2019-12-16 GC Agenda - Item 5 - Attachment 1 - Noosa Spit Shoreline Erosion Management Plan-Part 2

3.0 Geodetics and Data Reduction
For the Noosa River survey real-time positioning was provided via a direct Fugro Marinestar
G4+ tight coupling with the POS MV Primary GNSS antenna and GNSS inertial solution. This
aiding solution was at the ITRF2014 Ellipsoid. Transformation parameters to reduce the data
to GDA94 were registered within the POSView control software, and further reductions to
AUSGEOID09 were implemented in the QINSy logging software. Background to the reduction
process is shown in the bullet points below.
    •   Satellite positioning systems generate positions to the WGS84 datum. WGS84 is the
        World Geodetic System 1984 and is the main reference for all GPS-based
        measurement systems.
    •   Australia uses the GDA94 datum. Differences between WGS84 and GDA94 are
        small, but become significant for detailed survey operations, and change in time due
        to the movement of the Australian continent relative to the satellite constellation.
    •   MGA94 is a Universal Transverse Mercator (UTM) projection of GDA94 geographical
        coordinates.
    •   Real Time Kinematic PPP GNSS systems use a geostationary satellite to transmit
        corrections to the equipped GNSS antenna positioning unit, allowing much higher
        accuracy for positioning, generally to sub 15cm level.
    •   AUSGeoid09 is a geodetic model maintained online by the Australian Government
        Dept. of Resources, Energy and Tourism. This model describes the relationship
        between the ellipsoidal height (GDA94) and the orthometric height in AHD.


Following acquisition, the POS MV data were post-processed using the Trimble CentrePoint
RTX service to improve the accuracy of the ellipsoid-referenced height in GDA94. Trimble
RTX leverages real-time satellite and atmospheric data from a global network of tracking
stations, along with highly accurate models and algorithms to generate Trimble RTX
corrections. These corrections were used to provide 1-2 cm accuracy for the georeferencing
of the dataset to AHD.
AHD is the vertical datum requested by NC. Employing the method above ensures that both
high accuracy bathymetry and on-shore NC data are referenced to AHD. Spot checks of AHD
conformance with the new swath data were conducted by comparing contours derived from
the new data to previous charts created across the survey region (selecting those areas least
likely to have experienced any erosional or depositional changes). An example image is
shown in the figure below.




            Figure 7: Alignment of chart contours with 2019 swath bathymetry contours.




9                              Noosa Council - Noosa River Survey                        20.06.2019