Performance Assessment of a GPS Network RTK Service J. Aponte, X. Meng, A. Dodson, T. Moore, C. Hill IESSG, The University of Nottingham, UK M. Burbidge Leica Geosystems (UK)

Performance Assessment of a GPS Network RTK Service Content Objectives Leica SmartNet Methodology Quality Measures –Accuracy and Precision –Availability –Integrity –Repeatability –DOP Conclusions Future Work Acknowledgements

Performance Assessment of a GPS Network RTK Service Objectives Assess performance of SmartNet service from end users point of view, based on: –Accuracy –Precision –Integrity –Availability –Repeatability –Number of satellites and DOP

Performance Assessment of a GPS Network RTK Service Network RTK GPS Service: Leica SmartNet Partnership: Leica Geosystems and OSGB, OSI, and OSNI 142 RS – 16 RSs in Ireland. – 20 Leica RSs (8 GPS/GLONASS RSs). Operational from January 2006 in GB and July 2007 in Ireland. GPS receivers supporting RTCM formats 2.3/3.1 Leica SpiderNet RSs: Leica 500/1200 receivers and Chokering Antennas. NRTK GPS service for Great Britain and Ireland:

Performance Assessment of a GPS Network RTK Service Assessment Methodology AT502 DF Antenna Antenna Signal Splitter Leica Geosystems SR-530 GPS Receiver Leica Geosystems GX-1200 GPS Receiver Raw data logged in Receivers Memory Card for Post- processing Real Time NRTK solution saved in a Laptop for analysis (NMEA GGA format) RTCM 3.1 corrections received via GPRS Equipment Configuration NRTK Service tested as it is Static Tests: accuracy, precision, availability, integrity and repeatability Kinematic Tests: accuracy, availability and integrity TK1 covered a built-up area Influence number of GPS satellites and their geometry, age of the NRTK corrections (AoC)

Performance Assessment of a GPS Network RTK Service Assessment Methodology Static TestsKinematic Tests

Performance Assessment of a GPS Network RTK Service Quality Measures: Accuracy and Precision Accuracy and Precision Obtained during both Static and Kinematic Tests (NRTK Epochs). Accuracy averages: 0.70 to 1.27 cm Easting 5.22 to 3.08 cm Northing 4.55 to 3.23 cm Height Precision averages: +/ to 0.97 cm East +/ to 1.34 cm North +/ to 2.58 cm Height Accuracy (error), how far the coordinates observed during testing were from the true values. Precision, degree of closeness that repeated measurements displayed (Standard Deviation of the observations, 1 Sigma, about 68% of observations).

Performance Assessment of a GPS Network RTK Service Quality Measures: Accuracy and Precision ENH Errors during TS4.1 All Epochs NRTK Epochs

Performance Assessment of a GPS Network RTK Service Quality Measures: Accuracy and Precision Static TestsKinematic Tests Percentage of Observations with Accuracy better or worst than 5 cm.

Performance Assessment of a GPS Network RTK Service Quality Measures: Availability Availability, percentage of observations in which a NRTK solution (integer ambiguities resolved) was obtained NRTK Availability results Test Possible Epochs NRTK Epochs Availability (%) TS TS TS TS TS TS TS TK TK Detailed percentage of observations performed under the different solution types during tests.

Performance Assessment of a GPS Network RTK Service Quality Measures: Availability TK1 2D RMSE Errors as Observed in the Covered Route All Epochs 0 – 1 cm >5 cm 1 – 5 cm NRTK Epochs Factors Affecting the Availability during the Kinematic Tests

Performance Assessment of a GPS Network RTK Service Quality Measures: Integrity Integrity, percentage of NRTK observations with accuracy better than 5 cm. Percentage of observations with errors better than 5 cm (Integrity). ENH Errors during TS4.2 (NRTK Epochs).

Performance Assessment of a GPS Network RTK Service Quality Measures: Repeatability Repeatability, similarity between the errors obtained during two different tests carried out under similar conditions (NRTK Epochs) Repeatability between TS4.1 (Light Colour) and TS4.2 (Dark Colour) common epochs of a total of 6600 epochs. Repeatability between TS5.1 (Light Colour) and TS5.2 (Dark Colour) common epochs of a total of epochs.

Performance Assessment of a GPS Network RTK Service Positioning Quality Results N. SVs in view and DOP Influence of N. SVs in view and their geometry over the positioning solution Influence of the Number of GPS satellites in View over the Errors during TS4.2 (All Epochs). Influence of the HDOP over the Errors during TS4.2 (All Epochs).

Performance Assessment of a GPS Network RTK Service Conclusions SmartNet offers high centimetric accuracy (1.27 cm Easting, 3.08 cm Northing and 3.23 cm Height) for tests. It also achieves high precision (1-sigma) (+/ cm East, +/-1.34 cm North and +/ cm Height). Availability of the NRTK solution is the main drawback. Centimetric accuracy and precision only achieved during about 90% of the time in static tests and 58% during the kinematic tests. Lack of availability mainly due to external factors and not directly related to the NRTK systems: – GPS signal disturbances (blockage). – Low number of GPS satellites in view and bad DOP. – Interruptions of the GPRS communication link.

Performance Assessment of a GPS Network RTK Service Current and Future Work Investigating the impact of different commercial GSM/GPRS wireless services over the NRTK GPS availability. Examining the performance of the different NRTK concepts such as VRS and MAC. Study and development of NRTK GPS quality measures for service providers and final users.

Performance Assessment of a GPS Network RTK Service Acknowledgements UKs Engineering & Physical Sciences Research Council (EPSRC) for partially funding this project to the first author through its MTP scheme at the University of Nottingham. Special thanks to Leica Geosystems (UK) for providing, free of charge, the SmartNet connection used during this research. PhD studentship to the first author is jointly awarded by the EPSRC under its CASE PhD Studentship scheme and Leica Geosystems (UK).

Performance Assessment of a GPS Network RTK Service J. Aponte, X. Meng, A. Dodson, T. Moore, C. Hill IESSG, The University of Nottingham, UK M. Burbidge Leica Geosystems (UK)