Groundwater Imaging Pty Ltd
We specialise in towing geophysical equipment across farmland and inland waterways for the purpose of imaging the substrate groundwater and geological properties. Ancillary to this goal, we provide 3D graphics of our data and/or drillers logs from government databases. We offer hydrogeophysical and other electrical geophysical services to farmers, irrigation engineers, hydrogeologists and mineral explorers.
We investigate canal and reservoir seepage and bathymetry and site water bores. We conduct larger scale surveys for detailing coupled river-aquifer systems (connected surface water and groundwater systems), saline inflow to rivers, groundwater conceptual models, managed aquifer recharge sites, and land salinisation hazards. We also conduct mineral exploration on open farmland and rangeland.
We offer both a survey service as well as, in some cases, our technological solutions to others who may wish to do likewise. Our business involves three principle categories: Waterborne, land based and graphics.
Land Based Subsurface Groundwater Imaging
We can create easy to use
3D images of groundwater and geological properties simply by driving equipment across the land or water. This is useful for
water bore siting, detailing groundwater conceptual models, planning managed aquifer recharge, mineral exploration and land salination hazard mapping.
To
reveal variations in rock and sediment saturation and permeability, as well as groundwater salinity, we tow a trailer mounted time domain
electromagnetic (TDEM or TEM) system capable of
imaging electrical conductivity from the surface to in excess of 100m deep.
We also offer
geo-electric imaging (resistivity imaging) at soil (decimetre) and greater scales. This is useful for investigating
irrigation water and salt migration through soil.
Waterborne Subsurface Groundwater Imaging
From
irrigation canals, Groundwater Imaging indicate where freshwater seepage has flushed downwards into the substrate and where clay layers have confined seepage. In rivers and drains we indicate where infiltration into and out of the substrate occurs including where
saline groundwater inflows to waterways. When investigating coupled
river-aquifer systems we can also infer the extent and depth of
unsaturated substrate and dimensions of aquifers and impervious, confining basement rock features.
When
imaging substrate properties, we also collect bathymetric data. In our unique, cost effective approach, we float small electronic enclosures that tow streamers, sonar and ancillary devices such as laser rangefinders and geo-located, oriented video cameras along waterways. Principally, we image the
geo-electric (resistivity) substrate electrical conductivity (or its inverse, resistivity) at multiple depths beneath the beds of
waterbodies.
In a single pass along a
waterbody we can collect all this information.
Waterbody width and time lapse oriented photography may augment the principal datasets. We have a track record of economically surveying watercourses so difficult to navigate that competition does not emerge.
Graphics – 3D Hydrogeological Imaging
Three dimensional subsurface imaging is now within the grasp of anyone capable of operating Google Earth with the assistance of files we provide.
We present drillers logs (lithological logs) from government databases, as well as geophysical data we collect, in 3D graphics of the subsurface. We distribute such graphics to end users as files they can open, superimpose, and manipulate in
Google Earth and other 3D viewers.
Our geophysical data typically is presented in vertical sections wrapped along the track of our surveys.
We call these ribbon, or curtain, images. On occasions, density of data collected warrants presentation of depth slices or more elaborate iso-surfaces.
Software Applications
Groundwater Imaging Pty. Ltd. write software in Delphi and Visual Basic. Their flagship product is Hydro-Geo Imager which is designed to facilitate all phases of electrical conductivity imaging. Currently (Sept 2008) work is in progress for facilitating the 3D viewing capabilities of Hydro-Geo Imager within Google Earth Pro in 3D.
Groundwater Imaging are also working on a multi-depth EC database to make available the thousands of kilometres of data they and others have collected across Australia.
EM imaging technology is offered by others operating expensive, elaborate airborne geophysical systems (airborne EM). On open farmland or rangeland we may have an advantage while on smaller, goal oriented projects we can often complete entire surveys for less than the mobilisation costs of airborne EM systems. Our waterborne survey solutions offer data robustness, detail, diversity and comprehensiveness not possible with airborne systems. Where a high degree of detail must be mapped, especially in the midst of metallic interference, our system may offer the only survey solution.
Consider the following comparison table:
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Property
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Land Based Towed TEM |
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Airborne EM |
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Footprint |
Compact - Almost completely isolated to equipment dimensions at ground level where cultural interference is problematic; wider at depth. |
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Larger due to flying height; also, highly variable as flying height and orientation change continuously. Deleterious coupling with surface metallic features such as fences is maximised.
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Course Across Ground |
Very flexible – can be adjusted on-the-run according to survey findings. Confined by vegetation, fences and other obstacles - this is typically not problematic for groundwater investigations. Ability to change course to test responses of fences and then keep an appropriate separation.
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Limited to straight or slightly curved lines due to aircraft speed. Survey progresses too fast for comprehensive on-the-fly assessment of data and course adjustment.
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Cultural Interference |
Minimal coupling problem occurs until equipment passes right over or under metal objects. Effective survey has been conducted, in many instances, right beneath powerlines and within 1m of fences. The system cannot survey effectively over buried copper telecom cables and this often presents a problem when survey is restricted to road margins containing such cables.
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Coupling with surface metallic objects is maximised whenever such objects pass under the equipment footprint which may be several 10’s of metres wide at ground level.
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Near Surface Detail |
Having no air layer, and small footprint, near surface detail is maximised. Our system typically provides 1m depth resolution near the surface with turnoff of less than 3 uS possible and sampling at 500kHz. |
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Due to the need to penetrate and measure and compensate for a variable thickness air layer, some near surface resolution is lost. Such losses become extreme when part of the footprint crosses steep terrain covered with trees such as incised rivers and billabongs.
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Auxiliary Data Options |
DGPS or survey grade RTK DGPS topography, oriented located time lapse photography, magnetics and gamma ray spectrometry are available. Bore can be located and sampled, cultural features can be mapped, and geological mapping can occur en-route.
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DGPS topography, low-level video, magnetic and gamma ray spectrometry all are typically also available.
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Survey Speed |
5 to 10 km/hr. Slower speed permits much more stacking per km thus much greater signal to noise for equivalent power. Data can be sampled in much more detail with a moving average filter than for airborne systems.
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15 to 150 km/hr. 120km/hr typical. Data acquisition is much faster and thus less detailed but due to higher running costs of airborne systems, not necessarily cheaper.
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Mobilisation & Demobilisation Costs |
Only a lightweight trailer, 4wd and one operator need to mobilize. The survey trailer folds up and is mounted on a small dolly trailer in minutes for high speed road travel.
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An aircraft, pilot, aircraft maintenance personnel, bulky equipment, and a ground geophysical crew must mobilise.
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Additional Matters Relating to Waterborne Acquisition
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Waterborne Geo-electric
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Airborne EM |
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Response to
Tree Canopy
and River Incision |
Survey from the flat, consistent electrical conductivity water surface or the water bed permits acquisition of robust detail data in the substrate immediately beneath the water body bed.
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Errors in measuring and compensating for height above ground may be extreme over incised watercourses covered with tall dense riparian vegetation. |
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Depth Resolution |
Decimetre scale near-bed substrate resolution is possible with submerged streamers and sub-metre resolution is possible with floating streamers. Studies of canal siltation and hazards of saline inflow to rivers require such resolution.
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Resolution of a couple of metres near the water bed is estimated for conductive substrates. Steep incision of rivers and cultural features present along canals can render depth resolution ineffective. |
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Additional Parameters |
Professional sonar and RTK DGPS provide bathymetric data. Waterbody width can be added with laser rangefinders. Located, oriented, time-lapse photography. Mapping of cultural features. Continuous water property sampling (EC, pH, redox etc.). Substrate coring and permeability testing is feasible in a second pass.
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Located oriented video is typical. |
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Lateral coverage |
The waterborne system provides data only under and in very close proximity to the waterbody. |
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An airborne system is suited to acquiring multiple parallel passes of data along river corridors. Such data strongly compliments quality data collected along watercourses themselves with waterborne equipment.
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