Marine Magnetics Sentinel2 User manual

Sentinel2
Base Station Magnetometer
Operating Manual
Revision 1.2
2022-10
Marine Magnetics Corp
135 SPY Court
Markham, ON
L3R 5H6 Canada
Tel: : [phone]
Fax: [phone]
Email: [e-mail]
URL: www.marinemagnetics.com

Marine Magnetics Sentinel2 Base Station Magnetometer Operating manual
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Contents
1. Introduction ............................................................................................................................................................................................. 2
1.1. Interface cables ..........................................................................................................................................................3
1.2. Emergency pressure relief valve ................................................................................................................................4
1.3. Specifications .............................................................................................................................................................4
2. Deployment considerations for optimal effectiveness ............................................................................................................................ 5
2.1. Base Station distance from survey area .....................................................................................................................5
2.2. Deployment away from magnetic gradients ..............................................................................................................5
2.3. Stationary deployment...............................................................................................................................................6
2.4. Time Synchronization.................................................................................................................................................8
3. Operating the Sentinel2........................................................................................................................................................................... 9
3.1. Sentinel2 Operating Modes .......................................................................................................................................9
3.2. Turning ON / OFF......................................................................................................................................................10
3.3. Charging ...................................................................................................................................................................10
3.4. Storage and Caring for the device ............................................................................................................................10
3.5. Transporting the device ...........................................................................................................................................10
4. Web User Interface................................................................................................................................................................................ 11
4.1. Connecting to the Sentinel2 Wi-Fi............................................................................................................................11
4.2. Main screen..............................................................................................................................................................12
4.2.1. Time synchronization status ................................................................................................................................13
4.2.2. Selecting a mag sampling rate .............................................................................................................................13
4.3. GPS screen................................................................................................................................................................14
4.4. Settings screen .........................................................................................................................................................15
4.5. Logs screen ...............................................................................................................................................................16
4.5.1. Standard vs. Diagnostic data logs ........................................................................................................................16
4.5.2. Downloading data log files...................................................................................................................................16
4.6. Mag Terminal view...................................................................................................................................................17
4.7. Software Update procedure.....................................................................................................................................18
5. Deployment steps .................................................................................................................................................................................. 19
5.1. Land-based deployment...........................................................................................................................................19
5.2. Underwater deployment..........................................................................................................................................20
6. Troubleshooting..................................................................................................................................................................................... 21
7. Appendix A: Time synchronization details ............................................................................................................................................. 22

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1. Introduction
A base station magnetometer measures background noise caused by fluctuations in the earth’s magnetic field. Removing that noise from
the mobile magnetometer’s readings reveals the signal caused only by the features of the surveyed area, and makes survey data easier to
interpret.
Sentinel2 is an advanced new generation marine base station magnetometer with features such as Wi-Fi wireless interface for ease of
operation, integrated GPS for perfect time synchronization prior to each deployment, and an integrated tripod for easy deployments on
land or underwater, with a maximum depth rating of 1000m.
At the heart of Sentinel2 is an Overhauser-effect magnetometer sensor, which is omni-directional and offers high sensitivity and high
absolute accuracy, while requiring no maintenance. The Overhauser sensor inside the Sentinel2 is guaranteed to provide a drift-free
reference correction for all the unexpected and unpredictable daily variations in Earth’s ambient field.
High-visibility three-color RGB LEDs on the base of Sentinel2 use a combination of colors and pulse duration to communicate the system
status to the operator. For example, they signal each reading and indicate excessive magnetic gradients caused by the presence of nearby
magnetic sources.
Sentinel2 presents its own Wi-Fi access point that any device with a browser can connect to and access the web-based user interface to
monitor readings, configure settings and download collected data.
Buoy and ballast line attachment points are provided for underwater mooring deployments.
The combination of these features makes Sentinel2 a robust, reliable, and easy-to-operate reference magnetometer for both land and
underwater surveys.
Included with the Sentinel2 are an on/off wet-mate dongle (mag key), a charger cable with optional USB download connector, and a
universal charger adapter. An optional cable that allows operation while connected to external battery power is also available.
Refer to Section 5 for a quick summary of Sentinel2 deployment steps for land-based and underwater settings.
Figure 1-1 – Sentinel2 exterior features showing views with the integrated tripod in unfolded and folded positions

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Figure 1-2 – Sentinel2 bottom bulkhead features a wet mate connector, a sea ground lug and bright RGB LEDs.
1.1. Interface cables
The waterproof wet-mate connector at the base of the Sentinel2 can be used for plugging in all available cables.
The Mag Key is a waterproof submersible dongle that serves the function of an On/Off switch.
The standard charging cable is not waterproof and can only be used for charging the battery. An optional external power cable is required
for simultaneous operation and battery charging, and can be customized for length and type of charger connector.
An optional USB data download cable is also available, as an alternative to Wi-Fi data download method. The USB cable cannot be used
while the magnetometer is operating, and cannot provide a real-time interface to the magnetometer.

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1.2. Emergency pressure relief valve
Sentinel2 is equipped with an emergency pressure relief valve, to provide a safe relief mechanism in the event of unexpected internal
pressure build-up. Such pressure may be caused by the following highly unlikely (but nevertheless possible) circumstances:
•A leak that occurs at depth, under very high pressure, following which the device is raised back to surface level.
Such a leak may be caused by a damaged o-ring seal somewhere in the device.
•Damage to, or failure of the internal battery.
In its normal closed state, the pressure relief valve acts as a seal against leaks. Always check the status of this valve before each
deployment.
IMPORTANT:
Once tripped, the pressure relief valve becomes open and will remain in the open position until reset by the user.
Do not operate the device if the valve is in the tripped/open position. Disconnect all cables from the device and contact
Marine Magnetics technical support immediately.
Submerging the device with the pressure relief valve in the open state will cause leakage and possible damage to the internal
components of the device.
1.3. Specifications
Height on tripod 1.29 m ( 50.7 in )
Length (without tripod) 1.05 m ( 41.5 in )
Weight on land 17.7 kg ( 39 lbs )
Weight in water 5.9 kg ( 13 lbs )
Depth rating 1000 m ( 3,280 ft )
Battery life 30 hrs at 1 Hz (1 sample/sec)
40 hrs at 0.2 Hz (1 sample / 5 sec).
45 hrs at 0.1 Hz (1 sample / 10 sec)
Charging time 8-12 hours
Sensor type Overhauser
Sensitivity 0.01 nT
Absolute accuracy 0.1 nT
Range 18,000 – 120,000 nT
Sampling range 0.1 Hz – 4.0 Hz

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2. Deployment considerations for optimal effectiveness
For optimal effectiveness, the base station magnetometer must be:
•located relatively close to the survey area
•deployed away from sources of magnetic interference
•kept stationary throughout the survey
•synchronized with the mobile survey magnetometer
Refer to Section 5 for a quick summary of Sentinel2 deployment steps for land-based and underwater settings.
2.1. Base Station distance from survey area
For maximum effectiveness, a base station magnetometer needs to be deployed in a setting similar to that of the survey site, such that
both the base station and the survey magnetometer experience the same or very similar daily variation of the ambient magnetic field.
It is recommended to select a location with similar regional geology and within < 100 km of the survey site.
If the survey site is at shallow depth and reasonably close to shore, then the base station can be located on shore to simplify deployment
process. See Sections 2.1 and 2.3 for deployment recommendations.
For surveys taking place at remote offshore locations, or at significant depths, the base station should be deployed underwater, ideally to
a depth similar to that of the survey site.
Note that underwater deployment in sea water exposes the base station to the magnetic effects of moving salt water, which may result
in regular rhythmic ‘noise’ associated with surface waves and currents to be present in the captured data. Such ‘noise’ can be easily
filtered out during post processing.
2.2. Deployment away from magnetic gradients
To collect readings representative of ambient background magnetic variation, a base station magnetometer must be located away from
local sources of magnetic interference, and magnetic gradients. This will ensure that any variation in background field recorded by the
base station will be due to temporal atmospheric and solar effects, and unaffected by local gradients.
Strong magnetic gradients exist where the magnetic field changes rapidly over short distances. This can happen near objects containing
magnetic metals or minerals, or near electric currents. Most commonly this includes objects and structures containing iron and steel but
can also be accumulations of a variety of magnetic materials such, , magnetite, nickel, cobalt (commonly found in dark-colored igneous
rocks), or concrete containing gravel or iron rebar. Rocky outcrops, boulders and large accumulations of gravel or dark-colored sand may
also create magnetic anomalies in their vicinity.
The extent of magnetic interference created by a given object or structure is usually determined by its overall size and iron content. As a
general rule – large objects or structures have magnetic influences that extend over significant distances and create measurable magnetic
gradients tens or hundreds of meters away (e.g., buildings, vehicles or vessels). Small compact objects, even highly magnetic ones, create
magnetic anomalies concentrated in relatively small volume, and require the magnetometer to be closer in order to detect their
influence. Magnetic gradients created by compact objects usually decrease very rapidly over short distances, while those created by
larger objects decrease more slowly with distance. Magnetic gradients created by pipelines or electric currents decrease much slower
over distance and can be detected from further away compared to magnetic gradients created by isolated objects.
Sentinel2 contains no magnetic materials to guarantee operation free of measurement errors. When deployed, it is imperative that only
completely non-magnetic materials be used within several meters of the magnetometer, including the mooring hardware, shackles,
ballast, and buoys. Non-magnetic materials include brass, aluminum, titanium, plastic, or rope made of polymer or fiber. Although
stainless steel is commonly considered to be non-magnetic, it is too magnetic when it comes to highly sensitive magnetometers. Stainless
steel hardware must be kept at least 5m away from the Sentinel2 to prevent interference.
No stainless-steel rigging, shackles, swivels or fasteners shall be used anywhere within 5m of the Sentinel, as they will be picked up by the
sensitive instrument and recorded as unwanted ‘noise’ in the data.
Absolutely no iron or regular steel must be used anywhere within 10 meters of the instrument, including stainless steel braided cables.

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All rigging materials within 5m of the instrument must be made only of rope, plastic, titanium, brass, or aluminum fittings.
Other examples of magnetic interference include electrical power lines, vehicles and vehicle traffic, computers, smartphones, direct
electrical currents, and permanent magnets of any kind. Avoid any form of direct current (e.g., DC chargers or charging cables) near the
Sentinel2 during its operation, because direct current can produce significant magnetic fields.
Never bring powerful magnets anywhere near a magnetometer as it may cause permanent issues and impair its operation.
While it is difficult to provide specific guidelines for a safe distance from any given source of interference, the general recommendation is
to set up the base station magnetometer at least 100m away from any buildings or vehicles, 200m away from any major roadways or
marine traffic, and 1000m away from any high-voltage power lines, transformer stations, railroads, commercial shipping lanes or
industrial facilities. Avoid concrete surfaces and structures which may contain iron rebar and other magnetic materials.
Refer to Table 2-1 for a summary of minimum recommended separation distance between the Sentinel and an iron object of a given mass
to help prevent unwanted magnetic interference.
When deploying on lake bed or sea floor where overhead vessel traffic is expected, the Sentinel2 should be deployed to a depth of at
least 20m to prevent registering small motor boats, or 50-100m when larger vessels may be present.
Table 2-1 - Minimum required separation between the Sentinel2 and an iron object to prevent unwanted magnetic interference.
(Based on reducing magnetic effect to <0.1 nT)
Ferrous weight Minimum required separation to prevent magnetic interference
1 kg 8 m
10 kg 16 m
100 kg 35 m
1,000 kg 76 m
10,000 kg 164 m
2.3. Stationary deployment
Whenever a magnetometer begins moving relative to ground or seafloor, it stops being a base station and becomes a survey
magnetometer, recording spatial variation in the magnetic field in addition to the temporal variation. For this reason, any movement
should be avoided when choosing a deployment method. The best approach is to set up the base station on a firm level surface, lake bed
or seafloor, using the integrated tripod. The slope of the surface must not exceed 15 degrees from horizontal (27% slope). When strong
currents are expected, additional ballast must be tied to the anchor point to guarantee stability and prevent the instrument from swaying
and getting toppled. All such ballast must be completely non-magnetic: e.g., lead or brass/bronze, affixed with rope made from polymer
or fiber.Avoid using bricks and all forms of pottery because it is often magnetic. Do not use any steel or stainless-steel fasteners or
hardware to prevent magnetic interference.
When deploying underwater, ensure that the buoy line attached to the top of the Sentinel2 will not lift the device off the bottom, or
make it bounce or sway as a result of surface wave action and currents. It is recommended to provide a mechanism for isolating the
surface wave energy from the Sentinel. Consider attaching the surface buoy to a (non-magnetic) anchor weight, and then connecting it to
the Sentinel, to help isolate the device from all surface buoy vibrations and movements (see case “B” in Figure 2-1).
When deploying in mid water column, the recommended mooring style should have a subsurface float above the Sentinel2 (non-
magnetic); the surface buoy line should be connected to an anchor block on the lake bottom, rather than Sentinel2 itself. This will
prevent unwanted swaying and rotation and guarantee data free of unwanted noise (see case “D” in Figure 2-1).
Figure 2-1 shows several possible underwater deployment configurations.
NOTE:When deploying on land on multi-day projects, it is important to use the same location each day, to avoid shifts in base station
average between survey days caused by local magnetic gradients in the ground. For best results, mark the deployment location with a
non-magnetic marker, and re-use the same location each day.

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Figure 2-1 - Mooring configurations for underwater deployment. "B" is recommended for most situations. "C" and "D" are for deep water
deployment. A slack compensating mechanism is strongly recommended at the surface buoy to isolate the sentinel from surface wave
energy.
•A: Shallow lakes without current on fine weather days (without waves).
Surface buoy connected directly to the top of Sentinel; with slack compensation at the buoy.
•B: Recommended configuration for most situations.
Surface buoy connected to a small non-magnetic ballast on bottom, with a loose connection to the top of the Sentinel. The
ballast helps isolate the Sentinel from the vibration in the buoy line caused by surface waves and wind. The connecting line
must be at least 3m long. Ballast weight must be at least 4 kg (or heavier for wavy conditions) and must be made of lead, brass
or bronze. Use of bricks and cinder blocks not recommended, unless positioned > 10m away from the Sentinel.
•C: Mid-water deployment with a subsurface float and a bottom ballast anchor for deep water locations.
The subsurface float must offer at least 13 kg of lift capacity to help keep the Sentinel vertical and upright, and have
appropriate depth rating. Slack compensation must be provided between the subsurface float and the surface buoy to help
absorb wave energy. Acoustic release may be fitted between the Sentinel and bottom ballast, and must be at least 10m away
from the Sentinel to avoid magnetic interference.
•D: Mid-water deployment with a subsurface float and two bottom ballast anchors for deep water high-energy locations.
The subsurface float must offer at least 13 kg of lift capacity to help keep the Sentinel vertical and upright, and have
appropriate depth rating. Additional isolation from surface wave energy is ensured by the second ballast on the bottom, with a
loose connection to Sentinel’s ballast. Slack compensation must be provided below the surface buoy. Acoustic release may be
fitted between the Sentinel and bottom ballast, and must be at least 10m away from the Sentinel to avoid magnetic
interference. Anchor blocks must be non-magnetic, or be sufficiently separated from the Sentinel to prevent magnetic
interference. (Refer to Table 2-1).

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2.4. Time Synchronization
Base station and mobile magnetometers should each be synchronized to within 1 second of GPS UTC time before surveying.
The main purpose of the integrated GPS in the Sentinel2 is to ensure the accurate time synchronization of the magnetometer clock.
Once the initial GPS sync is obtained, the Sentinel’s internal clock and magnetometer clock will remain accurate for the duration of the
battery life. However if the Sentinel2 is powered off for several hours after last obtaining a GPS time sync, or started up at a location
without GPS signal, the user should ensure the internal time is set as accurately as possible using either a smartphone, or a computer that
is synchronized to Internet time. Refer to section 4.4 for details on setting the magnetometer clock via the Web UI Settings screen.
Table 2-2 lists the time reference device options for synchronizing the magnetometer clock, along with their availability and relative
accuracy.
Table 2-2 - Time synchronization device options
Time reference device Availability Accuracy
GPS Available whenever GPS signal fix can be
obtained (clear open sky view) Most accurate
Internal battery-powered clock Always available. Used automatically on
start-up if the initial GPS sync fails.
Not very accurate after several days since the last
GPS time sync
Smartphone Available whenever a smartphone
accesses the Sentinel2 Web UI via Wi-Fi
Considered accurate whenever a cellular
connection is available
Laptop / Tablet / Computer Available whenever a computer or tablet
accesses the Sentinel2 Web UI via Wi-Fi
Least accurate, due to absence of cellular
connection. Ensure your laptop or tablet clock is
set as accurately as possible. For best results:
ensure it is configured to auto-sync its date and
time to Internet time.
TIP: Try to get a good GPS time sync each time you use the Sentinel2 by selecting a location in an open area with a clear view of the sky to
guarantee a good initial GPS signal fix.
If GPS signal is unavailable at your selected deployment location, it is recommended to first power-up the device in an open area to
guarantee good GPS sync, and then transport it to the desired location for deployment. During the transport the magnetometer can be
set to idle mode (sampling off) until ready to deploy.
For further details on time synchronization in the Sentinel2, please refer to: Appendix A: Time synchronization details.

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3. Operating the Sentinel2
3.1. Sentinel2 Operating Modes
Sentinel2 has five operating modes outlined in Table 3-1:
Table 3-1 - Status LED colors during startup and normal operation
Mode Description LED status Wi-Fi Magneto
meter
OFF Sentinel2 is off,
except for the internal clock. Off OFF OFF
Starting-up
A sequence of powering up various
internal systems
and GPS signal search
Series of different color flashes :
Blue flashes during initial system power-up
Cyan flashes during GPS signal search (1).
Orange flash marks completion of start-up
OFF OFF
ON
All systems ON,
magnetometer resumes sampling at a
rate selected prior to shut down; or idle.
Web UI available.
Green flashes: magnetometer sampling, good sync (i.e. GPS or
smartphone sync)
Yellow flashes: magnetometer sampling, internal clock sync only.
Try syncing to a smartphone via Settings if GPS is unavailable.
Purple flashes: magnetometer sampling, poor reading quality due to
nearby magnetic interference.
Try repositioning the Sentinel2.
Red flashes: magnetometer ON but idle (not sampling)
Red constant: problem detected. Try restarting the Sentinel2.
ON ON
Shutting
down
A sequence of safely shutting down
various internal systems
Blue flashes during system shut-down sequence.
Do not re-connect the mag key dongle during this state.
OFF OFF
Charging only
Battery charging (2).
Wi-Fi enabled,
magnetometer disabled
White Duty-Cycle pulsing (3)
Pulse duration indicates % battery charge.
ON OFF
Notes:
1) During the start-up sequence, the Sentinel2 attempts to get a GPS signal lock for up to 35 seconds, during which the LED flashes cyan. If unable
to secure a GPS sync, Sentinel2 uses its internal clock to sync the magnetometer, and flashes yellow to indicate magnetometer sampling
without synchronization. Connecting a Wi-Fi client device synchronizes the magnetometer clock to the client device, and the LEDs flash green to
indicate reliable synchronization. When operating the Sentinel2 without GPS access, ensure that your client device has its clock set as
accurately as possible. A mobile phone with cellular connection is considered reliable. A laptop computer that has not been recently
synchronized to the internet time reference is less reliable.
2) Standard accessories supplied with Sentinel2 include a mag key (for normal operation) and charging cable (for charging only). An optional
external power cable must be used to enable the Sentinel2 magnetometer to operate while on external power or while charging. See Section
1.1 for details.
3) The state of the battery is indicated by the “duty cycle” of the light – i.e. the ratio between the time it’s on vs. the time it’s off. For example a
pulse that is on 50% of the time, and off 50% of the time indicates that the battery level is 50%. A short white pulse with a long pause between
pulses indicates a low battery. A long white pulse with a short pause indicates a high battery level.