Airborne Stinger Installation

Airborne methods are also being used increasingly for Environmental and Unexploded Ordnance Detection work where surveys are large enough to warrant the increased costs of fixed wing and helicopter mobilization and surveying. Other groups are evaluating cost-effective, ultra-light aircraft configured with magnetic sensors and gradiometers. GEM offers the advanced Potassium system for these kinds of work. Another common use for GEM systems is as a base station for airborne surveys.  Contractors are increasingly standardizing on the Overhauser magnetometer due to its inherent stability and proven record.

Bringing a New Focus to Resource Exploration

For the last 20 years, airborne magnetic data acquisition has remained largely static -- based on older generations of optically pumped Caesium technology. Now, however, there is a new option which delivers superior benefits and performance.

This web page is intended to highlight some of the benefits of the optically pumped Potassium technology while introducing the reader to solutions for helicopters, fixed wing and base station installations. Please use the following links to navigate to the section of most interest to you:

• Airborne System Overview

• Introducing the GSMP-30A Magnetometer / Gradiometer

• Helicopter Magnetometer Solutions

• Fixed-Wing Magnetometer Solutions

• Base Station Magnetometer Solutions

Airborne System Overview

GEM’s Airborne Solutions comprise the GSMP-30A Airborne magnetometer which can be installed in either helicopter or fixed-wing aircraft. Each type of installation has specific advantages:

• Helicopter produces high quality data in areas of rugged terrain where tight clearance and safety issues make it unfeasible to fly fixed-wing aircraft. They may also be used for small, localized surveys in remote areas where a helicopter can be accessed nearby.
  

  NEW:

  Complete Airborne Systems are Available:
  √ Bird
  √  Radar Altimeter
  √  GPS (20 Hz)
  √  Data Acquisition

  View the PDF Brochure

   

• Fixed-wing produces lowest noise and best positioning (for a proper installation). Fixed-wing surveys are typically conducted over large areas (>5000 square kilometres) over moderately rugged terrain.

Typical applications include mineral exploration; oil and gas exploration; environmental and engineering; and unexploded ordnance detection. These survey types are all characterized by the need for high sensitivity, high sampling and minimal heading error.

GEM’s base stations solutions comprise the GSM-19 ground magnetometer technology which also delivers a number of advantages for surveying, including high absolute accuracy for reliable measurement of the total field, fast sampling (up to 5 Hz) for acquisition of the most rapid diurnal changes, and programmability for flexibility in survey scheduling.

Introducing the GSMP-30A Magnetometer / Gradiometer     (Top)

Typical airborne magnetometer configurations include one or more sensors with pre-amplifier (electronics), processing / acquisition unit, compensation (optional), towed bird (for helicopter surveys), airfoil (i.e. pods) for housing units (optional), and navigation (optional).

GSMP-30A Airborne Magnetometer System

The GSMP-30A Airborne Potassium Magnetometer System is one of the most advanced, high sensitivity airborne magnetometer solutions commercially available. The Airborne GSMP-30A Potassium Magnetometer, with either its sensor installed in a towed-bird airfoil, or in a tail-stinger airfoil, is a superb high‑resolution instrument, capable of making a total‑field magnetic measurement 20 times per second (standard) and 100 times per second (optional).

For example, even in fixed-wing aircraft flying at 220 kph, a reading is being made approximately every 6 metres along the ground, which is equal to the resolution of most ground magnetometer surveys.  Rotary-wing aircraft typically fly at ½ the airspeed of fixed-wing aircraft, providing a high-resolution sample density on the ground of approximate 3.0 metres. The following lists the general components of the GSMP-30A system.

 GSMP-30A Sensor

The heart of GEM’s airborne helicopter and fixed-wing systems is the GSMP-30A sensor. It is a high performance potassium magnetometer, providing unmatched sensitivity in addition to near zero heading error effect. The GSMP-30A operates on principles similar to other alkali vapour magnetometers however it benefits from the unique nuclear properties of Potassium. It has greater than 0.0005 nT/Hz^1/2 sensitivity combined with ± 0.1nT absolute accuracy over its full temperature range. 

The inherent potential sensitivity resulting from the nuclear properties of potassium yields a high natural frequency of 7 Hz/nT -- twice the natural frequency of caesium. Also, the GSMP-30 offers a high insensitivity to orientation. In contrast to caesium units, virtually zero heading error results due to the nuclear properties of potassium.

GSMP-30A Electronics

Electronics are incorporated in a secure housing. These electronics control a variety of functions that are (in sequence):

• Analog board causes system to scan
• While it scans across, signal comes through pre-amplifier and is amplified
• Lock indication detects signal and stops the scan
• Depolarization is applied to make cell oscillate
• 5 Volt peak-to-peak sine wave is output for counting of Larmor frequency

GSMP-30A Processing / Acquisition

Internally, the system is set up to convert sine-wave signals and phase information into Larmor frequency and to output it via RS-232 for collection by computers or third-party data acquisition systems. There is no memory with this mode of operation hence the need for a PC or third-party acquisition system. Both can be supplied by GEM. In the case of a PC installation, the user also benefits from custom software for plotting traces and performing quality control interactively during flight.

Compensation and Pilot Guidance (Optional)

For highest quality results, it is desirable to perform compensation for aircraft and other magnetic effects, and to provide a facility for pilot guidance. The GEM GSMP-30 Airborne Potassium Magnetometer can be augmented with an Aeromagnetic Digital Compensator (ADC) that uses input from a Billingsley 3-axis fluxgate to determine the aircraft’s attitude and rate of change with respect to the earth’s magnetic field.

The compensation system identifies the permanent, induced and eddy current magnetic contributions of the aircraft and provides a correction to be applied to the raw magnetic data to remove noise related to aircraft motion. An optional pilot guidance navigation unit is available from a commercial source. This system guides the pilot along survey lines, keeping within pre-set tolerances.

Navigation

The Ashtech^® G12^TM GPS board from Thales Navigation sets the standard for superior performance in a wide assortment of high-accuracy marine, avionics and land navigation applications. Available in a board and sensor format, this powerful 12-channel receiver is the first of its kind to offer a 20hz update rate for real-time guidance, position and raw data output. The G12 offers differential accuracy better than 40 centimeters and position latency less than 50 milliseconds. It delivers precise three-dimensional positions to meet the demanding requirements of high-end OEM system integration.

The G12 incorporates all-in-view tracking of up to 12 satellites with a loss of lock re-acquisition time of less than 2 seconds, and delivers unsurpassed position accuracies of better than 40 centimeters, achieved immediately following satellite acquisition. The Strobe Correlator^TM technology provides unmatched code multipath mitigation, providing the best possible position accuracy. The G12 offers distinct timing options for precise timing and frequency, or time-tagging of positions, including 1 PPS time pulse, an event marker to time-tag a position, and a programmable measurement strobe that generates a pulse at a programmable interval in advance of measurements.

For more information, please refer to the following resources below:

• Brief Review of Quantum Magnetometers
• Advantages of Potassium over Caesium Magnetometers
• Technical Details - GSMP-30A Brochure
• Quote Request

Helicopter Magnetometer Solutions                                     (Top)

With the increased activity in airborne geophysics, earth science professionals are seeking solutions for acquiring high-quality helicopter airborne data at minimal cost. GEM is pleased to be able to offer such a solution based on its optically pumped Potassium technology. Main benefits include:

• Cost effective installation via an integrated set of acquisition components
• Easy operation using GEM's proven PC-based acquisition platform
• Elimination of costly data acquisition systems with PC-based acquisition
• Reliable acquisition of high resolution data via the most sensitive commercial airborne magnetometer / gradiometer on the market
• Accurate positioning of survey measurement locations with the system's integrated radar altimeter and GPS data
• Rapid downloading of results via high-speed RS-232 connection

Cost Effective Installation

With helicopter systems, sourcing and installation of components can be challenging; requiring significant research and time to identify an optimal solution. GEM's Helicopter Magnetics solution provides a complete set of components that are designed to interface easily with each other. Components include:

• Precision-designed bird for housing magnetic sensors, sensor electronics, GPS antenna, radar altimeter and batteries.
• State-of-the-art instrumentation including GEM's leading GSMP-30A magnetometer and Personal Computer, TRA3500 Terra Radar Altimeter and NovAtel GPS receivers with antenna.
• High-strength, kevlar reinforced tow and data communication cable

With all components in its Helicopter Magnetics solution, installation is quick and easy … simply requiring the operator to connect the tow / communication cable, bird and helicopter-based acquisition console, and start using the system.

Helicopter Bird (Single, Gradient or Triaxial)

GEM’s fiberglass bird is custom-designed for aerodynamic smoothness to ensure minimum vibration and for high-quality data acquisition. Birds are available with one, two or four sensors. All fittings are provided for securing the bird. The cable is used for in-flight transmission of data to the PC in the helicopter.

The Vertical Helicopter Gradiometer is a single axis system with two sensors; one above and one below. Differences between the two sensors are calculated and used to derive the vertical gradient at each survey location. The image below shows a Vertical Gradiometer.

The Tri-Directional Helicopter Gradiometer was the first three-axis gradiometer developed globally. Since its inception in the mid 1980s, the system has been outfitted with optically pumped Potassium sensors and has evolved into a reliable platform for different applications, including mineral exploration. The image below shows a four-component gradiometer system with skirt for in-flight stability.

This special gradiometer consists of a three-armed towed bird configured with 4 sensors for calculation of magnetic gradients, including vertical and horizontal across and along track gradients. Additional components include GPS for accurate positioning of the bird during flight. Data capture is either to a Personal Computer or a 3^rd party unit.

Traditional design criteria for electromagnetic (EM) birds were observed when the bird was designed. Requirements for rigidity are very much relaxed in comparison with EM birds. It is sufficient to measure gradients with 0.1% accuracy (up to 25 nT/m and beyond) as compared with EM measurements of some parts per million. The bird’s shell, therefore, was designed of sufficient diameter and wall thickness to accept the magnetometer sensor and support weight of sensors, fins, skirt, and its own weight with <0.1% change of relative sensor positions due to shell flexing.

The fins are spaced at 120 degrees to allow for simple calculation of gradients in all three directions; the average magnetic field of the two lower fins fall beneath the upper fin sensor to allow for vertical gradient determination; the average field of all three sensors falls in the centre of the bird shell to allow for simple determination of along-track gradient.

All three fins are 2.0m long to achieve a spacing for the vertical gradiometer equal to 3.0m. Horizontal across and along the track gradients are based on a sensor spacing of 3.45 and 3.76m, respectively, although the sensor in the bird shell can be moved along the shell to suit any potential requirements for along-track configurations.

The bird skirt is designed to allow for variable drag in order to experimentally optimize the bird stability and flight characteristics. To improve the distribution of weight along the bird shell, the fins are placed in front to overweight the skirt and to make the front end heavier in a stationary state. Pick-up points are selected closed to Euler minimum flexing points, although rigidity is not critical.

For more information on helicopter solutions, please refer to the following resources:

• Brief Review of Quantum Magnetometers
• Advantages of Potassium over Caesium Magnetometers
• Helicopter Brochure
• Tri-Axial Helicopter Brochure
• Tri-Axial Helicopter Paper (First Break)
• Quote Request

Fixed-Wing Magnetometer Solutions                                    (Top)

GEM’s solution for fixed-wing based magnetometers differs from its helicopter implementation in that fixed-wing installations are more advanced than helicopter systems; requiring special “cleaning” of the aircraft; magnetic compensation to remove effects related to the aircraft and its flight attitude; and possibly integrating / streaming results from other geophysical systems that are acquiring data in tandem.

Typical fixed-wing components include:

• One or more optically pumped Potassium sensors
• Data acquisition system
• Pilot guidance system
• Airborne compensation system
• Radar altimeter
• GPS navigation
• Connecting cables
• Wingtip or tail pods

With the exception of the optically pumped Potassium sensors, all other components are from third-party sources and are integrated into the installation to create a fully functioning system.

Optically Pumped Potassium Sensors

For fixed-wing applications, single or multiple sensors can be mounted using specially designed mounting brackets in wingtip or tail stingers. With the growing popularity of gradiometric measurements for airborne work, the norm today is toward multiple sensors … typically two (vertical or horizontal gradient) or four (tri-axial). GEM’s sensors represent a rugged and reliable choice for professionals seeking the latest in technologies along with superior performance characteristics.

Data Acquisition System

As GEM’s commitment is to specialize in the development of magnetic sensors and arrays, the company utilizes third-party data acquisition for its fixed-wing solutions. The choice of third-party unit is based on proven demonstration of capabilities and performance characteristics.

Pilot Guidance System

Again, GEM focuses on its sensor development; hence the company utilizes third-party guidance systems, incorporating aircraft guidance, operator information, data synchronization to GPS position, pilot guidance and more.

Airborne Magnetometer Compensation System

Real-time or post-flight compensation is also available. Compensation is achieved by combining the frequency measurement from the optically pumped Potassium (continuous reading) sensor with the measurements of analog outputs of a tri-axial fluxgate magnetometer. Advanced algorithms combine these measurements and eliminate most of the influence caused by airframe movement through the magnetic field - pitch, roll, yaw and aircraft heading. 

Radar Altimeter

Sending a continuous signal from a single antenna, the TRA3000 radar altimeter provides precise information from 2,500 feet to 40 feet. The transmitter / receiver and antenna fit in a single, lightweight, aerodynamic unit that can easily be installed on the fuselage or under the wing. Innovative design reduces the size and weight of the system and significantly increases transmitter efficiency.

GPS Navigation

The Ashtech^® G12^TM GPS board from Thales Navigation sets the standard for superior performance in a wide assortment of high-accuracy marine, avionics and land navigation applications. Available in a board and sensor format, this powerful 12-channel receiver is the first of its kind to offer a 20hz update rate for real-time guidance, position and raw data output. The G12 offers differential accuracy better than 40 centimeters and position latency less than 50 milliseconds. It delivers precise three-dimensional positions to meet the demanding requirements of high-end OEM system integration.

The G12 incorporates all-in-view tracking of up to 12 satellites with a loss of lock re-acquisition time of less than 2 seconds, and delivers unsurpassed position accuracies of better than 40 centimeters, achieved immediately following satellite acquisition. The Strobe Correlator^TM technology provides unmatched code multipath mitigation, providing the best possible position accuracy. The G12 offers distinct timing options for precise timing and frequency, or time-tagging of positions, including 1 PPS time pulse, an event marker to time-tag a position, and a programmable measurement strobe that generates a pulse at a programmable interval in advance of measurements.

Connecting Cables

All required connecting cables and mounting brackets, etc. are provided with the system.

Wingtip or Tail Pods

Typically some sort of housing is required for installation of the sensor and electronic components. This can be either a stinger on the tail or nose of an aircraft or in pods on the wingtips of an aircraft. The following shows the assembly (with mounting gymbal) in a tail stinger.

For more information on helicopter solutions, please refer to the following resources:

• Brief Review of Quantum Magnetometers
• Advantages of Potassium over Caesium Magnetometers
• Helicopter Brochure
• Tri-Axial Helicopter Brochure
• Tri-Axial Helicopter Paper (First Break)
• Quote Request

Base Station Magnetometer Solutions                                  (Top)

When working with magnetic data, it is important to consider the effects of phenomena such as daily magnetic drifts (diurnals) on the order of a few 10s of nT and micropulsations on the order of thousands of nT from the interaction of the solar wind with the earth's magnetic field.

GEM's base station offerings are designed using experience gained in long-term monitoring for magnetic observatory applications where it is essential to have stable, reliable and drift-free results for accurate compilation of results. This experience has led to GEM's position as a leading supplier of base station magnetometers for both airborne and ground survey applications.

The leading offering is the GSM-19W magnetometer that has recently been upgraded  in Version 7 systems with fast sampling (5 Hz), enhanced memory and noise-free sampling algorithms. These features complement other advantages of the system including its high sensitivity (0.015 nT); low power consumption; and minimal long term drift of 1 part per million per year (from observatory experience). An optically pumped Potassium base magnetometer is also available for users who require extremely sensitive readings at 0.0005 nT.

For more information, please refer to the following resources:

• Brief Review of Quantum Magnetometers
• Advantages of Overhauser Over Caesium Magnetometers
• Technical Details - GSM-19 Base Station Brochure
• Quote Request