Line guidance during airborne acquisition is accomplished using
Differential Global Positioning System (DGPS).
Final horizontal positioning of the aircraft during
bathymetric operations is typically accomplished using DGPS or Post
Processed Kinematic (PPK) GPS
solutions. The SHOALS-1000T is equipped with both OmniStar and CSI
Navbeacon DGPS receivers. If DGPS coverage is not available, if
DGPS coverage is not reliable, if use of a geoid model is permitted
or if topographic data are required on the same project, PPK GPS
positioning may be required. For PPK solutions, one or more ground-based
reference stations are required. This involves setting up at least
one dual frequency kinematic capable GPS receiver over a geodetic
control point at each station. If geodetic control does not exist
within the project area, it must first be established by extending
geodetic control to the project area. Final aircraft trajectories
are computed in post-processing using Applanix's POSPac software.
Here the ground-based dual frequency GPS data are combined with the
airborne dual frequency GPS data from the NovAtel Millennium card
in the POS AV. Reference station spacing will vary depending upon
the shape and size of the project area, but the aircraft should
never be more than 30km from a reference station while surveying.
Surveys must be scheduled to avoid periods of high Dilution of Precision
Final positioning of the aircraft during topographic
operations is typically accomplished using PPK GPS solutions, as