<s>
A	O
Doppler	B-Algorithm
radar	I-Algorithm
is	O
a	O
specialized	O
radar	B-Application
that	O
uses	O
the	O
Doppler	O
effect	O
to	O
produce	O
velocity	O
data	O
about	O
objects	O
at	O
a	O
distance	O
.	O
</s>
<s>
This	O
variation	O
gives	O
direct	O
and	O
highly	O
accurate	O
measurements	O
of	O
the	O
radial	O
component	O
of	O
a	O
target	O
's	O
velocity	O
relative	O
to	O
the	O
radar	B-Application
.	O
</s>
<s>
The	O
term	O
apply	O
to	O
radar	B-Application
systems	I-Application
in	O
many	O
domains	O
like	O
aviation	O
,	O
speed	O
guns	O
to	O
control	O
traffic	O
,	O
navigation	O
,	O
meteorology	O
,	O
etc	O
...	O
</s>
<s>
The	O
formula	O
for	O
radar	B-Application
Doppler	O
shift	O
is	O
the	O
same	O
as	O
that	O
for	O
reflection	O
of	O
light	O
by	O
a	O
moving	O
mirror	O
.	O
</s>
<s>
Since	O
for	O
most	O
practical	O
applications	O
of	O
radar	B-Application
,	O
,	O
so	O
.	O
</s>
<s>
Radars	B-Application
may	O
be	O
:	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
,	O
</s>
<s>
Frequency	B-Application
modulation	I-Application
(	O
FM	B-Application
)	O
.	O
</s>
<s>
This	O
effectively	O
eliminates	O
false	O
signals	O
produced	O
by	O
trees	O
,	O
clouds	O
,	O
insects	O
,	O
birds	O
,	O
wind	O
,	O
and	O
other	O
environmental	O
influences	O
but	O
various	O
inexpensive	O
hand	B-Algorithm
held	I-Algorithm
Doppler	B-Algorithm
radar	I-Algorithm
devices	O
not	O
using	O
this	O
may	O
produce	O
erroneous	O
measurements	O
.	O
</s>
<s>
CW	B-Algorithm
Doppler	I-Algorithm
radar	I-Algorithm
only	O
provides	O
a	O
velocity	O
output	O
as	O
the	O
received	O
signal	O
from	O
the	O
target	O
is	O
compared	O
in	O
frequency	O
with	O
the	O
original	O
signal	O
.	O
</s>
<s>
Early	O
Doppler	B-Algorithm
radars	I-Algorithm
included	O
CW	O
,	O
but	O
these	O
quickly	O
led	O
to	O
the	O
development	O
of	O
frequency	B-Application
modulated	I-Application
continuous	O
wave	O
(	O
FMCW	O
)	O
radar	B-Application
,	O
which	O
sweeps	O
the	O
transmitter	O
frequency	O
to	O
encode	O
and	O
determine	O
range	O
.	O
</s>
<s>
With	O
the	O
advent	O
of	O
digital	O
techniques	O
,	O
Pulse-Doppler	B-Algorithm
radars	I-Algorithm
(	O
PD	O
)	O
became	O
light	O
enough	O
for	O
aircraft	O
use	O
,	O
and	O
Doppler	O
processors	O
for	O
coherent	O
pulse	O
radars	B-Application
became	O
more	O
common	O
.	O
</s>
<s>
The	O
advantage	O
of	O
combining	O
Doppler	O
processing	O
with	O
pulse	O
radars	B-Application
is	O
to	O
provide	O
accurate	O
velocity	O
information	O
.	O
</s>
<s>
It	O
describes	O
the	O
rate	O
that	O
a	O
target	O
moves	O
toward	O
or	O
away	O
from	O
the	O
radar	B-Application
.	O
</s>
<s>
The	O
classic	O
zero	O
doppler	O
target	O
is	O
one	O
which	O
is	O
on	O
a	O
heading	O
that	O
is	O
tangential	O
to	O
the	O
radar	B-Application
antenna	O
beam	O
.	O
</s>
<s>
While	O
investigating	O
the	O
feasibility	O
of	O
whether	O
UWB	O
radar	B-Application
technology	O
can	O
incorporate	O
Doppler	O
processing	O
to	O
estimate	O
the	O
velocity	O
of	O
a	O
moving	O
target	O
when	O
the	O
platform	O
is	O
stationary	O
,	O
a	O
2013	O
ARL	O
report	O
highlighted	O
issues	O
related	O
to	O
target	O
range	O
migration	O
.	O
</s>
<s>
Firstly	O
,	O
the	O
radar	B-Application
is	O
more	O
robust	O
against	O
counter-measure	O
.	O
</s>
<s>
Low-flying	O
military	O
plane	O
with	O
countermeasure	O
alert	O
for	O
hostile	O
radar	B-Application
track	O
acquisition	O
can	O
turn	O
perpendicular	O
to	O
the	O
hostile	O
radar	B-Application
to	O
nullify	O
its	O
Doppler	O
frequency	O
,	O
which	O
usually	O
breaks	O
the	O
lock	O
and	O
drives	O
the	O
radar	B-Application
off	O
by	O
hiding	O
against	O
the	O
ground	O
return	O
which	O
is	O
much	O
larger	O
.	O
</s>
<s>
Doppler	B-Algorithm
radar	I-Algorithm
tends	O
to	O
be	O
lightweight	O
because	O
it	O
eliminates	O
heavy	O
pulse	O
hardware	O
.	O
</s>
<s>
Continuous-broadcast	O
,	O
or	O
FM	B-Application
,	O
radar	B-Application
was	O
developed	O
during	O
World	O
War	O
II	O
for	O
United	O
States	O
Navy	O
aircraft	O
,	O
to	O
support	O
night	O
combat	O
operation	O
.	O
</s>
<s>
This	O
enabled	O
bombers	B-Application
to	O
fly	O
an	O
optimum	O
speed	O
when	O
approaching	O
ship	O
targets	O
,	O
and	O
let	O
escort	O
fighter	O
aircraft	O
train	O
guns	O
on	O
enemy	O
aircraft	O
during	O
night	O
operation	O
.	O
</s>
<s>
These	O
strategies	O
were	O
adapted	O
to	O
semi-active	O
radar	B-Application
homing	O
.	O
</s>
<s>
In	O
1951	O
,	O
Carl	O
A	O
.	O
Wiley	O
invented	O
synthetic-aperture	O
radar	B-Application
,	O
which	O
,	O
though	O
distinct	O
from	O
mainstream	O
Doppler	B-Algorithm
radar	I-Algorithm
,	O
was	O
based	O
on	O
Doppler	O
principles	O
,	O
and	O
originally	O
patented	O
as	O
"	O
Pulsed	O
Doppler	B-Algorithm
Radar	I-Algorithm
Methods	O
and	O
Means	O
,	O
"	O
#3	O
,	O
196,436	O
.	O
</s>
<s>
Modern	O
police	O
radar	B-Application
are	O
a	O
smaller	O
,	O
more	O
portable	O
version	O
of	O
these	O
systems	O
.	O
</s>
<s>
Early	O
Doppler	B-Algorithm
radar	I-Algorithm
sets	O
relied	O
on	O
large	O
analog	O
filters	O
to	O
achieve	O
acceptable	O
performance	O
.	O
</s>
<s>
Digital	O
fast	O
Fourier	O
transform	O
(	O
FFT	O
)	O
filtering	O
became	O
practical	O
when	O
modern	O
microprocessors	B-Architecture
became	O
available	O
during	O
the	O
1970s	O
.	O
</s>
<s>
This	O
was	O
immediately	O
connected	O
to	O
coherent	O
pulsed	O
radars	B-Application
,	O
where	O
velocity	O
information	O
was	O
extracted	O
.	O
</s>
<s>
This	O
proved	O
useful	O
in	O
both	O
weather	O
and	O
air	B-Application
traffic	I-Application
control	I-Application
radars	B-Application
.	O
</s>
<s>
Because	O
of	O
the	O
low	O
pulse	O
repetition	O
frequency	O
(	O
PRF	O
)	O
of	O
most	O
coherent	O
pulsed	O
radars	B-Application
,	O
which	O
maximizes	O
the	O
coverage	O
in	O
range	O
,	O
the	O
amount	O
of	O
Doppler	O
processing	O
is	O
limited	O
.	O
</s>
<s>
The	O
Doppler	O
processor	O
can	O
only	O
process	O
velocities	O
up	O
to	O
±	O
1/2	O
the	O
PRF	O
of	O
the	O
radar	B-Application
.	O
</s>
<s>
This	O
is	O
not	O
a	O
problem	O
for	O
weather	B-Application
radars	I-Application
.	O
</s>
<s>
Velocity	O
information	O
for	O
aircraft	O
cannot	O
be	O
extracted	O
directly	O
from	O
low-PRF	O
radar	B-Application
because	O
sampling	O
restricts	O
measurements	O
to	O
about	O
75	O
miles	O
per	O
hour	O
.	O
</s>
<s>
Specialized	O
radars	B-Application
quickly	O
were	O
developed	O
when	O
digital	O
techniques	O
became	O
lightweight	O
and	O
more	O
affordable	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radars	I-Algorithm
combine	O
all	O
the	O
benefits	O
of	O
long	O
range	O
and	O
high	O
velocity	O
capability	O
.	O
</s>
<s>
Pulse-Doppler	B-Algorithm
radars	I-Algorithm
use	O
a	O
medium	O
to	O
high	O
PRF	O
(	O
on	O
the	O
order	O
of	O
3	O
to	O
30kHz	O
)	O
,	O
which	O
allows	O
for	O
the	O
detection	O
of	O
either	O
high-speed	O
targets	O
or	O
high-resolution	O
velocity	O
measurements	O
.	O
</s>
<s>
Normally	O
it	O
is	O
one	O
or	O
the	O
other	O
;	O
a	O
radar	B-Application
designed	O
for	O
detecting	O
targets	O
from	O
zero	O
to	O
Mach	O
2	O
does	O
not	O
have	O
a	O
high	O
resolution	O
in	O
speed	O
,	O
while	O
a	O
radar	B-Application
designed	O
for	O
high-resolution	O
velocity	O
measurements	O
does	O
not	O
have	O
a	O
wide	O
range	O
of	O
speeds	O
.	O
</s>
<s>
Weather	B-Application
radars	I-Application
are	O
high-resolution	O
velocity	O
radars	B-Application
,	O
while	O
air	O
defense	O
radars	B-Application
have	O
a	O
large	O
range	O
of	O
velocity	O
detection	O
,	O
but	O
the	O
accuracy	O
in	O
velocity	O
is	O
in	O
the	O
tens	O
of	O
knots	O
.	O
</s>
<s>
Antenna	O
designs	O
for	O
the	O
CW	O
and	O
FM-CW	O
started	O
out	O
as	O
separate	O
transmit	O
and	O
receive	O
antennas	O
before	O
the	O
advent	O
of	O
affordable	O
microwave	O
designs	O
.	O
</s>
<s>
In	O
the	O
late	O
1960s	O
,	O
traffic	O
radars	B-Application
began	O
being	O
produced	O
which	O
used	O
a	O
single	O
antenna	O
.	O
</s>
<s>
PD	O
radars	B-Application
operate	O
at	O
too	O
high	O
a	O
PRF	O
to	O
use	O
a	O
transmit-receive	O
gas	O
filled	O
switch	O
,	O
and	O
most	O
use	O
solid-state	O
devices	O
to	O
protect	O
the	O
receiver	O
low-noise	O
amplifier	O
when	O
the	O
transmitter	O
is	O
fired	O
.	O
</s>
<s>
Doppler	B-Algorithm
radars	I-Algorithm
are	O
used	O
in	O
aviation	O
,	O
sounding	O
satellites	O
,	O
Major	B-Application
League	I-Application
Baseball	I-Application
's	O
StatCast	O
system	O
,	O
meteorology	O
,	O
radar	B-Application
guns	O
,	O
radiology	O
and	O
healthcare	O
(	O
fall	O
detection	O
and	O
risk	O
assessment	O
,	O
nursing	O
or	O
clinic	O
purpose	O
)	O
,	O
and	O
bistatic	B-Algorithm
radar	I-Algorithm
(	O
surface-to-air	O
missiles	O
)	O
.	O
</s>
<s>
Partly	O
because	O
of	O
its	O
common	O
use	O
by	O
television	O
meteorologists	O
in	O
on-air	O
weather	O
reporting	O
,	O
the	O
specific	O
term	O
"	O
Doppler	B-Algorithm
Radar	I-Algorithm
"	O
has	O
erroneously	O
become	O
popularly	O
synonymous	O
with	O
the	O
type	O
of	O
radar	B-Application
used	O
in	O
meteorology	O
.	O
</s>
<s>
Most	O
modern	O
weather	B-Application
radars	I-Application
use	O
the	O
pulse-Doppler	B-Algorithm
technique	O
to	O
examine	O
the	O
motion	O
of	O
precipitation	O
,	O
but	O
it	O
is	O
only	O
a	O
part	O
of	O
the	O
processing	O
of	O
their	O
data	O
.	O
</s>
<s>
So	O
,	O
while	O
these	O
radars	B-Application
use	O
a	O
highly	O
specialized	O
form	O
of	O
Doppler	B-Algorithm
radar	I-Algorithm
,	O
this	O
type	O
of	O
radar	B-Application
is	O
much	O
broader	O
in	O
its	O
meaning	O
and	O
its	O
applications	O
.	O
</s>
<s>
The	O
work	O
on	O
the	O
Doppler	O
function	O
for	O
weather	B-Application
radar	I-Application
has	O
a	O
long	O
history	O
in	O
many	O
countries	O
.	O
</s>
<s>
In	O
June	O
1958	O
,	O
American	O
researchers	O
David	O
Holmes	O
and	O
Robert	O
Smith	O
were	O
able	O
to	O
detect	O
the	O
rotation	O
of	O
a	O
tornado	B-Language
using	O
the	O
mobile	O
continuous-wave	B-Algorithm
radar	I-Algorithm
(	O
photo	O
to	O
the	O
right	O
)	O
.	O
</s>
<s>
The	O
work	O
was	O
accelerated	O
after	O
such	O
event	O
in	O
the	O
United	O
States	O
as	O
the	O
1974	O
Super	O
Outbreak	O
when	O
148	O
tornadoes	B-Language
roared	O
through	O
thirteen	O
states	O
.	O
</s>
<s>
The	O
reflectivity	O
only	O
radar	B-Application
of	O
the	O
time	O
could	O
only	O
locate	O
the	O
precipitation	O
structure	O
of	O
the	O
thunderclouds	O
but	O
not	O
the	O
mesocyclonic	O
rotation	O
and	O
divergence	O
of	O
winds	O
leading	O
to	O
the	O
development	O
of	O
tornadoes	B-Language
or	O
downbursts	O
.	O
</s>
<s>
The	O
NSSL	B-Algorithm
Doppler	I-Algorithm
became	O
operational	O
in	O
1971	O
and	O
led	O
to	O
the	O
NEXRAD	B-Algorithm
network	O
being	O
deployed	O
at	O
the	O
end	O
of	O
the	O
1980s	O
.	O
</s>
<s>
Doppler	B-Algorithm
radars	I-Algorithm
were	O
used	O
as	O
a	O
navigation	O
aid	O
for	O
aircraft	O
and	O
spacecraft	O
.	O
</s>
<s>
By	O
directly	O
measuring	O
the	O
movement	O
of	O
the	O
ground	O
with	O
the	O
radar	B-Application
,	O
and	O
then	O
comparing	O
this	O
to	O
the	O
airspeed	O
returned	O
from	O
the	O
aircraft	O
instruments	O
,	O
the	O
wind	O
speed	O
could	O
be	O
accurately	O
determined	O
for	O
the	O
first	O
time	O
.	O
</s>
<s>
One	O
early	O
example	O
of	O
such	O
a	O
system	O
was	O
the	O
Green	O
Satin	O
radar	B-Application
used	O
in	O
the	O
English	O
Electric	O
Canberra	O
.	O
</s>
<s>
Similar	O
systems	O
were	O
used	O
in	O
a	O
number	O
of	O
aircraft	O
of	O
the	O
era	O
,	O
and	O
were	O
combined	O
with	O
the	O
main	O
search	O
radars	B-Application
of	O
fighter	O
designs	O
by	O
the	O
1960s	O
.	O
</s>
<s>
Its	O
major	O
shortcoming	O
in	O
practice	O
was	O
the	O
sea	O
state	O
,	O
as	O
a	O
calm	O
sea	O
gave	O
poor	O
radar	B-Application
returns	O
and	O
hence	O
unreliable	O
Doppler	O
measurements	O
.	O
</s>
