Transcript Mike Bedford LORAN-C - British Cave Research Association

British Cave Research Association
Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
LORAN-C
Friend or Foe?
Mike Bedford
Overview of Presentation
• LORAN-C is a radio navigation system
intended for marine use.
• It interferes with cave radios e.g. HeyPhone.
• Despite it making communication difficult,
there are some potential benefits for cavers.
• Here I provide background on LORAN-C and
discuss possible caving applications.
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Hyperbolic Navigation (1)
• LORAN-C is a hyperbolic
navigation system.
• Operates by measuring
time distance of arrival
of signals from a pair of
synchronised transmitters.
LOPs
Transmitter 1
Extended
Baseline
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Transmitter 2
Hyperbolic Navigation (2)
• By using two pairs
of transmitters a
fix can be obtained.
Tx 1
Tx 2
Tx 3
Ambiguity
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
LORAN-C Frequency
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100kHz centre frequency
99% of power within 90-110kHz…
… but high power transmitters
… therefore significant signal at 87kHz
… hence interference for cave radios
Later presentation on a method of preventing
Loran-C interference
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
LORAN-C Chains
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LORAN-C is organised in “chains”
A chain covers a geographical area
Chain comprises master station (M)…
… plus 2 – 4 slaves (W, X, Y, Z)
More than one chain might be detectable
So chains are differentiated by their Group
Repetition Interval (GRI)
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
LORAN-C Timing
~200S
1mS
2mS
M
X
Y
Z
M
ED(X)
ED(Y)
ED(Z)
GRI
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
LORAN-C Pulses
0
50
100
150
200
Timings from 3rd zero-crossing (30 S)
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Accuracy
• Unlike GPS, LORAN-C accuracy depends on
receiver location with respect to transmitters
• Best on baseline between master and slave
because LOPs are closer here
• Absolute accuracy 185 – 463m
• Repeatable accuracy 18 – 91m
• eLORAN improves this to 8 – 20m
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Underground Performance
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Accuracy inferior to GPS…
… but LORAN-C is available underground
But will signal strength by adequate?
Actually s/n is the most important factor and
less noise underground
• Patent Application WO 20061130223 claims
improved s/n underground
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Underground Accuracy
• Non-uniform geology
• Sloping surface topology
From
M
From
Z
From
Z
From
M
• Therefore accuracy possibly degraded
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Caving Applications
• Accuracy not nearly good enough for normal
surveying but…
• … “differential accuracy” may be good enough
for “rough and ready” surveying (e.g. new
cave on expedition)
• Repeatable accuracy might be good enough to
permit its use for underground route finding
(a contentious application)
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Future of LORAN-C (1)
• For years we’ve been expecting LORAN-C to be
phased out – good news for cave radio
• LORAN-C was turned off in North America
earlier this year
• LORAN-C chains in Europe were transferred
from US Navy to host nations in 1995
• Some have closed (e.g. Mediterranean Sea)
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Future of LORAN-C (2)
• North East Europe chains
were managed by NELS
• NELS agreement terminated in 2005
• However, ad hoc arrangement still exists
between host nations and most are
committed to continuation in the mid term
• Stations being upgraded to eLORAN
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Chayka
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Chayka was developed by USSR
Similar to LORAN-C
Same frequency but different pulse shape
Russian Chayka chains also remain operational
West Russia chain available in Eastern Europe
Some Loran-C receivers also use
Chayka signals
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Former NELS Chains
Transmitter Emission
Location
Designation Delay (µS)
Coordinates
Country
Latitude
Longitude
Power
(kW)
Lessay 6731 Chain
M
Lessay
France
49°08′55.224″N 01°30′17.029″W
250
X
13,000
Soustons
France
43°44′23.099″N 01°22′49.584″W
250
Y
27,300
Anthorn
UK
54°54′41.949″N 03°16′42.587″W
250
Z
42,100
Sylt
Germany
54°48′29.975″N 08°17′36.856″E
250
Bø
Norway
68°38′06.216″N 14°27′47.350″E
400
Bø 7001 Chain
M
X
14,100
Jan Mayen
Norway
70°54′51.478″N 08°43′56.525″W
250
Y
29,100
Berlevåg
Norway
70°50′43.014″N 29°12′15.980″E
250
Eiði
Faroe
62°17′59.837″N 07°04′26.079″W
400
Eiði 9007 Chain
M
W
14,200
Jan Mayen
Norway
70°54′51.478″N 08°43′56.525″W
250
X
28,000
Bø
Norway
68°38′06.216″N 14°27′47.350″E
400
Y
41,100
Værlandet
Norway
61°17′49.435″N 04°41′46.618″E
250
Sylt
Germany
54°48′29.975″N 08°17′36.856″E
250
Sylt 7499 Chain
M
X
14,100
Lessay
France
49°08′55.224″N 01°30′17.029″W
250
Y
29,500
Værlandet
Norway
68°38′06.216″N 14°27′47.350″E
250
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Former NELS & Chayka Chains
Berlevåg
Jan Mayen
Bø
Petrozavodsk
Eiði
Værlandet
Sylt
Slonim
Karachev
Rugby
Lessay
Soustons
Simferopol
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Where Next?
• LORAN-C receivers are cheap
• Former US users off-loading for a few dollars
• Time for some underground experiments?
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire
Thank you for Listening
Any Questions?
British Cave Research Association - Cave Technology Symposium 2010
17th April 2010, Horton-in-Ribblesdale, North Yorkshire