Abstract
Even though the entire Baltic Sea is included in previous geoid modelling projects such as the NKG2015 and EGG07, the accuracy of contemporary geoid models over marine areas remains unknown, presumably being offshore around 15–20 cm. An important part of the international cooperation project FAMOS (Finalising Surveys for the Baltic Motorways of the Sea) efforts is conducting new marine gravity observations for improving gravimetric quasigeoid modelling. New data is essential to the project as the existing gravimetric data over some regions of the Baltic Sea may be inaccurate and insufficiently scarce for the purpose of 5 cm accuracy geoid modelling. Therefore, it is important to evaluate geoid modelling outcome by independent data, for instance by shipborne GNSS measurements. Accordingly, this study presents results of the ship-borne marine gravity and GNSS campaign held on board the Estonian Maritime Administration survey vessel “Jakob Prei” in West-Estonian archipelago in June/July 2016. Emphasis of the study is on principles of using the GNSS profiles for validation of existing geoid models, post-processing of GNSS raw data and low-pass filtering of the GNSS results. Improvements in geoid modelling using new gravimetric data are also discussed. For example, accuracy of geoid models including the new marine gravity data increased 11 mm as assessed from GNSS profiles. It is concluded that the marine GNSS profiles have a potential in providing complementary constraints in problematic geoid modelling areas.
Highlights
An international cooperation project FAMOS (Finalising Surveys for the Baltic Motorways of the Sea) has been initiated to improve the gravimetric quasigeoid model that will be needed for the realisation of the Baltic Sea Chart Datum 2000 (BSCD2000) as the new common height reference system for the Baltic Sea hydrographic surveying and nautical charts (FAMOS 2017)
The goal is to improve the accuracy of GNSS (Global Navigation Satellite System) supported bathymetric measurements and navigation by computing a new 5 cm accuracy marine geoid model over the entire Baltic Sea
Three marine geoid models to be assessed by ship-borne GNSS profiles are as follows: (i) The official NKG2015 quasigeoid model released by the Nordic Geodetic Commission (NKG), see Ågren et al (2016) for further details; (ii) Model 1 – a preliminary NKG2015 quasigeoid model computed at Tallinn University of Technology (TTÜ) in 2016; (iii) Model 2 – another preliminary quasigeoid model computed to Model 1, but including the newly acquired marine gravity data
Summary
An international cooperation project FAMOS (Finalising Surveys for the Baltic Motorways of the Sea) has been initiated to improve the gravimetric quasigeoid model that will be needed for the realisation of the Baltic Sea Chart Datum 2000 (BSCD2000) as the new common height reference system for the Baltic Sea hydrographic surveying and nautical charts (FAMOS 2017). Some earlier studies have indicated that the precision of geoid models in coastal areas can suffer due to heterogeneity of regional gravity data (Liibusk, Ellmann 2015; Märdla et al 2017). Marine geoid models can be assessed by ship-borne GNSS measurements. The purpose of the study was to determine suitability of ship-borne GNSS measurements for complementing geoid modelling. Airborne laser scanning measurements (in conjunction with GNSS-IMU trajectory computations) in 2012 demonstrated further possibilities for determining sea surface heights (Gruno et al 2013) and subsequent validation of marine geoid models. The present study aims at assessing improvements in geoid models due to inclusion of new marine gravity data, collected on-board of a hydrographic survey vessel in and around West-Estonian Archipelago in 2016.
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