How will all the new GNSS signals help RTK surveyors?

Transcription

1 Proceedings of the SPATIAL SCIENCES & SURVEYING BIENNIAL CONFERENCE November 2011, Wellington, New Zealand How will all the new GNSS signals help RTK surveyors? ABSTRACT Craig Roberts School of Surveying and Spatial Information Systems University of New South Wales Sydney, NSW, 2052 In the next few years, surveyors using high productivity, real-time kinematic (RTK) positioning and indeed all other precision positioning users will be faced with a barrage of new global navigation satellite system (GNSS) signals from GPS, GLONASS, GALILEO and possibly COMPASS/Beidou2 as well as Satellite Based Augmentation Systems (SBAS) signals and Regional Navigation Satellite Systems (RNSS). New receivers with enhanced capabilities will enter the market and the old days of choosing which colour GPS receiver will be replaced by a myriad of new considerations. This paper will attempt to explain the benefits of the new signals that will be on offer in the next 5 or so years and hopefully provide a guide to RTK surveyors and precision positioning users to assist any purchases they intend to make. KEYWORDS: RTK, GNSS, Surveying, CORS, signals 1 INTRODUCTION Surveyors are the largest group of professionals dealing with high precision positioning using modern satellite signals. The cm-level demands of surveying has forced the utilisation of the Global Positioning System (GPS) signals beyond their original design by using differential techniques thereby achieving much higher precision and productivity. GLONASS is now a worthy competitor for GPS however many surveyors ignore the politics and simply use combined GPS/GLONASS receivers and benefit from the extra signals. This advance has coined the term Global Navigation Satellite Systems (GNSS). Simultaneously, the Chinese Compass/ Beidou2 system now comprises 9 functioning satellites in its growing constellation (June 2011) and the European Galileo system is set to launch its first operational satellites in October. The Japanese Quasi-Zenith Satellite System (QZSS) has launched its first satellite in November 2010 which heralds the beginning of a GNSS compatible Regional Navigation Satellite System (RNSS) in East Asia. Satellite based augmentation systems (SBAS) such as the US Wide Area Augmentation System (WAAS) (part of GPS), the European Geostationary Navigation Overlay Service (EGNOS) (part of Galileo), the Indian Regional Navigation Satellite System (IRNSS or GAGAN) and the Japanese Multi-functional Transport Satellite (MTSAT) Satellite-based Augmentation System (MSAS) add further complexity to a market already crowded with abbreviations. Add to this a myriad of free Precise Point Positioning (PPP) services and the commercial Wide Area Differential GPS (WADGPS) systems such as Omnistar and Starfire and the modern surveyor can be forgiven for feeling a little confused. This paper will attempt to overview all these services and highlight the benefits for high precision positioning surveyors.

2 2 SURVEYING WITH GNSS 2.1 GPS Surveying GPS surveying implies that high quality, dual frequency GPS receivers and antennas are used in a differential mode taking advantage of both pseudorange and carrier phase observables (ie L1 and L2 signals). Initially surveyors performed static GPS whereby two receivers (one called a base and the other a rover) observed the same constellation of satellites simultaneously. Data is returned to the office where it is downloaded and combined in a commercial software package. The software sorts and cleans the data and then employs a double differencing strategy designed essentially to count the number of L1 wavelengths between the satellite and receiver at the initial measurement epoch. This highly complex process is called ambiguity resolution (AR) or initialisation and allows high precision carrier ranging for as long as the signals are logged by the receiver (Rizos, 1997). This process does not occur instantaneously. Early static baseline processing required hours of data to ensure successful AR. The baseline between the base and rover antenna can be routinely measured to better than 10mm ± 1ppm over distances up to 20km. 2.2 RTK GPS Real time kinematic techniques evolved by simply installing a communications link between the base and rover receivers and performing the office processing at the rover in the field. Commercial RTK systems were first released for widespread use in 1993 (Large et al, 2001). At that time many issues such as fast and correct initialisation, reliable communications, usability and range were all in their infancy. As RTK systems evolved many of these issues were addressed, however the limited user range brought about by atmospheric errors between the base and rover receivers remained. Manufacturers developed new techniques to extend the baseline length whilst preserving the precision of positions. Few technical details were released to explain these advances, but it was clear that improvements in communications links as well as GPS signal processing and adaptive combinations of L1 and L2 code and carrier phase measurements using kalman filtering techniques were employed (Large et al, 2001). It allowed initialisation to occur over longer ranges (20-30km) even under mildly changeable ionospheric conditions. 2.3 Continuously Operating Reference Station (CORS) Networks Concurrently, continuously operating reference station (CORS) networks were being established for primarily scientific applications (Roberts and Stanaway, 2009), to catch an earthquake as it happened, or by governments for datum maintenance such has the Australian Fiducial Network (AFN) expanded to the Australian Regional Geodetic Network (ARGN) (Geoscience Australia, 2011a). Later state governments began to establish their own state-based CORS networks initially to reduce the cost of maintaining their ground mark infrastructure (Roberts, 2011). This new infrastructure promoted a greater uptake by land surveyors, particularly in rural areas, who began applying GPS to their traditional cadastral and engineering tasks. CORS data is broadcast onto the internet and, providing there is sufficient wireless network coverage, users no longer require their own base station 1. The limitations on base-rover distance brought about by atmospheric errors can also be overcome by using Network RTK techniques (Landau et al, 2002). However, the original motivation for establishing CORS networks evolved as new applications, new user groups and new business opportunities emerged (Roberts, 2011). Precision agriculture, construction, mining and emergency management all drove high productivity applications and services and shifted the focus for network administrators toward a more commercial outlook. The release of the new AusGeoid09 has also improved GNSS heighting opening the way for potentially more and new applications (Janssen and Watson, 2010). CORS 1 Actually most rural surveyors still use their own base station in areas without mob phone coverage.

3 network administrators are now faced with how to continue to service a diverse range of users with a myriad of new signals and GNSS services. 3 SATELLITE NAVIGATION SYSTEMS 3.1 Global Positioning System The basic concept of satellite positioning is one-way trilateration. The position of moving satellites must be known at a point in time (ephemeris) and signals sent from the satellites must contain timing information (codes). The receiving device must also have a clock and compare the incoming signals with its own identical codes. Because the wavelength of the codes does not propagate through the Earth s atmosphere, these codes are modulated onto carrier signals. The original intention of GPS positioning was to use the codes for point positioning at an accuracy of around 10m for military users and 100m for civilian users. Engineers developed differential techniques to enable surveyors to use the carrier signal for positioning as well. The first Block 1 experimental satellites were launched by the US Department of Defence (US DoD) in 1978 broadcasting the L1 carrier, carrying the C/A (civilian access or coarse acquisition) code and P (precise) code, and the L2 carrier (P code only) on frequencies MHz and MHz respectively. The Block II satellites began launching in 1989 and were capable of switching to Selective Availability (S/A) to degrade the accuracy of the civilian signal to provide 100m positioning for civilian users. Anti-Spoofing (A/S) was also switched on for these newer satellites which encrypted the L2 signal with an additional Y code and inhibited tracking of the L2 (since denoted L2(P/Y)) for high precision users (Hofmann-Wellenhof et al, 2008). Commercial GPS manufacturers devised methods of overcoming this A/S encryption by squaring, cross correlation and other more complex techniques. These patented semi-codeless techniques increased the cost of equipment especially for dual frequency users. On May 1, 2000 President Clinton ordered that S/A be switched off for all satellites. This was seen as the first step in the GPS modernisation phase. A/S encryption remained. The Block IIA and Block IIR (replacement) satellites only included minor design changes. The Block IIR-M (replacement modified) satellites were the first to offer the new L2C signal which is not encrypted with A/S and a more powerful signal. The Block IIF (follow-on) satellites (first launched in May 2010 currently 2 in orbit) are the first to offer triple frequency; that is L1 (C/A), L2C and the new L5 signal at a frequency of MHz. L5 is also an open frequency ie is not encrypted (Hofmann-Wellenhof et al, 2008). The code on the L5 signal has a higher chipping rate (10.23Mhz) than the L1 C/A and L2C code (1.023Mhz) which means the least count of the L5 measurement is 10 times finer 2. The US DoD have stated that they will not support the legacy L1 (C/A) / L2 (P/Y) signals after 2020 which means that surveyors will have to upgrade to L2C or L5 capable equipment to guarantee high precision performance (US Federal Register, 2008). 3.2 GLONASS GLONASS satellites were first launched in 1982, with a full constellation in early Economic challenges during the transition from the former Soviet Union to the now Russian Federation resulted in a lack of support for the GLONASS system which subsequently declined to 7 satellites in The Russian government has since strongly supported the revitalization of the GLONASS system with 22 operating GLONASS-M satellites in the current constellation (June 2011). The GLONASS-M satellites differ significantly from the GPS satellites. Whereas the GPS system uses codes to differentiate between satellites (code division multiple access - CDMA) the 2 Surveyors could imagine that the L1 C/A and L2C code is a cm ruler vs the L5C code as a mm ruler.

4 Russian system broadcasts two different frequencies for each satellite (frequency division multiple access FDMA). Consequently surveyors purchasing GPS/GLONASS equipment are also purchasing a more complicated hardware design to overcome this difference. The GLONASS system also operates on a different geodetic datum and time system (see Figure 5) therefore receiver hardware and software must also accommodate these parameters (Hofmann-Wellenhof et al, 2008). GLONASS is undergoing a modernisation phase. The first GLONASS-K satellite was launched in Feb It will transmit a new CDMA signal called L3 ( MHz) as well as the legacy FDMA signals. Subsequent GLONASS-K satellites will also transmit CDMA signals on the L1 and L2 bands as well as the FDMA legacy signals and will ultimately transition the whole constellation to a CDMA system to be more compatible with other GNSS systems. GLONASS will also offer an SBAS, called the System for Differential Correction and Monitoring (SDCM), using 24 ground stations in Russian territories and a new geostationary satellite transmitting correction and integrity data on the GPS L1 frequency (Urlichich, et al 2011). 3.3 Galileo The European Union (EU) have recognized the benefit of developing their own GNSS system to reduce their reliance on other satellite navigation systems and also to support strategic initiatives for EU member states. Much negotiation has resulted in an interoperability agreement (see section 4.2) with the US GPS system whereby both systems will broadcast L1 and L5-like signals promoting simplicity in receiver design for future GPS/ Galileo devices. Attempts were made to co-fund the system in a European public-private partnership arrangement but this was ultimately unsuccessful and on-going development will be funded from the public sector (Gibbons, 2007). Galileo has a great opportunity to leap frog the existing GPS and GLONASS systems whose technology is becoming dated and is slow to replenish with an obligation to provide an uninterrupted service. Galileo will provide an Open Service (OS), Commercial Service (CS), Safety-of-Life Service (SoL) and a Public Regulated Service (PRS) (for European security) (ESA, 2011). The Open Service will be of most interest to surveyors and will offer essentially two signals called E1 and E5 (similar to L1 and L5). The E1 signal, like the GPS L1 C/A code signal will have a chipping rate of Mhz. The E5 signal will not only replicate the L5 with a higher chipping rate of Mhz, but will also spread the signal over a wider bandwidth (ESA, 2010). The effect of this is that the E5 signal resolution will be as much as 3 times higher than that of the GPS L5 and stronger. Additionally there is less likelihood of multipath with this modern wide-band frequency. A higher chipping rate requires more power usage for the device and will more than likely increase the expense of the receiver (Avila- Rodriguez et al, 2008; Dempster and Rizos, 2009). The ground segment of the Galileo system supports the European Geostationary Navigation Overlay Service (EGNOS) and provides integrity information for the CS, SoL and PRS. 3.4 COMPASS/ Beidou2 Despite commencing development of their own GNSS after the EU, China currently has 9 satellites in orbit for their COMPASS/ Beidou2 3 system. Ongoing progress will move away from the Chinese military to the China Satellite Navigation Project Center (CSNPC) who will take charge of the future research, building, and management of the Chinese NSS. 3 The original Chinese RNSS Beidou has evolved into the global Compass system which is augmented by the new generation Beidou2 system, hence the double-barrelled name.

5 Initially plans are to establish a 12-satellite RNSS with a view to a full GNSS constellation by The space segment will consist of 30 medium earth orbit (MEO) satellites (similar to all other GNSSs mentioned) and 5 geostationary satellites. They will broadcast on 4 carrier frequency bands: MHz, MHz, MHz and MHz. It is intended that the Chinese signals will be compatible with GPS, GLONASS and Galileo receivers. Similar to Galileo, two types of services will be offered namely an open service providing positioning accuracy to within 10m (as well as velocity and timing services) and an authorised service for security purposes which offers integrity to authorised users (Pace, 2010, Gibbons, 2009, Gibbons, 2011). The Open Service includes a wide area differential positioning service providing 1-metre real time positioning (Li and Dempster, 2010). 3.5 Quasi-Zenith Satellite System (QZSS) The Quasi-Zenith Satellite System has been designed by the Japanese Space Association (JAXA) as an augmentation to the existing GPS system to provide high elevation satellites over Japan to overcome problems with navigation in urban canyons. The first satellite (denoted GPS PRN 193) was launched in September 2010 and is currently broadcasting L1 and L2C signals in test mode. The L5 and the new L1C GPS signal will also be broadcast in the near future (QZSS, 2010). GPS users can therefore seamlessly track PRN 193 as if it was part of the GPS constellation. There are plans for the QZSS system to comprise 7 satellites in total and become a Regional Navigation Satellite System (RNSS), that is standalone positioning even in the absence of other GNSS signals. Figure 1: QZSS ground track over Japan and Australia (Kogure, 2007). The great benefit of QZSS for Australian users is that the ground track passes high over Japan and still remains at a relatively high elevation over Australia. Australia therefore receives the benefit of extra signals by virtue of geography. 3.6 Satellite Based Augmentation Systems (SBAS) SBASs have evolved due to the modernisation of GPS and the development of Galileo. They comprise essentially a ground-based control segment which provides corrections which are broadcast to geostationary satellites which re-broadcasts these corrections to users. It is a global, pseudorange, DGPS service. In the case of the US Wide Area Augmentation System (WAAS), geostationary satellites not only provide a re-broadcasting communications link over large portions of the USA, but they also broadcast an extra GPS signal with correction messages, based on their monitoring ground based network, modulated onto this broadcast message. Users with a WAAS enabled firmware upgrade of their device can receive essentially DGPS corrected positioning to sub-metre precision within the coverage area (WAAS, 2011). This service is not available in Australia. Similarly EGNOS (EGNOS, 2011) and MSAS (only in limited regions in northern Australia) are also not available to Australian users (MSAS, 2011).

6 Two commercial services exist namely Omnistar (Omnistar, 2011) and Starfire (Starfire, 2011). The high precision services offered by the commercial operators actually utilise the carrier phase measurement, but require an initialisation time of up to 15 minutes. The repeatability of this initialisation is less robust than using CORS, AUSPOS or precise point positioning techniques (see section 5). Interestingly, most of these SBAS services will support the L5 signal. Figure 2: The range of GNSS, RNSS and SBAS globally (Adapted from Gakstatter, 2009). 4 COMBINATIONS OF SIGNALS Given the number of new and existing satellite positioning services, the days of the RTK surveyor simply buying gear off the shelf knowing that it tracks carrier phase L1 and L2 measurements are gone. As the different GNSS constellations evolve, surveyors will need to have a clearer understanding of the implications of one system versus another and even one signal versus another. However the modern surveyor with an operational grasp of these concepts and good business acumen will benefit from this knowledge. 4.1 Benefits of L2C and L5 The first block IIR-M satellite which broadcast the first L2C signal was available for users in GPS manufacturers began marketing campaigns to sell new L2C compliant gear, however with just one satellite, the benefits were very limited 4. Even now in 2011, only 9 L2C capable satellites (7 Block IIR-M and 2 Block IIF) are in orbit. 4 A minor immediate benefit of using just one L2C signal is apparent when RTK surveyors use GPS/GLONASS equipment. The GPS and GLONASS time systems are offset and usually one satellite from a positioning solution is required to solve for the time offset. However the L2C signal accommodates a time difference so that this satellite can also be used in the immediate solution. The GPS/GLONASS time offset changes slowly and is negligible over a 6 hr period.

7 The block IIF satellites also broadcast the L5 signal. This has significant advantages over the old L2 and even the new L2C signal. The L5 signal is 4 times more powerful than the L2C and has a longer code sequence which means it should exhibit better tracking in difficult environments such as under trees and in urban locations. The signal is also designed to reduce (but not eliminate) the effects of multipath. The original design of the GPS L1/ L2 carrier signals allowed a frequency separation which is exploited to mitigate the effects of the ionosphere over longer baselines. The L1/L5 combination has even greater frequency separation which promotes better ionospheric correction. The L5 frequency is designed for safety of life applications and is therefore located in the highly protected Aeronautical Radio Navigation Services band (Gakstatter, 2011). This guards against future interference and jamming issues currently being experienced by a commercial terrestrial wireless broadband internet provider in the USA (Cameron et al, 2011). The codes on both the L2C and L5 signals, unlike the existing P/Y code, are not encrypted. This means that complex and patented semi-codeless techniques needed to track the current L2 signal will not be necessary when a full constellation of new signals is available. The cost of GNSS receivers will likely fall dramatically as other manufacturers who do not have (or need) patents to track the new codes will enter the precision positioning marketplace. Another benefit of the new open codes is that now that the L2C/ L5 signal is easier to track (ie semi-codeless techniques no longer necessary) the signal is likely to be more stable in difficult environments. However there are only 9 new GPS satellites launched in the past 6 years and only 2 supporting L5. This is the benefit of the new GNSS systems such as Galileo, QZSS, some SBASs and even Compass/Beidou2. These new systems will support the L5 signal thereby accelerating the deployment of the new L5 signal in space. 4.2 Compatibility and Interoperability The modernisation of GPS and the revitalisation of GLONASS coupled with the likely development of Galileo were the catalyst for the new US Space-Based Position, Navigation and Timing (PNT) policy to define some new terms. Compatibility refers to the ability of the US and foreign space-based PNT services to be used separately or together without interfering with each individual service or signal, and without adversely affecting navigation warfare. Interoperability refers to the ability of civil US and foreign space-based PNT services to be used together to provide better capabilities at the user level than would be achieved by relying solely on one service or signal (Hein, 2006). These two new definitions were the cornerstone of subsequent negotiations between the US and EU when designing future modern Navigation Satellite Systems. 4.3 Benefits of the new NSSs Galileo will have the capacity to launch multiple satellites in one launch. The first operational Galileo satellites are due to launch in October It is conceivable that by 2014/15 approximately 12 GPS Block IIF and 18 Galileo satellites will be operational giving a constellation of 30 satellites. This will give rise to a new interoperable dual frequency RTK combination of L1/ L5 to be exploited by surveyors. Figure 3 illustrates how most of the GNSS/ RNSS providers are accommodating frequencies in the L1 and L5 bands. GLONASS stands out as the only FDMA

8 system and it is now clear why they too will move to CDMA capable satellites. They are also under pressure to not be isolated from all other service providers by continuing to support an L2 signal. Signal structure and bandwidth are foreign concepts to the RTK surveyor, however a little knowledge is useful. Chipping rate defines the resolution to which a raw measurement can be made. So the L5 (or E5) with a 10.23Mhz chipping rate will be a more precise measurement than a the L1 C/A (or E1) at a 1.023Mhz rate. However the power required to measure the L5/E5 signal is much higher which costs battery life. Figure 3: Current International Signal Plans for all planned GNSS and RNSS (Turner, 2010). The GPS/ Galileo signals are very weak and at the antenna are actually weaker than the background noise. The electronics inside the receiver use correlation techniques to retrieve the code. The GPS L1 C/A and the L5 use a narrow band signal. Galileo uses a wider band signal which improves both the code retrieval and the precision of the measurement on the code by a factor of ~3. The wider bandwidth also means the measurement of the signal is stronger (which is useful in difficult environments) and there is also significantly less likelihood of multipath error. The measurement on the E1 is therefore ~3 times more precise that the L1 C/A and the E5 is ~3 times more precise than the L5C, however the receiver requires more power to measure this wider band signal and this also presents an electronic constraint on the design of the device (Jinghui Wu, Personal communication, 2011). An improvement in these code measurements assists with carrier phase tracking and more robust initialisation for the RTK surveyor. Given that Galileo has the advantage of designing a GNSS from current technology (GPS started in 1978), it should be noted that the E1 signal still provides the lower chipping rate to be compatible with the many millions of existing L1 devices. It is conceivable in the future that new devices will operate on the higher resolution L5/E5 band providing higher precision positioning, but again this will require more battery power. The QZSS signal design is also notable as it provides signals in all bands and is currently a valuable test satellite for future combinations of signals from space. Additionally the ground track of this signal passes over Australia and will be a useful additional signal for surveyors (see Figure 1). Because it aligns with the GPS signal it can be tracked seamlessly with existing GPS equipment.

9 Another question should be raised about the effectiveness of a GPS-only triple frequency receiver. Currently there are only 2 satellites offering L1 C/A, L2C and L5C signals. The launch schedule for GPS would mean that even by 2020, there may only be triple frequency capable satellites in orbit with only the QZSS system providing interoperable signals (Figure 3). At the same time, there will be an interoperable constellation of 50+ GPS and Galileo satellites servicing the new L1/L5 linear combination. Will triple frequency offer extra benefit to the modern surveyor or is this a service more suited to a scientist? In short, triple frequency will allow instantaneous AR over longer distances. This is because traditional dual frequency combinations must either compute a baseline solution whilst ignoring the ionosphere (the next largest error source during double differencing) or vice versa. Triple frequency will allow multiple combinations to compute the baseline and account for the ionosphere thereby providing instantaneous positioning over longer baselines (Rizos, 2008). The control segment of all the GNSSs is also improving in terms of number and distribution of control stations as well as the resolution of raw measurements, orbit and atmosphere products. This in turn improves the accuracy of positioning for the user. SBAS accuracy using L1/L5 will be ~10cm as compared to ~60cm today using only L1 (Gakstatter, 2011). What impact will this new capability have on a new geodetic datum for Australia (Johnston and Morgan, 2010; Roberts, 2006; Stanaway and Roberts, 2010)? One of the great challenges of designing a GNSS receiver for users is marrying the different combinations of signals, datums and time systems to provide positioning services. Figures 4 and 5 illustrate the challenges that receiver designers face. Figure 4: GNSS and RNSS systems compared (Takasu, 2010).

10 Figure 5: Comparing the time systems and datums of GNSS services (Takasu, 2010). The combination of new GNSS and RNSS services presents challenges to CORS network providers who will be under pressure to service their users with suitable combinations of the modern signals. Will they support the new L1/ L5 combination only or provide full triple frequency GNSS services or a strategically distributed mixture of both? RTK surveyors will need to assess what their work requires and ensure their CORS providers support these requirements. 5 IMPACTS FOR RTK SURVEYORS The US DoD have stated that they will not support the legacy L1 (C/A) / L2 (P/Y) signals after 2020 which means that surveyors will have to upgrade to L2C or L5 capable equipment to guarantee high precision performance (US Federal Register, 2008). However the new open signals will not require patented semi-codeless methods of tracking (such as is currently required for the L2 (P/Y)). This will mean that many more manufacturers will be able to enter the market providing competition to the few manufacturers who currently hold patents. This should drive the price of a high precision GNSS receiver down dramatically. The antenna design will need to be more sophisticated to accommodate the new signals and this may increase but the overall RTK GNSS equipment should be much more affordable. The L1/L5 combination will supercede the current L1/L2 combination maybe as early as It is unlikely that RTK surveyors will use triple frequency due to lack of triple frequency equipped satellites (and possibly price) and indeed the requirement of such a long distance solution. The new signals are more powerful than the existing signals which means more robust tracking in difficult environments such as around buildings and trees which should be an advantage for urban RTK surveyors. The new Galileo signals, by virtue of their wider bandwidth, will also be more resistant to multipath. The higher chipping rate for the L5/ E5 signal will improve the pseudorange positioning which will increase the time to initialisation for RTK surveyors marginally. This is a minor benefit given that initialisation times are already typically 25 seconds. More signals however will mean a stronger solution as a result of improved dilution of precision and less likelihood of dropouts due to a lack of satellites. Australia is geographically well situated to benefit from the increase in new signals (ironically more than the US see Figure 6). Perhaps mission planning will become redundant.

11 Figure 6: Constellations GPS, Galileo, Glonass, Compass, QZSS, WAAS, EGNOS, MSAS, GAGAN, IRNSS (Dempster and Rizos, 2009). RTK surveyors working in remote locations can also produce MGA positions to 2cm accurately to support their work more efficiently as a consequence of improvements in the AUSPOS positioning service (Geoscience Australia, 2011b). This is a differential GPS processing service which is offered to users without cost to support high precision positioning. Recent densification of the contributing base stations as part of a large federal government grant (NCRIS project) have decreased the time needed to guarantee 2cm accurate solutions from 6hrs to just 1-2 hours depending on conditions. Precise point positioning (PPP) services are a worthy competitor for AUSPOS for static positions in remote locations. There are a number of global services provided (IGS, 2011), but the AUSPOS service provides MGA coordinates directly which are of most benefit to RTK surveyors in Australia. 6 CONCLUSION This paper has attempted to outline the many new GNSS systems and signals which will be available to RTK surveyors in the Australian region in the next few years. These new signals will require both users and CORS network service providers to upgrade their existing GNSS equipment. Hopefully this paper will assist purchasers to more carefully consider which combination of capabilities their new device will require. This brave new world of high precision positioning also challenges the RTK surveyor to look further at what other business opportunities their expertise may offer. New L1/L5 capable devices will likely be cheaper (as low as $1000(?) Gakstatter, (2010)) and provide more robust (and slightly more accurate) positioning. Is this a threat or opportunity? 7 ACKNOWLEDGEMENTS The author would like to thank Dr Jinghui Wu and Professor Andrew Dempster for useful discussion during the writing of this paper.

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