G-882
from Geometrics
The G-882 is the industry standard marine magnetometer. Very high resolution Caesium Vapour performance has been incorporated onto a low cost, small size, system for professional surveys in shallow water. High sensitivity at fast sample rates of total field measurements are maintained for all applications.
Features
- Streamlined design for tow safety
- Quick conversion from CG tow to nose tow, easy carry handles
- Highest Sensitivity in the industry, 0.004nT/root Hz
- Digital output, can be logged with MagLog™ software.
- Low weight, can be man handled
- New internal CM221 counter module, provides flash memory for storage of default parameter set by user.
- New Echosounder/altimeter option
- Zero phase lag on data
- True amplitudes reported
- Can be combined into gradient arrays, transverse, vertical or longitudinal
- Data from multiple magnetometers can easily be concatenated into a single data stream
The fast sample rate and high sensitivity design of the G-882 lends itself to configuring into transverse gradient arrays. When taking measurement of a magnetic gradient component it is critical that the sensors measure both simultaneously and have the ability to measure different field values. If when passing over a target, the same field value is measured by both sensors at any point in time, then that gradient measurement is of little or no value in target discrimination, this can occur if;
- The gradient array is too far away from the target, i.e. is too high in the water column.
- The magnetometers being used have insufficient sensitivity to be able to discriminate the small changes in field value over the width of the array.
- The gradiometer array is too small, so there is too little change in the magnetic field value over the width of the array for the magnetometers used to simultaneously measure a different field value.
The G-882 TVG frame ticks all of the boxes to help counter all 3 issues by being of a stable and hydro dynamic design to allow deeper towing, nearer to the sea bed where magnetic field gradients are greatest.
In shallow waters the G-882 can be deployed from a software Kevlar tow cable making deployment fast and simple. For greater deployment depths, or if deployed as an array on a TVG frame, a telemetry system can be utilised to run the system off a winch and wireline.
Product Dimensions
| Physical | Dimensions (L x W x H) | Weight |
|---|---|---|
| G-882 (instrument only) | 175cm x 28cm x 28cm | 18kg |
Technical Specifications
| Measured Quantity: | Total Magnetic field in nT typical sensitivity 0.02nT at 0.1sec sample interva |
|---|---|
| Operating Principle: | Self Oscillating split beam Optically pumped Caesium Vapour cell (non-radioactive) |
| Heading Error: | Less than +/- 1nT over entire 360° range |
| Absolute Accuracy: | Less than 3nT throughout range |
| Output: | RS232 @ 1200 to 19200 baud (other output rates on request) |
| Power Supply: | 24 to 32 VDC |
| Operating Temperature: | -35°C to + 50°C |
| Operating Range: | 20,000nT to 100,000nT |
| Pressure Rating: | 4000 psi (approx 2600 metres) |
| Operating Zones: | The earth's field vector should be at an angle of greater than 6° away from the sensor's equator and greater than 6° away from the sensor's long axis. Automatic hemisphere switching |
Shipping
| Contents | Dimensions (L x W x H) | Weight |
|---|---|---|
|
Case 1
G-882 instrument |
170cm x 50cm x 50cm | 60kg |
|
Case 2
Soft tow cable (150m) |
61cm x 61cm x 60cm | 32.5kg |
Data Sheet
- G-882 Datasheet (PDF)
Literature
- Computing the Pseudo Analytic Signal (PDF 422KB)
- Total Magnetic field Transverse Gradiometer for UXO (PDF 6MB)
Checklists
- Checklist for Data Storage and Transfer (PDF 249KB)
- Checklist for Data Processing (PDF 190KB)
- Checklist for Field Editing (PDF 244KB)
- Checklist for GPS Operating Procedures (PDF 231KB)
- Checklist for Instrument Storage (PDF 138KB)
- Checklist for Out of Box Equipment Tests (PDF 228KB)
Videos
-
https://www.youtube.com/watch?feature=player_embedded&v=70TRacT5RgI
(Duration - https://www.youtube.com/watch?feature=player_embedded&v=70TRacT5RgI) -
https://www.youtube.com/watch?feature=player_embedded&v=4utsCmvvaOg
(Duration - https://www.youtube.com/watch?feature=player_embedded&v=4utsCmvvaOg) -
https://www.youtube.com/watch?feature=player_embedded&v=q9H6OnV6INY
(Duration - https://www.youtube.com/watch?feature=player_embedded&v=q9H6OnV6INY) -
https://www.youtube.com/watch?feature=player_embedded&v=wKQ01ZOfYUs
(Duration - https://www.youtube.com/watch?feature=player_embedded&v=wKQ01ZOfYUs) -
https://www.youtube.com/watch?feature=player_embedded&v=5-BzFm6hA9o
(Duration - https://www.youtube.com/watch?feature=player_embedded&v=5-BzFm6hA9o) -
https://www.youtube.com/watch?feature=player_embedded&v=xKX7QmE3p_I
(Duration - https://www.youtube.com/watch?feature=player_embedded&v=xKX7QmE3p_I)
FAQ's
Signal strength below 400 in one heading and above 400 in the opposite heading. Sensor orientated at 45 degrees as per CSAZ solution for location.
Check the version of CSAZ. It needs to be the latest version which uses the World Magnetic Model (WMM) and not an old version using the IGRF model.
In the southern Baltic Sea CSAZ may suggest the optimal orientation for the G-882 Sensor is 45 degrees when surveying along a North-South heading, as seen in the following CSAZ solutions. However take care, keeping the sensor orientated vertically still produced an acceptable solution because the shaded green area is beyond the bold circumference located at 15◦ inclination (indicated by the purple arrow). If the green shaded area is over this line then the G-882 should achieved a signal strength over 400.
If in doubt also try the G-882 orientated vertically. Do not blindly follow CSAZ solution as the tool as limitations.
CSAZ assumes a uniform earth magnetic field. In a marine deployment the earths magnetic field may be being distorted by some ferrous objects. This could be the large magnetic field of the vessel or smaller magnetic fields on the frame. Is the signal strength is dropping below 400 in one heading but no the opposite heading then it could be the magnetic field around the sensors is changing. All induced magnetic fields will orientate to magnetic north. Therefore the sensor(s) will reside in a different part of the vessels or frames induce magnetic field when heading north compared to south. It could be that the magnetic influence of the vessel or frame could be just enough to push the earths magnetic field into a dead zone. Check all hardware on the frame is non ferrous and the offset of the frame to the vessel.
Why am I unable to Configuring MagLog with two concatenated G-882DIGITAL
Problem:
When using G-88x/823 input device it is not possible to enable Sensor 2,3,4…. in a concatenated group of G-882DIGITAL. Only the first G-882DIGTIAL in the concatenated sentence is available.
Solution:
Run MagLog and navigate to Configure -> Device buffers and settings then disable (uncheck) the Configure 88x magnetometer(s) for each survey option which will allow the user to freely set which Sensors are active or disabled.
Explanation:
Configure 88x magnetometer(s) for each survey option has to be turned off because the G-882/823 Configuration tool has been replaced by the G-882DIGITAL console program.
One of G-882/823 Configuration functions was to count the number of magnetometers which are present in a concatenated group. Because the G-882/823 Configuration tool cannot program the G-882DIGITAL instruments the software is unable to count the number of magnetometers in a concatenated group. As a result the OK button is unavailable (greyed out) and the only option is to cancel out of the window which in turn disables the ability to turn on additional sensors in the 88x 823 Settings window.
By disabling G-882/823 Configuration MagLog relies on the user to define the number of concatenated magnetometers within a group and define the number of channels for each sensor.
If the G-882DIGITAL are run in bypass mode G-882/823 Configuration will be able to communicate with the G-882, but Depth, Altitude, Pitch and roll will be unavailable because they are wired directly to the G-882 DIGITAL Accessory Board
