Halcrow Geomatics have a purpose-built, dedicated multibeam survey vessel, which can be transported by trailer to almost any location, be it coastal, inland waterway or lake/reservoir. This vessel is permanently mobilised with the multibeam sonar head and associated acquisition and positioning hardware and software, thus allowing a very fast mobilisation time.
Bathymetric data is collected using a Reson Seabat 8101 Multibeam Echo Sounder, operating at 240kHz. This system measures water depths across a wide swathe perpendicular to the vessel track, thus giving 100% coverage of bed features.
The primary positioning system used onboard is Differential GPS utilising corrections from the Thales Landstar network of DGPS stations. In addition, a remote DGPS receiver may be used to transmit corrections to the vessel should the spot beam satellite be masked by obstructions (eg. tree-lined banks). The telemetry system may also be used for transmitting RTK corrections to give centimetre accuracy.
The multibeam and GPS systems are integrated with an Applanix POS MV 320 (position and orientation system for marine vessels), which provides accurate navigation and attitude data to correct for the effects of vessel motion during the survey.
All survey data supplied is entirely digital. This includes bathymetric data incorporated with digital background mapping, reporting and photography. Data may be presented in a variety of formats, including 2D colour charts, 3D DTMs (which may also be merged with LIDAR data) and PDF documentation files. Volume calculations, difference plots, cross-sections and fly-throughs may also be produced.
