<s>
In	O
physics	O
,	O
backscatter	B-Algorithm
(	O
or	O
backscattering	B-Algorithm
)	O
is	O
the	O
reflection	O
of	O
waves	O
,	O
particles	O
,	O
or	O
signals	O
back	O
to	O
the	O
direction	O
from	O
which	O
they	O
came	O
.	O
</s>
<s>
It	O
is	O
usually	O
a	O
diffuse	O
reflection	O
due	O
to	O
scattering	O
,	O
as	O
opposed	O
to	O
specular	O
reflection	O
as	O
from	O
a	O
mirror	O
,	O
although	O
specular	O
backscattering	B-Algorithm
can	O
occur	O
at	O
normal	O
incidence	O
with	O
a	O
surface	O
.	O
</s>
<s>
Backscattering	B-Algorithm
has	O
important	O
applications	O
in	O
astronomy	O
,	O
photography	O
,	O
and	O
medical	B-Application
ultrasonography	I-Application
.	O
</s>
<s>
Backscattering	B-Algorithm
can	O
occur	O
in	O
quite	O
different	O
physical	O
situations	O
,	O
where	O
the	O
incoming	O
waves	O
or	O
particles	O
are	O
deflected	O
from	O
their	O
original	O
direction	O
by	O
different	O
mechanisms	O
:	O
</s>
<s>
Diffuse	O
reflection	O
from	O
large	O
particles	O
and	O
Mie	O
scattering	O
,	O
causing	O
alpenglow	O
and	O
gegenschein	O
,	O
and	O
showing	O
up	O
in	O
weather	B-Application
radar	I-Application
;	O
</s>
<s>
Inelastic	O
collisions	O
between	O
electromagnetic	O
waves	O
and	O
the	O
transmitting	O
medium	O
(	O
Brillouin	B-Algorithm
scattering	I-Algorithm
and	O
Raman	B-Architecture
scattering	I-Architecture
)	O
,	O
important	O
in	O
fiber	B-Architecture
optics	I-Architecture
,	O
see	O
below	O
;	O
</s>
<s>
Bragg	O
diffraction	O
from	O
crystals	O
,	O
used	O
in	O
inelastic	O
scattering	O
experiments	O
(	O
neutron	O
backscattering	B-Algorithm
,	O
X-ray	O
backscattering	B-Algorithm
spectroscopy	O
)	O
;	O
</s>
<s>
Compton	O
scattering	O
,	O
used	O
in	O
Backscatter	B-Algorithm
X-ray	O
imaging	O
.	O
</s>
<s>
Stimulated	O
backscatter	B-Algorithm
,	O
observed	O
in	O
non-linear	O
optics	O
,	O
and	O
described	O
by	O
a	O
class	O
of	O
solutions	O
to	O
the	O
three-wave	O
equation	O
.	O
</s>
<s>
In	O
these	O
cases	O
,	O
the	O
term	O
"	O
backscattering	B-Algorithm
"	O
just	O
designates	O
the	O
detector	O
location	O
chosen	O
for	O
some	O
practical	O
reasons	O
:	O
</s>
<s>
in	O
X-ray	O
imaging	O
,	O
backscattering	B-Algorithm
means	O
just	O
the	O
opposite	O
of	O
transmission	O
imaging	O
;	O
</s>
<s>
in	O
inelastic	O
neutron	O
or	O
X-ray	O
spectroscopy	O
,	O
backscattering	B-Algorithm
geometry	O
is	O
chosen	O
because	O
it	O
optimizes	O
the	O
energy	O
resolution	O
;	O
</s>
<s>
in	O
astronomy	O
,	O
backscattered	B-Algorithm
light	O
is	O
that	O
which	O
is	O
reflected	O
with	O
a	O
phase	O
angle	O
of	O
less	O
than	O
90°	O
.	O
</s>
<s>
Coherent	O
backscattering	B-Algorithm
is	O
observed	O
in	O
random	O
media	O
;	O
for	O
visible	O
light	O
most	O
typically	O
in	O
suspensions	O
like	O
milk	O
.	O
</s>
<s>
Backscattering	B-Algorithm
properties	O
of	O
a	O
target	O
are	O
wavelength	O
dependent	O
and	O
can	O
also	O
be	O
polarization	O
dependent	O
.	O
</s>
<s>
Backscattering	B-Algorithm
is	O
the	O
principle	O
behind	O
radar	O
systems	O
.	O
</s>
<s>
In	O
weather	B-Application
radar	I-Application
,	O
backscattering	B-Algorithm
is	O
proportional	O
to	O
the	O
6th	O
power	O
of	O
the	O
diameter	O
of	O
the	O
target	O
multiplied	O
by	O
its	O
inherent	O
reflective	O
properties	O
,	O
provided	O
the	O
wavelength	O
is	O
larger	O
than	O
the	O
particle	O
diameter	O
(	O
Rayleigh	O
scattering	O
)	O
.	O
</s>
<s>
So	O
the	O
backscattering	B-Algorithm
is	O
dependent	O
on	O
a	O
mix	O
of	O
these	O
two	O
factors	O
.	O
</s>
<s>
The	O
strongest	O
backscatter	B-Algorithm
comes	O
from	O
hail	O
and	O
large	O
graupel	O
(	O
solid	O
ice	O
)	O
due	O
to	O
their	O
sizes	O
,	O
but	O
non-Rayleigh	O
(	O
Mie	O
scattering	O
)	O
effects	O
can	O
confuse	O
interpretation	O
.	O
</s>
<s>
Rain	O
is	O
a	O
moderate	O
backscatter	B-Algorithm
,	O
being	O
stronger	O
with	O
large	O
drops	O
(	O
such	O
as	O
from	O
a	O
thunderstorm	O
)	O
and	O
much	O
weaker	O
with	O
small	O
droplets	O
(	O
such	O
as	O
mist	B-Application
or	O
drizzle	B-Application
)	O
.	O
</s>
<s>
Snow	O
has	O
rather	O
weak	O
backscatter	B-Algorithm
.	O
</s>
<s>
Dual	O
polarization	O
weather	B-Application
radars	I-Application
measure	O
backscatter	B-Algorithm
at	O
horizontal	O
and	O
vertical	O
polarizations	O
to	O
infer	O
shape	O
information	O
from	O
the	O
ratio	O
of	O
the	O
vertical	O
and	O
horizontal	O
signals	O
.	O
</s>
<s>
The	O
backscattering	B-Algorithm
method	O
is	O
also	O
employed	O
in	O
fiber	B-Architecture
optics	I-Architecture
applications	O
to	O
detect	O
optical	O
faults	O
.	O
</s>
<s>
Light	O
propagating	O
through	O
a	O
fiber	B-Architecture
optic	I-Architecture
cable	O
gradually	O
attenuates	O
due	O
to	O
Rayleigh	O
scattering	O
.	O
</s>
<s>
Faults	O
are	O
thus	O
detected	O
by	O
monitoring	O
the	O
variation	O
of	O
part	O
of	O
the	O
Rayleigh	O
backscattered	B-Algorithm
light	O
.	O
</s>
<s>
Since	O
the	O
backscattered	B-Algorithm
light	O
attenuates	O
exponentially	O
as	O
it	O
travels	O
along	O
the	O
optical	B-Architecture
fiber	I-Architecture
cable	O
,	O
the	O
attenuation	O
characteristic	O
is	O
represented	O
in	O
a	O
logarithmic	O
scale	O
graph	B-Application
.	O
</s>
<s>
If	O
the	O
slope	O
of	O
the	O
graph	B-Application
is	O
steep	O
,	O
then	O
power	O
loss	O
is	O
high	O
.	O
</s>
<s>
If	O
the	O
slope	O
is	O
gentle	O
,	O
then	O
optical	B-Architecture
fiber	I-Architecture
has	O
a	O
satisfactory	O
loss	O
characteristic	O
.	O
</s>
<s>
The	O
loss	O
measurement	O
by	O
the	O
backscattering	B-Algorithm
method	O
allows	O
measurement	O
of	O
a	O
fiber	B-Architecture
optic	I-Architecture
cable	O
at	O
one	O
end	O
without	O
cutting	O
the	O
optical	B-Architecture
fiber	I-Architecture
hence	O
it	O
can	O
be	O
conveniently	O
used	O
for	O
the	O
construction	O
and	O
maintenance	O
of	O
optical	B-Architecture
fibers	I-Architecture
.	O
</s>
<s>
The	O
term	O
backscatter	B-Algorithm
in	O
photography	O
refers	O
to	O
light	O
from	O
a	O
flash	O
or	O
strobe	O
reflecting	O
back	O
from	O
particles	O
in	O
the	O
lens	O
's	O
field	O
of	O
view	O
causing	O
specks	O
of	O
light	O
to	O
appear	O
in	O
the	O
photo	O
.	O
</s>
<s>
Photographic	O
backscatter	B-Algorithm
can	O
result	O
from	O
snowflakes	O
,	O
rain	O
or	O
mist	B-Application
,	O
or	O
airborne	O
dust	O
.	O
</s>
