The Scintrex CG5 Autograv has been the leading relative gravity meter for commercial mineral exploration and ground engineering studies for over a decade. In that time we have developed robust test procedures to ensure the instruments are operating within manufacturers specifications. It is our policy that all CG5s are setup to record data when they are not in service. This allows us to analyse the noise floor of each instrument and manually calculate the drift correction.
On returning to work after the new year bank holiday the data from all CG5s -which were not out on rental- was downloaded from the instruments. On analysing the data we noticed a significant tear in the measured gravitational acceleration at exactly 11:59pm on the 31/12/2016. The amplitude of the tear varied for each instrument, but the tear is always positive. The building was empty at the time, and the tilt values showed no environmental event which would have caused such a DC shift in the data. The measurement stability did not change after the tear event. The tear was present on all instruments.
Through further analysis we deduced the tear was caused by the new tide correction modal which took effect on the 1/1/2017. Scintrex corroborated our findings.
Although the tear has not affected the performance of the instruments, the tear was only discovered because we analyse the data before perform a manual drift correction. Those who use the automated drift correction might find the new drift value is significantly different from the previous value.
Action to be taken:
If the CG5 was set to perform an automatic drift correction spanning the dates of 31/12/2016 and the 1/1/2017 we suggest the new correction is disregarded and the instrument is placed by on drift correction for a further 24 hours.
If the instrument was set up for a manual drift correction the operator can calculate the new drift correction from measurements recorded after 1/1/2017. The performance of the instrument will not be affected.
For further information please feel free to contact us.
Transition Zone Magnetometer Array
30 October 2016
The tidal zone is by far the most challenging environment to survey. The ground conditions, tidal range and harsh saline environment constrain access and the type of equipment which can be utilised. In areas with large slow tidal ranges and gentle sloping shores the opportunity to survey the whole survey area may only be presented once or twice a year when the Luna orbit produces atypical tides.
Such a case was presented to Geomatrix earlier this year. In this particular case the client had specified the UXO survey had to be completed by a date. As a result we proposed developing a bespoke telemetry package for deploying an array of 4 x G-880 marine magnetometers off a sledge which could be partially submerged. Many of the system components were already available for rental and the concept behind the system was well understood.
The magnetometers selected for this application were the Geometrics G-880. The G-880s were the original caesium vapour marine magnetometer produced by Geometrics and have since been succeeded by the G-881 and G-882. The form factor of the G-880 resembles that of an airborne magnetometer like the G-823 or G-824 rather than a G-882. They are ideal for this application as the electronics bottle and sensor are housed in independent pressure vessels which keep the weight and size low and also permits sensor geometry to be flexible.
The sledge comprises of two fibreglass hulls which ride smoothly over uneven ground minimising the egress of noise into recorded data. The fibreglass hulls are designed to be light but durable with nylon skids to resist abrasive wear. The hulls are connected by two fibreboard decks held in place with nylon bolts. The platform is designed to be nonmagnetic and nonconductive yet robust and stable. Ports were made in the rear of the hull so additional weight could be added if the force from waves moved the sledge. Our main concern was that the elliptical wave motions would pick the sledge up and move it off line.
In order to keep the sensors isolated from the magnetic field of the vehicle and battery the telemetry system had to be able to provide power to the magnetometers and convey data back to the recording laptop over a 30m tow cable, and run from a 24V DC supply. With this in mind the telemetry system comprises a top end power data junction box and wet end electronics package which is placed on the sledge. The wet end electronics package includes a DC-DC inverter to ensure adequate power is received by all of the magnetometers. Serial data from the sensors is converted to UDP before being passed to the data recording device. As well as the Magnetometer data additional channels were included for GPS and a Gyro.
We have subsequently added the system to the rental pool. Please contact firstname.lastname@example.org for further information.
Iris Instruments Syscal Software- Instillation on Windows 10 anniversary update.
30 September 2016
It appears that in some instances the Windows 10 anniversary update can disrupt ProsysII, ElectrePro or Sysmar form running. An error message is presented informing the user the FTD2XX.DDL is missing.
In order to fix this issue it is necessary to uninstall all of the Syscal Utility programs, delete their respective directories under program files, and reinstall the latest version of the software from Iris Instruments Website.
In the latest version of RadExPro- RadExPro 2016.2- Deco have completely redesigned the main interface to make it even more intuitive. Processing modules can be linked graphically to produce complex relationships with flows. In addition a dedicated SEG-D revision 3 input module has been included, and 3 dimensional auto picking has been incorporated.
RadExPro is available for sale or rental form Geomatrix Earth Science. please feel free to contact us for a free trial.
Rental Pool Addition: EM61S coil
12 June 2016
As offshore UXO mitigation becomes more prevalent the demand for geophysical instrumentation for locating non-magnetic objects closure to the shore line has increased significantly. Working in the tilde zone is particularly challenging and traditional survey techniques and instrumentation is not ideally suited to the application. To address this specific issue Geomatrix have added an EM61S marine TDEM coil with 100m power data cable to the lease pool.
The coil can be mounted onto a sledge towed across the seabed. The sable sledge platform minimises the movement of the coil from the influence of swell and maintains a constant high above the seabed. In addition the EM61S is a Transient Electromagnetic system which can locate ferrous and non-ferrous objects.
Please feel free to contact us for further information and rental rates.