Experiment Relating to the Vertical Component of the Earth's Field

©Brooke Clarke 2003 - 2007


I used a Suunto Vector Wrist Computer (electronic based compass) for this experiment since a regular needle type compass will jam if it is turned on it's side.

Earth's Field at my Location

Using the Estimated Values of Magnetic Field Properties - I found the field at my location:
39.19 deg N, 123.16 deg W and about 1,000 ft elevation on 9/19/1999 to be:
D    16d 5.4m - magnetic declination
I    62d 28.7m - magnetic inclination (dip) measured from horizontal! i.e. it's about 38 deg away from vertical
H    23,376 nt - horizontal component (this is what a normal compass uses) about 1/2 the total field
X    22,460 nt - True rotational North component
Y     6,479 nt - East component
Z    44,862 nt - vertical component
F    50,587 nt - Total vector (SQRT(X*X + Y*Y + Z*Z)

Procedure 2

17 Nov. 2003

This procedure places one of the sensors so it sees the maximum value of the Earth's field and the other sensor is at right angles to the field and so does not see it, unless it's disturbed.
Leveled the tripod of a 60GT telescope and inserted a 2" PVC pile where the telescope usually goes.  With the pipe level rotated the azimuth for a reading of 90 degrees on the Suunto compass.
Note with the Suunto watch on your right wrist and your arm in front of your chest, like when you read it, it will indicate North if you're facing North.  That's the same as your forearm is on an East - West line.  So when the watch is strapped to a pipe that pointing North - South it will indicate either East or West, i.e. 90 degrees.
Now the watch is rotated 90 degrees around the pipe so the face is now on one side of the pipe.
Then the elevation is changed until the reading comes back to 90 degrees.
Now one of the internal sensors is aligned with the Earth's magnetic field and the other sensor is at right angles to the Earth's filed.  This can be confirmed by rotating the watch on the pipe.  In any position it reads 90 degrees +/- a degree.
Now if an Oldsmobile Intrigue is parked with the car centerline about 9 feet from the compass and the compass rotated about the pipe until the angle is furthermost from 90 degrees, this at about a 45 degree angle, then the compass reads 71 degrees.

This means that the car is disturbing the field at right angles to the main field and this is what could be used for a magnetic signature.

If the total field is 50,587 nT along the centerline of the pipe then for an indication of 71 degrees the field across from the pipe and at about a 45 degree angle relative to the ground (don't know how to explain that, but see the photo) then cross field is

Cross field / 50587 = TAN (90 - 71)
Cross field = 17,418 nT or 34.4 % of the Earth's field.

If the car is moved so that the center line is 12 feet from the compass it reads 82 degrees, still at about 45 degree rotation on the pipe.
100 * TAN(90 - 82) = 14 % of the Earth's field.

Procedure 3

It should be possible to orient the compass so that both sensors are at right angles to the Earth's field, i.e. they would both be reading no field under normal conditions.  But I need to scratch my head to figure out how to get there with a compass output, not individual sensor outputs.

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