Airborne Gravity Survey - frequently asked questions
An airborne gravity survey is carried out by aircraft using state-of-the-art technology to detect extremely small variations in the Earth’s gravity field.
These variations are related to differences in the density of rocks in the subsurface and can be interpreted to improve understanding about the location and shape of geological structures from ground level to a depth of more than 50 kms.
Gravity surveying is a passive technique. An airborne gravity survey is a cost-effective way of covering a very large area in a short time. It enables consistent regional coverage over varied landscapes.
The survey is being managed by the Geological Survey of Victoria (GSV), a scientific agency within the Victorian Government. The survey is funded via the Victorian Gas Program.
GSV has contracted CGG Aviation (Australia) Pty Ltd (CGG) to conduct the survey. CGG provides a range of technologies, services and equipment designed to acquire extremely precise data and images of the Earth's subsurface.
It also provides state-of-the-art software and services for analysing that data and developing a deeper understanding of the subsurface.
We routinely conduct geoscientific research to better understand Victoria’s geology and State-owned Earth resources. Low-level detailed aerial surveys have previously been conducted over Victoria.
Our surveys were flown from 1994 to 2001 at 80 metres above terrain and at 200 metres to 400m line spacing. Surveys in central, northern and western Victoria were flown with a fixed-wing aircraft, while surveys in the eastern highlands were flown with helicopters.
An airborne gravity survey was conducted in Gippsland in 2011. See the complete data for the 2011 airborne gravity survey.
Airborne gravity surveys are currently being flown in Western Australia and Queensland. Many other geophysical surveys are being flown across Australia and internationally.
No approvals other than Civil Aviation Safety Authority flight approvals are required for the survey because the aircraft is flying in public airspace.
Aircraft and equipment
The survey will be carried out by two small, fixed wing planes traveling at approximately 220 km per hour (or 62 metres per second).
A single engine Cessna Grand Caravan 208B will be used to conduct the onshore portion of the survey. The plane is white with the CGG brandmark on the nose; blue, green and orange marking on the side and tail.
A twin-engine aircraft will be used for the offshore component.
The gravity-sensing equipment carried in the aircraft is based on the principle of accelerometers. Accelerometers are also found in mobile phones and tablets, video game controllers, and drone flight stabilisation systems.
The technology records extremely small variations in Earth’s gravity field while operating in a moving aircraft.
The planes will be flying at a height of 150 metres (nearly 500 ft) across most of the survey area, which is public airspace and above the low flying height limit specified in the Australian Civil Aviation Regulations. Areas requiring greater clearance such as built-up areas will be flown at 300 metres (nearly 1,000 ft).
Protected seal breeding colonies and the whale nursery at Logans Beach, Warrnambool, will be overflown at 300 metres. The aircraft operator will also be in contact with local Department of Environment, Land, Water and Planning wildlife officers to determine any other areas being occupied by whales to be flown at 300 metres height.
The survey operator, CGG Aviation (Australia) Pty Ltd; is the holder of a CASA Low Flying Instrument (CASA.LOWFLY.0241), which permits them to fly at 80 metres (260 ft) over the tips of structures such as wind farms and transmission towers.
The survey commenced in August 2018 and is expected to be completed by the end of the year.
Flights will be conducted seven days a week during daylight hours and only in favourable weather.
The survey will be flown using a flight path of parallel lines spaced 500 metres apart in a NW-SE orientation. The line direction is approximately parallel to the coast.
The planes will be traveling at approximately 220 km per hour (or 62 metres per second) and most lines on the flight path will only be flown over once.
Contingencies for weather and other unanticipated events are built into the flying schedule.
The planes will be travelling at a cruising speed of approximately 220 km per hour at a minimum altitude of 150 metres (nearly 500 ft). The noise level on the ground will be transient and less than the noise of a passing motorbike.
No. The pilot will be fully occupied with flying the plane. They will however, respond to other aircraft in the area in accordance with Civil Aviation Safety Authority flight regulations.
The flight crew will usually consist of two people either two pilots or one pilot and one observer. In some instances, an operator may also be on board to monitor the survey equipment.
Gravity data acquisition is passive and does not emit any signal. The aircraft will use an airborne laser scanner to acquire local topography data which is an important dataset to support accurate gravity data processing.
For safety purposes, the aircraft also need to monitor their height above the terrain and use standard aircraft laser and radar altimeters to do this.
The aircraft will also record variations in the Earth’s natural magnetic field using a magnetometer. The magnetometer is also a passive system and does not emit any signal. The magnetic data will be used to complement the gravity data and provide more accurate mapping of the geology.
The aircraft will record video of its flight path to confirm ground conditions at the time of surveying. This imagery is of similar or lower quality to that provided by Google Earth, and is not for public release.
The only potential impact identified is from aircraft noise. The planes will be travelling at a cruising speed of approximately 220 km per hour at a minimum altitude of 150 metres. The noise level on the ground will be transient and less than the noise of a passing motorbike. Most lines on the flight path will only be flown over once.
To minimise any noise impact on protected marine mammals, the aircraft will increase elevation to 300 metres (the same as for built-up areas) over the Logans Beach whale nursery, and the Cape Bridgewater and Lady Julia Percy Island protected seal breeding colonies.
Marine mammals (including whales) will be monitored for any signs of disturbance. The survey operator will also be in regular contact with officers from the Department of Environment, Land, Water and Planning (DELWP) to identify areas being used by whales at the time of planned over-water flights and agree on suitable mitigation measures.
Birds are not expected to be unduly affected by the survey due to the transient nature and 150 metre altitude of the aircraft. Locations with known concentrations of birds such as the Gannet colonies on Lawrence Rocks, Point Danger near Portland and birds in other wetland areas will be highlighted in the project’s safety plan. The flight crew will report any brolga sightings to DELWP.
No. The only potential impact identified is from aircraft noise, which is transient and less than the noise of a passing motorbike. The planes will be traveling at approximately 220 km per hour (or 62 metres per second) and most areas on the flight path will only be flown over once.
There will be no impact on fishing or farming activities.
Survey results and privacy
The findings from the airborne gravity survey will complement a range of other scientific data (such as mapping, lab analysis, groundwater testing, drilling, seismic data) to enable a more thorough understanding of the subsurface. This survey has applications in natural resource management, land use planning, geothermal energy, underground gas storage potential and geological knowledge in general.
The data collected from this survey will be used by geologists to map rocks underground and help refine geological models of the Otway Basin (offshore, nearshore and onshore).
Geological modelling is a key tool to help inform future approaches to managing our natural gas resources.
Gravity and topography data collected during the survey do not provide any information about personal land use. The aircraft will acquire video data, which is of similar or lower resolution than Google Earth imagery.
This data will not be released to the public and does not provide any specific information about personal land use.
The data will be publicly released as soon as it is processed and final products have been completed. This will take several months and products are expected to be available on the Victorian Gas Program website in the first half of 2019.
The results of the survey will not directly detect the presence of gas.
The findings will greatly improve our understanding of the geology in the region.
To determine the locations of prospective and non-prospective areas for gas discoveries, geoscientists will assess the findings from the airborne gravity survey along with many other scientific and environmental studies (such as mapping, lab analysis, groundwater testing, drilling, seismic data) to enable a more thorough understanding of the subsurface.
No. Fracking to extract onshore unconventional gas is permanently banned in Victoria under the Resources Legislation Amendment (Fracking Ban) Act 2017. This decision was made for the protection of agriculture, the environment and regional communities.
Visit the Victorian Gas Program page for more information.
Page last updated: 02 Sep 2021