Surveying Equipment

Hydrographic units of the RAN operate a variety of sophisticated equipment for the collection of survey information. Some of the equipment includes:

Echo-sounders

Echo-sounders are still an essential tool in Hydrographic Surveys. Echo-sounders are used to measure the depth of water immediately below a survey vessel, a paper trace provides a permanent record whilst a digital output is fed to data logging computers. The RAN operates several precision echo-sounders including:

Differential Global Positioning Systems (DGPS)

DGPS is the principal system used to accurately determine the position survey vessels and hence the seabed features they are directing.  In recent years DGPS, using a network of 24 satellites launched by the US Department of Defence has become the principle positioning tool of surveyors world wide.

The principle of DGPS is that a reference station is established on a known survey point ashore. The reference station determines any errors in the GPS constellation and employs a radio link to pass corrections to ships. Accuracies in the order of 5 metres or less can be achieved with DGPS.

RAN Surveying ships currently use Fugro Wide Area DGPS globally, and MX Marine DGPS within the coastal waters of Australia.

Electronic Position Fixing (EPF) Systems

Although GPS based technology has replaced the principal requirement for other systems the RAN operates a terrestrial based positioning system, Racal Microfix, a medium range fixing system which can be used in conjunction with or independently of GPS positioning systems.

Tide Gauges

Observing tides is an essential part of a hydrographic survey. The height of tide needs to be determined to allow corrections to be applied to recorded depths. Every depth has the height of tide subtracted to ensure that depths shown on charts represent the least amount of water that can be expected regardless of the height of tide.

The InterOcean S4 Tide Gauge - resembling a yellow basketball with a steel shaft through its axis. It can be either bottom mounted or connected to shore by a communications cable. It is generally used in areas where establishing gauges close to shore is difficult or where no dry land exists.

Current Meters

Observing currents allows current information to be provided on charts and in associated publications to assist mariners in planning passages and to aid their understanding of the environment in which they are navigating.

The InterOcean S4 Current Meter – like its tide gauge cousin, this meter resembles a yellow basketball with a steel shaft through its 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.

Traditional Land Surveying Equipment

Total Stations (intelligent electronic theodolites), geodetic levels and electronic distance measuring equipment are used by Hydrographic Service personnel for fixing terrestrial marks, mapping the coastline and for calibrating ship based positioning systems.

Digital Data Logging Systems

All RAN survey vessels use computer based systems to log and process the data received from positioning systems and echo-sounders. These systems also interface with other sensors including laser ring gyros, platform motion sensors and auto-pilots.

Systems currently in service have separate data logging and processing systems. The front end systems are used only for controlling and logging survey information. The post-processing systems allow all logged data to be checked and edited if required. Final digital records are prepared on board the ships and represent the work completed during each survey season. These digital records are submitted to the Australian Hydrographic Office for archiving and inclusion with other historical records on the Digital Hydrographic Database.

The system currently in use:

GeoNav / Terramodel

Based on current PC technology, this system uses GeoNav, an Australian designed DOS based hydrographic data logging system and a Windows based modelling software package called Terramodel to prepare the final presentation of the data.

CARIS – HIPS & SIPS / Fledermaus

Based on advanced PC technology this data processing software is state of the art, allowing multi-beam 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 visualisation of the survey data for quality control purposes.