Inside the AHO
The RAN’s Hydrographic Ships (HS) and embarked Survey Motor Boats (SMBs), along with the Survey Motor Launches (SMLs), employ a variety of sophisticated survey equipment to acquire hydrographic data. In broad terms, some of the equipment includes:
Echo sounders remain an essential tool in the conduct of hydrographic surveys. Traditionally, single-beam echo sounders are used to measure the depth of water directly below the survey vessel. Multibeam echo sounders use a swath across-track, which allows depths to be obtained in waters extending beyond the ship’s side. This allows complete depth ensonification of the seafloor.
The echo sounders provide digital output, which is fed to the survey data logger computers. The Hydrographic Ships and Survey Motor Launches operate several precision echo sounders, including:
Fansweep 20 Multibeam Echo Sounder
Atlas Deso 15 Dual frequency, single-beam echo sounder (SMB only)
Atlas Deso 25 Dual frequency, single-beam echo sounder
Edgetech 4300 Towed high speed side scan sonar
Survey Motor Launch (HSS upgraded)
Reson Seabat 7125 Multibeam Echo Sounder
Kongsberg AE600 Dual frequency, single-beam echo sounder
Kongsberg AE600 Hull mounted side scan sonar
Klein 5000 Towed light weight side scan sonar
Survey Motor Launch (pre-Upgrade)
Atlas Deso 35 Dual frequency, single-beam echo sounder
Knudsen 320B Hull mounted side scan sonar
C-Max Towed light weight side scan sonar
Differential Global Positioning Systems (DGPS)
DGPS is the principal satellite-based, positioning system used to accurately determine the horizontal position of hydrographic survey vessels and seafloor features. The principle behind DGPS is by establishing a reference station over a known position of high accuracy; the GPS receiver can determine the horizontal error in position derived by the current satellite constellation. This error can be transmitted by radio link to the ships allowing a higher position accuracy to be derived from the ship-based GPS systems by applying the correction.
Hydrographic Ships and SMLs currently use Fugro Wide Area DGPS globally, and MX Marine DGPS within the coastal waters of Australia.
Electronic Position Fixing (EPF) Systems
Although satellite-based technology has replaced the principal requirement for other systems the RAN’s Hydrographic Service operates a terrestrial-based positioning system. The Racal Microfix is a medium range fixing system which can be used in conjunction with or independently of GPS positioning systems.
Observing tides is a critical part of any hydrographic survey. The height of tide needs to be determined to allow corrections to be applied to depths. Every depth recorded by the echo sounder has the height of tide subtracted to ensure that depths illustrated on the nautical chart represent the least amount of water that can be expected in average meteorological and astronomical conditions.
The InterOcean S4 Tide Gauge resembles a yellow basketball with a steel shaft through the axis. It can be either bottom-mounted or pedestal-mounted. The gauge can be downloaded, if deployed in close proximity to the shoreline, via a communications cable.
The Australian Hydrographic Service has recently purchased the RBR TGR1050P tide gauge. This tide gauge has been trialed and will be brought into service to compliment the S4 tide gauges. These tide gauges are considerably less cumbersome, easier to program and download.
Observing currents allows the mariner to better plan and execute a navigation plan. Ocean current information is illustrated on nautical charts and in associated publications.
The InterOcean S4 Current Meter - like the S4 Tide Gauge, this meter resembles a yellow basketball with a steel shaft through the axis. The meter is normally bottom-mounted but a submersible float is used to hold the meter in the part of the water column that is the subject of observation.
Land Surveying Equipment
Total Stations (intelligent, electronic theodolites), geodetic levels and electronic distance measuring equipment are used by the Hydrographic Service personnel for fixing terrestrial marks, charting the coastline and for calibrating ship-based positioning systems.
Digital Data Logging Systems
All hydrographic survey vessels employ integrated, computer-based, Hydrographic Survey Systems (HSS) to log and process the data received from positioning systems, echo sounders and sonar. The HSS is also interfaced with electronic navigation systems, including laser ring gyros, platform motion sensors and auto-pilots.
HSS currently in service have separate data logging and processing sub-systems. The ‘on-line’ system is used for controlling the ship’s track while acquiring hydrographic data. The ‘off-line’ or post-processing systems allow all logged hydrographic data to be check and edited if required. A Final Digital Record (FDR) is prepared onboard the ship and represents the work completed during each survey deployment. These digital records are submitted to the Australian Hydrographic Office (AHO) for quality control and, eventually, improvements to nautical charts. Where necessary, any remedial work identified from the rendered survey data can be re-allocated to another survey vessel for continuation. The survey data is archived and included with other historical data in the Digital Hydrographic Database (DHDB). The systems currently in use include:
Hydrographic Ships: CARIS - HIPS & SIPS / Fledermaus
Based on advanced PC-technology this data processing software is state of the art, allowing multibeam survey data to be advanced through the one package to a final digital record. Data compilation and validation is managed through to chart production. Fledermaus software allows high resolution visualization of the survey data for quality control purposes.
Survey Motor Launches (HSS Upgrade): QINSy / Fledermaus
Survey missions are created through a PC-based Mission Manager prior to commencing survey activities. Multibeam, singlebeam and sonar data can be combined during the post-processing routines in order to create a final digital record. Fledermaus software allows high resolution visualization of the survey data for quality control purposes.
Survey Motor Launches (pre-HSS Upgrade):
Based on old PC-technology, this system uses GeoNav, an Australian designed DOS-based hydrographic data logging system and a Windows-based modeling software package called Terramodel to prepare the final presentation of the data.