<s>
A	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
is	O
a	O
radar	B-Application
system	I-Application
that	O
determines	O
the	O
range	O
to	O
a	O
target	O
using	O
pulse-timing	O
techniques	O
,	O
and	O
uses	O
the	O
Doppler	O
effect	O
of	O
the	O
returned	O
signal	O
to	O
determine	O
the	O
target	O
object	O
's	O
velocity	O
.	O
</s>
<s>
It	O
combines	O
the	O
features	O
of	O
pulse	O
radars	B-Application
and	O
continuous-wave	B-Algorithm
radars	I-Algorithm
,	O
which	O
were	O
formerly	O
separate	O
due	O
to	O
the	O
complexity	O
of	O
the	O
electronics	O
.	O
</s>
<s>
The	O
first	O
operational	O
Pulse	B-Algorithm
Doppler	I-Algorithm
radar	I-Algorithm
was	O
in	O
the	O
CIM-10	O
Bomarc	O
,	O
an	O
American	O
long	O
range	O
supersonic	O
missile	O
powered	O
by	O
ramjet	O
engines	O
,	O
and	O
which	O
was	O
armed	O
with	O
a	O
W40	O
nuclear	O
weapon	O
to	O
destroy	O
entire	O
formations	O
of	O
attacking	O
enemy	O
aircraft	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
systems	O
were	O
first	O
widely	O
used	O
on	O
fighter	O
aircraft	O
starting	O
in	O
the	O
1960s	O
.	O
</s>
<s>
Earlier	O
radars	B-Application
had	O
used	O
pulse-timing	O
in	O
order	O
to	O
determine	O
range	O
and	O
the	O
angle	O
of	O
the	O
antenna	O
(	O
or	O
similar	O
means	O
)	O
to	O
determine	O
the	O
bearing	O
.	O
</s>
<s>
However	O
,	O
this	O
only	O
worked	O
when	O
the	O
radar	B-Application
antenna	O
was	O
not	O
pointed	O
down	O
;	O
in	O
that	O
case	O
the	O
reflection	O
off	O
the	O
ground	O
overwhelmed	O
any	O
returns	O
from	O
other	O
objects	O
.	O
</s>
<s>
This	O
gives	O
pulse-Doppler	B-Algorithm
radars	I-Algorithm
"	O
look-down/shoot	O
-down	O
"	O
capability	O
.	O
</s>
<s>
A	O
secondary	O
advantage	O
in	O
military	O
radar	B-Application
is	O
to	O
reduce	O
the	O
transmitted	O
power	O
while	O
achieving	O
acceptable	O
performance	O
for	O
improved	O
safety	O
of	O
stealthy	O
radar	B-Application
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
techniques	O
also	O
find	O
widespread	O
use	O
in	O
meteorological	B-Application
radars	I-Application
,	O
allowing	O
the	O
radar	B-Application
to	O
determine	O
wind	O
speed	O
from	O
the	O
velocity	O
of	O
any	O
precipitation	O
in	O
the	O
air	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
is	O
also	O
the	O
basis	O
of	O
synthetic	B-Application
aperture	I-Application
radar	I-Application
used	O
in	O
radar	B-Algorithm
astronomy	I-Algorithm
,	O
remote	B-Application
sensing	I-Application
and	O
mapping	O
.	O
</s>
<s>
In	O
air	B-Application
traffic	I-Application
control	I-Application
,	O
they	O
are	O
used	O
for	O
discriminating	O
aircraft	O
from	O
clutter	O
.	O
</s>
<s>
Besides	O
the	O
above	O
conventional	O
surveillance	O
applications	O
,	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
has	O
been	O
successfully	O
applied	O
in	O
healthcare	O
,	O
such	O
as	O
fall	O
risk	O
assessment	O
and	O
fall	O
detection	O
,	O
for	O
nursing	O
or	O
clinical	O
purposes	O
.	O
</s>
<s>
The	O
earliest	O
radar	B-Application
systems	I-Application
failed	O
to	O
operate	O
as	O
expected	O
.	O
</s>
<s>
Doppler	O
weather	O
effects	O
(	O
precipitation	O
)	O
were	O
also	O
found	O
to	O
degrade	O
conventional	B-Application
radar	I-Application
and	O
moving	O
target	O
indicator	O
radar	B-Application
,	O
which	O
can	O
mask	O
aircraft	O
reflections	O
.	O
</s>
<s>
This	O
phenomenon	O
was	O
adapted	O
for	O
use	O
with	O
weather	B-Application
radar	I-Application
in	O
the	O
1950s	O
after	O
declassification	O
of	O
some	O
World	O
War	O
II	O
systems	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
was	O
developed	O
during	O
World	O
War	O
II	O
to	O
overcome	O
limitations	O
by	O
increasing	O
pulse	O
repetition	O
frequency	O
.	O
</s>
<s>
Early	O
pulse-dopplers	B-Algorithm
were	O
incompatible	O
with	O
other	O
high	O
power	O
microwave	O
amplification	O
devices	O
that	O
are	O
not	O
coherent	O
,	O
but	O
more	O
sophisticated	O
techniques	O
were	O
developed	O
that	O
record	O
the	O
phase	O
of	O
each	O
transmitted	O
pulse	O
for	O
comparison	O
to	O
returned	O
echoes	O
.	O
</s>
<s>
The	O
Hughes	B-Device
AN/ASG	I-Device
-18	I-Device
Fire	I-Device
Control	I-Device
System	I-Device
was	O
a	O
prototype	O
airborne	O
radar/combination	O
system	O
for	O
the	O
planned	O
North	O
American	O
XF-108	O
Rapier	O
interceptor	O
aircraft	O
for	O
the	O
United	O
States	O
Air	O
Force	O
,	O
and	O
later	O
for	O
the	O
Lockheed	O
YF-12	O
.	O
</s>
<s>
The	O
US	O
's	O
first	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
,	O
the	O
system	O
had	O
look-down/shoot	O
-down	O
capability	O
and	O
could	O
track	O
one	O
target	O
at	O
a	O
time	O
.	O
</s>
<s>
It	O
became	O
possible	O
to	O
use	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
on	O
aircraft	O
after	O
digital	O
computers	O
were	O
incorporated	O
in	O
the	O
design	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
provided	O
look-down/shoot	O
-down	O
capability	O
to	O
support	O
air-to-air	O
missile	O
systems	O
in	O
most	O
modern	O
military	O
aircraft	O
by	O
the	O
mid	O
1970s	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
systems	O
measure	O
the	O
range	O
to	O
objects	O
by	O
measuring	O
the	O
elapsed	O
time	O
between	O
sending	O
a	O
pulse	O
of	O
radio	O
energy	O
and	O
receiving	O
a	O
reflection	O
of	O
the	O
object	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
is	O
based	O
on	O
the	O
Doppler	O
effect	O
,	O
where	O
movement	O
in	O
range	O
produces	O
frequency	O
shift	O
on	O
the	O
signal	O
reflected	O
from	O
the	O
target	O
.	O
</s>
<s>
Radial	O
velocity	O
is	O
essential	O
for	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
operation	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radars	I-Algorithm
exploit	O
this	O
phenomenon	O
to	O
improve	O
performance	O
.	O
</s>
<s>
is	O
the	O
distance	O
radar	B-Application
to	O
target	O
,	O
</s>
<s>
is	O
the	O
radar	B-Application
wavelength	O
,	O
</s>
<s>
This	O
allows	O
the	O
radar	B-Application
to	O
separate	O
the	O
reflections	O
from	O
multiple	O
objects	O
located	O
in	O
the	O
same	O
volume	O
of	O
space	O
by	O
separating	O
the	O
objects	O
using	O
a	O
spread	B-Architecture
spectrum	I-Architecture
to	O
segregate	O
different	O
signals	O
:	O
</s>
<s>
Rejection	O
speed	O
is	O
selectable	O
on	O
pulse-Doppler	B-Algorithm
aircraft-detection	O
systems	O
so	O
nothing	O
below	O
that	O
speed	O
will	O
be	O
detected	B-Algorithm
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
uses	O
the	O
following	O
signal	O
processing	O
criteria	O
to	O
exclude	O
unwanted	O
signals	O
from	O
slow-moving	O
objects	O
.	O
</s>
<s>
The	O
velocity	O
threshold	O
is	O
much	O
lower	O
for	O
weather	B-Application
radar	I-Application
.	O
</s>
<s>
In	O
airborne	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
,	O
the	O
velocity	O
threshold	O
is	O
offset	O
by	O
the	O
speed	O
of	O
the	O
aircraft	O
relative	O
to	O
the	O
ground	O
.	O
</s>
<s>
Surface	O
reflections	O
appear	O
in	O
almost	O
all	O
radar	B-Application
.	O
</s>
<s>
Ground	O
clutter	O
generally	O
appears	O
in	O
a	O
circular	O
region	O
within	O
a	O
radius	O
of	O
about	O
near	O
ground-based	O
radar	B-Application
.	O
</s>
<s>
This	O
distance	O
extends	O
much	O
further	O
in	O
airborne	O
and	O
space	O
radar	B-Application
.	O
</s>
<s>
Clutter	O
includes	O
weather	O
in	O
radar	B-Application
intended	O
to	O
detect	O
and	O
report	O
aircraft	O
and	O
spacecraft	O
.	O
</s>
<s>
Clutter	O
creates	O
a	O
vulnerability	O
region	O
in	O
pulse-amplitude	O
time-domain	O
radar	B-Application
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
corrects	O
this	O
as	O
follows	O
.	O
</s>
<s>
Allows	O
the	O
radar	B-Application
antenna	O
to	O
be	O
pointed	O
directly	O
at	O
the	O
ground	O
without	O
overwhelming	O
the	O
computer	O
and	O
without	O
reducing	O
sensitivity	O
.	O
</s>
<s>
Fills	O
in	O
the	O
vulnerability	O
region	O
associated	O
with	O
pulse-amplitude	O
time-domain	O
radar	B-Application
for	O
small	O
object	O
detection	O
near	O
terrain	O
and	O
weather	O
.	O
</s>
<s>
Clutter	O
rejection	O
capability	O
of	O
about	O
60dB	O
is	O
needed	O
for	O
look-down/shoot	O
-down	O
capability	O
,	O
and	O
pulse-Doppler	B-Algorithm
is	O
the	O
only	O
strategy	O
that	O
can	O
satisfy	O
this	O
requirement	O
.	O
</s>
<s>
Pulse	B-Algorithm
compression	I-Algorithm
,	O
and	O
moving	O
target	O
indicator	O
(	O
MTI	O
)	O
provide	O
up	O
to	O
25dB	O
sub-clutter	O
visibility	O
.	O
</s>
<s>
Aircraft	O
and	O
some	O
missiles	O
exploit	O
this	O
weakness	O
using	O
a	O
technique	O
called	O
flying	O
below	O
the	O
radar	B-Application
to	O
avoid	O
detection	O
(	O
Nap-of-the-earth	O
)	O
.	O
</s>
<s>
This	O
flying	O
technique	O
is	O
ineffective	O
against	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
provides	O
an	O
advantage	O
when	O
attempting	O
to	O
detect	O
missiles	O
and	O
low	O
observability	O
aircraft	O
flying	O
near	O
terrain	O
,	O
sea	O
surface	O
,	O
and	O
weather	O
.	O
</s>
<s>
Audible	O
Doppler	O
and	O
target	O
size	O
support	O
passive	O
vehicle	O
type	O
classification	O
when	O
identification	B-Device
friend	I-Device
or	I-Device
foe	I-Device
is	O
not	O
available	O
from	O
a	O
transponder	O
signal	O
.	O
</s>
<s>
This	O
means	O
a	O
helicopter	B-Application
sounds	O
like	O
a	O
helicopter	B-Application
,	O
a	O
jet	O
sounds	O
like	O
a	O
jet	O
,	O
and	O
propeller	O
aircraft	O
sound	O
like	O
propellers	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
by	O
itself	O
can	O
be	O
too	O
slow	O
to	O
cover	O
the	O
entire	O
volume	O
of	O
space	O
above	O
the	O
horizon	O
unless	O
fan	O
beam	O
is	O
used	O
.	O
</s>
<s>
This	O
approach	O
is	O
used	O
with	O
the	O
AN/SPS	O
49(V )	O
5	O
Very	O
Long	O
Range	O
Air	O
Surveillance	O
Radar	B-Application
,	O
which	O
sacrifices	O
elevation	O
measurement	O
to	O
gain	O
speed	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
antenna	O
motion	O
must	O
be	O
slow	O
enough	O
so	O
that	O
all	O
the	O
return	O
signals	O
from	O
at	O
least	O
3	O
different	O
PRFs	O
can	O
be	O
processed	O
out	O
to	O
the	O
maximum	O
anticipated	O
detection	O
range	O
.	O
</s>
<s>
This	O
is	O
known	O
as	O
dwell	B-Algorithm
time	I-Algorithm
.	O
</s>
<s>
Antenna	O
motion	O
for	O
pulse-Doppler	B-Algorithm
must	O
be	O
as	O
slow	O
as	O
radar	B-Application
using	O
MTI	O
.	O
</s>
<s>
Search	O
radar	B-Application
that	O
include	O
pulse-Doppler	B-Algorithm
are	O
usually	O
dual	O
mode	O
because	O
best	O
overall	O
performance	O
is	O
achieved	O
when	O
pulse-Doppler	B-Algorithm
is	O
used	O
for	O
areas	O
with	O
high	O
false	O
alarm	O
rates	O
(	O
horizon	O
or	O
below	O
and	O
weather	O
)	O
,	O
while	O
conventional	B-Application
radar	I-Application
will	O
scan	O
faster	O
in	O
free-space	O
where	O
false	O
alarm	O
rate	O
is	O
low	O
(	O
above	O
horizon	O
with	O
clear	O
skies	O
)	O
.	O
</s>
<s>
The	O
antenna	O
type	O
is	O
an	O
important	O
consideration	O
for	O
multi-mode	O
radar	B-Application
because	O
undesirable	O
phase	O
shift	O
introduced	O
by	O
the	O
radar	B-Application
antenna	O
can	O
degrade	O
performance	O
measurements	O
for	O
sub-clutter	O
visibility	O
.	O
</s>
<s>
The	O
signal	O
processing	O
enhancement	O
of	O
pulse-Doppler	B-Algorithm
allows	O
small	O
high-speed	O
objects	O
to	O
be	O
detected	B-Algorithm
in	O
close	O
proximity	O
to	O
large	O
slow	O
moving	O
reflectors	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
signal	I-Algorithm
processing	I-Algorithm
also	O
includes	O
ambiguity	O
resolution	O
to	O
identify	O
true	O
range	O
and	O
velocity	O
.	O
</s>
<s>
The	O
received	O
signals	O
from	O
multiple	O
PRF	O
are	O
compared	O
to	O
determine	O
true	O
range	O
using	O
the	O
range	B-Algorithm
ambiguity	I-Algorithm
resolution	I-Algorithm
process	O
.	O
</s>
<s>
The	O
received	O
signals	O
are	O
also	O
compared	O
using	O
the	O
frequency	B-Algorithm
ambiguity	I-Algorithm
resolution	I-Algorithm
process	O
.	O
</s>
<s>
The	O
range	O
resolution	O
is	O
the	O
minimal	O
range	O
separation	O
between	O
two	O
objects	O
traveling	O
at	O
the	O
same	O
speed	O
before	O
the	O
radar	B-Application
can	O
detect	O
two	O
discrete	O
reflections	O
:	O
</s>
<s>
The	O
velocity	O
resolution	O
is	O
the	O
minimal	O
radial	O
velocity	O
difference	O
between	O
two	O
objects	O
traveling	O
at	O
the	O
same	O
range	O
before	O
the	O
radar	B-Application
can	O
detect	O
two	O
discrete	O
reflections	O
:	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
has	O
special	O
requirements	O
that	O
must	O
be	O
satisfied	O
to	O
achieve	O
acceptable	O
performance	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
typically	O
uses	O
medium	O
pulse	O
repetition	O
frequency	O
(	O
PRF	O
)	O
from	O
about	O
3kHz	O
to	O
30kHz	O
.	O
</s>
<s>
Radar	B-Application
systems	I-Application
require	O
angular	O
measurement	O
.	O
</s>
<s>
Transponders	O
are	O
not	O
normally	O
associated	O
with	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
,	O
so	O
sidelobe	O
suppression	O
is	O
required	O
for	O
practical	O
operation	O
.	O
</s>
<s>
Tracking	O
radar	B-Application
systems	I-Application
use	O
angle	O
error	O
to	O
improve	O
accuracy	O
by	O
producing	O
measurements	O
perpendicular	O
to	O
the	O
radar	B-Application
antenna	O
beam	O
.	O
</s>
<s>
The	O
two	O
angle	O
error	O
techniques	O
used	O
with	O
tracking	O
radar	B-Application
are	O
monopulse	B-Algorithm
and	O
conical	O
scan	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
requires	O
a	O
coherent	O
oscillator	O
with	O
very	O
little	O
noise	O
.	O
</s>
<s>
Cavity	B-Architecture
magnetron	I-Architecture
and	O
crossed-field	O
amplifier	O
are	O
not	O
appropriate	O
because	O
noise	O
introduced	O
by	O
these	O
devices	O
interfere	O
with	O
detection	O
performance	O
.	O
</s>
<s>
The	O
only	O
amplification	O
devices	O
suitable	O
for	O
pulse-Doppler	B-Algorithm
are	O
klystron	O
,	O
traveling	O
wave	O
tube	O
,	O
and	O
solid	O
state	O
devices	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
signal	I-Algorithm
processing	I-Algorithm
introduces	O
a	O
phenomenon	O
called	O
scalloping	O
.	O
</s>
<s>
Scalloping	O
for	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
involves	O
blind	O
velocities	O
created	O
by	O
the	O
clutter	O
rejection	O
filter	O
.	O
</s>
<s>
Ringing	B-Algorithm
artifacts	I-Algorithm
pose	O
a	O
problem	O
with	O
search	O
,	O
detection	O
,	O
and	O
ambiguity	O
resolution	O
in	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
.	O
</s>
<s>
Second	O
,	O
the	O
shape	O
of	O
the	O
receive	O
pulse	O
is	O
adjusted	O
using	O
a	O
window	B-Language
function	I-Language
that	O
minimizes	O
ringing	O
that	O
occurs	O
any	O
time	O
pulses	O
are	O
applied	O
to	O
a	O
filter	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
is	O
generally	O
limited	O
to	O
mechanically	O
aimed	O
antennas	O
and	O
active	O
phased	O
arrays	O
.	O
</s>
<s>
Phase	B-Algorithm
shifter	I-Algorithm
settling	O
time	O
on	O
the	O
order	O
of	O
50ns	O
is	O
required	O
.	O
</s>
<s>
Most	O
antenna	O
phase	B-Algorithm
shifters	I-Algorithm
operating	O
at	O
PRF	O
above	O
1kHz	O
introduce	O
spurious	O
phase	O
shift	O
unless	O
special	O
provisions	O
are	O
made	O
,	O
such	O
as	O
reducing	O
phase	B-Algorithm
shifter	I-Algorithm
settling	O
time	O
to	O
a	O
few	O
dozen	O
nanoseconds	O
.	O
</s>
<s>
The	O
following	O
gives	O
the	O
maximum	O
permissible	O
settling	O
time	O
for	O
antenna	O
phase	B-Algorithm
shift	I-Algorithm
modules	I-Algorithm
.	O
</s>
<s>
T	O
=	O
phase	B-Algorithm
shifter	I-Algorithm
settling	O
time	O
,	O
</s>
<s>
The	O
antenna	O
type	O
and	O
scan	O
performance	O
is	O
a	O
practical	O
consideration	O
for	O
multi-mode	O
radar	B-Application
systems	I-Application
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
can	O
be	O
so	O
sensitive	O
that	O
diffraction	O
from	O
mountains	O
,	O
buildings	O
or	O
wave	O
tops	O
can	O
be	O
used	O
to	O
detect	O
fast	O
moving	O
objects	O
otherwise	O
blocked	O
by	O
solid	O
obstruction	O
along	O
the	O
line	O
of	O
sight	O
.	O
</s>
<s>
This	O
is	O
a	O
very	O
lossy	O
phenomenon	O
that	O
only	O
becomes	O
possible	O
when	O
radar	B-Application
has	O
significant	O
excess	O
sub-clutter	O
visibility	O
.	O
</s>
<s>
Refraction	O
and	O
ducting	O
use	O
transmit	O
frequency	O
at	O
L-band	B-Algorithm
or	O
lower	O
to	O
extend	O
the	O
horizon	O
,	O
which	O
is	O
very	O
different	O
from	O
diffraction	O
.	O
</s>
<s>
Refraction	O
for	O
over-the-horizon	B-Architecture
radar	I-Architecture
uses	O
variable	O
density	O
in	O
the	O
air	O
column	O
above	O
the	O
surface	O
of	O
the	O
earth	O
to	O
bend	O
RF	O
signals	O
.	O
</s>
<s>
Subclutter	O
visibility	O
is	O
the	O
ratio	O
of	O
the	O
smallest	O
signal	O
that	O
can	O
be	O
detected	B-Algorithm
in	O
the	O
presence	O
of	O
a	O
larger	O
signal	O
.	O
</s>
<s>
A	O
small	O
fast-moving	O
target	O
reflection	O
can	O
be	O
detected	B-Algorithm
in	O
the	O
presence	O
of	O
larger	O
slow-moving	O
clutter	O
reflections	O
when	O
the	O
following	O
is	O
true	O
:	O
</s>
<s>
The	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
equation	O
can	O
be	O
used	O
to	O
understand	O
trade-offs	O
between	O
different	O
design	O
constraints	O
,	O
like	O
power	O
consumption	O
,	O
detection	O
range	O
,	O
and	O
microwave	O
safety	O
hazards	O
.	O
</s>
<s>
σ	O
=	O
radar	B-Application
cross	O
section	O
,	O
or	O
scattering	O
coefficient	O
,	O
of	O
the	O
target	O
,	O
</s>
<s>
B	O
=	O
receiver	O
bandwidth	B-Algorithm
(	O
band-pass	O
filter	O
)	O
,	O
</s>
<s>
This	O
equation	O
is	O
derived	O
by	O
combining	O
the	O
radar	B-Application
equation	O
with	O
the	O
noise	O
equation	O
and	O
accounting	O
for	O
in-band	O
noise	O
distribution	O
across	O
multiple	O
detection	O
filters	O
.	O
</s>
<s>
The	O
value	O
D	O
is	O
added	O
to	O
the	O
standard	O
radar	B-Application
range	O
equation	O
to	O
account	O
for	O
both	O
pulse-Doppler	B-Algorithm
signal	I-Algorithm
processing	I-Algorithm
and	O
transmitter	O
FM	O
noise	O
reduction	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
signal	I-Algorithm
processing	I-Algorithm
integrates	O
all	O
of	O
the	O
energy	O
from	O
all	O
of	O
the	O
individual	O
reflected	O
pulses	O
that	O
enter	O
the	O
filter	O
.	O
</s>
<s>
This	O
means	O
a	O
pulse-Doppler	B-Algorithm
signal	I-Algorithm
processing	I-Algorithm
system	O
with	O
1024	O
elements	O
provides	O
30.103dB	O
of	O
improvement	O
due	O
to	O
the	O
type	O
of	O
signal	O
processing	O
that	O
must	O
be	O
used	O
with	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
.	O
</s>
<s>
These	O
improvements	O
are	O
the	O
reason	O
pulse-Doppler	B-Algorithm
is	O
essential	O
for	O
military	O
and	O
astronomy	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
for	O
aircraft	O
detection	O
has	O
two	O
modes	O
.	O
</s>
<s>
Once	O
a	O
reflection	O
has	O
been	O
detected	B-Algorithm
and	O
resolved	O
,	O
the	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
automatically	O
transitions	O
to	O
tracking	O
mode	O
for	O
the	O
volume	O
of	O
space	O
surrounding	O
the	O
track	O
.	O
</s>
<s>
Lock	O
exists	O
in	O
no	O
other	O
type	O
of	O
radar	B-Application
.	O
</s>
<s>
Lock	O
eliminates	O
the	O
need	O
for	O
human	O
intervention	O
with	O
the	O
exception	O
of	O
helicopters	B-Application
and	O
electronic	O
jamming	O
.	O
</s>
<s>
Weather	O
phenomenon	O
obey	O
adiabatic	O
process	O
associated	O
with	O
air	O
mass	O
and	O
not	O
Newtonian	O
mechanics	O
,	O
so	O
the	O
lock	O
criterion	O
is	O
not	O
normally	O
used	O
for	O
weather	B-Application
radar	I-Application
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
signal	I-Algorithm
processing	I-Algorithm
selectively	O
excludes	O
low-velocity	O
reflections	O
so	O
that	O
no	O
detections	O
occurs	O
below	O
a	O
threshold	O
velocity	O
.	O
</s>
<s>
The	O
target	O
Doppler	O
signal	O
from	O
the	O
detection	O
is	O
converted	O
from	O
frequency	O
domain	O
back	O
into	O
time	O
domain	O
sound	O
for	O
the	O
operator	O
in	O
track	O
mode	O
on	O
some	O
radar	B-Application
systems	I-Application
.	O
</s>
<s>
The	O
operator	O
uses	O
this	O
sound	O
for	O
passive	O
target	O
classification	O
,	O
such	O
as	O
recognizing	O
helicopters	B-Application
and	O
electronic	O
jamming	O
.	O
</s>
<s>
Special	O
consideration	O
is	O
required	O
for	O
aircraft	O
with	O
large	O
moving	O
parts	O
because	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
operates	O
like	O
a	O
phase-locked	O
loop	O
.	O
</s>
<s>
Blade	O
tips	O
moving	O
near	O
the	O
speed	O
of	O
sound	O
produce	O
the	O
only	O
signal	O
that	O
can	O
be	O
detected	B-Algorithm
when	O
a	O
helicopter	B-Application
is	O
moving	O
slow	O
near	O
terrain	O
and	O
weather	O
.	O
</s>
<s>
A	O
helicopter	B-Application
appears	O
like	O
a	O
rapidly	O
pulsing	O
noise	O
emitter	O
except	O
in	O
a	O
clear	O
environment	O
free	O
from	O
clutter	O
.	O
</s>
<s>
Microwave	O
Doppler	O
frequency	O
shift	O
produced	O
by	O
reflector	O
motion	O
falls	O
into	O
the	O
audible	O
sound	O
range	O
for	O
human	O
beings	O
(	O
)	O
,	O
which	O
is	O
used	O
for	O
target	O
classification	O
in	O
addition	O
to	O
the	O
kinds	O
of	O
conventional	B-Application
radar	I-Application
display	O
used	O
for	O
that	O
purpose	O
,	O
like	O
A-scope	O
,	O
B-scope	O
,	O
C-scope	O
,	O
and	O
RHI	O
indicator	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
must	O
be	O
multi-mode	O
to	O
handle	O
aircraft	O
turning	O
and	O
crossing	O
trajectory	O
.	O
</s>
<s>
Once	O
in	O
track	O
mode	O
,	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
must	O
include	O
a	O
way	O
to	O
modify	O
Doppler	O
filtering	O
for	O
the	O
volume	O
of	O
space	O
surrounding	O
a	O
track	O
when	O
radial	O
velocity	O
falls	O
below	O
the	O
minimum	O
detection	O
velocity	O
.	O
</s>
<s>
Doppler	O
filter	O
adjustment	O
must	O
be	O
linked	O
with	O
a	O
radar	B-Application
track	O
function	O
to	O
automatically	O
adjust	O
Doppler	O
rejection	O
speed	O
within	O
the	O
volume	O
of	O
space	O
surrounding	O
the	O
track	O
.	O
</s>
<s>
Multi-mode	O
operation	O
may	O
also	O
include	O
continuous	O
wave	O
illumination	O
for	O
semi-active	O
radar	B-Application
homing	O
.	O
</s>
