Ground Water Imaging Pty Ltd

We specialize 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.

Using our product HERBI we investigate canal and reservoir seepage and bathymetry. Using AgTEM we 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.

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See our Company Brochure for a printable summary  (June 2014):  (2MByte).

Also view the video below of HERBI and the video on the land based page of AgTEM. Our development continues so if you are interested in us fast tracking development of a product please email us.

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 bank scanners 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. For dams we can offer substrate images plus volume stage table survey.

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.

See videos of our equipment in action in Google+

 

Airborne EM Compared with Land Based and Waterborne Systems

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:

Property Land Based Towed TEM Airborne EM

Footprint

Compact
– Almost
completely isolated to equipment dimensions at ground level where
cultural interference is problematic; wider at depth.
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.

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.
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.

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.

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.

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.
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.

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.
DGPS topography, low-level video, magnetic and gamma ray spectrometry all are typically also available.

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.
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.

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.
An aircraft, pilot, aircraft maintenance personnel, bulky equipment, and a ground geophysical crew must mobilise.

Additional Matters Relating to Waterborne Acquisition

Waterborne Geo-electric
Airborne EM

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.
Errors in measuring and
compensating for height above ground may be extreme over incised
watercourses covered with tall dense riparian vegetation.

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.
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.

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.
Located oriented video is typical.

Lateral coverage
The waterborne system provides data only under and in very close proximity to the waterbody. 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.