<s>
Multifunction	B-Algorithm
Phased	I-Algorithm
Array	I-Algorithm
Radar	I-Algorithm
(	O
MPAR	B-Algorithm
)	O
was	O
an	O
experimental	O
Doppler	B-Algorithm
radar	B-Application
system	I-Application
that	O
utilized	O
phased	O
array	O
technology	O
.	O
</s>
<s>
MPAR	B-Algorithm
could	O
scan	O
at	O
angles	O
as	O
high	O
as	O
60	O
degrees	O
in	O
elevation	O
,	O
and	O
simultaneously	O
track	O
meteorological	O
phenomena	O
,	O
biological	O
flyers	O
,	O
non-cooperative	O
aircraft	O
,	O
and	O
air	B-Application
traffic	I-Application
.	O
</s>
<s>
From	O
2003	O
through	O
2016	O
,	O
there	O
was	O
one	O
operational	O
MPAR	B-Algorithm
within	O
the	O
mainland	O
United	O
States	O
—	O
a	O
repurposed	O
AN/SPY	O
-1A	O
radar	B-Application
set	O
loaned	O
to	O
NOAA	O
by	O
the	O
U.S.	O
Navy	O
.	O
</s>
<s>
The	O
MPAR	B-Algorithm
was	O
decommissioned	O
and	O
removed	O
in	O
2016	O
.	O
</s>
<s>
NOAA	O
and	O
the	O
FAA	O
plan	O
to	O
eventually	O
decommission	O
their	O
NEXRAD	B-Algorithm
,	O
TDWR	B-Algorithm
and	O
ASR	O
radars	B-Application
in	O
favor	O
of	O
several	O
hundred	O
phased	O
array	O
radars	B-Application
conceptually	O
similar	O
to	O
MPAR	B-Algorithm
.	O
</s>
<s>
The	O
MPAR	B-Algorithm
was	O
derived	O
from	O
a	O
U.S.	O
Navy	O
shipborne	O
radar	B-Application
,	O
the	O
AN/SPY	O
-1	O
.	O
</s>
<s>
First	O
seeing	O
service	O
beginning	O
in	O
1973	O
when	O
it	O
was	O
installed	O
on	O
the	O
USS	O
Norton	O
Sound	O
,	O
the	O
AN/SPY	O
-1	O
became	O
the	O
standard	O
air	B-Application
search	I-Application
radar	I-Application
of	O
the	O
U.S.	O
Navy	O
and	O
the	O
navies	O
of	O
several	O
other	O
allied	O
nations	O
.	O
</s>
<s>
During	O
use	O
,	O
it	O
was	O
discovered	O
that	O
the	O
false-alarm	O
rate	O
was	O
high	O
due	O
to	O
the	O
radar	B-Application
detecting	O
swarms	O
of	O
insects	O
and	O
clutter	O
from	O
nearby	O
mountainous	O
terrain	O
.	O
</s>
<s>
Although	O
problematic	O
for	O
a	O
military	O
air	O
defence	O
radar	B-Application
,	O
this	O
is	O
ideal	O
for	O
a	O
weather	B-Application
radar	I-Application
,	O
and	O
made	O
phased	O
array	O
radars	B-Application
a	O
prime	O
candidate	O
for	O
implementation	O
in	O
the	O
meteorological	O
spectrum	O
.	O
</s>
<s>
As	O
different	O
versions	O
of	O
the	O
AN/SPY	O
family	O
arose	O
through	O
the	O
1990s	O
,	O
in	O
2003	O
the	O
U.S.	O
Navy	O
loaned	O
a	O
surplus	O
AN/SPY	O
-1A	O
radar	B-Application
to	O
NOAA	O
for	O
meteorological	O
research	O
.	O
</s>
<s>
Conventional	O
radars	B-Application
typically	O
use	O
a	O
large	O
,	O
parabolic	O
dish	O
to	O
focus	O
the	O
radar	B-Application
beam	O
,	O
and	O
rely	O
on	O
motors	O
to	O
move	O
the	O
dish	O
in	O
azimuth	O
and	O
elevation	O
.	O
</s>
<s>
By	O
contrast	O
,	O
phased	O
arrays	O
are	O
an	O
antenna	B-Algorithm
array	I-Algorithm
,	O
composed	O
of	O
many	O
small	O
antennas	O
on	O
a	O
flat	O
panel	O
,	O
which	O
steer	O
the	O
radar	B-Application
beam	O
electronically	O
by	O
changing	O
the	O
phase	O
of	O
the	O
signal	O
emitted	O
from	O
each	O
antenna	O
element	O
.	O
</s>
<s>
This	O
means	O
that	O
four	O
panels	O
,	O
mounted	O
at	O
right	O
angles	O
to	O
each	O
other	O
,	O
are	O
required	O
to	O
provide	O
full	O
360°	O
coverage	O
—	O
or	O
,	O
fewer	O
panels	O
(	O
even	O
just	O
one	O
)	O
,	O
mounted	O
on	O
a	O
rotating	O
pedestal	O
as	O
with	O
a	O
conventional	O
dish	O
radar	B-Application
.	O
</s>
<s>
An	O
alternative	O
is	O
to	O
construct	O
the	O
radar	B-Application
out	O
of	O
many	O
tall	O
but	O
narrow	O
antenna	O
strips	O
arranged	O
in	O
a	O
cylinder	O
.	O
</s>
<s>
From	O
2003	O
to	O
2016	O
,	O
the	O
MPAR	B-Algorithm
formed	O
the	O
core	O
of	O
the	O
National	O
Weather	B-Application
Radar	I-Application
Testbed	O
(	O
NWRT	O
)	O
,	O
used	O
as	O
a	O
proof-of-concept	O
test	O
to	O
validate	O
the	O
meteorological	O
potential	O
of	O
phased	O
array	O
radars	B-Application
.	O
</s>
<s>
The	O
MPAR	B-Algorithm
provided	O
much	O
faster	O
volume	O
scans	O
,	O
comprehensive	O
wind	O
profiling	O
,	O
and	O
more	O
complete	O
insights	O
to	O
supercellular	O
structure	O
,	O
while	O
simultaneously	O
tracking	O
aircraft	O
.	O
</s>
<s>
Due	O
to	O
the	O
temporal	B-General_Concept
resolution	I-General_Concept
ranging	O
from	O
30	O
to	O
60	O
seconds	O
and	O
the	O
one-sector	O
scanning	O
solution	O
used	O
by	O
MPAR	B-Algorithm
,	O
severe	O
storm	O
and	O
tornado	O
warning	O
lead	O
times	O
increased	O
as	O
much	O
as	O
8	O
minutes	O
from	O
the	O
already	O
existing	O
13	O
minutes	O
.	O
</s>
<s>
One	O
drawback	O
of	O
the	O
MPAR	B-Algorithm
,	O
when	O
compared	O
to	O
the	O
currently-deployed	O
NEXRAD	B-Algorithm
radars	B-Application
,	O
was	O
that	O
MPAR	B-Algorithm
did	O
not	O
support	O
dual-polarization	O
—	O
that	O
is	O
,	O
the	O
polar	O
orientation	O
of	O
the	O
radar	B-Application
beam	O
.	O
</s>
<s>
Similarly	O
,	O
other	O
objects	O
—	O
snow	O
,	O
hail	O
,	O
birds	O
and	O
insects	O
,	O
smoke	O
—	O
also	O
reflect	O
the	O
radar	B-Application
beam	O
differently	O
in	O
the	O
two	O
planes	O
.	O
</s>
<s>
These	O
differences	O
are	O
measured	O
by	O
the	O
radar	B-Application
,	O
computer	O
algorithms	O
process	O
the	O
data	O
,	O
and	O
produce	O
conclusions	O
about	O
the	O
nature	O
of	O
the	O
detected	O
precipitation	O
.	O
</s>
<s>
Polarimetric	O
radar	B-Application
provides	O
improvements	O
in	O
tornado	O
detection	O
,	O
rainfall	O
rate	O
measurements	O
,	O
precipitation	O
type	O
discrimination	O
,	O
and	O
more	O
.	O
</s>
<s>
Dual-polarization	O
capability	O
was	O
rolled	O
out	O
to	O
the	O
existing	O
NEXRAD	B-Algorithm
radars	B-Application
beginning	O
in	O
2011	O
,	O
and	O
was	O
complete	O
by	O
April	O
2013	O
.	O
</s>
<s>
MPAR	B-Algorithm
,	O
being	O
a	O
1970s	O
design	O
,	O
did	O
not	O
have	O
polarimetric	O
capability	O
and	O
retrofitting	O
it	O
would	O
have	O
been	O
costly	O
,	O
if	O
not	O
impossible	O
.	O
</s>
<s>
This	O
limitation	O
was	O
addressed	O
in	O
the	O
MPAR	B-Algorithm
successor	O
(	O
see	O
section	O
below	O
)	O
.	O
</s>
<s>
Besides	O
meteorological	O
observation	O
,	O
MPAR	B-Algorithm
was	O
capable	O
of	O
air	B-Application
traffic	I-Application
surveillance	O
—	O
this	O
was	O
the	O
original	O
role	O
of	O
the	O
powerful	O
AN/SPY	O
-1	O
radars	B-Application
from	O
which	O
MPAR	B-Algorithm
was	O
derived	O
.	O
</s>
<s>
The	O
capability	O
to	O
detect	O
and	O
track	O
aircraft	O
while	O
simultaneously	O
monitoring	O
the	O
weather	O
attracted	O
the	O
attention	O
of	O
the	O
FAA	O
,	O
which	O
operates	O
numerous	O
radars	B-Application
for	O
air	B-Application
traffic	I-Application
control	I-Application
purposes	O
(	O
e.g.	O
,	O
ASR	O
series	O
)	O
,	O
as	O
well	O
as	O
localized	O
weather	B-Application
radars	I-Application
near	O
airports	O
(	O
TDWR	B-Algorithm
units	O
)	O
to	O
detect	O
dangers	O
to	O
aircraft	O
such	O
as	O
flocks	O
of	O
birds	O
,	O
wind	O
shear	O
,	O
and	O
microbursts	O
,	O
amongst	O
others	O
.	O
</s>
<s>
Nine	O
different	O
dish-based	O
radar	B-Application
models	O
could	O
be	O
replaced	O
by	O
one	O
phased	O
array	O
radar	B-Application
.	O
</s>
<s>
Consolidating	O
these	O
different	O
types	O
of	O
radars	B-Application
and	O
their	O
functions	O
into	O
one	O
model	O
would	O
lead	O
to	O
cost	O
savings	O
by	O
the	O
reduction	O
of	O
up	O
to	O
one	O
third	O
of	O
radars	B-Application
needed	O
,	O
streamlined	O
training	O
and	O
maintenance	O
,	O
and	O
an	O
increase	O
in	O
reliability	O
through	O
commonality	O
of	O
spare	O
parts	O
.	O
</s>
<s>
Although	O
MPAR	B-Algorithm
was	O
a	O
powerful	O
radar	B-Application
with	O
unique	O
features	O
unavailable	O
to	O
conventional	O
meteorological	O
and	O
air-surveillance	O
radars	B-Application
,	O
it	O
was	O
an	O
old	O
design	O
,	O
using	O
old	O
parts	O
,	O
and	O
its	O
hardware	O
upgrade	O
potential	O
was	O
severely	O
limited	O
;	O
in	O
many	O
respects	O
it	O
was	O
inferior	O
to	O
conventional	O
radars	B-Application
.	O
</s>
<s>
To	O
make	O
way	O
for	O
a	O
more	O
advanced	O
radar	B-Application
,	O
MPAR	B-Algorithm
was	O
decommissioned	O
and	O
removed	O
from	O
its	O
tower	O
structure	O
on	O
26	O
August	O
2016	O
.	O
</s>
<s>
MIT	O
Lincoln	O
Laboratory	O
headed	O
the	O
project	O
to	O
design	O
a	O
dual-polarity	O
MPAR	B-Algorithm
successor	O
,	O
incorporating	O
the	O
many	O
lessons	O
learned	O
from	O
the	O
development	O
and	O
operation	O
of	O
MPAR	B-Algorithm
.	O
</s>
<s>
The	O
prototype	O
,	O
called	O
the	O
Advanced	O
Technology	O
Demonstrator	O
(	O
ATD	O
)	O
,	O
was	O
installed	O
on	O
12	O
July	O
2018	O
on	O
the	O
tower	O
formerly	O
housing	O
the	O
MPAR	B-Algorithm
,	O
and	O
it	O
is	O
expected	O
to	O
become	O
fully	O
operational	O
in	O
2019	O
.	O
</s>
<s>
Like	O
MPAR	B-Algorithm
,	O
the	O
ATD	O
radar	B-Application
is	O
an	O
S	B-Algorithm
band	I-Algorithm
flat	O
panel	O
phased	O
array	O
with	O
a	O
90°	O
field	O
of	O
view	O
.	O
</s>
<s>
It	O
is	O
composed	O
of	O
76	O
square	O
panels	O
,	O
each	O
with	O
64	O
radiating	O
elements	O
(	O
for	O
a	O
total	O
of	O
4,864	O
elements	O
)	O
arranged	O
on	O
a	O
antenna	O
,	O
and	O
is	O
mounted	O
on	O
a	O
rotating	O
pedestal	O
similar	O
to	O
those	O
used	O
by	O
NEXRAD	B-Algorithm
dish	O
antennas	O
.	O
</s>
