GPR is renowned as a leader in its capacity to be able to solve the wide range of problems encountered by its clients, thanks to an impressive range of geophysical equipment available in-house.  We now have the capability to carry out land, marine and airborne surveys.

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HeliMAGer : Triaxial magnetic gradiometer

Geophysics GPR developed a new three-dimensional helicopter borne magnetic gradiometer for surveys with limited ground clearance.

The main advantage of our technique consists of the possibility to reconstruct the total magnetic field from the horizontal gradients. The resolution of the field obtained from such manipulations is estimated to be improved by 30 to 33 % (Hardwick, 1997) and therefore results in substantial savings on the total cost of the survey.

By its nature, gradients are not affected by cyclic daily variations such as diurnal effect. Consequently this exempts the usage of base stations for specific situations if encountered.

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Gamma-ray spectrometry - GRS-10 system

The GRS-10 system is a self calibrating Gamma Ray spectrometers using NaI (Tl) large volume detector arrays. Individual, independent, detector processing provides real time gain and linearity correction.

Ongoing research to improve the system stabilization algorithms make these spectrometer systems fully automated and self stabilizing on natural radioactive elements. This eliminates the requirement for regular, time consuming, and frequent system checking and re-calibration by the user. Furthermore it provides excellent accuracy and reliability of the gamma measurements.

The GRS-10 gamma ray spectrometer is widely used in mining exploration and mapping as well as in environmental studies and nuclear surveillance. With its high degree of accuracy and its reliability, the GRS-10 spectrometer is an excellent choice for every helicopter borne geophysical survey.

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Heliborne VLF - Very Low Frequency EM system

The multichannel Herz TOTEM-2A VLF system from RMS Instruments is mainly used for the interpretation of large scale geological features such as faults and conducting rock units.

The TOTEM-2A receives the magnetic component of fields radiated from VLF transmitters in the 15 to 25 kHz frequency range that are used for the purposes of navigation and communication with submarines. The parameters normally measured are the change in total field and the vertical quadrature component and the total field.

The TOTEM-2A data can also be used to map the surface ground resistivity of the heliborne survey area.

Because of its simplicity, size and ease of operation, this VLF system is an ideal add-on to existing heliborne geophysical exploration systems.

The basic principle behind bathymetry is the use of acoustic waves (in the range 30 to 250kHz) to measure the water depth.  A complete bathymetry system includes a vessel, an echo-sounder (analogue or digital) and a positioning system (DGPS or RTK).  The depth information is geo-referenced in real time and recorded on a portable computer on-board the boat.

Single beam systems are simpler and are used for small, shallow water surveys with difficult access.  Swath (or multi-beam) surveys are used for surveying large areas, such as ports, waterways, lakes and at sea.  Swath systems are capable of attaining 100% coverage of the bottom, over a width of 5-10 times water depth, and hence are very efficient once operating.

Typical uses for bathymetry are:

• Production of Digital Terrain Models (DTM) of the bottom for engineering design (tunnels, pipelines, bridges);
  
• Hydrographic surveys for navigational safety;
  
• Dredging control;
  
• Geotechnical studies.

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Current measurements

Current measurements consist of the precise measurement of the direction and speed of the water current in rivers, lakes or at sea.  GPR owns several types of current meters, for different water conditions.

The "S-4" current meter from Inter-Ocean is capable of measuring with precision the speed and direction of current, as well as depth (for use as a tide gauge) at 6-minute intervals over periods of several days.  Vertical current profiles can be measured using this instrument.

Typical applications include:

• Port redevelopment studies;
  
• Geotechnical studies;
  
• Environmental studies.
  

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Marine sediment sampling

Marine sediment sampling comprises two stages: firstly the correct location needs to be found using a GPS system, then the sample can be taken.  GPR possesses two types of sampler, a Benthos type sampler and standard grab samplers of various sizes.  The Benthos type sampler uses plastic tubing to extract core samples which are undisturbed, up to 2 metres long.  The grab sampler consists of a pair of steel jaws that close upon touching the bottom, hence collecting whatever sediments lay directly on the bottom.  The samples are sealed in airtight containers and clearly labelled for future examination.

Marine water sampling

Water sampling is carried out using a similar procedure to that of sediment sampling, except a special device designed to collect water samples is used instead of the sediment samplers.  The samples are placed in water tight containers and labelled, ready to be sent to the laboratory.  A conductivity, temperature salinity probe can also be used to obtain in-situ readings of these parameters in any water body.

Applications include:

• Port redevelopment;
  
• Geotechnical studies;
  
• Environmental studies.

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Marine magnetometry

Local variations in the Earth's magnetic field are most often caused by ferromagnetic objects or other magnetic objects located in the vicinity.  Through the measuring and recording of this variation, it is possible to detect objects submerged beneath the water (and sediments).  An accurate map of the object's position can be created by recording the sensor's position along with the magnetic variation.

Marine magnetic surveys are carried out using a magnetometer specially modified fro marine operations.  The magnetometer is installed in a water tight tow-fish, which is towed behind the vessel using a tow cable.  The sensor used most often is a proton precession or Overhauser type.

Typical applications include:

• Archaeology;
  
• Geological studies;
  
• Mineral exploration;
  
• Search and recovery of submerged objects.
  

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GPS positioning

Accurate positional information is an essential requirement for marine surveys, since there are no fixed reference points on water.  Today, GPS technology is employed by practically all of the marine industry for positioning.  Minimal positioning precision required for marine surveys is in the order of 2 metres. 

GPR makes use of Differential GPS systems (DGPS) for marine surveys.  These systems receive corrections from ground (Coast Guard) or satellite (WAAS, CDGPS) base stations to produce more accurate absolute position information (better than 2 meters) in real time.

For more demanding applications, GPS possesses a Trimble 5700 Real Time Kinematic system (RTK), which allows us to obtain precisions in the order of 2 cm for horizontal and 5 cm for vertical axis in real time, up to 25 km from the base station.  In addition, the system can be used to carry out static surveying, with millimetre level precision in the vertical and horizontal axes.  This system represents the state of the art for GPS systems today.

Applications:

• All marine surveys;
  
• Tidal measurements in real time;
  
• Static land surveying (high accuracy).

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Marine geological profiling

Marine geological profiling allows us to detect and to map interfaces between the various sedimentary layers or the overburden / bedrock interface beneath a body of water.  The technique is based on the principles of seismic reflection, i.e. the emission of a seismic wave into the subsurface, and the reception of the energy reflected by the various interfaces.

Marine profiling is carried out using two distinct types of equipment. The Sub bottom profiler or Chirp systems are integrated systems that are installed in a tow-fish and towed behind the vessel, close to the bottom.  These are essentially high frequency systems, which enables them to achieve high vertical resolution, but limits their depth penetration. 

The second type of system is the more traditional Boomer type systems which employ a separate energy source and a hydrophone streamer, towed behind the vessel, but which float at the surface.  The source can be an electric spark, an acoustic shock, or compressed air discharge.  Frequencies employed are in the 500 Hz range, which results in a lower resolution, but allows greater penetration into the subsurface.  The reflected energy is captured by sensitive hydrophones, and recorded on a multi-channel seismograph for future processing and analysis.

In certain conditions, a ground probing radar system can be used over water to replace the above mentioned systems.  However, the georadar system only works well in shallow fresh water environments, where the penetration required is minimal.

Typical applications include:

• Environmental studies;
  
• Geotechnical studies (tunnel, pipeline, bridge route corridors, etc.).

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Side-scan sonar

The side-scan sonar system enables the acquisition of images of the seabed including any underwater structures such as wrecks, dam walls, dikes, pipelines etc. through the use of acoustic waves.  One major advantage of this technique over the use of underwater video is its ability to obtain images similar to those of aerial photography, showing changes in the seabed composition as well as details of any submerged objects over a wide area, even in conditions of turbidity in the water.

GPR uses the Klein 595 dual frequency system, known as a work horse in the survey industry.  Data is recorded digitally, including positional information, and specialised software is used to create high resolution mosaics from the sonar data covering large areas of the seabed (SonarWiz and Sonar Web from Chesapeake technology).  The system can be used in rivers, on lakes or at sea. Different cable lengths are available for different water depths.

Typical applications:

• Search and recovery operations;
  
• Classification of the material on the seabed;
  
• Inspection of underwater structures such as pipelines, bridge pilings, dams, etc.

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Borehole geophysics

Geophysical borehole surveys can play a vital role in environmental studies, including the assessment of groundwater resources.  Geophysics GPR has been performing down-hole logging for over 2 decades.  We now have equipment based out of our Toronto office allowing us to offer faster, less expensive mob/demob. 

The following is a list of the tools available:

Borehole Radar: Fracture and fault characterization, karst imaging, detection of voids, thickness of aquifers and delineation of salt-water intrusion.

Seismic: Used for collecting in-situ physical properties of overburden and rock as well as imaging of fracture zones.

Caliper:  Useful for calculating drill-hole volumes, indicating zones of caving or roughness.

EM39 Induction Log: Used to generate conductivity profiles for the formation.  Used to distinguish different soil types in overburden or mapping and monitoring contaminants.

Self-Potential (SP): Can be related to relative water quality and to permeable zones in the stratigraphy.

Single-Point Resistivity (SPR)

Normal Resistivity: Related to water quality, lithological and structural changes.

Gamma Ray: Provides an indicator of clay or shale content. 

Density log (Gamma-Gamma): Can be related to porosity, rock strength, fracture density and lithology.

Porosity log (Thermal Neutron): Can be related to porosity and saturation.

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Electromagnetic methods

The use of the properties of electromagnetism constitutes a large part of the domain of geophysics.  A multitude of different instruments exist, all based on the same basic principle, but having certain differences in the way data is acquired and processed. 

The basis of the electromagnetic technique is the use of a coil with an alternating current circulating within it.  This causes a magnetic field to be created around the coil.  In reaction, a secondary field is created in the ground, to try to counteract the influence of the primary field from the coil.  It is this secondary magnetic field that is measured and analysed in different ways, depending on the application. 

Typical applications are:

• Detection of buried metallic objects;
  
• Contaminant mapping;
  
• Groundwater exploration;
  
• Minerals exploration (ground and airborne);
  
• Environmental applications.

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Gravimetry

Gravimetry is a potential field technique which measures variations in the Earth's gravitational field.  These variations are caused by density contrasts in the near surface rock and sediment.  Gravimetric surveys are carried out using extremely sensitive instruments capable of measuring tiny variations in the gravitational field.  These surveys are always carried out in conjunction with a precise topographic survey, to enable terrain corrections to be carried out.

Typical applications are:

• Regional geological mapping;
  
• Oil and gas exploration;
  
• Mineral exploration;
  
• Sediment thickness studies;
  
• Archaeological surveys;
  
• Void detection.
  

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Magnetic techniques

This method is a passive method since it only measures the existing magnetic field strength, it does not amplify or modify it in any way.  It is most often used in areas with minimal urban infrastructure, which tends to make interpretation difficult.  A magnetometer can measure the total magnetic field strength passing through its sensor through the application of the principles of nuclear physics and quantum mechanics.  Different types of magnetometer exist, each with different levels of precision and resolution.  Most common are proton precession magnetometers, with caesium vapour magnetometers used for more specialised applications such as airborne surveys,

Typical applications are as follows:

• Location of buried ferromagnetic objects;
  
• Archaeology;
  
• Mineral exploration;
  
• Geological mapping.
  

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Vibration and noise monitoring

Since its foundation in 1974, GPR has been involved in the measuring and analysis of noise and vibrations in order to minimise discomfort to people and to avoid damage to structures and equipment. We make use of a range of different instruments to measure vibrations and noise caused by blasting, pile driving, dynamic compaction, construction, traffic, etc.

Typical applications are:

• Provide professional consulting services to engineering companies during the planning phase;
  
• Provide vibration monitoring and analysis services to contractors during the construction phase;
  
• Potential risk evaluation and expert's reports for insurance companies;
  
• Provide specialised services for the specific problems associated with the installation of certain delicate equipment or structures.

Follow the links below for specific services:

Risk analysis and technical specifications
Mines and quarries
Construction, traffic and sensitive equipment
Sales and rental of seismographs

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Microseismic NDT

The basis of the microseismic technique is the in-situ measurement of the speed of propagation of high frequency seismic waves in concrete structures. The speed and attenuation of these waves is influenced by the soundness (quality) of the concrete structure.  Hence, sound concrete would be characterised by higher seismic velocities and little attenuation, whereas weathered or deteriorated concrete would be characterised by lower seismic velocities and high attenuation. The data from accelerometers or geophones is recorded by a high speed data acquisition device, such as GPR's Microsis® system. Data from several channels can be recorded and analysed in near real time to determine the relevant parameters.

Typical applications are as follows:

• Characterisation of the deterioration of concrete in urban infrastructure;
  
• Characterisation of the deterioration of rigid roadways and bridge decks;
  
• Measure the mechanical elasticity modulus of concrete or bedrock;
  
• Identify the interfaces between different surface materials (e.g. in a road surface).

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Streaming potential 

Water flowing through a porous medium gives rise to a streaming potential, which can be measured though the use of a series of electrodes linked to a recording device. Anomalies in the order of tens of millivolts can indicate zones of preferential flow or channelling.

Applications of this technique are:

• Detection of leaks in dams and dikes
  
• Hydrogeology and geothermal power, where one is interested in the flow of water in the ground.  

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Ground penetrating radar (GPR)

Ground penetrating radar (or GPR) is a technique based on the use of focused radar energy which penetrates the ground and is reflected back by any interfaces encountered. Recent technological advances have led to much more compact and better quality systems which can be used by a single operator.  A range of different frequency antennae are available for different applications.  Lower frequency antenna such as the 40 MHz are used for geological mapping, whereas the higher frequency antenna such as the 1500 MHz are used for detailed examination of concrete structures. Depths of penetration vary from several centimetres to tens of metres.  GPR is an efficient means of acquiring large quantities of data in a short time and with minimal preparation.  However, like all of the techniques, GPR does have its limitations.

Typical applications include:

• Scanning of concrete structures for the location of conduits and reinforcement bars;
  
• Geological mapping of areas of complex geology, bedrock profiling;
  
• Bathymetry over rapids / white water sections using a helicopter;
  
• Road radar surveys to determine the thickness of the bitumen cover along highways or in parking lots;
  
• Environmental studies;
  
• Archaeology.

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Radiometrics

This technique is based on the fact that radioactive elements are quite abundant in nature, and their effects can easily be detected by a scintillation counter / spectrometer. This device is a specialised crystal coupled to a photoamplifier system, and is able to detect a range of radioactive elements by measuring the energy band of the particles emitted.

Typical applications include:

• Mineral exploration
  
• Geological mapping
  
• Environmental studies

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Electrical methods

The basic principle behind electrical methods is the injection of DC current into the ground using a pair of electrodes.  This current causes a potential difference in the ground which is measured by a separate pair of electrodes.  The voltage measured can then, using the parameters of the survey, be converted into an apparent resistivity value.  This value can provide a range of information regarding the material being tested.  Different types of soil compositions have different resistivities. Variations of the method include electrical resistivity, self potential, and induced polarisation.  Each of these methods can be used for a wide range of applications.

A number of different electrode configurations can be employed for electrical surveys, including Vertical Electric Soundings (VES), 2-D and 3-D Electrical Resisitivity Tomography (ERT) pseudosections, 2-D dipole-dipole gradient maps (in the horizontal plane) of resistivity and induced polarisation.  The depth of investigation is a function of the electrode spacing, the greater the spacing, the deeper the investigation.

Typical applications are as follows:

• Geological mapping;
  
• Hydrogeology (water flow);
  
• Environmental studies (contaminant flow, groundwater quality);
  
• Mineral exploration (induced polarisation surveys).

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Borehole seismic surveys

Borehole seismic surveys can be carried out in several different ways. The Down-hole technique consists of measuring the arrival of seismic waves emitted from the surface in increments down the borehole. The Cross-hole technique uses a seismic source located in an adjacent borehole. The receiver in both cases is a tri-axial geophone, which usually clamps to the walls of the borehole. This enables profiles of seismic velocities from compressional (P) waves as well as shear (S) waves to be obtained. Accurate 2-D maps of seismic velocity variations between boreholes can be produced by processing the data using specialised software.

Typical applications of this method are:

• Determination of rock or concrete quality through the estimation of the dynamic coefficients of the materials
  
• Detection of faults and shear zones in bedrock

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Seismic reflection surveys

Deep seismic reflection surveying is the most advanced technique in geophysics today, thanks to its application on a huge scale for oil and gas exploration.  This technique does, however, have other applications on a smaller scale, such as for civil engineering project site investigation.  The methodology is identical, but the equipment and parameters are adjusted to provide a higher resolution at shallow depths.

Seismic energy is generated at the surface using either impulsive sources (dynamite) or continuous sources (Vibroseis). The returned energy is recorded by a series of geophones installed along lines at the surface.  Reflection of the energy is caused by contrasts in acoustic impedance between the various strata. Data processing is a complex sequence of operations carried out usually on powerful computers using specialised software. The final product is a 2-D or 3-D dataset of seismic reflectors, which can then be correlated to specific geological interfaces through the use of borehole information.

Applications include:

• Oil and gas exploration;
  
• Geological mapping studies;
  
• Mineral exploration;
  
• Civil engineering site investigations.

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Seismic refraction surveys

Seismic refraction uses the same equipment as for reflection work, but using a different geometry for the source and receiver layout. The principle for seismic refraction is to provoke seismic waves which travel along the interface between two different strata in the ground.  What we are looking for are the first arrivals, which are the waves which have been refracted at the critical angle between two strata. The production of time-distance plots for the data allows us to calculate the apparent seismic velocities and layer thicknesses in each of the strata present, including the bedrock.

Typical applications of seismic refraction are:

• Bedrock profiling and location of faults and fracture zones;
  
• Determine the thickness of the various overburden layers;
  
• Calculate the modulus of elasticity of the various layers;
  
• Determine the depth to the water table;
  
• Identify sub-vertical geological contacts.

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Seismic resonance (TISAR)

Testing and Imaging using Seismic-Acoustic Resonance (TISAR) is a recently developed method for high resolution seismic investigation at shallow depths. A seismic resonance survey consists of creating vibrations at the right frequency at the surface and then recording the seismic resonance produced in the time domain, using dedicated receivers.  Differing resonances are produced where there are changes in the elasticity or density, such as at strata interfaces and fractures in the bedrock. Data processing allows the production of geological sections, which require calibration from borehole data, as with seismic refraction and reflection.

Seismic resonance enables very high resolution data at shallow depth to be obtained, but is not suited to intermediate to deep investigations. For this we recommend seismic reflection or seismic tomography.

Typical applications for TISAR are:

• Bedrock profiling;
  
• Overburden strata profiling;
  
• Identify sub-horizontal geological contacts;
  
• Locate small fractures and faults in the bedrock.

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Down hole electrical tomography

This method consists of measuring the electrical resistivity of the ground through the use of a specialised borehole probe.  This method allows us to sample the ground surrounding the borehole up to 300 metres in depth.  In addition, a cross hole technique can be employed to obtain a 2-D resistivity section between two boreholes.

Typical applications include:

• Resistivity variations down a borehole can be correlated to stratigraphic changes;
  
• Identify the upper and lower extent of an aquifer;
  
• Saline intrusion mapping in coastal areas;
  
• Environmental applications such as contaminant flow mapping, groundwater quality mapping;
  
• Down hole IP can be used for characterisation of mineral deposits;
  
• Correlation of resistivity data with other borehole data allows lateral extrapolation (e.g. porosity, permeability, saturation). 
  

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Seismic tomography

Seismic tomography, as with medical tomography, allows us to image the interior of a given structure.  The principle of this technique is the travelling of seismic waves inside the structure. 

The general sequence is the generation of a seismic wave in a borehole whose influence is recorded by a series of geophones (or hydrophones) in an adjacent borehole.  Throught the application of mathematical operators on the whole dataset, a slice of the spatial distribution of seismic velocities of propogation in the material is obtained for a section between two boreholes.  The propogation speed of the seismic waves is related to the mechanical properties of the medium.

Seismic tomography can be employed in situations where problems are suspected, or sections suspected of containing concealed problems.  In addition, the method can be used to verify the integrity and quality of the materials used during construction.

Other typical uses for this technique are:

• Quantitative evaluation of any material by seismic velocity analysis;
  
• Diagnosis of problem areas in 2-D or 3-D;
  
• Quality control tool for structural repairs.

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Radar tomography

This method consists of the use of a specialised set of borehole antennae in adjacent boreholes, one transmitter and one receiver. This technique can be employed to obtain a 2-D section showing the changes in the electromagnetic propagation speed between two boreholes using the same software as for seismic tomography. The technique is very efficient and has an exceptional resolution.

Typical applications include:

• Trace stratigraphic changes between boreholes
  
• Identify faults and shear zones in bedrock
  
• Identify presence of voids in karst formations
  
• Porosity / saturation estimates of geological formations or earth dams

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Ultrasound

The non-destructive technique of ultrasound scanning is based on the measuring of the speed of propogation of ultrasound waves and their attenuation, which is affected by the quality of the material (e.g. concrete or rock). Hence, good quality concrete is characterised by higher propagation speed and lower attenuation, while poor quality concrete exhibits slower propagation speed with higher attenuation. Piezoelectric devices are used to generate and measure the ultrasonic waves from the surface of the structure being examined, or the rock sample. The Microsis® acquisition system records the received signal from the piezoelectric devices and carries out real time analysis to determine the propagation speeds and attenuations, allowing calculation of the mechanical properties of the rock or concrete.

Typical applications for this technique are:

• Estimation of the deterioration of concrete parts of urban infrastructure at high resolution;
  
• Characterise the level of deterioration of rock;
  
• Measure the elastic modulus of concrete or rock;
  
• Detect voids in concrete structures and rock.

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