This project investigates whether 3D-positioning at sea can be improved by processing real-time positioning data. SWEPOS-based RTK (accurate GNSS) was used to log positions data on a hydrographic survey vessel along Sweden’s east and north coast for 7 days. However, because of the long distance between the vessel and the reference stations the positioning solutions do not always have high accuracy. This problem generates a large interest to research how processing real-time data could improve position accuracy. Processing positioning data is done through Applanix IN-fusion PPK (Post-Processed Kinematic) and PPP (Precise Point Positioning) loosely coupled concept. The positioning accuracy of these methods are compared against one another and against collected data in real-time (RTK). The vertical component are being assessed further in detail to evaluate the accuracy of these methods and the data is presented in respect to vertical positioning and height. However, solely processing the vessels positioning according to the PPP or PPK concept is not enough to get a good positioning vertically, as the vessels positioning height also depends on the vessels dynamic movements. Including the vessel’s dynamic movement’s leads not only to a higher positioning accuracy but also to a more accurate description of the shape of the water surface. The shape of the water surface is an important component for the modelling of the geoid, as the water mass distribution affects gravitational measurements and calculations by water mass variations. The future goal, is that vessels should be able to collect data which can be used to correct the present geoid model, only by using GNSS technique and water level corrections from reference stations. Furthermore, good hydrographic data and accurate GNSS height provides preconditions to introduce a 3D-navigational system. A system like this could calculate if the present draught is compatible with the future depth conditions along the route. The system can thereby support the navigator with suggestions of speed adjustments at optimal moments to avoid running aground. Initially, the different post-processing methodology’s ability to improve position accuracy are evaluated. The observations presented in this project indicate that position accuracy varies depending on which method is used. The results show that the vertical measurement uncertainty (RMS) values are lowest when using the processing methods based on the PPK concept. The RMS mean value using PPP processing methodology show a higher value than the real-time solutions. In this case, by adjusting the real-time solutions by processing according to the PPK method, the vessels vertical position can be corrected with a mean value of 5 cm. In the secondary process, the GNSS height from the PPK processing methodology was used together with static and dynamic corrections to approximate the actual water level. This project demonstrates the potential of using this type of process to get a more accurate picture of the present water surface.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:su-150152 |
| Date | January 2017 |
| Creators | Wilhelmsson, Emelie |
| Publisher | Stockholms universitet, Institutionen för naturgeografi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | Swedish |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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