<s>
A	O
radar	B-Algorithm
tracker	I-Algorithm
is	O
a	O
component	O
of	O
a	O
radar	B-Application
system	I-Application
,	O
or	O
an	O
associated	O
command	O
and	O
control	O
(	O
C2	O
)	O
system	O
,	O
that	O
associates	O
consecutive	O
radar	B-Application
observations	O
of	O
the	O
same	O
target	O
into	O
tracks	O
.	O
</s>
<s>
It	O
is	O
particularly	O
useful	O
when	O
the	O
radar	B-Application
system	I-Application
is	O
reporting	O
data	O
from	O
several	O
different	O
targets	O
or	O
when	O
it	O
is	O
necessary	O
to	O
combine	O
the	O
data	O
from	O
several	O
different	O
radars	B-Application
or	O
other	O
sensors	O
.	O
</s>
<s>
A	O
classical	O
rotating	O
air	O
surveillance	O
radar	B-Application
system	I-Application
detects	O
target	O
echoes	O
against	O
a	O
background	O
of	O
noise	O
.	O
</s>
<s>
In	O
addition	O
,	O
noise	O
in	O
the	O
radar	B-Application
receiver	O
will	O
occasionally	O
exceed	O
the	O
detection	O
threshold	O
of	O
the	O
radar	B-Application
's	O
Constant	B-Algorithm
false	I-Algorithm
alarm	I-Algorithm
rate	I-Algorithm
detector	O
and	O
be	O
incorrectly	O
reported	O
as	O
targets	O
(	O
known	O
as	O
false	B-Error_Name
alarms	I-Error_Name
)	O
.	O
</s>
<s>
The	O
role	O
of	O
the	O
radar	B-Algorithm
tracker	I-Algorithm
is	O
to	O
monitor	O
consecutive	O
updates	O
from	O
the	O
radar	B-Application
system	I-Application
(	O
which	O
typically	O
occur	O
once	O
every	O
few	O
seconds	O
,	O
as	O
the	O
antenna	O
rotates	O
)	O
and	O
to	O
determine	O
those	O
sequences	O
of	O
plots	O
belonging	O
to	O
the	O
same	O
target	O
,	O
whilst	O
rejecting	O
any	O
plots	O
believed	O
to	O
be	O
false	B-Error_Name
alarms	I-Error_Name
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
radar	B-Algorithm
tracker	I-Algorithm
is	O
able	O
to	O
use	O
the	O
sequence	O
of	O
plots	O
to	O
estimate	O
the	O
current	O
speed	O
and	O
heading	O
of	O
the	O
target	O
.	O
</s>
<s>
When	O
several	O
targets	O
are	O
present	O
,	O
the	O
radar	B-Algorithm
tracker	I-Algorithm
aims	O
to	O
provide	O
one	O
track	O
for	O
each	O
target	O
,	O
with	O
the	O
track	O
history	O
often	O
being	O
used	O
to	O
indicate	O
where	O
the	O
target	O
has	O
come	O
from	O
.	O
</s>
<s>
When	O
multiple	O
radar	B-Application
systems	I-Application
are	O
connected	O
to	O
a	O
single	O
reporting	O
post	O
,	O
a	O
multiradar	B-Algorithm
tracker	I-Algorithm
is	O
often	O
used	O
to	O
monitor	O
the	O
updates	O
from	O
all	O
of	O
the	O
radars	B-Application
and	O
form	O
tracks	O
from	O
the	O
combination	O
of	O
detections	O
.	O
</s>
<s>
In	O
this	O
configuration	O
,	O
the	O
tracks	O
are	O
often	O
more	O
accurate	O
than	O
those	O
formed	O
from	O
single	O
radars	B-Application
,	O
as	O
a	O
greater	O
number	O
of	O
detections	O
can	O
be	O
used	O
to	O
estimate	O
the	O
tracks	O
.	O
</s>
<s>
In	O
addition	O
to	O
associating	O
plots	O
,	O
rejecting	O
false	B-Error_Name
alarms	I-Error_Name
and	O
estimating	O
heading	O
and	O
speed	O
,	O
the	O
radar	B-Algorithm
tracker	I-Algorithm
also	O
acts	O
as	O
a	O
filter	O
,	O
in	O
which	O
errors	O
in	O
the	O
individual	O
radar	B-Application
measurements	O
are	O
smoothed	O
out	O
.	O
</s>
<s>
In	O
essence	O
,	O
the	O
radar	B-Algorithm
tracker	I-Algorithm
fits	O
a	O
smooth	O
curve	O
to	O
the	O
reported	O
plots	O
and	O
,	O
if	O
done	O
correctly	O
,	O
can	O
increase	O
the	O
overall	O
accuracy	O
of	O
the	O
radar	B-Application
system	I-Application
.	O
</s>
<s>
A	O
multisensor	B-Algorithm
tracker	I-Algorithm
extends	O
the	O
concept	O
of	O
the	O
multiradar	B-Algorithm
tracker	I-Algorithm
to	O
allow	O
the	O
combination	O
of	O
reports	O
from	O
different	O
types	O
of	O
sensor	O
-	O
typically	O
radars	B-Application
,	O
secondary	O
surveillance	O
radars	B-Application
(	O
SSR	O
)	O
,	O
identification	B-Device
friend	I-Device
or	I-Device
foe	I-Device
(	O
IFF	B-Device
)	O
systems	O
and	O
electronic	O
support	O
measures	O
(	O
ESM	O
)	O
data	O
.	O
</s>
<s>
A	O
radar	B-Application
track	O
will	O
typically	O
contain	O
the	O
following	O
information	O
:	O
</s>
<s>
There	O
are	O
many	O
different	O
mathematical	O
algorithms	O
used	O
for	O
implementing	O
a	O
radar	B-Algorithm
tracker	I-Algorithm
,	O
of	O
varying	O
levels	O
of	O
sophistication	O
.	O
</s>
<s>
However	O
,	O
they	O
all	O
perform	O
steps	O
similar	O
to	O
the	O
following	O
every	O
time	O
the	O
radar	B-Application
updates	O
:	O
</s>
<s>
Using	O
this	O
information	O
,	O
the	O
radar	B-Algorithm
tracker	I-Algorithm
attempts	O
to	O
update	O
the	O
track	O
by	O
forming	O
a	O
weighted	O
average	O
of	O
the	O
current	O
reported	O
position	O
from	O
the	O
radar	B-Application
(	O
which	O
has	O
unknown	O
errors	O
)	O
and	O
the	O
last	O
predicted	O
position	O
of	O
the	O
target	O
from	O
the	O
tracker	O
(	O
which	O
also	O
has	O
unknown	O
errors	O
)	O
.	O
</s>
<s>
unknown	O
target	O
movement	O
models	O
)	O
,	O
non-Gaussian	O
measurement	O
or	O
model	O
errors	O
,	O
non-linear	O
relationships	O
between	O
the	O
measured	O
quantities	O
and	O
the	O
desired	O
target	O
coordinates	O
,	O
detection	O
in	O
the	O
presence	O
of	O
non-uniformly	O
distributed	O
clutter	O
,	O
missed	O
detections	O
or	O
false	B-Error_Name
alarms	I-Error_Name
.	O
</s>
<s>
In	O
the	O
real	O
world	O
,	O
a	O
radar	B-Algorithm
tracker	I-Algorithm
typically	O
faces	O
a	O
combination	O
of	O
all	O
of	O
these	O
effects	O
;	O
this	O
has	O
led	O
to	O
the	O
development	O
of	O
an	O
increasingly	O
sophisticated	O
set	O
of	O
algorithms	O
to	O
resolve	O
the	O
problem	O
.	O
</s>
<s>
Due	O
to	O
the	O
need	O
to	O
form	O
radar	B-Application
tracks	O
in	O
real	O
time	O
,	O
usually	O
for	O
several	O
hundred	O
targets	O
at	O
once	O
,	O
the	O
deployment	O
of	O
radar	B-Application
tracking	O
algorithms	O
has	O
typically	O
been	O
limited	O
by	O
the	O
available	O
computational	O
power	O
.	O
</s>
<s>
In	O
this	O
step	O
of	O
the	O
processing	O
,	O
the	O
radar	B-Algorithm
tracker	I-Algorithm
seeks	O
to	O
determine	O
which	O
plots	O
should	O
be	O
used	O
to	O
update	O
which	O
tracks	O
.	O
</s>
<s>
By	O
a	O
statistical	O
approach	O
,	O
such	O
as	O
the	O
Probabilistic	B-Algorithm
Data	I-Algorithm
Association	I-Algorithm
Filter	I-Algorithm
(	O
PDAF	O
)	O
or	O
the	O
Joint	B-Algorithm
Probabilistic	I-Algorithm
Data	I-Algorithm
Association	I-Algorithm
Filter	I-Algorithm
(	O
JPDAF	B-Algorithm
)	O
that	O
choose	O
the	O
most	O
probable	O
location	O
of	O
plot	O
through	O
a	O
statistical	O
combination	O
of	O
all	O
the	O
likely	O
plots	O
.	O
</s>
<s>
This	O
approach	O
has	O
been	O
shown	O
to	O
be	O
good	O
in	O
situations	O
of	O
high	O
radar	B-Application
clutter	O
.	O
</s>
<s>
Track	O
initiation	O
is	O
the	O
process	O
of	O
creating	O
a	O
new	O
radar	B-Application
track	O
from	O
an	O
unassociated	O
radar	B-Application
plot	O
.	O
</s>
<s>
When	O
the	O
tracker	O
is	O
first	O
switched	O
on	O
,	O
all	O
the	O
initial	O
radar	B-Application
plots	O
are	O
used	O
to	O
create	O
new	O
tracks	O
,	O
but	O
once	O
the	O
tracker	O
is	O
running	O
,	O
only	O
those	O
plots	O
that	O
could	O
n't	O
be	O
used	O
to	O
update	O
an	O
existing	O
track	O
are	O
used	O
to	O
spawn	O
new	O
tracks	O
.	O
</s>
<s>
Typically	O
a	O
new	O
track	O
is	O
given	O
the	O
status	O
of	O
tentative	O
until	O
plots	O
from	O
subsequent	O
radar	B-Application
updates	O
have	O
been	O
successfully	O
associated	O
with	O
the	O
new	O
track	O
.	O
</s>
<s>
The	O
most	O
common	O
criterion	O
for	O
promoting	O
a	O
tentative	O
track	O
to	O
a	O
confirmed	O
track	O
is	O
the	O
"	O
M-of-N	O
rule	O
"	O
,	O
which	O
states	O
that	O
during	O
the	O
last	O
N	O
radar	B-Application
updates	O
,	O
at	O
least	O
M	O
plots	O
must	O
have	O
been	O
associated	O
with	O
the	O
tentative	O
track	O
-	O
with	O
M	O
=3	O
and	O
N	O
=	O
5	O
being	O
typical	O
values	O
.	O
</s>
<s>
If	O
a	O
track	O
was	O
not	O
associated	O
with	O
a	O
plot	O
during	O
the	O
plot	O
to	O
track	O
association	O
phase	O
,	O
then	O
there	O
is	O
a	O
chance	O
that	O
the	O
target	O
may	O
no	O
longer	O
exist	O
(	O
for	O
instance	O
,	O
an	O
aircraft	O
may	O
have	O
landed	O
or	O
flown	O
out	O
of	O
radar	B-Application
cover	O
)	O
.	O
</s>
<s>
Alternatively	O
,	O
however	O
,	O
there	O
is	O
a	O
chance	O
that	O
the	O
radar	B-Application
may	O
have	O
just	O
failed	O
to	O
see	O
the	O
target	O
at	O
that	O
update	O
,	O
but	O
will	O
find	O
it	O
again	O
on	O
the	O
next	O
update	O
.	O
</s>
<s>
position	O
,	O
heading	O
,	O
speed	O
and	O
possibly	O
acceleration	O
)	O
of	O
the	O
target	O
and	O
predict	O
the	O
new	O
state	O
of	O
the	O
target	O
at	O
the	O
time	O
of	O
the	O
most	O
recent	O
radar	B-Application
measurement	O
.	O
</s>
<s>
It	O
then	O
forms	O
a	O
weighted	O
average	O
of	O
this	O
prediction	O
of	O
state	O
and	O
the	O
latest	O
measurement	O
of	O
state	O
,	O
taking	O
account	O
of	O
the	O
known	O
measurement	O
errors	O
of	O
the	O
radar	B-Application
and	O
its	O
own	O
uncertainty	O
in	O
the	O
target	O
motion	O
models	O
.	O
</s>
<s>
the	O
relationship	O
between	O
the	O
radar	B-Application
measurements	O
and	O
the	O
target	O
state	O
)	O
and	O
the	O
state	O
equations	O
(	O
i.e.	O
</s>
<s>
The	O
Kalman	O
filter	O
assumes	O
that	O
the	O
measurement	O
errors	O
of	O
the	O
radar	B-Application
,	O
and	O
the	O
errors	O
in	O
its	O
target	O
motion	O
model	O
,	O
and	O
the	O
errors	O
in	O
its	O
state	O
estimate	O
are	O
all	O
zero-mean	O
with	O
known	O
covariance	O
.	O
</s>
<s>
In	O
situations	O
where	O
the	O
target	O
motion	O
conforms	O
well	O
to	O
the	O
underlying	O
model	O
,	O
there	O
is	O
a	O
tendency	O
of	O
the	O
Kalman	O
filter	O
to	O
become	O
"	O
overconfident	O
"	O
of	O
its	O
own	O
predictions	O
and	O
to	O
start	O
to	O
ignore	O
the	O
radar	B-Application
measurements	O
.	O
</s>
<s>
As	O
each	O
radar	B-Application
update	O
is	O
received	O
every	O
possible	O
track	O
can	O
be	O
potentially	O
updated	O
with	O
every	O
new	O
update	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
it	O
is	O
popular	O
for	O
problems	O
of	O
ground	O
target	O
tracking	O
in	O
Airborne	B-Algorithm
Ground	I-Algorithm
Surveillance	I-Algorithm
(	O
AGS	O
)	O
systems	O
.	O
</s>
<s>
The	O
IMM	O
is	O
an	O
estimator	O
which	O
can	O
either	O
be	O
used	O
by	O
MHT	O
or	O
JPDAF	B-Algorithm
.	O
</s>
<s>
While	O
MHT	O
or	O
JPDAF	B-Algorithm
handles	O
the	O
association	O
and	O
track	O
maintenance	O
,	O
an	O
IMM	O
helps	O
MHT	O
or	O
JPDAF	B-Algorithm
in	O
obtaining	O
a	O
filtered	O
estimate	O
of	O
the	O
target	O
position	O
.	O
</s>
<s>
The	O
EKF	O
is	O
an	O
extension	O
of	O
the	O
Kalman	O
filter	O
to	O
cope	O
with	O
cases	O
where	O
the	O
relationship	O
between	O
the	O
radar	B-Application
measurements	O
and	O
the	O
track	O
coordinates	O
,	O
or	O
the	O
track	O
coordinates	O
and	O
the	O
motion	O
model	O
,	O
is	O
non-linear	O
.	O
</s>
<s>
The	O
unscented	O
Kalman	O
filter	O
and	O
particle	B-Algorithm
filters	I-Algorithm
are	O
attempts	O
to	O
overcome	O
the	O
problem	O
of	O
linearising	O
the	O
equations	O
.	O
</s>
<s>
The	O
particle	B-Algorithm
filter	I-Algorithm
could	O
be	O
considered	O
as	O
a	O
generalisation	O
of	O
the	O
UKF	O
.	O
</s>
<s>
The	O
particle	B-Algorithm
filter	I-Algorithm
is	O
notable	O
in	O
its	O
ability	O
to	O
handle	O
multi-modal	O
distributions	O
(	O
i.e.	O
</s>
