Analysis of Resolution Capability in Both Horizontal and Vertical Directions Between Successive Multi-Beam Surveys Utilizing Various Kinematic Global Navigation Satellite System Techniques
In a recent study conducted by Christopher McHugh, Ian Church, David Maggio, and Min Sung Kim, the post-processed methods of Post-Processing Kinematic (PPK) and Real-Time Kinematic (RTK) have been identified as the most reliable Global Navigation Satellite System (GNSS) methods for use in the Mississippi Sound area. These techniques are particularly beneficial in situations with varying DOPs, increasing baselines, and internet outages.
Satellite-based positioning systems are subject to various error sources, including atmospheric effects, satellite errors, multipath effects, obstructions and signal blockage, receiver noise and clock errors. These errors can significantly impact positional accuracy.
However, RTK and PPK positioning methods address these issues by using carrier-phase measurements, differential corrections from a base station, multi-constellation and multi-frequency GNSS use, and sophisticated filtering and error modeling. These techniques enable centimeter-level accuracy in real-time with RTK and slightly higher accuracy with PPK, post-collection.
RTK excels in immediate navigation and control, while PPK offers higher accuracy due to its ability to utilise more comprehensive data and process when time constraints are less stringent. Both methods rely on relative positioning, using a stationary base station to correct rover errors caused by the main error sources, allowing precise positioning despite inherent satellite and atmospheric errors.
According to Teunissen and Kleusberg's (1998) simple orbital equation, orbital errors are negligible for kinematic techniques as long as the baseline between the receiver and base station is small compared to the high altitude of the satellites. The largest uncertainty in satellite-based positioning comes from satellite clock drift, which can cause a range error of 300 meters for a clock error of 1 microsecond.
The study, which used two GNSS Topcon GR3 receivers to collect PPK and RTK data, found that RTK performed well for days with good DOPs and more than 8 satellites, but could not maintain ambiguity fixes for baselines larger than 3 km. Ellipsoid-referenced surveys in the Mississippi area are recommended to use post-processed data for repeatable surveys with low uncertainties.
To achieve real-time kinematic efficiency, networked RTK reference stations and additional cell towers should be set up on barrier island systems in the Mississippi area. Atmospheric delays in satellite-based positioning are always changing due to the state of the Ionosphere and Troposphere, and they cannot be fully eliminated with the double difference technique.
The project also highlighted the importance of high-accuracy GNSS techniques for hydrographic surveying, a method that requires surveying to the ellipsoid. Measurement noise, any noise caused by previously unaccounted for uncertainties and electrical noise from the receiver, and multipath effects, signals reflected off surfaces like buildings or terrain, are the two uncertainties that cannot be eliminated with the double difference technique in satellite-based positioning.
In conclusion, the post-processed methods of PPK and RTK offer reliable solutions for precise positioning in the Mississippi Sound area, despite the challenges posed by atmospheric effects, satellite errors, multipath effects, obstructions and signal blockage, receiver noise and clock errors, and internet outages. The study underscores the need for networked RTK reference stations and additional cell towers to improve real-time kinematic efficiency in the region.
[1] Teunissen, P. J. N., & Kleusberg, A. (1998). Carrier-Phase Surveying: Techniques and Applications. John Wiley & Sons. [5] Zumberge, J. R., & Wald, E. M. (1997). GPS Carrier-Phase Surveying. John Wiley & Sons.
- Ocean mapping, a field heavily relying on hydrographic survey, can greatly benefit from the reliable solutions offered by the post-processed methods of PPK and RTK for precise positioning, particularly in the challenging environments with varying DOPs, increasing baselines, and internet outages.
- Interestingly, marine science can leverage the advancements in technology, such as GPS receivers, to achieve centimeter-level accuracy in real-time with RTK and slightly higher accuracy with PPK, which can contribute significantly to studies in various marine conditions.
- Education and self-development can also benefit from these techniques, as they delve into the intricacies of science, including how satellite-based positioning systems work, the challenges they face, and the methods used to address them, such as carrier-phase measurements, differential corrections, multi-constellation and multi-frequency GNSS use, and sophisticated filtering and error modeling.
- Moreover, the findings of this study have implications beyond the marine realm, as space and astronomy fields may also find value in the high-accuracy GNSS techniques, opening doors for new explorations that demand precise positioning, from earth observation to space missions.
