GEM Systems Inc., a Canadian manufacturer of high precision geophysical mapping instruments, has launched the GSM-90AVU(B), a Very Low Frequency (VLF) Electromagnetic Method (EM) survey instrument (“towed bird”) designed to be suspended on a sling from a drone, at the Prospectors & Developers Association of Canada (PDAC) convention in Toronto on March 3. The unit maps electromagnetic resistivity in the ground and is suitable for mineral or water exploration, bedrock mapping, fault detection for earthquake research, locating underground pipelines, or other near subsurface surveying tasks.
The company, founded in 1980, manufactures a line of magnetometers and gradiometers for ground operators, earth monitoring, aircraft (helicopter and fixed-wing), and drones. However, the VLF-EM bird is not a magnetometer or gradiometer like GEM’s other systems; it passively picks up the continuous broadcasts from distant time signal or military naval transmitters around the world at frequencies below 30kHz with two sensors (each tuned to a different transmitter), measuring vertical deviations due to the ground conditions below the sensors. In some areas where coverage of distant transmitters may not be ideal, a localized transmitter can be used.
The company says that this solution provides precise data cost-effectively compared to ground or aircraft based measurement. Flying at 100ft (30m) altitude with the bird on a 33ft (10m) tow line, at a minimum speed of 10m/s to minimize drag, a VTOL drone (generally a powerful multi-copter) can cover ground 6-10 times faster than a walking operator, in all types of terrain, without exposing an operator to risk. Compared to manned aircraft data acquisition, the GSM-90AVU(B) suspended from a drone can be flown at night, in poor visibility conditions, and over topography dangerous to aircraft which are usually at minimum 300ft (90m) altitude.
GEM Systems says their rugged VLF-EM bird is designed to be towed from any VTOL (Vertical Takeoff and Landing) c-drone which can lift the 13lb (6kg) load, for example the DJI Wind4/Wind8 or Matrice 600 Pro models, the Freefly Alta8, the VulcanUAV Black Widow, or the Versadrones Heavy Lift Octocopter; note that winged drones designed for efficient surveying such as the Parrot eBee X, Delair UX11, or WingtraOne tailsitter are designed for lighter payloads. As is often the case in surveying, the flight path is prepared in advance with an autopilot such as Pix4D, running back and forth along predefined GPS waypoints.
The unit transmits XYZ format data over a radio link to the system’s collapsible radio mast and Windows PC base station computer, an optimized Panasonic Toughbook running GEMDAS and GEMLink+, GEM’s bespoke software for data acquisition and file transfer, respectively. The firm recommends optionally running Emtomo’s VLF2DMF software for conversion of the multifrequency source data to human readable graphs.
The GSM-90AVU(B)’s 1.3Ah onboard lithium battery will outlast the flight time of most large c-drones; the battery can be swapped out if necessary. The bird’s length is 5ft (1,5m). Operating temperature range is said to be -40°F to 120°F (-40°C to +50°C), so if your c-drone can handle it, the bird should be able to. Customized cases for the system (bird, radio antenna, ground control station) are included, and the entire system has a three-year warranty. The company does not publish list prices, preferring to tailor instruments in custom configurations for a quote after assessing the needs of each client.