<s>
Automatic	B-Algorithm
target	I-Algorithm
recognition	I-Algorithm
(	O
ATR	O
)	O
is	O
the	O
ability	O
for	O
an	O
algorithm	O
or	O
device	O
to	O
recognize	O
targets	O
or	O
other	O
objects	O
based	O
on	O
data	O
obtained	O
from	O
sensors	B-Application
.	O
</s>
<s>
Target	B-Algorithm
recognition	I-Algorithm
was	O
initially	O
done	O
by	O
using	O
an	O
audible	O
representation	O
of	O
the	O
received	O
signal	O
,	O
where	O
a	O
trained	O
operator	O
who	O
would	O
decipher	O
that	O
sound	O
to	O
classify	O
the	O
target	O
illuminated	O
by	O
the	O
radar	B-Application
.	O
</s>
<s>
This	O
can	O
be	O
useful	O
for	O
everything	O
from	O
recognizing	O
an	O
object	O
on	O
a	O
battlefield	O
to	O
filtering	O
out	O
interference	O
caused	O
by	O
large	O
flocks	O
of	O
birds	O
on	O
Doppler	O
weather	O
radar	B-Application
.	O
</s>
<s>
Possible	O
military	O
applications	O
include	O
a	O
simple	O
identification	O
system	O
such	O
as	O
an	O
IFF	B-Device
transponder	I-Device
,	O
and	O
is	O
used	O
in	O
other	O
applications	O
such	O
as	O
unmanned	O
aerial	O
vehicles	O
and	O
cruise	O
missiles	O
.	O
</s>
<s>
Target	B-Algorithm
recognition	I-Algorithm
has	O
existed	O
almost	O
as	O
long	O
as	O
radar	B-Application
.	O
</s>
<s>
Radar	B-Application
operators	O
would	O
identify	O
enemy	O
bombers	O
and	O
fighters	O
through	O
the	O
audio	O
representation	O
that	O
was	O
received	O
by	O
the	O
reflected	O
signal	O
(	O
see	O
Radar	B-Application
in	O
World	O
War	O
II	O
)	O
.	O
</s>
<s>
Target	B-Algorithm
recognition	I-Algorithm
was	O
done	O
for	O
years	O
by	O
playing	O
the	O
baseband	B-Algorithm
signal	I-Algorithm
to	O
the	O
operator	O
.	O
</s>
<s>
Listening	O
to	O
this	O
signal	O
,	O
trained	O
radar	B-Application
operators	O
can	O
identify	O
various	O
pieces	O
of	O
information	O
about	O
the	O
illuminated	O
target	O
,	O
such	O
as	O
the	O
type	O
of	O
vehicle	O
it	O
is	O
,	O
the	O
size	O
of	O
the	O
target	O
,	O
and	O
can	O
potentially	O
even	O
distinguish	O
biological	O
targets	O
.	O
</s>
<s>
Several	O
classifications	O
schemes	O
that	O
have	O
been	O
developed	O
use	O
features	O
of	O
the	O
baseband	B-Algorithm
signal	I-Algorithm
that	O
have	O
been	O
used	O
in	O
other	O
audio	O
applications	O
such	O
as	O
speech	B-Application
recognition	I-Application
.	O
</s>
<s>
Radar	B-Application
determines	O
the	O
distance	O
an	O
object	O
is	O
away	O
by	O
timing	O
how	O
long	O
it	O
takes	O
the	O
transmitted	O
signal	O
to	O
return	O
from	O
the	O
target	O
that	O
is	O
illuminated	O
by	O
this	O
signal	O
.	O
</s>
<s>
Fourier	B-Algorithm
transform	I-Algorithm
analysis	O
of	O
this	O
signal	O
is	O
not	O
sufficient	O
since	O
the	O
Fourier	B-Algorithm
transform	I-Algorithm
cannot	O
account	O
for	O
the	O
time	O
varying	O
component	O
.	O
</s>
<s>
The	O
simplest	O
method	O
to	O
obtain	O
a	O
function	O
of	O
frequency	O
and	O
time	O
is	O
to	O
use	O
the	O
short-time	B-Algorithm
Fourier	I-Algorithm
transform	I-Algorithm
(	O
STFT	B-Algorithm
)	O
.	O
</s>
<s>
However	O
,	O
more	O
robust	O
methods	O
such	O
as	O
the	O
Gabor	B-Algorithm
transform	I-Algorithm
or	O
the	O
Wigner	O
distribution	O
function	O
(	O
WVD	O
)	O
can	O
be	O
used	O
to	O
provide	O
a	O
simultaneous	O
representation	O
of	O
the	O
frequency	O
and	O
time	O
domain	O
.	O
</s>
<s>
This	O
is	O
done	O
by	O
modeling	O
the	O
received	O
signal	O
then	O
using	O
a	O
statistical	O
estimation	O
method	O
such	O
as	O
maximum	O
likelihood	O
(	O
ML	O
)	O
,	O
majority	O
voting	O
(	O
MV	O
)	O
or	O
maximum	B-General_Concept
a	I-General_Concept
posteriori	I-General_Concept
(	O
MAP	O
)	O
to	O
make	O
a	O
decision	O
about	O
which	O
target	O
in	O
the	O
library	O
best	O
fits	O
the	O
model	O
built	O
using	O
the	O
received	O
signal	O
.	O
</s>
<s>
Studies	O
have	O
been	O
done	O
that	O
take	O
audio	O
features	O
used	O
in	O
speech	B-Application
recognition	I-Application
to	O
build	O
automated	B-Algorithm
target	I-Algorithm
recognition	I-Algorithm
systems	O
that	O
will	O
identify	O
targets	O
based	O
on	O
these	O
audio	O
inspired	O
coefficients	O
.	O
</s>
<s>
Mel-frequency	B-Algorithm
cepstral	I-Algorithm
coefficients	I-Algorithm
(	O
MFCC	O
)	O
.	O
</s>
<s>
The	O
baseband	B-Algorithm
signal	I-Algorithm
is	O
processed	O
to	O
obtain	O
these	O
coefficients	O
,	O
then	O
a	O
statistical	O
process	O
is	O
used	O
to	O
decide	O
which	O
target	O
in	O
the	O
database	O
is	O
most	O
similar	O
to	O
the	O
coefficients	O
obtained	O
.	O
</s>
<s>
A	O
wide	O
range	O
of	O
features	O
and	O
detection	B-General_Concept
algorithms	O
can	O
be	O
used	O
to	O
accomplish	O
ATR	O
.	O
</s>
<s>
In	O
order	O
for	O
detection	B-General_Concept
of	O
targets	O
to	O
be	O
automated	O
,	O
a	O
training	O
database	O
needs	O
to	O
be	O
created	O
.	O
</s>
<s>
An	O
example	O
of	O
a	O
detection	B-General_Concept
algorithm	O
is	O
shown	O
in	O
the	O
flowchart	O
.	O
</s>
<s>
Convolutional	B-Architecture
neural	I-Architecture
network	I-Architecture
(	O
CNN	B-Architecture
)	O
-based	O
target	B-Algorithm
recognition	I-Algorithm
is	O
able	O
to	O
outperform	O
the	O
conventional	O
methods	O
.	O
</s>
<s>
The	O
overall	O
CNN	B-Architecture
networks	O
structure	O
contains	O
7	O
convolution	O
layers	O
,	O
3	O
max	O
pooling	O
layers	O
and	O
a	O
Softmax	O
layer	O
as	O
output	O
.	O
</s>
