Geometrics G-864 User manual

User Manual
for
G-864 Cesium Backpack Magnetometer
and
G-864G Cesium Backpack Gradiometer
P/N 770-00105-01 Rev. A2
January 2023
COPYRIGHT © 2023

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Geometrics, Inc.
Geometrics Europe
2190 Fortune Drive
San Jose, CA 95131 USA
PH: [phone] Visual GPS Application Program
FAX: [phone]
We declare under our sole responsibility that our marine magnetometers, models G-864 and to which this declaration relates are in
conformity with the following standards:
EN 55022: 1995, EN50082-2 : 1995, ENV 50140: 1994, ENV 50141 : 1994, EN 61000-4-2: 1995, EN 61000-4-4: 1995
per the provisions of the Electromagnetic Compatibility Directive 89/336/EEC of May 1989 as Amended by 92131/EEC of 28
April 1992 and 93/68-EEC, Article 5 of 22 July 1993.
The Technical documentation required by Annex IV(3) of the Low Voltage Directive is maintained by Christopher Leech of Geometrics
Europe (address below).
The authorized representative located within the Community is:
Geometrics Europe
Christopher Leech
20 Eden Way
Leighton Buzzard
Beds LU7 4TZ, U.K.
PH: [phone]
FAX: [phone]
Mark Prouty, President
San Jose, CA, USA
CE
March 14, 2003
Sunnyvale, California, USA
EC DECLARATION OF CONFORMITY
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Warning
This is a Class A product. In a domestic environment this product may cause radio
interference in which case the user may be required to take adequate measures.

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Table of Contents
1.0 Geometrics’ G-864 Cesium Backpack Magnetometer ............................................. 7
1. Sensor Performance................................................................................................................. 7
2. Environmental Considerations ............................................................................................... 8
1.1.1 Vibration ............................................................................................................................................... 8
1.1.2 Temperature ......................................................................................................................................... 8
2.0 Unpacking the G-864 ................................................................................................ 9
3. System Inventory ..................................................................................................................... 9
4. Battery Options ...................................................................................................................... 11
5. Getac Tablet ............................................................................................................................ 12
6. Data Logger Box Components .............................................................................................. 12
2.1.1 Recessed Power Button ...................................................................................................................... 13
2.1.2 Reset Button ....................................................................................................................................... 13
2.1.3 USB Port and Cover ............................................................................................................................ 13
2.1.4 LED Status Lights ................................................................................................................................ 13
2.1.5 Heat Sink ............................................................................................................................................. 14
2.1.6 Connectors ......................................................................................................................................... 14
7. Backpack Adjustments and Assembly.................................................................................. 14
2.1.7 Adjusting the Backpack to the Individual User ................................................................................. 14
8. Mounting and Connecting the Battery................................................................................. 16
9. Mounting and Connecting the GPS....................................................................................... 16
10. Backpack Mounted Sensor Configuration ....................................................................... 17
11. Staff Mounted Sensor Configuration: Single Sensor ...................................................... 20
12. Staff Mounted Sensor Configuration: Gradiometer........................................................ 27
3.0 Survey Manager ....................................................................................................... 31

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13. Managing Projects in Survey Manager ............................................................................ 32
14. Creating a New Survey in Survey Manager...................................................................... 32
15. Converting Survey Data Files in Survey Manager ........................................................... 34
16. Creating GPX Route Files in Survey Manager .................................................................. 34
17. MagNav User Interface Software ...................................................................................... 35
18. Moving Projects from Survey Manager to MagNav ........................................................ 35
19. Creating New Projects in MagNav .................................................................................... 36
20. Starting a Survey in MagNav............................................................................................. 36
21. Surveying with Marked Navigation in MagNav............................................................... 38
22. Correcting Mistakes ........................................................................................................... 39
23. Deleting a Project in MagNav............................................................................................ 40
4.0 MagMap & MagPick ................................................................................................. 40
1. CSAZ ............................................................................................................................. 42
Cesium Sensor Active Zones .......................................................................................................... 42
Cesium Sensor Orientation for Worldwide Operation................................................................. 42
Mid-latitude Zone ........................................................................................................................... 45
Polar Zones...................................................................................................................................... 46
Equatorial Zone............................................................................................................................... 47
2. Troubleshooting Table ................................................................................................ 48
3. Firmware and Software Updates ................................................................................ 51
Geometrics Survey Manager.......................................................................................................... 51
Geometrics G-864 Embedded........................................................................................................ 51
Geometrics MagNav ....................................................................................................................... 52
4. Surveying Principles .................................................................................................... 54
Guidelines for Small Ground Magnetometer Surveys................................................................. 54

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Number of People........................................................................................................................... 54
Survey Efficiency............................................................................................................................. 54
Layout of the Survey Track ............................................................................................................ 55
Diurnal Correction .......................................................................................................................... 56
Survey Accuracy.............................................................................................................................. 56
Survey Credibility ........................................................................................................................... 57
Location of Small Objects within Associated Anomalies............................................................. 57
5. G-864 Backpack Magnetometer Specifications .......................................................... 59

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1.0 Geometrics’ G-864 Cesium Backpack Magnetometer
Geometrics, Inc. is known worldwide for our total field magnetometers and is a leader in
magnetometer development. Our magnetic sensors measure the total magnetic field (total
field) without directional information. In other words, they take the scalar measurements of the
magnetic field, and produce a value that is the magnetic field intensity, regardless of the
direction in which the field propagates.
Magnetometers measure the Earth’s magnetic field, which occurs naturally and varies with
time and in the presence of ferrous materials. Magnetometers are used in a variety of
applications and are modified for airborne, marine, and land-based surveys. They can be used
to map and locate man-made objects or be used to detect naturally occurring iron or other
ferrous minerals associated with economic ore deposits. For example, the mineral magnetite
is often associated with kimberlite pipes (diamonds), native gold, copper, and other economic
deposits.
Man-made ferrous objects, such as those associated with archaeology, civil engineering,
unexploded ordnance, etc., alter the Earth’s magnetic field in a way that is detectable with a
magnetometer. The strength of the altered field depends on many factors, including the size,
iron content, orientation, and depth of the ferrous object. More detailed information on
magnetic theory and survey design can be found in the Applications Manual for Portable
Magnetometers , available on the Resources page of our website,
https://www.geometrics.com/resources/.
The G-864 Backpack Magnetometer System is based around the highly adaptable G-862
airborne magnetometer sensor. We chose this sensor for its adaptability to different survey
types. The G-862 is an optically pumped, cesium, total field magnetometer sensor, which uses
the non-radioactive isotope of cesium, in gas form, to make a measurement of the earth’s
magnetic field. For details on the internal operation of this sensor, please see the research
paper on our website Resources page, by keyword searching “Optically-pumped Cesium
Magnetometers.”
1. Sensor Performance
The G-862 sensor operates over the earth's magnetic field range of 20,000 to 100,000 nT.
Absolute accuracy depends on the sensor orientation, internal light shift, and the accuracy of
the external counter's time base. An error due to sensor orientation does not exceed ± 0.25 nT
or 0.5 nT peak-to-peak (p-p) throughout the active zones.
For optimal signal levels while surveying in the far northern and southern latitudes, the sensor
will be mounted at 45º; for mid latitude zones including as far south as Northern S. America,
the sensor will be mounted vertically. In a narrow band about the earth’s magnetic equator

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(note not zero latitude necessarily), the sensor will be mounted at 45º or horizontally, with the
top of the sensor tilted either North or South as the surveyor walks the survey line. To verify
which zone the survey area is in, please see Appendix I: CSAZ for more detailed information.
Like all magnetometers, performance is primarily dependent upon the counting circuitry
employed and the quality of the installation procedures. Compensation and/or noise reduction
techniques may be required to minimize magnetic effects caused by navigational and
positional errors, radiated electromagnetic noise, and heading error. A complete list of system
specifications can be reviewed in Appendix VII: G-864 Backpack Magnetometer Specifications.
2. Environmental Considerations
Optically pumped magnetometers are more sensitive to magnetic field variation than proton
and fluxgate types. To realize the full performance of the cesium-vapor technology, special
precautions must be taken during planning and execution of the installation.a
1.1.1 Vibration
Intense vibration of system circuitry can induce micro-phonic noise and shorten the life of
system components. The intense vibrations are typically not seen in a walking survey, however
if in larger arrays the system is mounted on a cart behind an ATV it may be a concern. Some
attachment points may be prone to intense vibration, and we recommend the use of good
quality shock mounts that are designed to isolate the sensor components from as much of the
intense vibration as possible.
Special care should be taken in securing or routing the cable to reduce the risk of encountering
hard or sharp objects that could damage the cable. Those components used to mount the
sensor or any or any objects near this sensor should be non-magnetic to minimize the system
heading error.
1.1.2 Temperature
The G-864 system is designed to operate over an ambient temperature range of -35 to +50°C.
In an enclosed region it may be necessary to provide adequate cooling by free-flowing air. If
the sensor and electronics are in an unconfined region, convection cooling is generally
adequate. The cesium lamp only needs to dissipate 3 to 4 watts of heat and when operating in
cold regions providing some insulation or baffling will help reduce the sensor’s power
consumption.
The sensor requires a minimum warm up period of 10-15 minutes. In cold regions the warmup
period will be longer and, to avoid delay, we recommend that the sensor power be left on
overnight when ambient temperatures are expected to fall below -10°C.

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2.0 Unpacking the G-864
The components shipped with the system will vary depending on the configuration ordered.
The G-864 is configurable to address the survey needs of both near and deep surface
investigations. Deeper geological investigations require a sensor mounted further from the
ground surface to remove the sensor from the magnetic effects of surface debris or other near
surface artifacts. For near surface investigations, such as archaeology and UXO surveys, having
the sensor closer to the ground is important to enhance the size of the target anomaly.
Moreover, for near surface surveys, having multiple sensors as a linear array allows the operator
to cover more area in a single survey line, as well as calculate the gradient measurement which
will provide more information on the targets located in the data.
For deep search, the G-864 is configured with the sensor mounted onto a backpack and
extending above the operator’s head. The sensor will be connected to the electronics module
by a 3ft. (1m) cable, to fit onto the backpack without snagging branches or other obstructions.
For near surface investigations, the G-864 is configured with either one or two sensors (for the
gradiometer configuration) and mounted onto an aluminum staff assembly that is positioned
out in front of the surveyor. The sensor(s) will be connected to the electronics module by a 9ft.
(2.7m) cable, to allow for mounting on a staff for carrying or on a cart for towing behind a
vehicle. The sensor electronics module is well suited to act as a counterweight on the staff to
make a balanced unit for easy surveying.
3. System Inventory
Below is a list of parts and quantities included in the single sensor Magnetometer System with
Backpack Mounted or Staff Mounted Sensor, and the dual sensor Gradiometer System with
Staff Mounted Sensors. *Batteries and Quantities depend on Battery Option chosen at time of
order.

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P/N
Description
Backpack Mount
Staff
Mount
Gradiometer
900-00390-02
G-864 BACKPACK ASSEMBLY
1
1
1
900-00308-01
G-864, TABLET GETAC & CHARGER
1
1
1
860-00162-01
G864 TABLET CHEST HARNESS
1
1
1
860-00128-01
GPS ASSEMBLY-TALLYSMAN
1
1
1
850-00005-01
CARRYING CASE ASSEMBLY
1
1
2
900-00342-33
G-862 CESIUM ELECTRONICS & SENSOR
W/3 FOOT CABLE
1
none
none
840-00095-01
G-864, DATA-LOGGER TO MAG 3FT
CABLE, SINGLE MAG
1
none
none
820-00630-12
180 DEGREE SENSOR CLAMP ASSY, G-
864 (Clamp & 1ft Staff)
1
1
2
820-00595-01
G-86X ELECTRONICS CLAMP ASSY
W/LOCKING KNOBS
2
2
4
900-00342-39
G-862 CESIUM ELECTRONICS & SENSOR
W/9 FOOT CABLE
none
1
2
840-00095-02
G-864 DATA-LOGGER TO MAG 7.5FT
CABLE, SINGLE MAG
none
1
none
840-00207-01
G-864, 2 MAG GRADIOMETER MAG TO
DATALOGGER CABLE
none
none
1
820-00123-01
LOCKING SENSOR STAFF B
2
5
5
820-00127-01
LOCKING STAFF JOINING KIT
none
none
1
340-00022-02
GRADIOMETR TEE-LOCKING TYPE
none
none
1
820-00109-01
ASSY, G-86X STRAP HANGER-STAFF END
none
1
1
335-00071-01
STRAP, SUPPORT
none
1
1

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P/N
Description
Backpack Mount
Staff
Mount
Gradiometer
820-01048-01
LONG STRAP CLAMP ASSY
none
1
1
445-00313
8 INCH CABLE GRIP STRIP (I PKG)
0
1
1
170-00044
AC ADAPTER PLUG KIT
1
1
1
820-00232-01
BATTERY-LI-PO TYPE 29.2V*
2 if ordered
2 if ordered
2 if ordered
820-00303-01
LITHIUM BATTERY CHARGER ASSEMBLY
– POWERSTREAM*
1 if ordered
1 if ordered
1 if ordered
840-00127-01
BATTERY ADAPTER JUMPER ASSEMBLY-
POWERSTREAM*
1 if ordered
1 if ordered
1 of ordered
820-00231-01
BATTERY PACK-LEAD ACID*
2 if ordered
2 if ordered
2 if ordered
820-00348-01
ASSY, BATT. SPACE 24VCD 1.5A CHRGR
TESTED*
1 if ordered
1 if ordered
1 if ordered
840-00176-01
ADAPTER CBL, CHARGER TO BATTERY
PACK*
1 if ordered
1 if ordered
1 if ordered
900-00393-01
G-864, LEAD ACID BATTERY POUCH*
1 if ordered
1 if ordered
1 if ordered
* Ordered separately.
For the most current part numbers and options please contact a Geometrics salesperson at
[email protected].
4. Battery Options
The G-864 offers two battery options, Lead Acid or Lithium Polymer (Li-Po). The batteries
shipped with the system will be the batteries requested at the time of order. Lead acid batteries
have traditionally been used in our backpack systems. The Li-Po battery was designed to offer
a more lightweight, longer lasting battery solution to customers.
Li-Po batteries must be discharged to 30% before they can ship, so these batteries will need
to be charged when received. The Li-Po battery consists of two packs of cells, each at 88W-hr
rating, which, with the correct documentation, is below the current standards for shipping on
planes. Check airline and/or courier regulations before shipping these batteries. Geometrics is

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not responsible for any issues with Li-Po battery transport after it has been shipped from the
factory.
The Lead Acid battery packs are fully charged before leaving the factory. However, depending
on storage time, they may need to be recharged.
Lead Acid batteries will power the single sensor system for ~5 hours and the gradiometer for
~3 hours. The Li-Po batteries will power the single sensor system for ~7 hours and the
gradiometer for ~5 hours. Cold temperatures will increase magnetometer current
requirements and decrease battery capacity. Recharge time is approximately 6 to 8 hours per
battery.
NOTE: To best maintain battery life, periodically charge the batteries (about every 4 months)
when not in use.
5. Getac Tablet
The G-864 uses a Getac ZX70 Android tablet as the main data logging, and user interface device.
This model is a ruggedized tablet that has been modified to reduce the magnetic
characteristics of the tablet for a clean survey. One of the main modifications is the removal of
the speaker components, which are very magnetic.
Getac offers a warranty on their products. Register the tablet to take full advantage of
the warranty, and make warranty claims on the Getac website:
https://support.getac.com/.
Geometrics cannot support issues that arise from utilizing tablets that are not shipped with the
system from the factory. The data logging software was tested with the latest version of
Android at the time of shipping and will be maintained to the latest standard at each
subsequent release.
6. Data Logger Box Components
The G-864 data logger box is attached to the aluminum frame of the Mystery Ranch Backpack.
The pack frame commercial hardware has been replaced with brass and aluminum parts,
removing all ferromagnetic components to keep the system magnetic self-signature to a
minimum, thus reducing heading error and other platform noise. Never replace hardware with
untested bolts, nuts, or rings. Always test the hardware first by turning on the magnetometer
and moving the hardware near the sensor. System components should have less than 0.5nT
effect at 2ft (0.6m) from the sensor.

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2.1.1 Recessed Power Button
The power button is located on the bottom, left side of the data logger box. Turn the system
on only after all cables are connected. The button should turn green to show that power is
applied. The button will recess into the box when pressed.
2.1.2 Reset Button
The reset button is located at the top of the box and used if the G-864 processor is not
responding. A reset will not fully turn off the magnetometer, so the sensors do not need to be
warmed up again.
2.1.3 USB Port and Cover
The data logger box includes a USB port on the top of the box for data storage and firmware
updates. If for any reason the data connection is lost, or the data is corrupted or accidentally
erased on the tablet, the USB stick will have a backup record for data processing. The USB
provided is 32GB, which can store up to 2 years of continuous data before needing to be
replaced.
2.1.4 LED Status Lights
The backpack electronics box has five LEDs that are labeled to indicate their meaning. These
LEDs help to ensure the system is working properly and to help when troubleshooting.
Blue POWER LED - signifies that the battery is connected and has sufficient voltage to power
the system.
White PPS LED - signifies the system is receiving and is locked to PPS signal. This LED will be off
if no PPS is detected. The PPS message is essential for surveying accurately for timing purposes
and a survey should not begin without first having the white PPS LED active.a
Orange GPS LED - signifies that the logger box is receiving GPS messages. The system requires
both the GPGGA and GPRMC messages. The GPGGA is used for counting the number of
satellites and time information. The RMC message is used for the date to be included in the final
exported data. The orange LED will blink at the rate of the GPS message (1Hz).
Green MAG LED - signifies that magnetometer data is being received. The green LED will blink
at the rate of the magnetometer sample rate.
Red USB LED - a slow flash signifies that data is being written to the storage unit.

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2.1.5 Heat Sink
There is a heat sink on the backpack to allow heat generated from the internal electronics to
dissipate and avoid overheating inside the box. It is important to keep this heat sink clean and
intact. If wear and tear is observed on the heat sink, please contact Geometrics to evaluate if it
needs to be replaced.
2.1.6 Connectors
Located underneath the data logger box are connectors marked to represent the appropriate
device to be connected. Each connector has a different number of pins. Note that the matching
cable connectors are keyed and contain an outer ring. With the cable connector and data
logger box connector touching, rotate the cable connector until the keys align, then
tighten the outer ring to secure the connection. Forcing the connectors together could
potentially damage the pins, requiring the unit to be returned for repair.
7. Backpack Adjustments and Assembly
The backpack provides an ergonomic, and relatively lightweight solution for carrying the
magnetometer in a secure manner over harsh terrain. The backpack consists of a military-grade,
fabric Mystery Ranch pack, an aluminum frame, data logger box, and one aluminum staff pole
with bolt lock screws. The sensor and sensor electronics, GPS receiver, battery, staff assembly,
and cables will need to be connected and assembled.
2.1.7 Adjusting the Backpack to the Individual User
The Mystery Ranch Pack Frame is professional grade with a sliding Velcro secured adjustment
system. The first time the pack frame is worn, it may be necessary to adjust the fit for the
individual user.
1. Put the pack on, connect the waistband buckle and connect the smaller buckle
supporting the shoulder straps. Adjust both to fit comfortably. Note where the shoulder
harness pads come to rest on the shoulders. The wearer may find the straps are too high
or too low. Adjust the straps until you achieve the correct fit, which is where most
weight is resting on the hips and only about 20% is on the shoulders.
2. To extend or compress the shoulder harness, disconnect the buckles above the
shoulder harness, peel back the flap, and locate the black plastic Velcro Release Tool as
shown by the white arrow in the figure below.

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3. Remove the Velcro Release Tool and insert it between the shoulder harness and the
pack frame, breaking loose the Velcro.
a.
b.
4. Move the shoulder harness section up and down to correctly position the height of the
shoulder pads.

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c.
5. When the correct height of the shoulder harness is achieved, remove the Velcro Release
Tool, and then replace the tool in its original pocket. Reconnect the buckles and put the
pack on one last time to verify the fit.
8. Mounting and Connecting the Battery
Depending on the batteries ordered, the backpack frame components will be slightly different.
1. Mounting
a. To mount the lithium polymer battery, place it in the frame backpack support
with the Caution Sticker facing up.
b. To mount the lead acid battery, place it in the bag.
2. Locate the battery cable and the connector on the battery. With the two connectors
touching, rotate the cable connector until the keys line up and then tighten the outer
ring to secure the connection.
3. Locate the connector on the data logger box labeled BATTERY. Feed the battery cable
through the opening behind the battery and make the connection. For image of proper
connection, please see the image in the below section.
9. Mounting and Connecting the GPS
The G-864 comes with a non-magnetic Tallysman GPS. This specific antenna was chosen for its
non-magnetic properties which allows the GPS to be mounted within 1ft. of the sensor and not
interfere with the magnetic measurements. The GPS can be mounted on either side of the
backpack frame.

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1. To mount the GPS, line up the open slit on the GPS antenna with the black knob on the
aluminum staff on the backpack and tighten the knob.
2. Wrap excess cable around the aluminum staff or bunch at the bottom of the backpack
to protect the cable from getting snagged during a survey. Secure with cable tie wraps.
3. Feed the GPS cable through the opening behind the battery to the connector labeled
GPS on the data logger box. With the two connectors touching, rotate the cable
connector until the keys line up and then tighten the outer ring to secure the
connection.
10. Backpack Mounted Sensor Configuration
Magnetometers with 3ft sensor-to-electronics cables are suitable for the backpack mounted
configuration.
1. To assemble the sensor onto the backpack, first place two electronics clamps around
the electronics bottle, keeping the clamps loosely fitted.

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d.
2. On the backpack, loosen the lower knob securing the aluminum staff section and lift it
from the bottom support.
3. Line up the open holes on the electronics clamps with the aluminum staff while re-
inserting the section into the bottom support on the pack frame. Tighten the black knob
securing the aluminum staff into the bottom support.

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e.
4. Secure the electronics clamps to hold the electronics bottle in place by first tightening
the bolt lock closest to the aluminum staff section, and then tightening the other bolt
lock to secure the sensor in place.
5. At the top of the same aluminum staff section, mount the sensor clamp, securing it to
the staff with the bolt lock.
6. Place the sensor in the sensor clamp and tighten the bolt lock closest to the sensor to
hold the sensor in place. Avoid overtightening as the sensor clamp can crack if too much
pressure is applied.
7. Finally, connect the sensor data cable to the sensor electronics bottle. Then, feed the
sensor data cable through the opening behind the battery, and connect it to the
matching connector on the data logger box labeled MAG.

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f.
8. It may be necessary to adjust the sensor orientation for the requirements of the survey
location. Please see section below: Sensor Orientation and Adjustments.
11. Staff Mounted Sensor Configuration: Single Sensor
Magnetometers with 9ft sensor-to-electronics cables are required for the staff mounted sensor
configuration. In this configuration, the electronics bottle will be the counterweight to the
sensor on the staff assembly.