<s>
Distributed	B-Algorithm
temperature	I-Algorithm
sensing	I-Algorithm
systems	O
(	O
DTS	O
)	O
are	O
optoelectronic	O
devices	O
which	O
measure	O
temperatures	O
by	O
means	O
of	O
optical	B-Architecture
fibres	I-Architecture
functioning	O
as	O
linear	O
sensors	B-Application
.	O
</s>
<s>
Temperatures	O
are	O
recorded	O
along	O
the	O
optical	B-Application
sensor	I-Application
cable	O
,	O
thus	O
not	O
at	O
points	O
,	O
but	O
as	O
a	O
continuous	O
profile	O
.	O
</s>
<s>
Thermal	O
changes	O
along	O
the	O
optical	B-Architecture
fibre	I-Architecture
cause	O
a	O
local	O
variation	O
in	O
the	O
refractive	O
index	O
,	O
which	O
in	O
turn	O
leads	O
to	O
the	O
inelastic	O
scattering	O
of	O
the	O
light	O
propagating	O
through	O
it	O
.	O
</s>
<s>
Molecular	O
vibrations	O
at	O
high	B-Algorithm
frequencies	I-Algorithm
(	O
10	O
THz	O
)	O
are	O
responsible	O
for	O
Raman	B-Architecture
scattering	I-Architecture
.	O
</s>
<s>
As	O
a	O
result	O
of	O
the	O
damping	O
of	O
the	O
light	O
in	O
the	O
quartz	O
glass	O
fibres	O
through	O
scattering	O
,	O
the	O
location	O
of	O
an	O
external	O
physical	O
effect	O
can	O
be	O
determined	O
so	O
that	O
the	O
optical	B-Architecture
fibre	I-Architecture
can	O
be	O
employed	O
as	O
a	O
linear	O
sensor	O
.	O
</s>
<s>
Optical	B-Architecture
fibres	I-Architecture
are	O
made	O
from	O
doped	O
quartz	O
glass	O
.	O
</s>
<s>
When	O
light	O
falls	O
onto	O
these	O
thermally	O
excited	O
molecular	O
oscillations	O
,	O
an	O
interaction	O
occurs	O
between	O
the	O
light	O
particles	O
(	O
photons	B-Application
)	O
and	O
the	O
electrons	O
of	O
the	O
molecule	O
.	O
</s>
<s>
Light	O
scattering	O
,	O
also	O
known	O
as	O
Raman	B-Architecture
scattering	I-Architecture
,	O
occurs	O
in	O
the	O
optical	B-Architecture
fibre	I-Architecture
.	O
</s>
<s>
The	O
light	O
scattered	O
back	O
from	O
the	O
fibre	B-Architecture
optic	I-Architecture
therefore	O
contains	O
three	O
different	O
spectral	O
shares	O
:	O
</s>
<s>
the	O
anti-Stokes	B-Algorithm
line	I-Algorithm
components	O
with	O
photons	B-Application
shifted	O
to	O
shorter	O
wavelength	O
(	O
higher	O
frequency	O
)	O
than	O
the	O
Rayleigh	O
scattering	O
.	O
</s>
<s>
The	O
local	O
temperature	O
of	O
the	O
optical	B-Architecture
fibre	I-Architecture
is	O
derived	O
from	O
the	O
ratio	O
of	O
the	O
anti-Stokes	O
and	O
Stokes	O
light	O
intensities	O
.	O
</s>
<s>
There	O
are	O
two	O
basic	O
principles	O
of	O
measurement	O
for	O
distributed	O
sensing	O
technology	O
,	O
OTDR	B-Protocol
(	O
Optical	B-Protocol
Time	I-Protocol
Domain	I-Protocol
Reflectometry	I-Protocol
)	O
and	O
OFDR	B-Application
(	O
Optical	O
Frequency	O
Domain	O
Reflectometry	O
)	O
.	O
</s>
<s>
OTDR	B-Protocol
was	O
developed	O
more	O
than	O
20	O
years	O
ago	O
and	O
has	O
become	O
the	O
industry	O
standard	O
for	O
telecom	O
loss	O
measurements	O
which	O
detects	O
the	O
—	O
compared	O
to	O
Raman	O
signal	O
very	O
dominant	O
—	O
Rayleigh	O
backscattering	O
signals	O
.	O
</s>
<s>
The	O
principle	O
for	O
OTDR	B-Protocol
is	O
quite	O
simple	O
and	O
is	O
very	O
similar	O
to	O
the	O
time	O
of	O
flight	O
measurement	O
used	O
for	O
radar	B-Application
.	O
</s>
<s>
Alternative	O
DTS	O
evaluation	O
units	O
deploy	O
the	O
method	O
of	O
Optical	O
Frequency	O
Domain	O
Reflectometry	O
(	O
OFDR	B-Application
)	O
.	O
</s>
<s>
The	O
OFDR	B-Application
system	O
provides	O
information	O
on	O
the	O
local	O
characteristic	O
only	O
when	O
the	O
backscatter	O
signal	O
detected	O
during	O
the	O
entire	O
measurement	O
time	O
is	O
measured	O
as	O
a	O
function	O
of	O
frequency	O
in	O
a	O
complex	O
fashion	O
,	O
and	O
then	O
subjected	O
to	O
Fourier	B-Algorithm
transformation	I-Algorithm
.	O
</s>
<s>
The	O
essential	O
principles	O
of	O
OFDR	B-Application
technology	O
are	O
the	O
quasi	O
continuous	O
wave	O
mode	O
employed	O
by	O
the	O
laser	O
and	O
the	O
narrow-band	O
detection	O
of	O
the	O
optical	O
backscatter	O
signal	O
.	O
</s>
<s>
Binary	B-Error_Name
Golay	I-Error_Name
code	I-Error_Name
.	O
</s>
<s>
In	O
contrast	O
to	O
OTDR	B-Protocol
technology	O
,	O
the	O
optical	O
energy	O
is	O
spread	O
over	O
a	O
code	O
rather	O
than	O
packed	O
into	O
a	O
single	O
pulse	O
.	O
</s>
<s>
Thus	O
a	O
light	O
source	O
with	O
lower	O
peak	O
power	O
compared	O
to	O
OTDR	B-Protocol
technology	O
can	O
be	O
used	O
,	O
e.g.	O
</s>
<s>
The	O
detected	O
backscatter	O
needs	O
to	O
be	O
transformed	O
—	O
similar	O
to	O
OFDR	B-Application
technology	O
—	O
back	O
into	O
a	O
spatial	O
profile	O
,	O
e.g.	O
</s>
<s>
In	O
contrast	O
to	O
OFDR	B-Application
technology	O
,	O
the	O
emission	O
is	O
finite	O
(	O
for	O
example	O
128	O
bit	O
)	O
which	O
avoids	O
that	O
weak	O
scattered	O
signals	O
from	O
far	O
are	O
superposed	O
by	O
strong	O
scattered	O
signals	O
from	O
short	O
distance	O
,	O
improving	O
the	O
Shot	O
noise	O
and	O
the	O
signal-to-noise	O
ratio	O
.	O
</s>
<s>
The	O
temperature	O
measuring	O
system	O
consists	O
of	O
a	O
controller	O
(	O
laser	O
source	O
,	O
pulse	O
generator	O
for	O
OTDR	B-Protocol
or	O
code	O
generator	O
for	O
Code	O
Correlation	O
or	O
modulator	O
and	O
HF	B-Algorithm
mixer	O
for	O
OFDR	B-Application
,	O
optical	O
module	O
,	O
receiver	O
and	O
micro-processor	O
unit	O
)	O
and	O
a	O
quartz	B-Architecture
glass	I-Architecture
fibre	I-Architecture
as	O
line-shaped	O
temperature	O
sensor	O
.	O
</s>
<s>
The	O
fibre	B-Architecture
optic	I-Architecture
cable	O
(	O
can	O
be	O
70km	O
in	O
length	O
)	O
is	O
passive	O
in	O
nature	O
and	O
has	O
no	O
individual	O
sensing	O
points	O
and	O
therefore	O
can	O
be	O
manufactured	O
based	O
on	O
standard	O
telecoms	O
fibres	O
.	O
</s>
<s>
Because	O
the	O
system	O
designer/integrator	O
does	O
not	O
have	O
to	O
worry	O
about	O
the	O
precise	O
location	O
of	O
each	O
sensing	O
point	O
the	O
cost	O
for	O
designing	O
and	O
installing	O
a	O
sensing	O
system	O
based	O
on	O
distributed	O
fibre	B-Algorithm
optic	I-Algorithm
sensors	I-Algorithm
is	O
greatly	O
reduced	O
from	O
that	O
of	O
traditional	O
sensors	B-Application
.	O
</s>
<s>
Additionally	O
,	O
because	O
the	O
sensing	O
cable	O
has	O
no	O
moving	O
parts	O
and	O
design	O
lives	O
of	O
>30years	O
,	O
the	O
maintenance	O
and	O
operation	O
costs	O
are	O
also	O
considerably	O
less	O
than	O
for	O
conventional	O
sensors	B-Application
.	O
</s>
<s>
Additional	O
benefits	O
of	O
fibre	B-Architecture
optic	I-Architecture
sensing	O
technology	O
are	O
that	O
it	O
is	O
immune	O
to	O
electromagnetic	O
interference	O
,	O
vibration	O
and	O
is	O
safe	O
for	O
use	O
in	O
hazardous	O
zones	O
(	O
the	O
laser	O
power	O
falls	O
below	O
the	O
levels	O
that	O
can	O
cause	O
ignition	O
)	O
,	O
thus	O
making	O
these	O
sensors	B-Application
ideal	O
for	O
use	O
in	O
industrial	O
sensing	O
applications	O
.	O
</s>
<s>
With	O
regards	O
to	O
the	O
construction	O
of	O
the	O
sensing	O
cable	O
,	O
although	O
it	O
is	O
based	O
on	O
standard	O
fibre	B-Architecture
optics	I-Architecture
,	O
care	O
must	O
be	O
taken	O
in	O
the	O
design	O
of	O
the	O
individual	O
sensing	O
cable	O
to	O
ensure	O
that	O
adequate	O
protection	O
is	O
provided	O
for	O
the	O
fibre	O
.	O
</s>
<s>
This	O
must	O
take	O
into	O
account	O
operating	O
temperature	O
(	O
standard	O
cables	O
operate	O
to	O
85°C	O
,	O
but	O
it	O
is	O
possible	O
to	O
measure	O
up	O
to	O
700°C	O
with	O
the	O
correct	O
design	O
)	O
,	O
gaseous	O
environment	O
(	O
hydrogen	O
can	O
cause	O
deterioration	O
of	O
the	O
measurement	O
though	O
"	O
hydrogen	B-Device
darkening	I-Device
"	O
aka	O
attenuation	O
of	O
the	O
silica	O
glass	O
compounds	O
)	O
and	O
mechanical	O
protection	O
.	O
</s>
<s>
In	O
the	O
oil	O
and	O
gas	O
industry	O
an	O
XML	B-Protocol
based	O
file	O
standard	O
(	O
WITSML	O
)	O
has	O
been	O
developed	O
for	O
transfer	O
of	O
data	O
from	O
DTS	O
instruments	O
.	O
</s>
<s>
The	O
advantage	O
of	O
purely	O
passive	O
optical	B-Application
sensor	I-Application
technology	O
is	O
the	O
lack	O
of	O
electric	O
or	O
electromagnetic	O
interaction	O
.	O
</s>
<s>
Temperature	O
distributions	O
can	O
be	O
used	O
to	O
develop	O
models	O
based	O
on	O
the	O
Proper	O
Orthogonal	O
Decomposition	O
Method	O
or	O
principal	B-Application
component	I-Application
analysis	I-Application
.	O
</s>
<s>
Distributed	B-Algorithm
temperature	I-Algorithm
sensing	I-Algorithm
can	O
be	O
deployed	O
successfully	O
in	O
multiple	O
industrial	O
segments	O
:	O
</s>
<s>
Fiber	B-Architecture
Optics	I-Architecture
Opens	O
Window	O
on	O
Stream	O
Dynamics	O
.	O
</s>
<s>
Parlange.Distributed	O
Fiber	B-Architecture
Optic	I-Architecture
Temperature	O
Sensing	O
for	O
Hydrologic	O
Systems	O
.	O
</s>
<s>
Locating	O
illicit	O
connections	O
in	O
storm	O
water	O
sewers	O
using	O
fiber-optic	B-Architecture
distributed	B-Algorithm
temperature	I-Algorithm
sensing	I-Algorithm
.	O
</s>
<s>
Clemens	O
,	O
Fibre-optic	B-Architecture
distributed	B-Algorithm
temperature	I-Algorithm
sensing	I-Algorithm
in	O
combined	O
sewer	O
system	O
,	O
Water	O
Science	O
Technology	O
.	O
</s>
<s>
Assessment	O
of	O
detection	O
limits	O
of	O
fiber-optic	B-Architecture
distributed	B-Algorithm
temperature	I-Algorithm
sensing	I-Algorithm
for	O
detection	O
of	O
illicit	O
connections	O
.	O
</s>
<s>
Searching	O
for	O
storm	O
water	O
inflows	O
in	O
foul	O
sewers	O
using	O
fibre-optic	B-Architecture
distributed	O
temperature	O
sensing.Water	O
Science	O
and	O
Technology	O
.	O
</s>
