Final vertical positioning during bathymetric operations is typically
accomplished using tides or water level data. Where bathymetric
data are required relative to a tidal datum, the use of tidal data
are most often required. Depending upon the specification, this could
involve predicted tides, observed tides from a public domain source
or observed tides from a project specific tide gauge. If a local
gauge is required, it may be necessary to "tie-in" to
an established vertical benchmark. It may be possible to derive
bathymetry data relative to a tidal datum without actually collecting
tidal data, if the relationship between the
tidal datum and the ellipsoid is well known within the project area.
In this case, ellipsoid elevations would first be computed using
PPK GPS solutions and a geoid model would be applied to shift the
vertical elevations to the geoid.
Final vertical positioning during topographic operations
is typically accomplished using PPK GPS solutions, as described