, PPP Fixed, & PPP Kinematic. How is one different from another?
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The major difference is how to handle the position parameters in the filter. In PPP-Fixed mode, the position parameters are constrainted to the priori coordinates with a rather small variance, so its estimates almost does not change no matter the observations good or bad. PPP-Static mode consider the position parameter as a random random constant parameter, whose variance-covariance will decrease as the observation accumulation. Hence its position estimates will convergent to a certain value since the contribution of the new observations decrease. PPP Kinematic mode consider the position parameter as random variables, whose variance-covariance will be re-initialized every epoch. Hence its estimates will be noiser than the other two mode, but it is necessary for processing kinematic data unless you have other information like IMU observations.
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If the geodetic coordinates (φ,λ,h) of the ground station (e.g., GPS station) is known, how can the pressure, temperature, and relative humidity of this station be predicted at different times?. I'm looking for a mathematical model+modeling data, not instruments (equipment) used. If you have any information about this, please share it here.
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You might be biased against measurements because you feel you cannot afford them. But often there are meteorological networks nearby - based on stations, weather radar, lidar, GPS dual frequency electron density, meteorological satellites, and many amateur networks. One measurement is sometimes worth 10 supercomputer's. You did not say what you are trying to do, or where. The location matters a lot - for the complexity of the modeled region, for the sparsity or abundance of continuous data stream, and for the possibility of others working on the same place.
I found that many of the seismic stations are recording meteorological data. Because when you work at parts per million or parts per billion problems the atmospheric variations are often one of the largest variations. Sometimes simple correlations remove or identify the the big variations. But I found that imaging arrays ultimately are needed.
I am sorry I cannot answer you more clearly. You don't say your restraints in terms of computing resources. If you have 10 supercomputer nodes, there are one set of options. If you have only a Raspberry Pi, then something else is needed.
I am sitting here listening to a lightning storm passing over the area. It reminds me of all the electromagnetic sensor methods for monitoring weather in 3D and quantitatively. You did not say how long your project related to the question might be. If it is a casual "I wonder?" or "a ten year plan", the methods are different.
I see you are working with geopotential. The daily variations of the gradient of the potential are easily measurable. After subtracting the sun moon portion of that, the largest component is the local atmosphere. I mentioned the seismic stations measuring temperature, pressure, humidity, acoustic. That is because the acceleration is correlated with atmospheric events and properties.
The most cost effective way to get good estimates for different locations is to use a combination of all the available continuous data streams and their correlations, then use algorithms that can run on low cost equipment. But all that is set by what you are trying to accomplish.
Atomic clocks are "direct geopotential sensors". You might want to look more closely at gravimeters and gravity gradiometers. Again, I cannot tell what you are trying to do, so I cannot be more specific. But generally the gravimeter networks are more sensitive to meteorological changes. I am trying to set up gravitational imaging arrays to 3D image the atmosphere for cities that also have 3D weather radar and climate models at sufficient resolution - for correlations. The less expensive gravitational sensors, once calibrated, are not bound by electromagnetic noise or weather conditions as much.
You seem to be assuming "I can get some data more easily by running a model". But often the best models are proprietary or horribly difficult to run. Then your best bet is to locate places on the Internet where the data is served continuously. The European Space Agency has a rather large project on global climate change that has to estimate global climate at any location over long time periods. Their model outputs are available. They keep moving things around, but you might try looking here - https://spacedata.copernicus.eu/ just to get some sense of what is going on. Brian Bramanto link is good. But the global climate model community is large and varied, and has many applications.
All their models, and any model you find will have to have been calibrated using real data, to be of any use. So whether you tap the raw data, or they do it and feed you the processed results - you are ultimately looking at measurements by someone. Usually many someones.
Looks like you and I are in the same project. You might want to take a closer look at Mossbauer methods for measuring the geopotential. That is the first absolute gravitational potential measurement. Also, the neutrino and cosmic ray networks are getting to the level of sensitivity and temporal resolution they can pick up daily and hourly variations driven by local pressure temperature humidity. Their results depend on the local atmospheric density.
Rather than TPH, you might want to think more in terms of mass density variations. PV = nRT is really very useful. n(i) = ParticlesPerCubicMeter(i) = MassDensity * AvagadrosNumber/ MolecularWeight(i) for sets of molecular and atomic species. i is the index for the species. It might seem trivial, but if you have to use it a million times and it gets embedded in thousands of different models, it is good to bring it out explicitly to be able to combine results from many groups.
Richard Collins, The Internet Foundation
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About GNSS ionospheric model
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Nequick topside model
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I want to log GPS/GNSS data on an iPhone/iPad and look for a dedicated app. I want to log as much data as possible (DOPS, satellite data [strength, number, position,...], used constellations, frequencies...) over a longer period of time. Additional data from other internal sensors (IMU) would also be ideal. The recording should not depend on the position change, ideally in NMEA or RAW and stored locally. Other data formats are also possible if they contain the necessary information.
Does anyone know such an app for IOS? I have tried dozens and have not found one that meets the requirements.
Thanks
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Thank you for your answer. The programme works smoothly, even in the combination of GNSS and other sensors. It is also available for iOS and Android. It still has one weakness. GPS/GNSS/Location alone provides the number of satellites, in combination with other sensors this number of satellites is missing. Nevertheless, I will use this app.
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What is the position error limit for GPS aided INS sensor fusion for small rockets?
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Dear Researchers
How can we connect an GNSS external antenna to mobile phones?
What GNSS antennas can we use for this?
I will be grateful for your answers.
MB
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Depends on what kind of phone you have. Many Android (older) Phones use U.FL connectors (https://en.wikipedia.org/wiki/Hirose_U.FL) . You can just disconnect the original antenna and replace it with the new one. On new ones you might have to solder a coax cable onto the PCB.
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Satellite Laser Ranging (SLR) and Global Navigation Satellite System (GNSS) both measure the ellipsoidal heights. Which measurement of ellipsoidal height is more accurate?
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In the ITRF2014, the vertical (height) components of coordinates are slightly better for GNSS than for SLR: ca. 5 or 6 mm vs. 8 mm WRMS averages, see Table 2 in Altamimi et al., ITRF2014: A new release of the International Terrestrial Reference Frame modeling nonlinear station motions, 2016. (The full text is freely available at http://onlinelibrary.wiley.com/doi/10.1002/2016JB013098/full and was also reproduced in IERS Technical No. 38 "Analysis and results of ITRF2014", available for download at https://www.iers.org/TN38.) However, these are mean values for permanent stations and long measurements. A short measurement of a single GNSS station will be considerably worse.
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Global Navigation Satellite System
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thanks Endeshaw for your information
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I mean besides the official interface control documents provided for GPS, Galileo, GLONASS, and BeiDou, is there a relatively recent document that lists the services broadcasted and the main signal characteristics (e.g. carrier, modulation, chiprate) at least for these global systems?
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Thank you very much
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can anyone give an article related to this question?
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This free eBook (100 pages) may be helpful for general questions on GNSS observations: http://arf.berkeley.edu/files/attachments/equipment/NovAtel-Intro-to-GNSS2015.pdf
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The L5 signals from GNSS (US GPS/NaVIC/GLONASS) are being explored for wide applications. With focus on assessing the errors in (GPS) location data, what are the fundamental steps involved in determining errors or corrections that are necessary. Key points on validation mechanism.
I am exploring this topic and it will great if specific literature on fundamentals corrections adopted on processing of L5 signals can be highlighted.
Thanks in advance.
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You can read this paper:
Testing GPS L5 Tracking Algorithms and their Impact on Positioning Accuracy
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I tried to compute IRIDIUM SV ECEF coordinates using standard IS-GPS-200D almanac procedure. I downloaded TLE file with IRIDIUM SVs parameters from Celestrak. I successfully managed to convert/compute almost all necessary data for the calculation from TLE. I miss only RoRAAN (OMEGA dot). Could you give me some advice? Is it derived from B* drag term? Thank you in advance.
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Thank you for the reply. Please excuse me the delay with response. I found your answer very helpful. I'm going to implement your code into my calculation. I will let you know about the result. Best regards, PSD
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Dear Colleagues,
I've intended to write a research article dealing with variances of unmodeled effects that limit accuracy of GNSS relative positioning. This article would be a continuation of my several-year well-documented research that is based on 2-Way Nested ANOVA.
Due to a shortage of other GNSS raw data, I've used only GPS raw data in my research so far. However, for this study, I need epoch-wise ambiguity-fixed baseline solutions, necessarily obtained by post-processing of multi-GNSS (GPS, BeiDou, Galileo, GLONASS, ...) raw data in, for example, Bernese or any other advanced processing 'machine' (with the use of all proposed corrections along with the IGS final product data).
I offer a collaboration to anyone who provide those input data for the study.
P.S: Please, if any interest, send me a private RG message to give you detailed information.
Respectfully
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Besides positioning solutions, Global Navigation Satellite Systems (GNSS) receivers can provide a reference clock signal known as Pulse-per-Second (PPS or 1-PPS). A TTL electrical signal that is used in several applications for synchronization purposes.
  1. Is the PPS physically generated through a digitally-controlled oscillator (or line driver) whose offset is periodically re-initialized by the estimated clock bias (retrieved by means of PVT algorithms)?
  2. Are there any specific filters/estimators devoted to a fine PPS generation and control?
  3. Does some colleague know any reference providing technical details on this aspect?
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we worked on the design and implementation of of a GPS receiver for the sake of extracting the one PPS, we could realize the signal acquisition phase and the tracking phase where we could generate a copy of the carrier with reduced frequency and of the pn conde clock generator. BY dividing these signal with appropriate division ratio one can get the one PPS. Its stability was to be evaluated. But the last divider stage is not yet realized and we plan to realize it and after that evaluate its accuracy and stability. please see the papers:
Once achieved I will notify you.
Best wishes
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I am researching a method to speed up the GPS acquisition in cold start. Rather than an exhaustive search on all satellites, I observed that the satellite distribution can give some information to reduce the number of searches.
For example, if I can find the first satellite with Doppler value. I think there exists some way to calculate the probability of detection of other satellites.
Could you recommend some references to start looking at?
Thank you.
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I had done a similar task before. That was about predicting satellite locations based on orbital data and time.
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My research is related to the Ionospheric disturbances for an earthquake, and the point of my question is after I calculated and plotted the Ionospheric Pierce Point (IPP) & Sub-Ionospheric Point (SIP) trajectories, and the values of STEC and their anomalies from the closest satellite to the epicenter of an earthquake area by using several observation stations from sugar, I stopped on the step of calculating or plotting the STEC & VTEC for all my GPS stations because I don't know even I don't have the Matlab script for it. (please provide me a full Matlab script for it) with thanks
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The subframe parameters are mentioned along with scaling factors in the ICD. How to use them while extracting navigation parameters from binary data?
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Convert the binary number to decimal and multiply with the scaling factor to get the proper value.
If the data is in 2's complement format, then Abdul Malik Khan Abdul Malik Khan convert q number to decimal and multiply the scaling factor.
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I was looking into GNSS derived TEC data and most of the data were missing and repeatedly occuring. What is the most precise way to handle those missing data? I guess interpolation is not good enough to perform for a large number of missing data.
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There are a lot of websites with GNSS data,
It is better to select periods with good continuous data sets
sincerely
Christine
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I want to compare two TEC models. Except the comparison of diurnal vTEC, I want to analyze deviation in mean monthly vTEC by taking single airthematic average for whole month. While doing so, I am averaging quiet day as well as disturbed day TEC. But my study is not adressing the performance of models in disturbed or quiet day. Study is focused on overall performance. So, what I believe is if two models are predicting TEC of same location then both should give the similar average for the month. But I want to confirm, wheather other statistical factor effects the value while mixing quiet day and disturbed day TEC or not?? Is this concept significant in comparing two TEC models?
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In my opinion, it's better to distinguish the study into disturbed and quiet period to validate the performance of the model. This is because, the average value of the entire month sometime fails to address the storm effect on the vTEC. By dividing the study into two separate categories, we will have better overview of their overall performance.
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I need information on the power of the transmitting antennas of the GNSS satellites and the signals they transmit. Is there an official&technical report, data set or published research article on this?
I would be very grateful for your help.
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The explanation of your question here may not be enough, but I have had studies in this field and I suggest the following articles to you. I hope they help.
  • 10.1007/s00190-017-1082-2
  • 10.1155/2016/2154763
  • 10.1007/s00190-017-1082-2
  • 10.3390/data5010018
Wishing you the best on your way.
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I am interested in the changes in the vibration response of a long-span bridge structure before and after damage. I am developing a dynamic characteristic identification method, which is tested only with simulated data. It will be very helpful with the actual dynamic deformation data to verify this method' capcity of identifying the changes in the characteristics such as the frequency extracted from the monitoring series before and after the structure's damaged.
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If you can send me some relevant GNSS monitoring data , you will be gratefully acknowledged in my future publications.
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In the U.S., Executive Order 13905( Federal Register : Strengthening National Resilience Through Responsible Use of Positioning, Navigation, and Timing Services) signed 02-12-2020, ordered several federal agencies to conduct vulnerability assessments related to critical infrastructure. I'm looking for qualified opinions / research on the potential for degradation or loss of access to GPS / GNSS to potentially impact critical infrastructure at hydro-electric dams.
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Well, 'Yes'. And not just the obvious spatial difficulties, it is the reliance on timing signals. The epicenter is NIST: Overview at https://www.nist.gov/news-events/news/2021/02/nist-finalizes-cybersecurity-guidance-positioning-navigation-and-timing and from there are other domain specific documents like https://www.nist.gov/news-events/news/2019/08/situational-awareness-electric-utilities-nist-publishes-cybersecurity
Behind all these is usually quite a paper trail of conference presentations, meeting transcripts, etc. from stakeholders providing input, usually referenced in the bibliographies of the documents. The exceptions are, obviously, classified content with specifics on actual incidents and unresolved current vulnerabilities.
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In the relativistic theory for synchronization between satellite and ground atomic clocks, the major sources of relativistic effects are relative motion between the two clocks and the movement of clocks in a gravitational potential.
I am looking for the recent research and adapted clock correction models that have been modified on this topic as well as what are factors must be considered when comparing the proper/coordinate time of a clock at rest on the geoid and a clock in Earth orbit satellite?
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When they first sent up GPS satellites, they programmed them with what they believed to be the correct relativistic changes that would be needed which would affect GPS location determinations. They also installed a programmable system within these satellites that can be reprogrammed from the ground, and they could upload any changes when the satellite was overhead.
What they found was that the relativity program the system was given was not accurate enough for GPS system calculations. They tried to correct these equations and related program for a period of time but finally gave up. Instead they uploaded a programmed algorithm that they believed could make the necessary corrections based upon information from the ground coming from one or more additional GPS satellites. The new system worked. So now all relativity corrections of GPS satellites are now based upon a self-correcting algorithm using new information from the ground and other GPS satellites on an ongoing basis.
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Different Global Navigation Satellite Systems are vulnerable to different kinds of intereferne, some are intentional while others are unintentional. Jamming and spoofing are 2 types of intentional intereferne that affect the accuracy of a GNSS or RNSS measurements
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I think in order to cancel the intercept signal you have to detect it and that what you want to realize by your software defined radio. So need a software defined radio developing kit that work in the frequency band of the global position systems. You may use the national instrument software defined radio kits which are based on Ettus kits.
Here I would like to pay your attention that the GPS signals are spread spectrum signals which are primarily more immune against narrow band jamming.
So, may not need extra precautions against the interference.
One must study how far these signals are immune against jamming.
I would like that you refer to the paper in the link which deals with generations
and
Best wishes
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I am working on a GNSS/INS tight integration model for vehicle localization during loss of GNSS such as under parking, dense trees etc. using IMU measurements only with the positioning error less than 2 meters for at least 1 minute. However, positioning error is quickly increasing in the absence of GNSS as well as velocity error. I am trying to adopt NHC (non-holonomic constraint) model along IMU measurements. However, accuracy is not much improved. I studied several papers related to NHC model and theoretically NHC model should work. Can anyone guide me to integrate NHC model and IMU especially in the real time implementation perspective in the NED/ECEF frame of reference. Thanks in advance.
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Based on my experiences on implementing NHC on real products, there are some challenges:
1 - Misalignment between vehicle body frame and IMU frame may be estimated, you can detect it when plotting the signals in the rear-wheel frame.
2 - If the vehicle turns drastically or jumps, NHC should be deactive.
3 - The measurement noise covariance matrix for NHC should be adaptively tuned.
You can have a look at Groves's book Principles of GNSS, Inertial, and Multisensor Integrated Navigation Systems.
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Recently I have some ideas and wanna do some research on the building/bridge deformation monitoring. However, I don't have the data right now. Can anyone provide the data? Much thanks!
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Depends on your study area. Local bodies and organisations sometimes observe these values and most often they are happy to share it for research work.
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I know the tight integration improves the performance of GNSS receiver in terms of position, velocity and attitude. Normally, we assume that tight integration can handle the short term loss of GNSS signals. However, for a moving vehicle where attitude is quickly changing, loss of GNSS results in accumulation of position and velocity error. Can we model the attitude/ heading change to reduce the accumulated error ?
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I didn't fully get your question, if you are integrating INS with GNSS, there are error states for the heading errors, and also there are error states for the sensor errors that might be based on something like Gauss-Markov models. Therefore, if your model is well-tuned, the attitude errors and sensor errors should be well-estimated before the outage which reduces the error accumulation.
Other vehicle constraints can also be used in the absence of GNSS to reduce the error accumulation (in land vehicles) such as Nonholonomic constraints (NHC), Zero-velocity update (ZUPT), and Zero Integrated heading Rate (ZIHR).
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Does anyone working in the field of GNSS multi-agent/multi-receiver positioning know public data repositories including high-rate positioning data (> 10 Hz PVT solutions)?
Urban or mild-urban track logs obtained through high-accuracy GNSS/INS/RTK receivers are valuable options (sub-meter accuracy).
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Perhaps you could consider the IGS MGEX products. This RINEX files mostly contain data from all GNSSs.
Good luck!
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I'd like to use the VADASE approach for Hungarian GNSS observations in RINEX format wrt to the Zagreb earthquake in 2020. It would be a great help if you had any software tools available for use. I'm looking forward to your answer!
Thank you in advance!
BEst regards,
Szabolcs Rozsa
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The web-based online PPP processing services (e.g. AUSPOS) have ITRF2014 output (not the WGS84 output). Thanks!
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There is no need to transform the ITRF2014 coordinates. "ITRF20014, ITRF2008 and WGS84 (G1674) are likely to agree at the centimeter level", see https://confluence.qps.nl/qinsy/latest/en/international-terrestrial-reference-frame-2014-itrf2014-182618383.html .
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i want to prospect ground water in rocky terrain using satellite imagery. i need to know the most suitable data to be use, the method of extraction and the procedure for achieving it. Thank you in anticipation of your useful contribution.
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For automatic lineament extraction, you can achieve this by applying a combination of the following softwares: Arcmap 10.0+, ENVI 5.1, PCI GEOMATICA 2016, ROCKWORKS 16.
STEP1: Use ENVI software to perform principal component analysis (PCA) on the spectral image band of Landsat8.
STEP2: GEOMATICA is used to perform an automatic lineament delineation from the PC1.tiff generated from ENVI. This is done with the aid of lineament extraction algorithm in the Tool from toolbar
STEP3: ARCMAP is used for handling extracted lineament (splitting compound line into simple lines, editing lineament attribute, exporting lineament as cad file
STEP4: ROCKWORKS is used to process the exported lineament Cad file to determine the trend of the lineament and hence generating rose diagram.
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I did some experiments in Indonesia. Nowadays RTK GNSS receivers seem to work better when under vegetation canopy (fixing ratio more than 90%). Is this real, or just a system tweak?
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The improvement is mainly because of large number of GNSS satellites above the receiver (GNSS) at any given point of time. This primarily improve the error adjustments and thus increase the accuracy. However, the issues under canopy still remains to some extent depending on its density.
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Elevations in S0 Terrengmodell Svalbard (dataset by Norwegian Polar Institute, 10.21334/npolar.2014.dce53a47) are above sea level. I have some GNSS measurements above WGS84 ellipsoid and want to compare them with S0 DTM, hence I need to know the conversion from original above-sea-level altitudes to WGS84 elevations. I am not sure what conversion was used to construct S0 Terrengmodell - was it one of global geoid models (EGM96, maybe?) or some local height system corrections. I can't find any data myself (in Eglish at least). Does anybody know this technical details?
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as Elevations in S0 Terrengmodell based on mean sea level or the geoid, and since WGS84 ellepsoidal heights were based on the ellepsoid surface, you have to know the geoid height (i.e the difference between the ellepsoid surface and the surface of the geoid - mean sea level surface) to convert the ellepsoidal heights to mean sea level heights which are comparable with the S0 DTM.
For accurate conversion ask for the Norwegian geoid model for the area under consideration, otherwise you can get the estimated geoid from the EGM2008 global geoid model.
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I am working on some research related to the enhancement of smartphone positioning technologies. I am curious about the format of the GNSS data stream from GNSS chipset on smartphone. I've been researching on the use of external GNSS receiver to enhance the positioning of smartphone users e.g using GNSS module from u-blox, skytraq etc.
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1. Suggestion: Why you are using external receiver/s to improve the positioning, I mean you can use built-in system to improve the solution. contact me for further help.
2. In your case, use Matlab, goGPS, GoogleEarthPro, GPS Track Editor, SBG Center or any other related live simulations where you can see each and every details you required.
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Hello,
I saw that in the rinex format there is a transmission time for the broadcast ephemeris. 
 I was wondering where in the nav message (i.e. which subframe/word number) is the transmission time being transmitted?
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I believe this is when this particular ephemeris dataset is either first broadcast or first received by a ground receiver.
For GPS this is roughly 2-hours before the Toe
For GLONASS this is roughly 15-minutes before Toe
For Galileo, it's a bit puzzling that the transmission time is like 11-minutes or so after Toe. Does anyone know why?
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I'm looking for information on the size of the global satellite industry - both commercial and whatever information is available on government. I'd like to know more about the number of satellites in the various orbits, number of geosynchronous satellites, construction and launch cost data, and potential future uses.
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Euroconsult's report
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I am using a SPIRENT simulator to generate GNSS and WASS signals. I am receiving the RF signal on a NovAtel receiver. The NovAtel connect software shows that the WAAS signals are available but it indicates that “the WASS signals are not used in the solution”, Any one can help?
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First, is the receiver authorized for WAAS? You have to purchase that option and have it enabled on the receiver with the auth code. Assuming that you have a WAAS enabled receiver use the following commands for WAAS:
psrdiffsource sbas
sbascontrol enable waas
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Hello Everyone,
I have a very basic question regarding BPSK modulation.
I am working on GNSS signals, and I came across BPSK(5) modulation scheme. But I don't know that what this "5" means?
As per my understanding, this only tells about the chipping rate of the modulating signal. which is 1.023Msps in BPSK(1), and here it is BPSK(5), so it means that the chipping rate would be 5*1.023Msps.
Can someone please make it clear for me that my understanding is correct OR is there something else that I am not getting?
Thank you
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Hi,
Yes it's exctly that ! The numbre inside the bracket is in reference of the GPS spreading code frequency, 1.032MHz.
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I want to know if it is possible to estimate coefficients of Marini-Murray mapping function from GNSS data in PPP processing. Or there will be a strong correlation with ZTD?
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of course*
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I am trying to use GAMP (GNSS Analysis software for Multi-constellation and multi-frequency Precise positioning) in my research, and I have a question.
How can I obtain single solution for ppp_static mode?
In other word, I want the final coordinates of the station instead of all epochs coordinates.
Attached configure file and position file.
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Interpreting your output file in matrix form, here is the description for the columns:
  1. Column 1: 4-digit year
  2. Column 2: month
  3. Column 3: day
  4. Column 4: hour
  5. Column 5: minute
  6. Column 6: second
  7. Column 7: GPS week
  8. Column 8: GPS seconds of week
  9. Column 9: East-coordinate
  10. Column 10: North-coordinate
  11. Column 11: Up-coordinate
  12. The associated errors are contained in 12th, 13th ...and nth column. These are provided with respect to epoch in your output file.
  13. You can get the mean of 12th, 13th and 14th column to obtain errors in East, North and Up components.
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In the Global Navigation Satellite System (GNSS) online processing services, there are two algorithms for the solution: Double Difference (DD) and Precise Point Positioning (PPP).
My question: which one gives a precise solution in the following time periods:
1- At the duration between (1 - 3 hours).
2- At the duration more than 10 hours.
Thanks for your Interest...
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You're welcome Murtadha Sarhan ,
I'm pretty sure DD will achieve better results than PPP.
Generally each country has its densified network of continuous GNSS tracking stations with adjusted coordinates (or known coordinates), i.e., an official geodetic reference system.
IGS network stations are really scarce, when you want to work with a short baseline and reduce tracking time.
One suggestion is to track a vertex (Base) for a longer time (for example, 4 hours) and simultaneously track other vertices for 15 min (Semi kinematic Method - Stop and Go), with baselines smaller than 20 km. With this method you can achieve accuracy better of a few centimeters.
If the Base has known coordinates, then you can apply directly the DD method, but if it is not known (which happens in most cases), you should perform static relative processing with the closest stations of the geodetic network in your region.
It's a little complicated to explain everything with a few words, but I hope you have understood the main idea.
I suggest consulting the following book:
Satellite Geodesy, 2nd Ed. Günter Seeber
It covers very well all these methods of positioning.
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Presently, I am determining local geoid model of an area using the gravimetric-geometric method and I am sensing that there would be large differences between the known orthometric heights of selected points and the orthometric heights of the same points obtained from the local geoid model, someone should please tell me what to do in such situation.
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Dear Okiemute,
I agree with Dr. Ruby. Just want to add, go for 7-parameter model to account for bias and tilts in the geometric and gravimetric values. It presents better results as compared to 4-paramter model.
Regards,
Ropesh Goyal
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VTEC data calculated from GNSS observations, need to plot it over a regional area but the format as ionex file and calculated within 15min /day
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Dear Mohamed Freeshah,
you could try my Python script (https://github.com/Albom/GNSS_utils/blob/master/test_ionex.py). It produces output data in gnuplot data format. It also possible to plot world map on the same plot.
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Ussually, we use running average to detrend total electron content (TEC) data from GPS(GNSS) and to filter required period range. Could someone recomend a paper devoted to comparison of different filters for this purpose.
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Dear Yury,
Check out this paper...
"Identification of vertical total electron content by time series analysis, Digital Signal Processing 19(4):740-749, 2009 by Erdogan H and Arslan N."
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How to calculate Ionospheric Pierce Point value from azhimut and elevation angles for a dual frequency GNSS data?
I would like to work out the height of maximum electron density of ionosphere.
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You can use the papers previouly cited together with Lat and Long of the location of the receiver. But for such calculation, there is no need of a dual frequncy dara!
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Regularly, geodesists at international colloquium wonder what is the next big step in geodesy (see Geodesy and its future, A. Dermanis & F. Sanso /the role of geodesy – C. Rizos – FIG 2012). If we exclude engineering applications associated with the rise of GNSS and all the new constellations (GLONASS, Beidou, Gallileo,…) which will indubitably promote new technological niches in the Location Based Services market beyond navigation and tracking applications.
We are then left with the applications of geodesy to geosciences a.k.a environmental geodesy- e.g. . the study of reference frame in geophysics with plate tectonics movement & earth rotation; oceanography with multiple applications including the measurements of tides, height datum and bathymetry; in climate change – geodesists estimate the sea-level rise around the world. Nowadays, geodesists need to analyse different satellite missions (GNSS, GRACE, satellite altimetry …) and correlate various observations in order to produce robust models and describe/discover new natural phenomena. Thus, does the future of environmental geodesy rely on AI and big data algorithms to process & analyse large amount of data and build empirical models used in the analysis/prediction of natural phenomena? With the need to monitor closely climate change, geodesists will be involved in studies involving the data analysis of future satellite missions (see my previous question on “big data and climate change”).
Last but not least, with the willingness of exploring Mars and other planets, a future field of interest may be the application of geodesy in the analysis of geophysical phenomena occurring on those planets…. What do you think?
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alright. All clear. Thanks for sharing.
Best Wishes, Jean-Philippe
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Hello,
Let us assume we have a cellular antenna. I consider the frequency 800 MHz. I want to co-locate next to my antenna GNSS and SDARS antennas. The 2nd and 3rd harmonics of 800 MHz fall in the L1 band of GPS and SDARS range, respectively. What considerations must be taken regarding the isolation between antennas? is it enough to have a large isolation, or would I need ,too, to have a strong attenuation at the 1600 and 2400 MHz?
Thank you1
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Montaha,
Adding to the colleagues above, i would like to comment your question from the fundamental point of view. You have three antennas which lay near to each other,
One transmit antennas and two receiving antennas. Every antenna has its own port to connect it to its rf front end. Assume this ports are P1,P2,and P3, respectively.
If the antennas are couples you can measure the coupling between them by the transmission coefficients S21,and S31 with anrtenna 1 is the transmitting antenna. In order to measure how far the antennas are isolated from each other you have to measure S21 and S31 at the intended frequency.
As isolation between antennas increase S21 and S31 will get smaller. For complete isolation S21 and S31 will be zero and the attenuation will be infinity.
So, things are put in its context.
Best wishes
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It's true that elevation from GPS receivers are measured from the ellipsoid as a reference rather than the geiod/mean sea level (MSL). This topic is a little trick though.
But my question is whether there are specialized GPS receivers that are capable of doing the conversion from ellipsoid to orthormetric and hence output othormetric elevation. Or is there any way any GPS receiver can be tweaked to do this calculation automatically?
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GPS/GNSS receivers do not give orthometric heights, they only give ellipsoidal heights. This is because, the heights are geometric as they are computed with respect to the ellipsoid. Orthometric heights are obtained with respect to the geoid/MSL. Orthometric heights can only be obtained from processed GPS/GNSS observations if the local geoid model of the area of observation is applied.
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Hi,
working with extended and unscented Kalman filter brings me to the question, how I can compare them in simulations as fair as possible.
My first intent was to choose the process noise matrix Q and measurement noise matrix R for both filters in the same way.
I found out, that my UKF works much better for 10*R, while the EKF is more accurate for 1*R. I do offline simulations for a navigation problem, using measured IMU and GNSS data.
My feelings says me, that even for same noise matrices, the comparison is not as easy as I thought, because of the sigma points building procedure and so on...
I found that paper:
which says that EKF can perform better covariance estimations in certain regions (higher mean estimates).
Has somebody some tips for me, regarding that topic?
Best regards,
Max
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For nonlinear estimation, both the EKF and the UKF are approximate strategies. The propagation of the error covariance matrix P is simplified by the use of Jacobian in the EKF and the choice of sigma points in the UKF.
Though Q and R matrices generally refer to the process noise covariance and measurement noise covariance respectively, they can also compensate for the errors in the approximation of the propagation of the error covariance P. That is, in the EKF Q can be tuned such that it compensates for the loss of higher order information that result from linearization. The same holds for the UKF too.
To sum up, Q and R can be tuned to represent a little more than process noise and measurement noise for nonlinear Kalman-based estimation schemes. This gives rise to difficulty in tuning for some applications. Since you work with simulated data, you can easily verify if your tuning is reasonably correct by checking if the actual error covariance is approximately close to the one obtained by the filter. This implies that the estimation scheme works reasonably well. In the absence of the true state value as happens in real-world situations, the innovations can be compared.
Coming to the specific case, if you want to do the fair comparison tune both the estimation schemes separately to obtain the best results. Then compare them as pointed out early.
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Dear all
if I have the SD carrier-phase measurements how can I compute the SD residuals? Do i need to calculate the SD residuals before fixing the integer ambiguity?
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you can compute the SD as
SD = PR - Range
Where PR is measure psuedorange and range can be calculated through distance equation, using own and satellite position.
In ground based systems, survey techniques are utilized to find the own position, which is a preferred method. However in dynamic situations, the measured position can be used as own position. Using measured position in SD is not suitable for finding the error corrections, but could use for integrity calculations.
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Automatic Dependent Surveillance Broadcast (ADS-B) is a key avionics technology used for aviation cooperative surveillance (i.e., aircraft separation assurance and collision avoidance). However, the absence of adequate security features makes this system vulnerable to a number of cyber-physical threats (jamming, spoofing, meaconing, etc.). What technological solutions can be introduced to address this challenge?
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Dear Charles,
Thank you very much for your message and for the valuable documents. I am also very actively involved in this line of research. A recent paper on GNSS performance threats and augmentation strategies in aviation was recently published in JPAS (for convenience, the link is provided below):
In addition to addressing GNSS issues, it would be nice working together and investigating the feasibility of specific safety features that could be included in the ADS-B data-link as well.
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I am working on GNSS signal L5 band. I want to obtain the I/Q signal from it with a PXIe-5624R IF Digitizer. Does the sampling frequency is enough for that application ?
Moreover, does someone have some exemple of the implementation of the PXIE-5624R in Labview environnement ? No one are provided by NI...
Great Regards
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Direct sampling of RF signal requires a notch filter at front-end to reject signal in other bands, otherwise all unwanted signals will also get sampled.
2GS/s is more than enough for working on L5.
The advantage of Direct sampling is that you do not need down conversion, but the requirement of notch filter is too stringent that it is impossible to be realized.
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To get the STEC i want IONEX file of IRNSS data. Any way to get it ?
is it possible to extract the STEC from RINEX file ?
Any suggestions ?
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IRNSS RINEX files provides you raw measurements (observation file), satellite ephemeris (nav files). They do not have slant TEC values, you will need to compute them from these measurements.
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I have 24 hours dual frequency GPS observations of 10 points 
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Just a quick update: The Bern server has been changed to a new host name. The CODE maps can now be retrieved from here: ftp://ftp.aiub.unibe.ch/CODE/
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Anyone out there, please help me with this. I can't understand what vertical delay values are used here and how to put that in the matrix ?
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thank you so much sir
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I never use Bernese to process GNSS data before
Is there anyone can help me?
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I briefly explain the methodology i used for the GNSS processing, I hope it may help you!
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GNSS Processing - PPP
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there is very good open source GAMP software . I am using it for multi-signals, Its free
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Over the past decades, there has been some interest in performing data wipe-off for processing GNSS signals (e.g. GPS L1 C/A) as a pilot signal. Knowledge of the navigation data allows a receiver to preemptively remove it, transforming the data signal into a pilot signal, and thereby allowing the receiver to perform arbitrarily long coherent integration. The benefits of this include weak-signal processing and, in some cases, multi-path mitigation.
Techniques to do this currently include prediction of large parts of the navigation data, given knowledge of the data structure and observed patterns in the repetition of data (there are many patents on this technique); or the more simple approach of using a reference receiver with a clear view of the sky to observe and relay the data bits.
Both of these approaches have limitations: the prediction of navigation data might not be perfect, and there are always epochs where the data is either (predictably) unknown, or is guessed in error; while the use of a reference receiver incurs a latency.
One approach to circumvent both of these problems would be to listen to the navigation data while it is in uplink from the ground-segment. This would simultaneously avoid the errors incurred by guessing the navigation data; while also avoiding the delay associated with a reference receiver gathering the data.
Given the link budget for uplink stations, it is likely that sufficient power might be observed in the side-lobes of the uplink station, for a nearby ground-based observer to readily demodulate the data.
Can any researchers out there confirm whether this is possible, or if it is being done? Are there any obvious flaws in this approach – perhaps some that I am missing?
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sounds interesting. but, I think this would be useful not because of the signal propagation time (120-130 ms) but because it takes so long (i.ie. few minutes ) to download the message via the satellite signal which might be obtained at much higher rate through internet or other networks.
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I would like to know how can I determine the DOP (Dilution of Precision) at any point in time based only on NMEA messages recorded by mobile phone? I want to check whether the HDOP, stores in NMEA GGA message, is correct. Is it possible? Do You suggest something else?
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Hi dear Mariusz
You can find your phone on the link:
Please make sure, that your phone support GNSS data, then there are several number apps to procces them.
Best regards
Arash
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GPS - Global Positioning System
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Thank you Kartik for your additional information
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Some people think that DGPS only applies to GPS code measurements techniques. In contrast, the phase measurements are called  as relative. Is it true?
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"Some people think that DGPS only applies to GPS code measurements techniques. In contrast, the phase measurements are called  as relative. Is it true?"
I think there is a mix of terms that should be clearified, so better think of Concepts and Methods / Techniques.
There are two concepts to obtain positions (and other estimates) out of GPS/GNSS observations:
  • Absolute positioning (error budget has to be known, estimated for any terms in the observation equation; zero-differencing)
  • Relative positioning (error budget is canceled out or reduced to a minimum due to observation differences)
Differential GPS is a techniques that is used with code observations only, the accuracy is around 0.5 - 1.0m depending on the equipment used in the application. With this technique, its possible to achieve respectable estimates by using single-frequency receivers only. Nevertheless, differential GPS is a relative method as observations are improved (error budget is reduced) due to differences of observations.
You are also right that the term of relative positioning is ofthe used in combination with the phase measurements, for example during coordinate estimation in networks (dual frequency, code+carrier, single/double differencing). One prominent example for real time applications is RTK (real time kinematic), which is also a relative method, but uses the combination of code and phase and is applied to dual-frequency equipment/observations.
I think from my side, there is always the need to name the concept and the method / technique:
  • concept: absolute positioning: (method: single point positioning (SPP) for code; precise point positioning (PPP) for code+phase observations)
  • concept: relative positioning (method: Code - DGPS/DGNSS, Code+Carrier: Double differencing (DD), single differencing (SD), real time kinematic (RTK), etc.)
Hope this helps to clearify the issue.
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a recommendation for a lecture of GNSS reference book
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books written by prof. Bernard Hofmann-Wellenhof et al., or by prof. Alfred Leick.
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What kind of position accuracy measures do you use to determine the positioning accuracy of GNSS receivers?
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Concerning accuracy and precision, always I saw that that most of people make confusion. In the paper from Novatel, provided by Emilio Ramirez-Juidias also there is a misunderstanding. Accuracy, by definition is composed of bias and precision, ie, systematic and random errors. And always, if the precision is not good, the same will occur with accuracy. In the figure 1 provided in the paper, one of the example is not correct. The third one, where they say High accuracy, and low precision, should be Low accuracy as well. Like defined by Gauss, long time ago, one measure of accuracy may be given by sqrt(bias^2+precision^2). In a nutshell, the problem is to think that the bias is the accuracy.
GPS can provide very high precision (cm to mm) and if all systematic errors are very well modelled, can also provide high accuracy.
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Different smartphone use differenct GNSS receivers. What is their static and dynamic accuracy?
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Dear Prof. Specht,
your reseach meets my interests since my colleagues and me are working on smartphone's GNSS capability together with students for geodetic purposes (students project).
You asked for the accuracy of different GNSS receiver types for different manufactures. The question is: On which kind of accuracy you are interested in? Positioning? Timing? Velocity? Are you interested in the overall P-N-T accuracy? There are also important points like stability and continuity of observation types like carrier phase and code phase (pseudorange) as well as the performance of the used/installed antenna.
From my geodetic point of view it is the optimal procedure to determine the precision and accuracy of your unit out of the raw data which your unit provides.
Current Android systems (up to Android 7) support to access the real raw-data like carrier phase, code phase (pseudo ranges) and signal-to-noise (C/N0) ratio. At least the carrier phase observation is highly interesting for using smart devices as smartphones in high precision positioning. Besides of classical SPP-Algorithms (single point positioning) the carrier phases allows you to use PPP (precise point positing).
Please find a list of how to access raw data in smartphones:
Here is a very intersting aticle on how the performance of different units could be evaluated:
Beside of this, if you have access to a smartphone which is capable to store GNSS raw data, you could use a RINEX logger app:
to store observations in an independent format (RINEX - receiver indepenent Eexchange format) for further post-processing.
I really recommend the remarks of Pawel Prestrzelski.
Perhaps, clarify which kind of observation type (carrier phase or code phase) you are using and for which observation type you like to calculate the accuracy and / or precision.
as recommended by Pawel Prestrzelski please really make use of the raw measurements that your unit possible provides. The preprocessed solutions (internal position solution etc.) are in most of the cases a rough/errorneous solution or a solution with furhter conditions, which are not reported transparently. Your device could be more accurate and precise, if your data is processed with own algorithms and stochastical models where you know and can control everything.
To compare the units and to evaluate the accuracy and precision, I suppose the following procedure:
static:
  • capture data for 24 hours (maybe repeat for 2-3 days) on a fixed, static, repeatable mounting,
  • take care of the entire conditions around the smartphone (location of antenna, where is the smartphone located during measurments, buildings etc.) and take possible obstructions into account
  • compare the continuity of code phases (pseudo ranges) and carrier phases, maybe you have also access to the doppler and the signal-to-noise ration (C/N0).
  • calculate your ow position solution algorithm.
In our project we use the following method, to evaluate the quality of smart devices:
kinematic:
  • RTK-unit for reference solution
  • record observation on trajectories (RINEX) with smartpone and simultanously with RTK-unit.
  • compare online quality of both trajectories (rough test only) and post-process both trajectories while the RTK-Trajectory will be your target trajectory.
  • process form these data the precision, accury and correctness of your trajectories captures with smart devices.
....furhtermore, applications like PPP-RTK are highly interesting for such approaches.
From my experiences and point of view, the accuracy and precision of your smart devices is (1) strongly depending on the quality of the observation data delivered by the units and (2) depending on the algorithms you use, to process your observation for Positioning, Navigation and Timing (PNT).
Hopefully my remarks assist you by answering your questions.
Best regards,
tobias
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Can integer-phase-clock-products be used for real-time PPP? Does it have a real-time stream?
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Yes, apparently. I have not tried it but I know that there are dedicated real-time streams  CLK11, CLK93 available at products.igs-ip.net 
You may access those data streams using RTKLIB or BNC software. You may also look through the source table and find them at that host using your web browser.
To access the data streams you will need to register here: https://register.rtcm-ntrip.org/cgi-bin/registration.cgi
You may find description of the streams using the link below.
Best regards,
Leonid
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I’m doing a little research about the real impact of threats (jamming, spoofing, meaconing) in GPS+SBAS certified aviation receivers and how realistic the authentication need would be. Any comment, suggestion, information about research articles you could give me, will be helpful. Thank you very much in advance for your time and help.
Best regards,
Adriana.
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We have touched a little on this in SESAR - see enclosed papers. It's possible that Rainer Kölle or John Hird may have some additional input,
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In GPS precise point positioning (PPP), we get several corrections from IGS. My question is about how to utilize these corrections in an accurate way.
1. Is there a free software to interpolate orbits and sat. clk from SP3c file? I want these results not the final positioning solution.
2. Is there is an automatic way (via software)  get the satellite antenna phase center offset and variation?
3. Do we need to use the earth rotation parameters if I am doing my code in the ECEF frame and not transforming to inertial frame?
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Just to clarify, I am somehow now  able to answer my questions:
1. some commercial software like Bernese is doing the interpolation. However, doing my own code for Lagrange interpolation of order 9  gave me very good results. 
2. I couldn't find an online tool to read the atx file, but with some coding skills and following the format of the file, we can make a code for ourselves. Otherwise, the Phase center offsets can be take copy and paste from the file knowing its location there (this is not good if it will be needed frequently).
3. No, we don't. (It might be needed in the tidal and other detailed corrections, still not sure but to reach the centimeter-level accuracy, you don't need it as long as you work in the ECEF frame.
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I am performing a static PPP positioning and I have got the precise ephemeris from IGS rapid corrections. I got bad results compared to the satellite positions estimated by the NovAtel receiver which should not be the case. The precise data itself even before interpolation has around 300-1000 meter error compared to estimated position by receiver! What am I missing?
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Dear Mohamed, i do not process PPP in separated parts. I´ve  used the software available at Canadian Spatial Reference System (CSRS) page, for automatic processing.
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I want the function (java code) of finding the Longitude, latitude and altitude of a location in smartphone when using four positioning systems (GPS , GLONASS, BeiDou, Galileo). In other words, how the geographical location is extracted in phones by receiving signals from multi-GNSS systems
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Hi,
it's not so simple, since it's not just a couple of functions you are looking for. You might want to take a look here for a basic introduction to code-only positioning: http://www.navipedia.net/index.php/Code_Based_Positioning_(SPS)
But the whole process is long and complex. If you wish to go through code that does the positioning, you can take a look here:
...but then you would have a simple epoch-by-epoch code-only positioning, which is not as complex as what your phone does for positioning. But it's the basis to get there.
Then if you want to consider also the problem of multi-GNSS, you have to take into account also the so-called inter-system biases (ISB). However, I would suggest to start from a GPS-only solution, then move to multi-GNSS once you have understood it.
Cheers,
Eugenio
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In VTEC maps that have been created from GNSS differential phase measurements of the TEC, the ionospheric pierce point is often shown. TEC that is measured over 20 200 km is mapped to somewhere between 400-600 km.
In GNSS computerized Ionospheric tomography (CIT), the electron density maps are only shown to an upper altitude of 600-1000 km.
Above what altitude is the contribution to the TEC considered negligible? Stankov et al. 2003 state, "The electron density above approximately 2000 km contributes little (less than 5%) to the integrated electron content and above the mean height of the plasmapause (25,000 km) the contribution is negligible." I seem to recall reading the contribution above 1000 km "is negligible" in another paper. What is the consensus?
Please provide a reference for a characteristic altitude.
For completeness, I believe the lower limit of the TEC integral is at about 60 km, assuming the tropospheric contribution is also negligible. Please correct me if I'm wrong.
Cheers,
Alex
Stankov et al., 2003,  A new method for reconstruction of the vertical electron density distribution in the upper ionosphere and plasmasphere, available from: http://onlinelibrary.wiley.com/doi/10.1029/2002JA009570/full
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It depends on your location; although, 1000km is too low a boundary even in the best cases. At high latitudes, where there is virtually no plasmasphere, the contribution above 1500-2000km or so is generally negligible; however, at the equator one would have to consider electron density out to the plasmapause region. This will also depend on time of day, season, geomagnetic activity, and solar activity. For your own reference, try creating a few electron density profiles with the Gallagher Plasmaspheric Model (an extension of the IRI). See the following for some codes: https://plasmasphere.nasa.gov/models/ These models can at least give you a rough feel to assess the significance of plasmaspheric TEC in the context of what you're interested in researching and provide a starting point.
There has been a considerable amount of work done by Andrew Mazzella and his colleagues on assessing the plasmaspheric contribution and effects on GPS observations. I would consult his work as well.
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Hello everybody. I am interested on studies about the use of GPS/GNSS stations on geodynamics. Someone could sugest me some bibliography? Thanks in advance!
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Agarval M, Singh R, Meshram MK (2013) Linearly polarized planar inverted F-antenna for Global Positioning System and woldwide interoperability for microwave access applications. IET Microw. Anten. Propag. 7(12): 991-998
Ahn J, Kim S, Byun J, Kim AS, Kim Y (2013) Compact PCB-embedded GPS antennas loaded with a coupling strip and lumped elements for mobile phones. Microw. Opt. Technol. Lett. 55(2): 363-366
Akala AO, Rabiu AB, Somoye EO, Oyeyemi EO, Adeloye AB (2013) The response of African equatorial GPS-TEC to intense geomagnetic storms during the ascending phase of solar cycle 24. J. Atmos. Solar-Terr. Phys. 98: 50-62
Akala AO et al. (2013) Comparison of equatorial GPS-TEC observations over an African station and American station during the minimum and ascending phases of solar cycle 24. Ann. Geophysicae 31(11): 2085-2096
Aktuğ B, Yildirim O (2013) Regularized estimation of Euler pole parameters. Earth Planets and Space 65(7): 699-705
Aktuğ B et al. (2013) GPS constraints on the deformation of Azerbaijan and sorrounding regions. J. Geodynamics 67(SI): 40-45
Aktuğ B et al. (2013) Deformation of Central Anatolia: GPS implications. J. Geodynamics 67(SI): 78-96
Alam N, Kealy A, Dempster AG (2013) Cooperative inertial navigation for GNSS-challenged vehicular environments. IEEE Trans. Intell. Transp. Syst.14(3): 1370-1379
Alba D, Fairley P (2013) Interplanetary GPS comes a step closer. IEEE Spectrum 50(7): 11-13
Alem LN, Passini HF, Minutta RA (2013) Embedded system for the command of a high-gain antenna pedestal with GPS coordinates. IEEE Latin Am. Trans. 11(1): 190-195
Alfonsi L et al. (2013) Comparative analysis of spread-F signature and GPS scintillation occurrences at Tucumán, Argentina. J. Geophys. Res.-Space Phys 118(7): 44483-4502
Al-Shaery A, Zhang S, Rizos C (2013) An enhanced calibration method of GLONASS inter-channel bias for GNSS RTK. GPS Solutions 17(2): 165-173
Amerian Y, Hossainali MM, Voooghi B (2013) Regional improvement of IRI extracted ionospheric electron density by compactly supported base functions using GPS observations. J. Atmos. Solar-Terr. Phys. 92: 23-30
Amerian Y, Voosoghi B, Hossainali MM (2013) Regional ionosphere modeling in support of IRI and wavelet using GPS. Acta Geophys. 61(5): 1246-1261
Amiri-Simkooei AR (2013) On the nature of GPS draconitic year periodic pattern in multivariate position time series. J. Geophys. Res.-Solid Earth118(5): 2500-2511
Amiri-Simkooei AR, Zangeneh-Nejad F, Asgar J (2013) Least-squares variance component estimation applied to GPS geometry-based observation model. J. Surv. Eng. 139(4): 176-187
Anquela AB, Martin A, Berné JL, Padin J (2013) positioning. J. Surv. Eng. 139(1): 47-58
Ao CO, Haij AJ (2013) Monitoring the width of the tropical belt with GPS radio occultation nmeasurements. Geophys. Res. Lett. 40(23): 6236-6241
Aoyama Y, Doi K, Shibuya K, Ohta H, Tsuwa I (2013) Near real-time monitoring of flow velocity and direction in the floating ice tongue of the Shirase Glacier using low-cost GPS buoys. Earth Planets and Space 65(2): 103-108
Aranzulla M, Cannavo F, Scollo S, Puglisi G, Imme G (2013) Volcanic ash detection by GPS signal. GPS Solutions 17(4): 485-497
Ardaens JS, D'Amico S, Cropp A (2013) GPS-based relative navigation for the Proba-3 formation flying mission. Acta Astronautica. 91: 341-355
Astafyeva E, Rolland L, Lognonne P, Khelfi K, Yahagi T (2013) Parameters of seismic source as deduced from 1Hz ionospheric GPS data: Case study of the 2011 Tohoku-oki event. J. Geophys. Res.-Space Phys 118(9): 5942-5950
Bachman W, Oliveira M, Xu J, Sabina E (2013) Household-level global positioning system travel data to measure regional traffic congestion. Transp. Res. Record 2308: 10-16
Bakula M (2013) Study of reliable rapid and ultrarapid static GNSS surveying for determination of the coordinates of control points in obstructed conditions. J. Surv. Eng. 139(4): 188-193
Banville S, Langley RB (2013) Mitigating the impact of ionospheric cycle slips in GNSS observations. J. Geod. 87(2): 179-193
Basha G, Ratman MV, Manjula G, Sekhar AVC (2013) Anomalous propagation conditions observed over a tropical station using high-resolution GPS radiosonde observations. Radio Sci. 48(1): 42-49
Bevis M, Brown A, Kendrick E (2013) Devising stable geometrical reference frames for use in geodetic studies of vertical crustal motion. J. Geod.87(4): 311-321
Bhuyan PK, Hazarika R (2013) GPS TEC near the crest of the EIA at 95 degrees E during the ascending half of solar cycle 24 and comparison with IRS simulations. Adv. Space Res. 52(7): 1247-1260
Bidaine B, Lonchay M, Warnant R (2013) Galileo single frequency ionospheric correction: performance in terms of position. GPS Solutions 17(1): 63-73
Bierlaire M, Chen JM, Newman J (2013) Aprbabilistic map matching method for smartphone GPS data. Transp. Res. (Part C) 26: 78-98
Blewitt G, Kreemer C, Hammond WC, Goldfarb JM (2013) Terrestrial reference frame NA 12 for crustal deformation studies in North America. J. Geodyn. 72: 11-24
Blondi R, Ho SP, Randel W, Syndergaard S, Neubert T (2013) Tropical cyclone cloud-top height and vertical temperature structure detection using GPS radio occultation measurements. J. Geophys. Res.-Atmospheres 118(11): 5247-5259
Bonafoni S et al. (2013) Assessment of water vapor retrievals from GPS receiver netwok. GPS Solution 17(4): 475-484-1322
Bonforte A, Guglielmino F, Puglisi G (2013) Interaction between magma intrusion and flank dynamics at Mt. Etna in 2008, imaged by integrated dense GPS and DInSAR data. Geochem. Geophys. Geosyst. 14(8): 2818-2835
Bonnefond P, Exertier P, Laurain O, Thibaut P, Mercier F (2013) GPS-based sea level measurements to help the characterization of land contamination in coastal areas. Adv. Space Res. 51(8): 1383-1399
Boroujeni BY, Frey HC, Sandhu GS (2013) Road grade measurement using in-vehicle, stand-alone GPS with barometric altimeter. J. Transp. Eng.139(6): 605-611
Bos MS, Fernandes RMS, Williams SDP, Bastos L (2013) Fast error anaysis of continuous GNSS observations with missing data. J. Geod. 87(4): 351-360
Botteron C et al. (2013) Soil moisture & snow properties determination with GNSS in Alpine environments: Challenges, status, and perspectives.Remote Sens. 5(7): 3516-3543
Boutiouta S, Lahcene A (2013) Preliminary study of GNSS meteorology techniques in Algeria. Int. J. Remote Sens. 34(14): 5105-5118
Bowling T, Calais E, Haase JS (2013) Detection and modelling of the ionospheric perturbation caused by a space shoutle launch using a network of ground-based Global Positioning System stations. Geophys. J. Int. 192(3): 1324-1331
Branzanti M, Colosimo G, Crespi M, Mazzoni A (2013) GPS near-real-time coseismic displacements for the Great Tohoku-Oki earthquake. IEEE Geosci. Remote Sens. Lett. 10(2): 372-376
Brenot H et al. (2013) Preliminary signs of the initiation of deep convection by GNSS. Atmos. Chem. Phys. 13(11): 5425-5449
Cahyadi MN, Heki K (2013) Ionospheric disturbances of the 2007 Bengkulu and the 2005 Nias earthquakes, Sumatra, observed with a regional GPS network. J. Geophys. Res.-Space Phys 118(4): 1777-1787
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