One of the more perplexing findings presented in the History Channel program The Secret of Skinwalker Ranch involves the detection of positioning errors when GPS is used. The team at Skinwalker Ranch (SWR) attaches GPS receivers to nearly everything … rockets, vehicles, balloons and even drilling rigs. Often the positions recorded via GPS substantially differ from the physically known locations of the receivers.
I have noticed that oftentimes the functioning of GPS is described as being a form of triangulation. Strictly speaking this is incorrect. Triangulation involves determining a location by measuring the angles between a target and at least three transmission sources. In the case of GPS, these “sources” are satellites. GPS does not compute locations based on angles (triANGLulation) but rather by trilateration.
Rather than measuring angles, trialateration is time-based. The GPS satellites broadcast a signal which propagates in an isotropic (in all directions) pattern. While the signals form a sphere emanating from the satellite, we can simplify the visualization by displaying the pattern as a circle. Please excuse the crudeness of the title diagram. It is an attempt to illustrate the concept of trilateration. The measurement by the GPS receiver (target) of the time the signal takes to go from the satellite determines the distance. Where the circles overlap is where the target is located and, based on the timing of the signals, a location is computed.
There are a few things which can affect the accuracy of GPS.
• One error is the Geometric/Position Dilution of Precision (GDOP/PDOP). This basically means that signals from more satellites that a GPS receiver “sees” (geometric) can raise the accuracy of position determination. Also, the further the satellites are spaced apart (position), the greater the accuracy.
• Atmospheric refraction also affects computed location of a target. This is seen as the signal passes through the boundary between the earth’s ionosphere and the troposphere. This, however, is compensated for by the GPS system using two signals at different frequencies which diffract differently.
• Errors can also be introduced by multipath effects where the satellite signal gets reflected (bounces off) things like buildings and mountains. These reflected signals cause interference which can “confuse” GPS receivers and introduce positioning errors since the receiver detects the same signal twice, but at different distances.
• The atomic clocks used by the GPS satellites are accurate to about a nanosecond. A variation in the synchronization of the clocks between different satellites can introduce positioning errors, but they are generally small … perhaps a couple of meters. Similarly if the exact position of the GPS satellites (ephemeris) is uncertain, then the distance calculation will also vary.
• There is also a man-made source of positioning inaccuracies. Prior to the year 2000, the US government added time-varying code to the GPS systems to intentionally reduce the accuracy of positioning, primarily out of military concerns. This intentional degradation of the GPS signal is called selective availability. When enabled, selective availability resulted in horizontal positioning errors of 50 meters and vertical errors of 100 meters. This could be compensated for by differential GPS so the selective availability feature was turned off in 2000.
Some positioning errors can be corrected. Differential GPS is more accurate than standard GPS but it requires two receivers. One of the receivers gets a signal directly from the satellites and another from a fixed source at a known location which is also communicating with the satellites. There is also a correction routine known as Satellite-Based Augmentation System (SBAS) where the satellite broadcasts a corrected error in real-time along with the GPS signal.
So – What is happening at SWR to cause GPS signals to register positions with horizontal and vertical discrepancies? That is hard to answer. IMO the leading candidates are GDOP/PDOP errors, multipath errors and selective availability. Even though the 31 currently active navigation satellites have software that technically had selective availability inactivated, there are ways it can be either reintroduced with updates or activated if it is in the code but dormant. This form of “spoofing” could result in positioning errors if some organization wanted to deliberately mislead researchers at the ranch.
One suggestion I have for the SWR team to consider using a differential GPS system. Maybe they can erect a stationary tower some distance from the Triangle/mesa area which also communicates with the satellites and relays this to one of the two receivers at the target.
I honestly do not know what is causing the detected variances of GPS positions at SWR. The above mentioned possibilities are rather mundane explanations for the discrepancies. Another often cited possibility is that there is a localized distortion of spacetime at SWR which would cause timing variances and thus positioning errors. Of the more exotic propositions, I favor the spacetime distortion theory. Potentially this could be the result of a gravitational “bending” spacetime, but this would require a huge amount of mass. Other theories for curving spacetime include wormholes, Krasnikov tubes and even the fields surrounding a warp drive powered craft. Your guess is as good as mine.
One of the more perplexing findings presented in the History
Channel program The Secret of Skinwalker Ranch
involves the detection of positioning errors when GPS is used. The team at Skinwalker Ranch (SWR) attaches GPS
receivers to nearly everything … rockets, vehicles, balloons and even drilling
rigs. Often the positions recorded via
GPS substantially differ from the physically known locations of the receivers.
I have noticed that oftentimes the functioning of GPS is
described as being a form of triangulation.
Strictly speaking this is incorrect.
Triangulation involves determining a location by measuring the angles
between a target and at least three transmission sources. In the case of GPS, these “sources” are
satellites. GPS does not compute locations based on angles (triANGLulation) but rather by trilateration.
Rather than measuring angles, trialateration is
time-based. The GPS satellites broadcast
a signal which propagates in an isotropic (in all directions) pattern. While the signals form a sphere emanating
from the satellite, we can simplify the visualization by displaying the pattern
as a circle. Please excuse the crudeness
of the diagram below. It is an attempt
to illustrate the concept of trilateration. The measurement by the GPS receiver
(target) of the time the signal takes to go from the satellite determines the
distance. Where the circles overlap is where
the target is located and, based on the timing of the signals, a location is
computed.
There are a few things which can affect the accuracy of
GPS.
·
One error is the Geometric/Position Dilution of Precision (GDOP/PDOP). This basically means that signals from more satellites
that a GPS receiver “sees” (geometric) can raise the accuracy of position
determination. Also, the further the satellites are spaced apart (position),
the greater the accuracy.
·
Atmospheric refraction also affects computed location
of a target. This is seen as the signal passes through the boundary between the
earth’s ionosphere and the troposphere.
This, however, is compensated for by the GPS system using two signals at
different frequencies which diffract differently.
·
Errors can also be introduced by multipath
effects where the satellite signal gets reflected (bounces off) things like
buildings and mountains. These reflected
signals cause interference which can “confuse” GPS receivers and introduce
positioning errors since the receiver detects the same signal twice, but at
different distances.
·
The atomic clocks used by the GPS satellites are
accurate to about a nanosecond. A variation in the synchronization of the clocks
between different satellites can introduce positioning errors, but they are
generally small … perhaps a couple of meters.
Similarly if the exact position of the GPS satellites (ephemeris) is
uncertain, then the distance calculation will also vary.
·
There is also a man-made source of positioning inaccuracies.
Prior to the year 2000, the US government added time-varying code to the GPS
systems to intentionally reduce the accuracy of positioning, primarily out of
military concerns. This intentional
degradation of the GPS signal is called selective
availability. When enabled, selective
availability resulted in horizontal positioning errors of 50 meters and vertical
errors of 100 meters. This could be
compensated for by differential GPS so the selective availability feature was
turned off in 2000.
Some positioning errors can be corrected. Differential GPS is more accurate than
standard GPS but it requires two receivers.
One of the receivers gets a signal directly from the satellites and
another from a fixed source at a known location which is also communicating
with the satellites. There is also a correction routine known as Satellite-Based
Augmentation System (SBAS) where the satellite broadcasts a corrected error in
real-time along with the GPS signal.
So – What is happening at SWR to cause GPS signals to
register positions with horizontal and vertical discrepancies? That is hard to
answer. IMO the leading candidates are
GDOP/PDOP errors, multipath errors and selective availability. Even though the 31 currently active navigation
satellites have software that technically had selective availability inactivated,
there are ways it can be either reintroduced with updates or activated if it is
in the code but dormant. This form of “spoofing”
could result in positioning errors if some organization wanted to deliberately
mislead researchers at the ranch.
One suggestion I have for the SWR team to consider using a
differential GPS system. Maybe they can
erect a stationary tower some distance from the Triangle/mesa area which also
communicates with the satellites and relays this to one of the two receivers at
the target.
I honestly do not know what is causing the detected
variances of GPS positions at SWR. The
above mentioned possibilities are rather mundane explanations for the discrepancies.
Another often cited possibility is that there is a localized distortion of
spacetime at SWR which would cause timing variances and thus positioning errors.
Of the more exotic propositions, I favor the spacetime distortion theory. Potentially this could be the result of a
gravitational “bending” spacetime, but this would require a huge amount of mass. Other theories for curving spacetime include
wormholes, Krasnikov tubes and even the fields surrounding a warp drive powered
craft. Your guess is as good as mine.
.
Target
