Do the math
One of the common challenges with airborne surveys is that the geophysical sensor system must be designed and implemented effectively to provide useful data while keeping costs down. Traditional survey companies would have you believe that airborne geophysical survey systems must be large, heavy, complex, and expensive to work properly. Their systems were not designed to allow for the unique operating characteristics of helicopters. Large helicopters and excessive flight heights are required to compensate for poor system design. The costs of their high fuel burn and complex maintenance requirements are passed on to the customer. At the same time, external sensors means that they must be flown at higher altitudes which limits the resolution and detection of small geophysical sources which are typically sought in mineral exploration applications.
Our solution
At Precision GeoSurveys, we are always working to provide our customers with superior geophysical data at a lower cost. A thorough knowledge of helicopters and the latest advances in exploration technology was combined to design airborne systems capable of producing the very highest quality of geophysical data, especially in low-level surveys. Our multi-sensor survey systems are fully integrated with dedicated helicopters flown by pilots highly skilled at the unique characteristics of low-level survey flying in mountainous terrain. We use the latest advances in digital technology, state-of-the-art sensor design, and composite materials to build geophysical systems custom-installed on our own helicopters, eliminating equipment set-up and pilot training delays.
Aircraft
Precision GeoSurveys specializes in airborne magnetic and radiometric surveys. In order to collect the high resolution data that our clients demand, we use Bell 206B, Bell 206L, and Eurocopter AS350 helicopters due to their proven safety, reliability, performance, and fuel economy. When it comes to collecting high-quality geophysical data in challenging terrain, you can't beat the low and slow capabilities of a helicopter.
GPS Navigation System
To collect high quality geophysical data, you need to know where you are. The heart of our systems is a Garmin 12-channel, WAAS-capable, Global Positioning System accurate to within 2 meters. Garmin's systems are capable of collecting reliable position data below the rotating rotor system of a helicopter. The GPS is coupled with a Pico AGIS-L data logger-pilot steering display for pilot navigation and real-time digital data recording. We strive for survey line accuracy of +/- 10 meters (terrain dependant), achievable on a routine basis by our pilots who are specialists at this type of work.
Time-Domain Electromagnetics
To map variations in conductivity in the subsurface, we use the Aerodat ATEM time-domain EM system. Time-domain electromagnetics involves generating an electromagnetic field which induces a series of currents in the earth at increasing depths over time. These currents, in turn, create magnetic fields which can be measured to map subsurface conductive properties. Because measurements are made while the transmitter current is turned off, the more sensitive measurement of the magnetic field generated by the subsurface enhances resolution of conductive features at great depth. The ATEM system has been specially designed to deliver aerodynamic properties suitable for use in mountainous terrain without compromising power or resolution.
Multi-channel Radiometrics
To collect radiometric data (natural radioistope concentrations of U, Th, and K) we use Pico Envirotec GRS-10 intelligent spectrometers. Spectrometer detectors are always mounted inside the helicopter (cargo box or cargo floor) to allow low-level flight patterns without the compromise of slung geophysical sensors. The spectrometer is self-calibrating and outputs the full 256 (512) channel radiometric spectrum for processing using PC-based Praga-3 software.
For routine surveys we use two 4.2 litre NaI(Tl) crystals (total of 8.4 liters) shielded against cosmic radiation with RayShield® gamma-attenuating material to provide a very high signal/noise ratio without having to resort to complex and heavy upward-looking detectors. For specialty surveys requiring high definition radiometric data we use additional crystal volume (up to 16.8 liters downward plus 4.2 liters upward).
Flying low level, terrain-following, flights by helicopter provides high downward-looking sensitivity and a high signal/noise ratio which reduces complex mathematical data reduction procedures. Low-level survey flights have the added bonus of enhancing identification of subtle radioactive sources, such as potassium alteration zones in porphyry environments, thorium enrichments associated with rare earth (REE) mineralization, and veins and boulders mineralized with uranium, which may not be detectable by surveys flown at higher altitudes.
Airborne Magnetometer Sensor
A Scintrex CS-3 non-radioactive cesium sensor is used to sample the earth's magnetic field at 10 Hz. The orientation of the sensor is adjustable, to provide optimum coupling with the earth's magnetic field on reciprocal headings. The measurement range of this state-of-the-art magnetometer is 15,000 nT to 100,000 nT with a peak to peak noise envelope of 0.002 nT in the 0.01 to 1 Hz bandwidth. The final data are tie line levelled and/or micro-levelled and includes corrections for diurnal fluctuations, IGRF and system parallax. Mounting the magnetic sensor in a fixed boom configuration helps to ensure that the geophysical data are collected at a low and uniform height above the Earth's surface, and optimizes the flight characteristics for simultaneous radiometric data collection. For specialized survey requirements, we offer a multi-sensor configuration to provide 3-axis magnetic gradients useful for identifying shallow targets in flat terrain.
Magnetic Compensator
Magnetometer Boom
PortabilityWhile we normally operate our own helicopter integrated with a multi-sensor geophysical system, we can also ship selected components or our entire system to survey sites anywhere on the globe. Installations in a wide variety of aircraft are possible, using our pilots or local pilots. Frequency-Domain Electromagnetics
Download more information.
|
During survey flights, movement of the survey aircraft interferes slightly with the geomagnetic field which is being measured. This small but significant variance is corrected in real time with a Bartington Mag-03 three-axis fluxgate magnetic field sensor, which provides reliable vector measurements of static and non-static magnetic fields in all three orthoganol axes. High-altitude compensation flights with prescribed pitch, roll, and yaw maneuvers "train" the compensation system for magnetic latitude, flight line orientations, and individual aircraft. A Figure of Merit (FOM) is calculated for each of the 36 specified flight maneuvers to less than 3 nT for the four cardinal survey flight directions.
The MMS-4 magnetometer processor is a high resolution (0.2 pT), fast sampling (20 Hz) magnetometer processor unit that continuously measures the magnetic signals from up to four magnetometer sensors. It is carried on board the aircraft and provides real-time magnetic compensation of the airframe motion.
The multichannel RMS Herz TOTEM-2A VLF-EM system receives the electromagnetic component of fields radiated from remote or local VLF transmitters in the 15 to 25 kHz frequency range. This is a state-of-the-art sytem with a built-in sferics filter and selectable frequencies. Components normally measured are the change in total field, the vertical quadrature component, and the total field. As this system can process two frequencies from two spatially separated transmitters simultaneously, gradient measurements are possible. The receiver is totally passive and is ideal for conductivity measurements in the near-surface environment.
Precision's fully certified (Supplementary Type Certificate) nose-mounted stinger carries the magnetometer sensor and VLF-EM receiver. The forward part of the stinger system contains the CS-3 magnetometer sensor, the central part contains the magnetic compensator and the VLF-EM receiver, and the aft part contains the laser altimeter. This innovation eliminates the traditional towed bird system and offers significant advantages in data quality, pilot work load reductions, survey flight efficiencies, and safety in all types of terrain.
The aft end of the magnetometer boom contains an Acuity AccuRange AR3000 laser altimeter to provide the pilot with terrain guidance. The infrared laser is eye-safe (Class 1) and is accurate to within 10 cm. Data from the laser altimeter are recorded to assist in data processing and, when combined with 3D GPS position data, have the added benefit of producing digital topographic maps (DTM) of the survey area.
Precision uses computer-controlled Geometrics G-856AX, Scintrex EnviPro, and GEM GSM-19 proton magnetometers with well proven proton precession technology, allowing accurate measurements to be made with virtually no dependence upon variables such as sensor orientation, temperature, or location. These units provide repeatable absolute total field magnetic readings, traceable to the National Bureau of Standards. Data are recorded digitally from a fixed ground position near the survey area for monitoring, recording, and correction of the earth's diurnal field shift.
A Pico Airborne Geophysical Information System (AGIS) digital data logger collects and records all applicable geophysical and navigational data, including X-Y-Z GPS position data, time, date, 256 channels of radiometrics, total field magnetics, compensated total field magnetics, two-channel VLF-EM, laser altimeter, barometric pressure, temperature, and humidity. Real-time QA/QC software provides data which are monitored in flight by a geophysicist or trained geophysical operator.
To measure and detect the conductivity (and its inverse resistivity) of geological features such as massive sulfides, graphite, silicification, water tables, and kimberlite pipes, we use the Hummingbird frequency-domain EM system. This is the world's only operational, fully digital, HEM system. The multi-frequency EM system measures the in-phase and quadrature responses from multiple coil pairs in a tubular bird, towed beneath a low-flying helicopter, using multiple simultaneous frequencies of 880, 980, 6600, 7000, and 34,000 Hz.
For detailed ground radiometric surveys such as rare earth element (REE) exploration, uranium target follow-up, and potassium alteration mapping, we use a Pico GRS-2 spectrometer which is fully integrated with GPS navigation and a digital data logger. Detector volume is 0.35 liters with full 256 channel resolution. The GRS-2 system can be backpack mounted, or carried by ATV or other vehicle at speeds up to about 40 km/h. This system is available for rent, or we can provide an operator.