What Constitutes GNSS - Essay Example

GNSS By Table of Contents Table of Contents INTRODUCTION 3 GNSS 3 METHODOLOGY 11 Online services 13 TRANSFORMATIONS 13 RESULTS AND ANALYSIS 17 CONCLUSIONS 21 REFERENCES 22 INTRODUCTION GNSS are the assemblages of the satellites designed to offer positioning and timing information for the users on Earth. It has made navigation affordable for most people since it enable estimation of position, velocity and time through processing signals transmitted from the satellites within the known orbits. Global positioning system is the most significant and universal utility within the modern navigation. GPS consists of ostensibly twenty-four satellites in roughly twelve-hour orbit. During GNSS measurement, a number of errors reduce the position ground precision. Accomplishment of survey grade precisions for engineering work demands mitigation of the underlying errors. Differential (D) GNSS methods are usually utilized to lessen the majority of errors whilst reference stations having known coordinates allow the measurement of the relative errors. Relative errors are as the modification parameters in actual time or corresponding post analysis. Moreover, it has been the chief surveying method used to accomplish centimeter precisions for the previous decades. Precise Point Positioning (PPP) is as an alternative to differential technique. PPP accomplishes centimeter accuracies were utilizing solely by a single receiver through precise orbital and clock data rather than standard broadcast navigation message within post positioning. Conventional means of undertaking post processing are through online PPP post processing services. The paper aims at assessing the PPP method for surveying in terms of the x,y and z accuracies accomplished from the corresponding online PPP post-processing services. Presently no research has been undertaken regarding the use of PPP measurements within Ireland. Since GNSS orbit and clock products are known nature global, PPP is swiftly becoming a method that has the possible of substituting underlying range limited GNSS relative positioning techniques GNSS GNSS consist of three main satellite technologies namely GPS, Glonass, and Galileo. Each of the components of GNSS includes three segments. The three segments are space, control, and user segments. The parts are identical for the three satellite technologies thus making up the GNSS. Currently, the complete satellite technology is the GPS technology and majority of the prevailing universal applications associated with the GPS technology. Thus, GNSS technology will be active subsequent to the operation of the Galileo and the corresponding reconstruction of the Glonass in future. i. Global Positioning System GPS has a massive substantial effect on positioning, triangulation, timing and monitoring applications. It offers mainly coded satellite signals that can be processed in a GPS receiver, permitting the receiver to approximate the position, velocity, and time. Four GPS satellite signals employed in the computation of the positions, which occurs in three dimensions, and the corresponding time offset within the receiver clock. GPS comprises three principal components. Space segment possesses GPS satellites. Moreover, the space vehicles send radio signals from the corresponding space. The control section consists of the system of tracking stations situated in the universe. GPS User Segment of the GPS receivers and the relevant user community. GPS receivers convert space vehicle signals into the underlying position, velocity, and time approximates. The satellites are in six primary orbital planes on circular orbits with an underlying altitude of approximately 20,200km above the prevailing surface of the Earth, mainly inclined at 55 degrees with respect to the underlying equator. a. GPS Signals The generated signals on board of the satellites are from generation of the fundamental frequency approximated to be 10.23MHZ. The signals are usually controlled by an atomic clock and possess stability within a particular range. Two carrier signals within the L-band are by integer multiplication of the fundamental frequencies. The carriers are usually biphase modulated by the codes to offer satellite clock readings to the corresponding receiver and transmit information encompassing orbital parameters. Moreover, the codes consist of the sequence with the states +1/-1 mainly corresponding to the prevailing binary values 0 or 1. Moreover, the biphase modulation is undertaken by 180 degrees shift in the carrier phase whenever alteration contained code state. The signal broadcast by the underlying satellite is spectrum signal, which correspondingly makes is less susceptible to the jamming. The fundamental concept of the spread spectrum method is that the prevailing information waveform possessing small bandwidth is through modulation of the large bandwidth waveform. The generation of the pseudo-random sequence (PRN) within the codes is based on the utilization of an electronic hardware device known as tapped response shift register. The device is capable of generating a big diversity of pseudo-random codes, which reoccur after particular period. Moreover, the receiver could differentiate the underlying signals emanating from diverse satellites since the receiving C/A code possess low cross- correlation that is peculiar to one another. The navigation message entails 25 frames with each frame containing 1500 bit, and every frame is partitioned into five subframes with 300 bit. The prevailing information is by the navigation message that is intermittently restructured by the corresponding control segment. ii. Glonass Glonass satellite –based navigation system offers the positioning and the corresponding timing information to the users. Moreover, Glonass space segment entail 24 satellites evenly distributed within three orbits separated by 120 degrees in the equatorial plane. Satellite orbital altitudes are approximated to be 19,130km above the underlying ground surface. The prospect of the Glonass seems uncertain because the economic problems. Moreover, the number of the operational satellites was steadily decreasing over the previous years. Glonass transmit C/A code on the L1, P-code and corresponding L2. Moreover, the Glonass observables are identical to the GPS. The main difference amidst GPS and Glonnas is that of the Glonass that utilizes Frequency Division Multiple Access (FDMA) technology to differentiate the underlying signals of diverse satellites. Nevertheless, GPS and Galileo use Code Division Multiple Access (CDMA) to distinguish amidst the satellites. All the Glonass satellites transmit similar C/A and P-codes but with considerably diverse carrier frequencies. iii. Galileo Galileo is an initiative of the state- of- the art global navigation satellite system that offers a highly precision, wanranted global positioning service under the watch of the civilian management. It normally provides independent navigation and positioning services with dual global satellite navigation systems, the GPS, and Glonass. Galileo segments possess some modification making it differ from GPS. It has significant extension of execution of the global section for the integrity monitoring. a. Space segment The space segment consists of 30 Medium Earth Orbiting satellites, distributed equally and regularly over the three-orbit planes. The underlying projected altitude is slightly bigger than the corresponding GPS 23, 616km with the inclination of 56 degrees. b. Ground segment The Galileo ground segment is the role of administering constellation of navigation satellites. It curbs core operations of the navigation mission. Navigation mission includes orbit determination of the satellites, clock synchronization, and determination and dissemination of the integrity information encompassing warning alerts in time-to-alarm demands, at global level. International GNSS Service (IGS) PPP demands precise orbit and clock files to calculate the exact position of the underlying receiver. Errors within the satellites orbit and clock data can results in in precision. IGS is a voluntary federation of the worldwide agencies that utilizes a global GNSS tracking network of more than 300 stations to gather GPS and GLONASS data used to calculate the accuracy orbit and corresponding clock products. Numerous national geodetic agencies coupled with GNSS users interested within the geodetic positioning have adopted the underlying IGS accuracy orbits to accomplish the centimeter-level precision thus ensuring the long-term orientation frame steadiness. The prevailing IGS products encompass numerous diverse qualities, which are by the 12 IGS Analysis Centres (AC) around the universe. IGS products are utilized at the actual time of the original session with the superior quality coordinates achievable using final products having a latency extending to a maximum of two weeks. A noteworthy advancement is within the precision for the IGS products over the underlying broadcast ephemeris. The broadcast ephemeris orbital precision is normally 100cm whilst the IGS Ultra-Rapid orbital precision is 5cm. Accuracy facilities have maintained a direct connection in a globally integrated reference frame, which is typically consistent with the present International Terrestrial Reference Frame (ITRF). IGS products are in the number of the online post processing services, which apply diverse algorithms to calculate the receiver’s accuracy position. Product Parameter Accuracy Latency Broadcast Orbit 100cm Real Time Clock 5 ns RMS 2.5 ns SDev Ultra Rapid (Predicted) Orbit 5cm Real Time Clock 3 ns RMS 1.5 ns SDev Ultra Rapid (Estimated) Orbit 3cm 3-9hrs Clock 150 ps RMS 50 ps SDev Rapid Orbit 2.5cm 17-41hrs Clock 75 ps RMS 25 ps SDev Final Orbit 2.5cm 12-18 days Clock 75 ps RMS 20 ps SDev Table 2: IGS Product Table PLANNING GNSS DATA Unobstructed planning the choice of the best time undertakes GNSS measurements depend on on the survey of the developing number of satellites available of both NAVSTAR GPS and GLONASS constellations. Numerous commercial software suites permit GNSS planning for individual points in evaluation of the visible satellites from the given elevation angle. Thus, offering map designating their number, and their corresponding geometric configuration, DOP index at diverse time steps during the chosen time span. 1. GNSS planning with IGS GNSS planning software is as modules of the existing  Free and Open Source GIS GRASS. It permits the identification of the optimal locations to undertake the survey within a particular study temporal window or corresponding best time interval for the survey campaign within a particular area. Moreover,it takes into consideration the prevailing realistic barriers to satellite signals due to the terrain morphology and constructions inevitably. Bearing in consideration the underlying of the GIS setting, the procedure for developing maps of accurate satellites visibility known as accurate planning entails three logical steps. These three logical steps are computation of the barriers to the satellite signals due to the terrain morphology, determination of the prevailing relative position of satellite receiver and checking of the visibility of every satellite. Moreover, it is usually subsequence by developing of maps depicting the number of the underlying visible satellites, PDOP (Positioning Dilution of Precision) index. It also has the index of visibility proportion in every cell of the analyzed region. A first module, r. Obstruction determines accurate impediments on the location from the three-dimensional models of the prevailing orographic surface building. The barrier computation is based on the determination of the existing maximum elevation of the obstacles within the territory. Maximum elevation is commonly undertaken by determining the uppermost line of sight amidst all position lines linking the observation position at any other point within the DSM along the fixed azimuthal direction. The operation is fully automatic and is undertaken for every cell scanning for the whole horizon with the azimuth perseverance set by the user, developing the polar pattern of barrier for every position. The substantial computational computation is usually compensated by the demand to perform this calculation only once when the period in which GNSS planning has to be presumptuous invariance of barrier in time. Moreover, the module r.obstruction demnads  in input the underlying DSM of the location under consideration, the azimuthal tenacity coupled with the cut-off angle, which depicts the minimum barrier perspective. r.planning .static is the second module, which aids in the determination of the  satellites position at every time from the values of the Keplerian parameters, offered by the almanac file of the obtainable GNSS constellation. The relative positions amidst satellites and positions on the ground is attained by moving from the conventional celestial reference system (CCRS) to a reference system locally defined with respect to the underlying barycenter of the location. Moreover, the verification of the real visibility of every satellite is achieved by comparing azimuth and elevation of barriers and the satellites at given period. The cells where the underlying numbers are convincingly visible satellites discernibility are equivalent greater than 4, the code, which can assess the PDOP index. Therefore, realistic maps of the satellite visibility and the corresponding of PDOP are attained both examined for the individual moments defined by the operator. In the case queries are undertaken for the time window, and the outcomes are relative to the worst configurations in every cell within the entire time interval. For instance, the corresponding to the smallest number of the satellite and to the supreme PDOP index CONTINUOUSLY OPERATING REFERENCE SYSTEM (CORS) Majority of the CORS systems utilize the RINEX format for the underlying data distribution. Since different manufacturers make the CORS GPS receivers, and the corresponding users of the CORS data are frequently, operating brands of the receivers, users regularly deals with the mixture of the receivers. CORS systems are constituted to enable transfer of GPS data within the exclusive receiver data format from the corresponding CORS site to a central facility. Moreover, the data are on the occasional basis within files containing data gathered within the specific duration. Similarly, the data might be sent to a near continuous stream for the successive file formation at the underlying central facility. Nevertheless, the data are frequently conveyed to the principal facility after the observation files are available thus robotically processed via the suitable RINEX transformation utility to produce corresponding RINEX files that are accessible for the distribution. OSi RINEX data RINEX data was developed in 1989 in association to the GPS Exchange Formats. The fundamental function of the RINEX is mainly to rectify the prevailing GPS data points that are from the corresponding GPS receiver. Moreover, their GPS receivers are employed by members of the OSi field staff as they regularly record the fundamental dimensions of the new building with at least  four satellites. The satellites have clocks on board their underlying crafts, which records accurate time for computation of the coordinates of the GPS receivers on Earth. The GPS receiver also has a clock within its frame, and the duration of time corresponds to the wavelength recorded from the satellite to the GPS receiver. In case the clock on the underlying satellite is not, within the sync with the time on the prevailing GPS receiver. Moreover, the  non-precision reading is recorded and consequently incorrect coordinates for the position on the Earth where the existing is Ossie is taken as the correct result. PRECISE POINT POSITIONING (PPP) POST-PROCESSING SERVICES Precise Point Positioning (PPP) is the location technique that uses broadly and freely available GNSS orbit and clock rectification products mainly to execute point positioning utilizing a sole GNSS receiver. PPP procedure differs from the DGNSS positioning methods since the differential method demands access to the underlying interpretations of more position stations within the already known coordinates. Moreover, PPP offers a positioning solution within a dynamic, global reference frame entailing the ITRF. Thus, negating any local distortions related to the corresponding differential positioning methods when the underlying local coordinates are employed at the prevailing CORS. Nevertheless, comprehension of the implications of transforming amidst a global and relevant national datum is fundamental. Numerous Post processing software the governments’ agencies, colleges, industries, and personnel have advanced products executing the PPP processing strategy in recent years. PPP algorithms utilizing undistinguished carrier phase observations have been executed by diverse means since every application use peculiar baseline tools and processing strategies. In an attempt to provide free processing tools users, upload their corresponding RINEX data, observed within a static mode to the prevailing post-processing website and their respective configured location is then returned in specified duration. 1. PPP Services i. Post-processed PPP Post-processed PPP provides equivalent precisions to the DGNSS positioning methods. Free PPP post-processing services namely Auto-GIPSY and corresponding CSRS-PPP offer converted float solutions at the centimeter level thus permitting a feasible different to the post-processed DNGNSS explanations. Users upload their prevailing observed RINEX data files to the online services, and the corresponding coordinate solutions for the underlying GNSS receiver’s positions that are typically spontaneously. ii. Real time PPP Operating within real-time is more challenging as compared to the operating within the post-processed mode. In DNGNSS methods, the prevailing data ought to be transmitted to the user receivers. User receiver are offered by the by the CORS network either as direct wireless connection from the underlying nearest reference receiver for the primary user or through a connection to the central network command centre. RINEX format RINEX format is well-defined worldwide format for GPS observation data that are normally autonomous of the brand of the prevailing GPS receiver utilized to gather the data (Gao, 2006, pp16-28). Since different manufacturers make the CORS GPS receivers and the corresponding users of the CORS data are frequently, operating brands of the receivers, users typically deals with the mixture of the receivers, RINEX is presently the best means of tackling the condition. METHODOLOGY For this study, three different surveys were performed (Survey A, Survey B and Survey C) as outlined in table 5. The above static surveys differed in terms of measurement period, duration of the survey and instrumentations of the survey thus enhancing a comparative analysis of the conditions. A test site was established on the roof of Dublin Institute of Technology (DIT) over an Ordinance Survey Ireland passive IRENET control point (D147) as shown in figure 1. Static baseline data was consequently post processed from multiple CORS stations in the region using Trimble Business Center (TBC). Table 5: Instrument Settings during Field Survey Trimble R10 (Survey A) Date Carried Out 11th February 2014 Survey Time 10:39:45 -13:59:15 Survey Duration 3h 19m 30s Antenna Height 1.568m Datum WGS84 Elevation Cut-Off 10 Degrees Recording intervals 15 Seconds Figure 1: Instrument set up over D147 Online services Upon conversion of data to RINEX format, it was sent to online post processing services as listed in table six and discussed as bellow, Table 6: Online Services Submission Information (NS- Not Stated) Online Services Supported Devices Data Required Satellite Data Used Registration Needed R10 5800 Trimble RTX ✔ X RINEX/ .TO/ .DAT GPS/GLONASS Yes Trimble RTX: the R10 data can only be used with the service as the 5800 receiver which was not listed in the experiment. As Trimble RTX supports T02 file formats, the unconverted raw material was submitted. Reference frame was ITRF2008. TRANSFORMATIONS The online post processing services reply their solution via e-mail in the ITRF08 well co-ordinate system at the current epoch. A variety of the services like magic GNSS and CSRS-PPP return the ITRF co-ordinates in latitude and longitude (Geodetic format) while the rest of the system reply the ITRF co-ordinates in both Geodetic and Cartesian (x, y, z) formats. It should be observed that OPUS returns IGS08 co-ordinates, which are most cases referred as being coincident with ITRF08. Ireland’s projected co-ordinate system is ITM, a co-ordinate transformation was necessary from ITRF to ITM. By the use of Helmert 7-parameter transformation with the published parameters, the ITM co-ordinates were computed from the ITRF08 co-ordinates. Several different steps were used to convert ITRF08 (Cartesian) and ITRF08(Geodetic) to the final ITM co-ordinates as reported in figure 2 and figure 3, respectively. The initial transformation was from ITRF08 (Cartesian) to ITM. The initial stage of the process was to transform the ITRF08 co-ordinates to ETRF2000 while ITRF08 Cartesian coordinates (x1, y1, z1) were transformed to ETRF2000 coordinates (x2, y2, z2) using the 7-parameter Helmert transformation equation illustrated in equation one:  Eq. 1 Where; X1, y1, z1-ITRF08 Cartesian coordinates D-Scale factor between the two systems Rx, Ry, Rz-X,Y,Z rotation angle in radians between the two systems TX, TY, TZ-Geometric X, Y,Z translations (velocity) The above equation was further simplified by multiplying the matrices: X2 = X1 + TX + D*X1 + RY*Z1 – RZ*Y1 Y2 = Y1 + TY + D*Y1 – RX*Z1 + RZ*X1 Z2 + Z1 + TZ + D*Z1 + RX*Y1 – RY*X1 For this experiment, Altamimi’s EUREF Symposium supplied the parameters of the transformation; Table 7: ITRF08 - ETRF2000 Parameters (Altamimi, 2011) ITRF Solution TX mm TY mm TZ mm D RX mm RY Mm RZ mm ITRF2008 52.1 49.3 -58.5 1.34 0.891 5.39 -8.712 Rates 0.1 0.1 -1.8 0.08 0.081 0.49 -0.792 Most of the results were provided by the online services were in ITRF08 @ epoch 2014. Putting the parameters and their rates into use, the ITRF08 coordinates were transformed into ETRF200 @ epoch 2014. Errors are introduced during the calculation of the transformation due to the nature of the parameters while general accuracies of the transformation formulas are 1-2 centimeters. The coordinates of ETRF2000 were in the Cartesian co-ordinates system but needed to be converted into a geodetic co-ordinates system, which was used subsequently in the OSi’s online co-ordinates converter. The ETRF2000 Cartesian co-ordinates (X2,Y2, Z2) were converted to ETRF2000 Geodetic co-ordinates (( 2,  2) referenced to the GRS80 ellipsoid using the sequence of the standard equations illustrated from Equation 2-Equation 7:  Eq. 2  Eq. 3  Eq. 4  Eq. 5  Eq. 6  Eq. 7 Where: X2, Y2, Z2 – ETRF2000 Coordinates  = Latitude (decimals of a degree) λ 2  = Longitude (decimals of a degree)  = Prime vertical radius of curvature a = Semi-major axis of the GRS80 ellipsoid (6,378,137.000 m) e2 = Eccentricity squared of the GRS80 ellipsoid (0.006 694 380 022 90)  = Ellipsoidal Height As  was unknown in the above equations, to compute for v and, an interactive process was implored. When  and  were computed,  was used as an input into  equatiod n and the process repeated. Conversion between Cartesian –Geodetic and versa rounding errors were introduced into the computation (Gao, 2006, pp16-28). To minimize these errors, the geodetic co-ordinates were calculated to five decimal places. The co-ordinates were then ready to be used in the OSi’s co-ordinate converter thus allows the ETRF geodetic coordinates to be projected into ITM. Another set of transformations carried out were ITRF08 (Geodetic) to ITM, the only difference between this transformation and ITRF08 (Cartesian) to ITM was the initial step; the Geodetic co-ordinates had to be converted into Cartesian before the transformation could be computed. ITRF08 Geodetic co-ordinates (,) referenced to GRS80 ellipsoid was converted to ITRF08 Cartesian co-ordinates (X2, Y2, Z2) using the following sequence of the standard equations (Eq. 8-Eq.12):  Eq. 8  Eq. 9  Eq. 10  Eq. 11  Eq. 12 Where: = Prime vertical radius of curvature a = Semi-major axis of the GRS80 ellipsoid (6,378,137.000 m) e2 = Eccentricity squared of the GRS80 ellipsoid (0.006 694 380 022 90) = Latitude (decimals of a degree) = Longitude (decimals of a degree) h = Ellipsoidal Height (metres) Once the first step was complete, the entire process was the same as the previous transformation. RESULTS AND ANALYSIS The results obtained using the online post processing services were precisely accurate and are listed in Table 8. Figure 4 illustrates the coordinate differences in E, N and H. Table 8: D147 Known vs. Online Services (Survey A) Figure 4:D147 Known vs. Online Services Graph (Survey A) Most horizontal positions computed by the PPP online services were within width of one centimeter of the known D147 coordinates while vertical positions were less than three centimeters considered acceptable because vertical accuracy is generally 2-3 times less accurate. Taking into account the observed time of survey A was 3 hours 19 minutes, these results were deemed to be very good with respect to both AUSPOS and OPUS recommendation of 6 hours of observation to yield centimeter accuracy. The Trimble RTX services stipulates that every an hour of data, 2 centimeters accuracies can be achieved while 24 hours of data can yield I centimeter accuracies. The results of Trimble’s RTX service went beyond centimeter accuracies with no or less difference in the Easting, while a 2mm difference in nothing and a 4 mmdifference in height was observed. The accuracy level exhibited is always achieved only by static survey and indicates that RTX can be used to establish reliable control. CSRS-PPP, AUSPOS and OPUS could also be lined up for establishing 2D control but the computed heights have a difference greater than 5 millimeter. Industrial standard accuracy for setting a vertical control is always +/- 5 millimeter (RICS 2010). GNSS technique has an error that is more exhibited in the vertical direction. Always vertical estimates are weaker as due to the combination of satellite geometry, strong correlations to other parameters such as antenna phase and atmospheric delays, which is experienced even in real time as well as post processing applications. In several occasions, GNSS techniques always results in geometrical heights which are different from physical heights ( sensitive to gravity) Figure 5 illustrates the 2D positions of each point plotted in ITM with a proper view of the horizontal spatial relationship where each point has to D147. Well evidenced is the fact that the GNSS computed position is an outlier. Survey B results is well illustrated in table 8. An observation time for this survey was established to be 1 hour and 9 minutes. For this case the Trimble RTX were accurately as quoted in the Trimble website where 1 hour of data resulted in 2 centimeter accuracies. AUSPOS and MAGIC GNSS both resulted in poor Easting positions but highly accurate Northing positions 2 millimeters. Again, this survey proved that Trimble RTX and CSRS-PPP had significantly better height accuracy as compared to other services. Hence it was concluded that more accurate height values resulted from better online algorithms and more appropriate reference stations, especially in the case of Trimble RTX. Table 8: D147 Known vs. Online Services (Survey B) From the surveys, it was established that an observation time of 3 hours is sufficient to produce centimeter accuracies. Three hours and less observation times produce accuracies undesirable for setting- out control. Other than Trimble RTX, it was extremely difficult to assess why one service was better than the other, while some of the services returned processing reports, properly identifying the IGS CORS site used in the solution, for example AUSPOS used 13 IGS CORS to process the solution as seen in figure 5.1, but failed to produce a better solution than OPUS which only involved three stations. Trimble RTX uses its specific global tracking network with more than 100 reference stations with a regional CORS network used to determine the local atmospheric corrections. The advantage exists that Trimble has operational CORS network in Ireland; the RTX service will definitely produce the best reliable results. As depicted in table 9, the quick and final solution only increased in accuracy by a small margin from an ultra- quick solution. The rapid and final solutions were established to be the same. This is found to be unusual as the quick products are available within seven hours of the observation, while the final products are only available within 12 days of the observation. The IGS also stipulates that the final products should be utilized to yield the best positional accuracy. Table 9: Difference between International GNSS Service Products CONCLUSIONS The main objective of this study was to establish the accuracies achievable from online PPP ( post processing services. A general conclusion was arrived at that online PPP post processing services for positioning yielded a remarkable accurate results. The horizontal difference between the TBC post processed coordinates from static measurements and online PPP services coordinates for control point D147 were all set at millimeter level. This shown that the processes and algorithms used in the study are robust. Form the study, Trimble RTX tended to produce the most the most reliable results in the vertical section, thus proving PPP to be a suitable alternative technique to establish control. Furthermore, the quality of the online PPP post processing services was shown to depend on the observation time period and the lengthier the observation time, the most effective way of improving the solution to achieve millimeter accuracy. The above results presented methodology for using PPP services in Ireland and are the initial signs of PPP capabilities. The entire study has only determined PP accuracies at a single point with a small sample of data and a further study with a view of determining PPP accuracies on several OSi passive control points with different observation times is recommended within Ireland which would provide a more clear indication of PPP accuracies. The methodology developed in this paper seeks to provide a guideline for future research. REFERENCES Altamimi, Z 2011, Transformation from ITRF to ETRF2000, presented to EUREF Symposium 2011, Chisinau, Moldova, May 25-28th. Bisnath, S. Collins, P. Heroux, P and Lahaye, F 2010, Undifferenced GPS Ambiguity Resolution using the Decoupled Clock Model and Ambiguity Datum Fixing, PPP-Wizard, viewed Feburary 2014, http://www.ppp-wizard.net/Articles/Collins_Navigation_v57n2_2010_accepted.pdf ESA 2011, Precise Point Positioning, European Space Agency viewed October 2013, http://www.navipedia.net/index.php/Precise_Point_Positioning Gao, Y 2006, Precise Point Positioning and its Challenges, Aided-GNSS and Signal Tracking, Inside GNSS, vol. 1, no. 8, pp. 16-18. Huber, K, Heuberger, F, Abart, C,, Karabatic, A, Weber, R & Berglez, P 2010, PPP: Precise point positioning-constraints and opportunities. Paper presented to FIG Congress 2010, Sydney, Australia, April 11-16th. Jivall, J 2013, Simplified transformations from ITRF2008/IGS08 to ETRS89 for maritime applications, Lantmateriet Sweden, viewed April 2014, https://www.lantmateriet.se/Global/Kartor%20och%20geografisk%20information/GPS%20och%20m%C3%A4tning/Geodesi/Transformationer/Simplified_trans_ITRF2008_ETRS89_maritime.pdf Kouba, J 2009, A guide to using International GNSS Service (IGS) products, Natural Resources Canada, Ontario, Canada Marreiros, J.P 2012, Kinematic GNSS Precise Point Positioning - Applications to marine Platforms, Ph.D. thesis, Universidade do Porto. Mooney, K 2009, Co-ordinate Systems (PowerPoint Presentation), Spatial Information Sciences, DIT, Dublin. O’Mahony, K 2014, An Evaluation and analysis of the achievable accuracies from online Point Positioning PPP Post-Processing Services in Ireland, Undergraduate thesis, Dublin Institute of Technology May 2014. RICS 2010, Guidelines for the use of GNSS in land surveying and mapping, 2nd edn, Royal Institute of Chartered Surveyors, Coventry, UK. Rizos, C, Janssen, V, Roberts, C and Grinter, T. 2012. Precise Point Positioning: Is the Era of Differential GNSS Positioning Drawing to an End? Paper presented at FIG Working Week 2012. Rome, Italy, May 6-10th. Tekmon Geomatics 2013, Satellite Orbit Errors, viewed Feburary 2014. http://tekmon.gr/tag/satellite-orbit-errors/> Silver, M 2013, Seven Alternatives to OPUS GPS Post-Processing During U.S Federal Government Shutdown, GPS World, viewed October 2013. http://gpsworld.com/7-free-alternatives-opus-post-processing-in-government-shutdown/ Van Sickle, J 2009 GPS for Land Surveyors, 3rd edn, Taylor & Francis, New York. Read More