<s>
The	O
railSAR	B-Algorithm
,	O
also	O
known	O
as	O
the	O
ultra-wideband	O
Foliage	O
Penetration	O
Synthetic	B-Application
Aperture	I-Application
Radar	I-Application
(	O
UWB	O
FOPEN	O
SAR	B-Application
)	O
,	O
is	O
a	O
rail-guided	O
,	O
low-frequency	B-Algorithm
impulse	O
radar	O
system	O
that	O
can	O
detect	O
and	O
discern	O
target	O
objects	O
hidden	O
behind	O
foliage	O
.	O
</s>
<s>
It	O
was	O
designed	O
and	O
developed	O
by	O
the	O
U.S.	O
Army	O
Research	O
Laboratory	O
(	O
ARL	O
)	O
in	O
the	O
early	O
1990s	O
in	O
order	O
to	O
demonstrate	O
the	O
capabilities	O
of	O
an	O
airborne	O
SAR	B-Application
for	O
foliage	O
and	O
ground	B-Algorithm
penetration	I-Algorithm
.	O
</s>
<s>
However	O
,	O
since	O
conducting	O
accurate	O
,	O
repeatable	O
measurements	O
on	O
an	O
airborne	O
platform	O
was	O
both	O
challenging	O
and	O
expensive	O
,	O
the	O
railSAR	B-Algorithm
was	O
built	O
on	O
the	O
rooftop	O
of	O
a	O
four-story	O
building	O
within	O
the	O
Army	O
Research	O
Laboratory	O
compound	O
along	O
a	O
104-meter	O
laser-leveled	O
track	O
.	O
</s>
<s>
At	O
the	O
time	O
,	O
the	O
railSAR	B-Algorithm
fell	O
into	O
the	O
highest	O
category	O
of	O
UWB	O
radar	O
systems	O
,	O
operating	O
across	O
a	O
950MHz-wide	O
band	O
from	O
40MHz	O
to	O
1GHz	O
on	O
a	O
pulse	O
strength	O
of	O
2.5	O
megawatts	O
.	O
</s>
<s>
It	O
provided	O
fully	O
polarimetric	O
,	O
high	B-Algorithm
resolution	I-Algorithm
radar	O
data	O
and	O
possessed	O
185%	O
bandwidth	O
compared	O
to	O
other	O
radar	O
systems	O
that	O
had	O
less	O
than	O
25%	O
bandwidth	O
.	O
</s>
<s>
Applications	O
of	O
the	O
railSAR	B-Algorithm
technology	O
range	O
from	O
military	O
uses	O
such	O
as	O
detecting	O
landmines	O
and	O
stationary	O
targets	O
in	O
hiding	O
for	O
reconnaissance	O
purposes	O
to	O
commercial	O
uses	O
,	O
including	O
cable	O
and	O
pipe	O
detection	O
,	O
oil	O
and	O
water	O
table	O
measurements	O
,	O
and	O
environmental	O
remediation	O
.	O
</s>
<s>
The	O
development	O
of	O
the	O
railSAR	B-Algorithm
began	O
in	O
1988	O
as	O
part	O
of	O
an	O
exploratory	O
research	O
program	O
that	O
aimed	O
to	O
create	O
technology	O
that	O
could	O
detect	O
targets	O
camouflaged	O
or	O
hidden	O
by	O
trees	O
and	O
foliage	O
cover	O
.	O
</s>
<s>
While	O
early	O
efforts	O
faced	O
considerable	O
challenges	O
,	O
advancements	O
in	O
analog-to-digital	O
(	O
A/D	O
)	O
converter	O
technology	O
,	O
source	O
technology	O
,	O
and	O
signal-processing	O
power	O
allowed	O
ARL	O
researchers	O
to	O
produce	O
a	O
realizable	O
system	O
and	O
grasp	O
a	O
better	O
understanding	O
of	O
foliage	O
and	O
ground	B-Algorithm
penetrating	I-Algorithm
radar	I-Algorithm
.	O
</s>
<s>
The	O
railSAR	B-Algorithm
had	O
four	O
1	O
,	O
35	O
m	O
(	O
4	O
,	O
5	O
ft	O
)	O
long	O
,	O
linear	O
200-ohm	O
TEM	O
horn	O
antennas	O
,	O
two	O
for	O
transmitting	O
and	O
two	O
for	O
receiving	O
,	O
mounted	O
on	O
a	O
rotating	O
,	O
non-conducting	O
frame	O
that	O
was	O
anchored	O
on	O
a	O
hinged	O
plate	O
constructed	O
out	O
of	O
aluminum	O
honeycomb	O
and	O
covered	O
in	O
anechoic	O
foam	O
.	O
</s>
<s>
In	O
1995	O
,	O
the	O
design	O
of	O
the	O
railSAR	B-Algorithm
was	O
incorporated	O
into	O
the	O
development	O
of	O
the	O
boomSAR	B-Algorithm
in	O
an	O
effort	O
to	O
produce	O
a	O
mobile	O
,	O
high	O
signal-to-noise	O
radar	O
.	O
</s>
<s>
By	O
2016	O
,	O
the	O
railSAR	B-Algorithm
had	O
been	O
moved	O
from	O
the	O
rooftop	O
of	O
the	O
building	O
to	O
an	O
indoor	O
facility	O
and	O
had	O
been	O
subjected	O
to	O
several	O
weight	O
reductions	O
and	O
redesigns	O
.	O
</s>
<s>
In	O
general	O
,	O
radar	O
systems	O
perform	O
foliage	O
and	O
ground	B-Algorithm
penetration	I-Algorithm
more	O
effectively	O
with	O
lower	O
frequencies	O
,	O
because	O
longer	O
wavelengths	O
can	O
penetrate	O
opaque	O
structures	O
deeper	O
than	O
shorter	O
wavelengths	O
.	O
</s>
<s>
But	O
in	O
exchange	O
for	O
greater	O
penetration	O
capabilities	O
,	O
the	O
lower	O
frequencies	O
provide	O
a	O
lower	O
image	B-Algorithm
resolution	I-Algorithm
.	O
</s>
<s>
In	O
order	O
to	O
reliably	O
receive	O
a	O
UWB	O
signal	O
given	O
such	O
low	O
power	O
per	O
frequency	O
,	O
the	O
UWB	O
radar	O
system	O
must	O
either	O
open	O
itself	O
to	O
noise	O
with	O
the	O
use	O
of	O
a	O
high	O
sampling	B-Algorithm
rate	I-Algorithm
receiver	O
,	O
incorporate	O
signal	O
average	O
which	O
lowers	O
the	O
data	O
rate	O
,	O
or	O
increase	O
to	O
high	O
signal	O
transmit	O
power	O
which	O
presents	O
interference	O
to	O
other	O
receivers	O
.	O
</s>
<s>
However	O
,	O
the	O
combination	O
of	O
low	B-Algorithm
frequency	I-Algorithm
and	O
high	B-Algorithm
resolution	I-Algorithm
present	O
in	O
UWB	O
radars	O
proved	O
to	O
be	O
extremely	O
desirable	O
for	O
foliage	O
and	O
ground	B-Algorithm
penetration	I-Algorithm
,	O
in	O
which	O
the	O
increased	O
bandwidth	O
presented	O
a	O
distinct	O
advantage	O
over	O
its	O
costs	O
.	O
</s>
<s>
In	O
an	O
effort	O
to	O
attain	O
the	O
necessary	O
frequencies	O
for	O
adequate	O
penetration	O
while	O
balancing	O
the	O
processing	O
costs	O
associated	O
with	O
ultra-wideband	O
,	O
the	O
railSAR	B-Algorithm
was	O
designed	O
to	O
identify	O
mine	O
clusters	O
over	O
very	O
large	O
areas	O
rather	O
than	O
detect	O
each	O
individual	O
mine	O
hidden	O
in	O
the	O
soil	O
and	O
foliage	O
.	O
</s>
<s>
The	O
railSAR	B-Algorithm
was	O
initially	O
constructed	O
to	O
look	O
north	O
over	O
the	O
north	O
parking	O
lot	O
of	O
the	O
ARL	O
compound	O
as	O
its	O
target	O
area	O
,	O
which	O
was	O
mainly	O
populated	O
by	O
deciduous	O
trees	O
.	O
</s>
<s>
The	O
radar	O
system	O
required	O
about	O
80	O
hours	O
to	O
collect	O
one	O
complete	O
aperture	O
of	O
high-resolution	B-Algorithm
,	O
fully	O
polarimetric	O
data	O
.	O
</s>
<s>
Creating	O
the	O
radar	O
image	O
required	O
the	O
railSAR	B-Algorithm
to	O
limit	O
the	O
Fourier	O
processing	O
to	O
very	O
small	O
patches	O
within	O
the	O
image	O
area	O
.	O
</s>
<s>
Despite	O
its	O
use	O
of	O
low-frequency	B-Algorithm
signals	O
,	O
the	O
railSAR	B-Algorithm
was	O
capable	O
of	O
achieving	O
high	B-Algorithm
resolution	I-Algorithm
by	O
moving	O
along	O
the	O
rail	O
and	O
transmitting	O
and	O
receiving	O
returns	O
in	O
the	O
direction	O
perpendicular	O
to	O
the	O
line	O
of	O
motion	O
along	O
the	O
rail	O
.	O
</s>
<s>
During	O
performance	O
analysis	O
tests	O
,	O
the	O
railSAR	B-Algorithm
achieved	O
a	O
recognition	O
probability	O
of	O
90	O
percent	O
with	O
a	O
relatively	O
low	O
false-alarm	O
rate	O
.	O
</s>
