Precision is a subjective word in the world of GNSS. For some applications, metre-level accuracy is “good enough”, even with the potential for errors and position jumps. Other applications require highly precise centimetre-level positioning that is reliable and available 24/7 over a wide area.
Whatever the desired accuracy, advances in GNSS correction services have greatly improved the availability and performance of positioning solutions. Sara Masterson, business development manager of correction services at NovAtel,
said, “The corrections industry overall is constantly evolving and improving the available correction service options in support of the user community, extending the range and types of conditions under which the service can be delivered.”
Back to Basics
Selection of the appropriate augmentation method or correction service depends on the performance required for each application. There are essentially four levels of positioning: standalone uncorrected; positioning derived from publicly available correction services such as the WAAS network in North America or Europe’s EGNOS system; positioning solutions derived from globally available subscription-based L-band services; and regional/ local RTK network solutions.
Standalone uncorrected and WAAS/EGNOS type solutions provide accuracies ranging from 1-10 metres. On the other end of the scale, RTK correction networks provide the most accurate centimetre-level solutions. While L-band solutions deliver corrections directly to the GNSS receiver via satellite, RTK solutions require a base station and a radio to get the corrections needed, limiting operator flexibility and increasing total system cost and complexity.
With subscription-based L-band correction services, users receive Precise Point Positioning (PPP) corrections to help mitigate and remove measurement errors and position jumps. PPP solutions utilize modeling and correction products including precise satellite clock and orbit data to enhance accuracy. Such services range in price from $300 to $4,000 per year, depending on the desired accuracy, end user application and subscription duration.
Every subscription based L-band correction service provides improved levels of accuracy and ensures consistent global performance. NovAtel CORRECT with PPP utilizes correction data from TerraStar. The TerraStar network provides continuous coverage worldwide, with 80 GNSS reference stations located around the globe and 3 widely-distributed Network Control Centers to deliver data over seven independent satellite beams. With full redundancy built in, the TerraStar network offers the most reliable source of L-band corrections in the marketplace.
TerraStar supplies data directly to the NovAtel GNSS receiver and offers two levels of positioning accuracy: TerraStar-C which delivers 4 centimetre-level positioning with instant re-convergence after short GNSS outages and TerraStar-L with horizontal position accuracy of 40 cm.
Today TerraStar services are being used by NovAtel customers in a wide range of applications including precision agriculture, ground-based vehicle mapping, surveying, and unmanned air and land-based applications. These users are selecting TerraStar services primarily because the same solution can be applied across global fleets of equipment and because no additional equipment is required beyond the GNSS receiver and antenna they are already using from NovAtel. For example, precision agriculture users know that TerraStar corrections will help them optimize row spacing in order to reduce costs from materials like seed and fertilizer. Unmanned applications can rely on TerraStar corrections to maintain a precise position regardless of where the vehicle is operating. While RTK and SBAS networks are available in many regions, NovAtel customers can rely on TerraStar services to push the boundaries of where precise GNSS positioning is possible. As the benefits of the global TerraStar services become more widely understood, the variety of applications taking advantage of these services will continue to grow.
Choosing between the various augmentation and correction options, including commercial L-band services, depends on the accuracy, cost and location requirements of the application. Masterson said, “In today’s market, it’s all about flexibility to choose the right accuracy and performance for the application.”