<s>
Terminal	B-Algorithm
Doppler	I-Algorithm
Weather	I-Algorithm
Radar	I-Algorithm
(	O
TDWR	B-Algorithm
)	O
is	O
a	O
Doppler	B-Application
weather	I-Application
radar	I-Application
system	O
with	O
a	O
three-dimensional	O
"	O
pencil	O
beam	O
"	O
used	O
primarily	O
for	O
the	O
detection	O
of	O
hazardous	O
wind	O
shear	O
conditions	O
,	O
precipitation	O
,	O
and	O
winds	O
aloft	O
on	O
and	O
near	O
major	O
airports	O
situated	O
in	O
climates	O
with	O
great	O
exposure	O
to	O
thunderstorms	O
in	O
the	O
United	O
States	O
.	O
</s>
<s>
Several	O
similar	O
weather	B-Application
radars	I-Application
have	O
also	O
been	O
sold	O
to	O
other	O
countries	O
such	O
as	O
China	O
(	O
Hong	O
Kong	O
)	O
.	O
</s>
<s>
Funded	O
by	O
the	O
United	O
States	O
Federal	O
Aviation	O
Administration	O
(	O
FAA	O
)	O
,	O
TDWR	B-Algorithm
technology	O
was	O
developed	O
in	O
the	O
early	O
1990s	O
at	O
Lincoln	O
Laboratory	O
,	O
part	O
of	O
the	O
Massachusetts	O
Institute	O
of	O
Technology	O
,	O
to	O
assist	O
air	B-Application
traffic	I-Application
controllers	I-Application
by	O
providing	O
real-time	O
wind	O
shear	O
detection	O
and	O
high-resolution	O
precipitation	O
data	O
.	O
</s>
<s>
The	O
primary	O
advantage	O
of	O
TDWRs	B-Algorithm
over	O
previous	O
weather	B-Application
radars	I-Application
is	O
that	O
it	O
has	O
a	O
finer	O
range	O
resolutionmeaning	O
it	O
can	O
see	O
smaller	O
areas	O
of	O
the	O
atmosphere	O
.	O
</s>
<s>
The	O
reason	O
for	O
the	O
resolution	O
is	O
that	O
the	O
TDWR	B-Algorithm
has	O
a	O
narrower	O
beam	O
than	O
traditional	O
radar	O
systems	O
,	O
and	O
that	O
it	O
uses	O
a	O
set	O
of	O
algorithms	O
to	O
reduce	O
ground	O
clutter	O
.	O
</s>
<s>
TDWR	B-Algorithm
uses	O
a	O
carrier	O
wave	O
in	O
the	O
frequency	B-Algorithm
band	I-Algorithm
of	O
5600	O
–	O
5650MHz	O
(	O
5cm	O
wavelength	O
)	O
,	O
with	O
a	O
narrow	O
beam	O
and	O
angular	O
resolution	O
of	O
0.5	O
degrees	O
,	O
and	O
has	O
a	O
peak	O
power	O
of	O
250kW	O
.	O
</s>
<s>
The	O
reason	O
for	O
this	O
difference	O
is	O
that	O
the	O
width	O
resolution	O
being	O
angular	O
,	O
at	O
larger	O
range	O
the	O
width	O
of	O
the	O
beam	O
becomes	O
quite	O
large	O
and	O
to	O
obtain	O
a	O
better	O
averaging	O
of	O
data	O
in	O
a	O
resolution	O
volume	O
,	O
one	O
has	O
to	O
increase	O
the	O
number	O
of	O
range	O
pulse	O
bins	B-Data_Structure
.	O
</s>
<s>
Because	O
of	O
the	O
Pulse	O
Repetition	O
Frequency	O
(	O
PRF	O
)	O
used	O
,	O
there	O
is	O
aliasing	B-Error_Name
and	O
the	O
maximum	O
non-ambiguous	O
velocity	O
is	O
.	O
</s>
<s>
TDWR	B-Algorithm
can	O
perform	O
near-surface	O
scans	O
at	O
a	O
0.1-0.3	O
degree	O
angle	O
of	O
inclination	O
from	O
the	O
Earth	O
's	O
surface	O
every	O
minute	O
.	O
</s>
<s>
A	O
NEXRAD	B-Algorithm
weather	B-Application
radar	I-Application
currently	O
used	O
by	O
the	O
National	O
Weather	O
Service	O
(	O
NWS	O
)	O
is	O
a	O
10cm	O
wavelength	O
(	O
2700-3000MHz	O
)	O
radar	O
capable	O
of	O
a	O
complete	O
scan	O
every	O
4.5	O
to	O
10	O
minutes	O
,	O
depending	O
on	O
the	O
number	O
of	O
angles	O
scanned	O
,	O
and	O
depending	O
on	O
whether	O
or	O
not	O
MESO-SAILS	B-Algorithm
is	O
active	O
,	O
which	O
adds	O
a	O
supplemental	O
low-level	O
scan	O
while	O
completing	O
a	O
volume	O
scan	O
.	O
</s>
<s>
The	O
range	O
resolution	O
of	O
the	O
TDWR	B-Algorithm
is	O
nearly	O
twice	O
that	O
of	O
that	O
classic	O
NEXRAD	B-Algorithm
scheme	O
.	O
</s>
<s>
However	O
,	O
this	O
finer	O
resolution	O
is	O
only	O
available	O
up	O
to	O
from	O
the	O
radar	O
;	O
beyond	O
that	O
,	O
the	O
resolution	O
is	O
close	O
to	O
that	O
of	O
the	O
NEXRAD	B-Algorithm
.	O
</s>
<s>
However	O
,	O
since	O
August	O
2008	O
,	O
oversampling	O
on	O
NEXRAD	B-Algorithm
has	O
increased	O
its	O
resolution	O
in	O
lower	O
elevations	O
in	O
reflectivity	O
data	O
to	O
by	O
0.5	O
degree	O
,	O
and	O
increased	O
the	O
range	O
of	O
Doppler	B-Algorithm
velocity	O
data	O
to	O
.	O
</s>
<s>
This	O
lessens	O
the	O
advantages	O
of	O
TDWR	B-Algorithm
for	O
those	O
elevations	O
.	O
</s>
<s>
The	O
TDWRs	B-Algorithm
and	O
NEXRADs	B-Algorithm
complement	O
each	O
other	O
with	O
overlapping	O
coverage	O
,	O
each	O
designed	O
to	O
optimally	O
view	O
different	O
airspace	O
regimes	O
.	O
</s>
<s>
TDWR	B-Algorithm
's	O
rapid	O
update	O
rate	O
over	O
short	O
range	O
(	O
55	O
nmi	O
range	O
)	O
captures	O
microscale	O
weather	O
events	O
quickly	O
in	O
terminal	O
airspace	O
.	O
</s>
<s>
NEXRAD	B-Algorithm
is	O
a	O
long	O
range	O
radar	O
(	O
200	O
nmi	O
range	O
)	O
designed	O
to	O
serve	O
multiple	O
en	O
route	O
functions	O
at	O
high	O
altitude	O
,	O
above	O
terminal	O
airspace	O
,	O
and	O
far	O
between	O
terminals	O
.	O
</s>
<s>
NEXRAD	B-Algorithm
's	O
slower	O
update	O
rate	O
covering	O
a	O
wider	O
volume	O
,	O
captures	O
mesoscale	O
weather	O
events	O
.	O
</s>
<s>
This	O
is	O
a	O
serious	O
drawback	O
to	O
using	O
TDWR	B-Algorithm
,	O
as	O
the	O
signal	O
can	O
be	O
strongly	O
attenuated	O
in	O
heavy	O
precipitation	O
.	O
</s>
<s>
When	O
heavy	O
rain	O
is	O
falling	O
on	O
the	O
radome	O
,	O
the	O
range	O
of	O
the	O
TDWR	B-Algorithm
is	O
further	O
limited	O
.	O
</s>
<s>
Finally	O
,	O
hail	O
in	O
a	O
thunderstorm	O
scanned	O
by	O
a	O
TDWR	B-Algorithm
can	O
entirely	O
block	O
the	O
signal	O
as	O
its	O
size	O
is	O
larger	O
than	O
the	O
wavelength	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
the	O
TDWR	B-Algorithm
,	O
this	O
means	O
the	O
velocity	O
of	O
precipitations	O
moving	O
at	O
a	O
speed	O
beyond	O
away	O
or	O
toward	O
the	O
radar	O
will	O
be	O
analyzed	O
incorrectly	O
because	O
of	O
aliasing	B-Error_Name
.	O
</s>
<s>
NEXRAD	B-Algorithm
has	O
a	O
threshold	O
that	O
is	O
twice	O
as	O
high	O
(	O
)	O
and	O
thus	O
less	O
processing	O
and	O
interpretation	O
are	O
needed	O
.	O
</s>
<s>
Because	O
of	O
this	O
,	O
the	O
resolution	O
of	O
radar	O
reflectivity	O
for	O
small	O
scale	O
features	O
such	O
as	O
mesocyclones	O
might	O
be	O
better	O
in	O
TDWR	B-Algorithm
,	O
but	O
the	O
velocity	O
resolution	O
may	O
be	O
worse	O
,	O
or	O
at	O
the	O
very	O
least	O
incorrectly	O
analyzed	O
.	O
</s>
<s>
Thus	O
,	O
it	O
is	O
best	O
to	O
use	O
the	O
TDWR	B-Algorithm
in	O
conjunction	O
with	O
a	O
traditional	O
NEXRAD	B-Algorithm
nearby	O
to	O
ensure	O
that	O
nothing	O
is	O
missed	O
.	O
</s>
<s>
In	O
contrast	O
to	O
NEXRAD	B-Algorithm
,	O
which	O
has	O
national	O
coverage	O
of	O
the	O
contiguous	O
United	O
States	O
(	O
although	O
with	O
some	O
holes	O
due	O
to	O
terrain	O
)	O
,	O
TDWR	B-Algorithm
has	O
sporadic	O
coverage	O
meant	O
for	O
major	O
airports	O
.	O
</s>
<s>
While	O
certain	O
areas	O
of	O
the	O
country	O
(	O
the	O
Northeast	O
megalopolis	O
,	O
the	O
states	O
of	O
Ohio	O
and	O
Florida	O
,	O
and	O
the	O
southwestern	O
quarter	O
of	O
Tornado	O
Alley	O
in	O
Oklahoma	O
and	O
Texas	O
)	O
have	O
a	O
high	O
density	O
of	O
TDWR	B-Algorithm
units	O
,	O
others	O
(	O
the	O
entire	O
West	O
Coast	O
,	O
the	O
northern	O
Great	O
Plains	O
and	O
Rocky	O
Mountains	O
,	O
portions	O
of	O
the	O
Deep	O
South	O
,	O
and	O
a	O
stretch	O
running	O
from	O
northern	O
Pennsylvania	O
through	O
upstate	O
New	O
York	O
and	O
into	O
northern	O
New	O
England	O
)	O
have	O
no	O
TDWR	B-Algorithm
coverage	O
at	O
all	O
.	O
</s>
<s>
The	O
National	O
Severe	O
Storms	O
Laboratory	O
(	O
NSSL	O
)	O
has	O
a	O
program	O
of	O
development	O
and	O
improvement	O
of	O
radar	O
products	O
extracted	O
from	O
data	O
obtained	O
from	O
TDWR	B-Algorithm
and	O
NEXRAD	B-Algorithm
radars	O
.	O
</s>
<s>
NSSL	O
has	O
been	O
providing	O
TDWR	B-Algorithm
data	O
to	O
NWS	O
office	O
since	O
the	O
late	O
1990s	O
.	O
</s>
<s>
The	O
NWS	O
's	O
Radar	O
Operations	O
Center	O
(	O
ROC	O
)	O
,	O
although	O
focused	O
on	O
the	O
NEXRAD	B-Algorithm
network	O
,	O
also	O
works	O
with	O
TDWRs	B-Algorithm
.	O
</s>
