<s>
Millimeter-wave	O
cloud	O
radars	B-Application
,	O
also	O
denominated	O
cloud	O
radars	B-Application
,	O
are	O
radar	B-Application
systems	I-Application
designed	O
to	O
monitor	O
clouds	O
with	O
operating	O
frequencies	O
between	O
24	O
and	O
110GHz	O
(	O
Table	O
1	O
)	O
.	O
</s>
<s>
Accordingly	O
,	O
their	O
wavelengths	O
range	O
from	O
1mm	O
to	O
1.11cm	O
,	O
about	O
ten	O
times	O
shorter	O
than	O
those	O
used	O
in	O
conventional	O
S	B-Algorithm
band	I-Algorithm
radars	B-Application
such	O
as	O
NEXRAD	B-Algorithm
.	O
</s>
<s>
The	O
main	O
purpose	O
of	O
these	O
radars	B-Application
is	O
the	O
investigation	O
of	O
cloud	O
properties	O
and	O
evolution	O
.	O
</s>
<s>
They	O
typically	O
operate	O
at	O
35GHz	O
in	O
the	O
Ka	O
band	O
and	O
at	O
94GHz	O
in	O
the	O
W	B-Algorithm
band	I-Algorithm
,	O
where	O
the	O
atmospheric	O
transmission	O
is	O
maximum	O
.	O
</s>
<s>
Millimeter	B-Algorithm
cloud	I-Algorithm
radars	I-Algorithm
have	O
a	O
high	O
temporal	O
and	O
range	O
resolution	O
:	O
temporal	B-General_Concept
resolution	I-General_Concept
is	O
adjustable	O
and	O
typically	O
ranges	O
from	O
1	O
to	O
10	O
seconds	O
,	O
while	O
the	O
ranges	O
from	O
a	O
few	O
meters	O
for	O
cloud	O
radars	B-Application
using	O
frequency	O
modulation	O
of	O
the	O
transmitted	O
signal	O
(	O
e.g.	O
</s>
<s>
4	O
m	O
for	O
the	O
Frequency-Modulated	O
Continuous-Wave	O
(	O
FMCW	O
)	O
94GHz	O
cloud	O
radar	B-Application
operating	O
at	O
)	O
,	O
to	O
several	O
meters	O
for	O
magnetron	O
based	O
cloud	O
radars	B-Application
(	O
e.g.	O
</s>
<s>
The	O
maximum	O
detection	O
range	O
is	O
between	O
14	O
and	O
20km	O
and	O
the	O
Doppler	B-Application
velocity	O
resolution	O
is	O
of	O
few	O
cm/s	O
.	O
</s>
<s>
Most	O
of	O
the	O
cloud	O
radars	B-Application
are	O
polarimetric	O
,	O
being	O
able	O
to	O
measure	O
the	O
particles	O
irregularity	O
by	O
means	O
of	O
the	O
linear	O
depolarization	O
ratio	O
(	O
)	O
.	O
</s>
<s>
Usually	O
they	O
operate	O
pointing	O
to	O
the	O
zenith	O
,	O
but	O
an	O
increasing	O
number	O
of	O
them	O
have	O
nowadays	O
scanning	O
units	O
,	O
that	O
allow	O
to	O
retrieve	O
additional	O
information	O
such	O
as	O
volume	O
information	O
when	O
performing	O
various	O
Range	O
Height	O
Indicator	O
(	O
RHI	O
)	O
scans	O
at	O
different	O
angles	O
and	O
at	O
a	O
relatively	O
high	O
speed	O
,	O
and	O
vertical	O
wind	O
profiles	O
,	O
when	O
performing	O
Plan	B-Algorithm
Position	I-Algorithm
Indicator	I-Algorithm
(	O
PPI	O
)	O
at	O
few	O
degrees	O
from	O
the	O
zenith	O
.	O
</s>
<s>
Regarding	O
the	O
different	O
cloud	O
radars	B-Application
operating	O
wavelengths	O
,	O
it	O
must	O
be	O
taken	O
into	O
account	O
that	O
longer	O
wavelengths	O
are	O
less	O
attenuated	O
by	O
drizzle	B-Application
and	O
rain	O
,	O
while	O
shorter	O
wavelengths	O
are	O
more	O
sensitive	O
to	O
smaller	O
particles	O
.	O
</s>
<s>
Accordingly	O
,	O
radar	B-Application
signals	O
are	O
less	O
attenuated	O
in	O
Ka-band	O
than	O
in	O
W-band	O
,	O
while	O
W-band	O
radars	B-Application
are	O
able	O
to	O
detect	O
smaller	O
particles	O
.	O
</s>
<s>
Even	O
though	O
,	O
the	O
cloud	O
radar	B-Application
beams	O
are	O
much	O
less	O
attenuated	O
by	O
cloud	O
or	O
precipitation	O
particles	O
than	O
the	O
lidar	O
beam	O
.	O
</s>
<s>
Cloud	O
radars	B-Application
are	O
used	O
nowadays	O
to	O
determine	O
cloud	O
boundaries	O
(	O
e.g.	O
</s>
<s>
Furthermore	O
,	O
cloud	O
radars	B-Application
are	O
being	O
used	O
for	O
entomology	O
studies	O
for	O
more	O
than	O
40	O
years	O
,	O
since	O
Ka	O
and	O
W-band	O
radars	B-Application
detect	O
almost	O
exclusively	O
insect	O
targets	O
on	O
warm	O
cloudless	O
days	O
,	O
and	O
more	O
recently	O
are	O
also	O
used	O
for	O
the	O
study	O
of	O
giant	O
aerosols	O
.	O
</s>
<s>
Even	O
though	O
most	O
cloud	O
radar	B-Application
systems	I-Application
are	O
ground-based	O
,	O
they	O
can	O
also	O
be	O
airborne	O
and	O
space-based	O
.	O
</s>
<s>
Examples	O
of	O
airborne	O
systems	O
are	O
cloud	O
radars	B-Application
installed	O
on	O
HALO	O
(	O
High	O
Altitude	O
and	O
Long	O
Range	O
Research	O
Aircraft	O
)	O
and	O
Wyoming	O
KingAir	O
Research	O
Aircraft	O
.	O
</s>
<s>
The	O
first	O
spaceborne	O
CPR	O
with	O
Doppler	B-Application
capability	O
will	O
be	O
launched	O
in	O
March	O
2023	O
aboard	O
the	O
Earth	O
Clouds	O
,	O
Aerosols	O
and	O
Radiation	O
Explorer	O
(	O
EarthCARE	O
)	O
mission	O
.	O
</s>
<s>
Pulsed	O
Radar	B-Application
systems	I-Application
are	O
considered	O
active	O
instruments	O
because	O
they	O
transmit	O
in	O
the	O
atmosphere	O
an	O
electromagnetic	O
wave	O
and	O
receive	O
the	O
signal	O
reflected	O
back	O
from	O
the	O
atmosphere	O
.	O
</s>
<s>
In	O
such	O
radars	B-Application
,	O
the	O
antenna	O
sends	O
out	O
the	O
electromagnetic	O
wave	O
,	O
and	O
then	O
collects	O
the	O
returned	O
signal	O
.	O
</s>
<s>
Radars	B-Application
are	O
composed	O
of	O
different	O
hardware	O
parts	O
,	O
each	O
of	O
which	O
contains	O
different	O
elements	O
.	O
</s>
<s>
This	O
EM	O
wave	O
is	O
sent	O
to	O
the	O
atmosphere	O
:	O
every	O
pulse	O
is	O
scattered	O
by	O
a	O
volume	O
of	O
air	O
filled	O
with	O
hydrometeors	O
and	O
comes	O
back	O
to	O
the	O
radar	B-Application
.	O
</s>
<s>
Such	O
echoes	O
are	O
received	O
continuously	O
at	O
the	O
radar	B-Application
antenna	O
after	O
a	O
delay	O
equal	O
to	O
the	O
time	O
taken	O
by	O
the	O
wave	O
to	O
reach	O
the	O
target	O
and	O
come	O
back	O
to	O
the	O
radar	B-Application
.	O
</s>
<s>
The	O
number	O
of	O
distinct	O
resolution	O
volumes	O
in	O
space	O
from	O
which	O
the	O
radar	B-Application
collects	O
information	O
is	O
equal	O
to	O
the	O
number	O
of	O
samples	O
that	O
are	O
collected	O
by	O
the	O
radar	B-Application
between	O
any	O
two	O
radar	B-Application
pulses	O
.	O
</s>
<s>
As	O
radar	B-Application
transmits	O
coherent	O
pulses	O
with	O
a	O
certain	O
pulse	O
repetition	O
frequency	O
(	O
PRF	O
)	O
,	O
the	O
doppler	B-Application
processing	O
technique	O
is	O
applied	O
.	O
</s>
<s>
The	O
result	O
of	O
the	O
FFT	O
is	O
a	O
complex	O
spectrum	O
where	O
is	O
the	O
Doppler	B-Application
frequency	O
.	O
</s>
<s>
Usually	O
numerous	O
targets	O
are	O
present	O
in	O
the	O
sample	O
volume	O
of	O
the	O
radar	B-Application
.	O
</s>
<s>
the	O
returned	O
power	O
in	O
any	O
interval	O
of	O
the	O
frequency	O
shift	O
allows	O
the	O
detection	O
of	O
the	O
Doppler	B-Application
spectrum	O
.	O
</s>
<s>
This	O
is	O
illustrated	O
in	O
the	O
Figure	O
on	O
the	O
right	O
,	O
where	O
a	O
sketch	O
of	O
the	O
Doppler	B-Application
spectrum	O
is	O
shown	O
.	O
</s>
<s>
From	O
the	O
Doppler	B-Application
spectrum	O
the	O
reflectivity	O
can	O
be	O
calculated	O
using	O
the	O
expression	O
:	O
</s>
<s>
The	O
integral	O
of	O
the	O
spectral	O
power	O
is	O
called	O
the	O
0-moment	O
of	O
the	O
Doppler	B-Application
spectrum	O
,	O
which	O
equals	O
the	O
reflectivity	O
.	O
</s>
<s>
Further	O
,	O
the	O
first	O
moment	O
(	O
)	O
and	O
the	O
second	O
moment	O
(	O
)	O
of	O
the	O
Doppler	B-Application
spectrum	O
can	O
be	O
calculated	O
:	O
</s>
<s>
The	O
first	O
moment	O
of	O
the	O
Doppler	B-Application
spectrum	O
is	O
the	O
mean	O
Doppler	B-Application
velocity	O
.	O
</s>
<s>
The	O
second	O
moment	O
is	O
called	O
the	O
Doppler	B-Application
width	O
.	O
</s>
<s>
It	O
corresponds	O
to	O
the	O
variance	O
of	O
the	O
Doppler	B-Application
spectrum	O
.	O
</s>
<s>
The	O
Doppler	B-Application
width	O
basically	O
is	O
a	O
measure	O
of	O
the	O
width	O
of	O
the	O
spectrum	O
of	O
the	O
detected	O
velocities	O
.	O
</s>
<s>
The	O
expressions	O
to	O
calculate	O
the	O
Kurtosis	B-Error_Name
and	O
the	O
Skewness	B-General_Concept
are	O
coming	O
out	O
of	O
mathematical	O
statistics	O
several	O
formulations	O
are	O
used	O
.	O
</s>
<s>
Some	O
of	O
them	O
can	O
be	O
found	O
in	O
the	O
quoted	O
literature	O
in	O
Kurtosis	B-Error_Name
section	O
.	O
</s>
<s>
Mean	O
Doppler	B-Application
velocity	O
can	O
be	O
seen	O
as	O
the	O
mean	O
frequency	O
of	O
a	O
power	O
spectrum	O
(	O
Doppler	B-Application
velocity	O
)	O
of	O
the	O
backscattered	B-Algorithm
power	O
.	O
</s>
<s>
Given	O
the	O
mean	O
Doppler	B-Application
velocity	O
(	O
mean	O
frequency	O
of	O
the	O
power	O
spectrum	O
)	O
of	O
the	O
measured	O
volume	O
along	O
the	O
line	O
of	O
sight	O
-	O
the	O
radial	O
velocity	O
.	O
</s>
<s>
For	O
vertical	O
measurements	O
,	O
the	O
Doppler	B-Application
velocities	O
is	O
the	O
sum	O
of	O
terminal	O
velocity	O
of	O
particles	O
,	O
caused	O
by	O
gravity	O
force	O
,	O
and	O
air	O
motions	O
within	O
the	O
measured	O
volume	O
.	O
</s>
<s>
In	O
order	O
to	O
obtain	O
the	O
terminal	O
velocity	O
from	O
the	O
cloud-radar	O
observations	O
,	O
the	O
influence	O
of	O
air	O
motions	O
that	O
shift	O
the	O
spectrum	O
have	O
to	O
be	O
removed	O
from	O
the	O
Doppler	B-Application
spectra	O
,	O
improving	O
in	O
this	O
way	O
the	O
microphysics	O
representativity	O
.	O
</s>
<s>
An	O
approach	O
to	O
correct	O
this	O
shift	O
is	O
given	O
by	O
Kollias	O
et	O
al.	O
,	O
improving	O
the	O
accuracy	O
of	O
the	O
relation	O
between	O
the	O
corrected	O
Doppler	B-Application
velocity	O
and	O
the	O
particle	O
fall	O
velocities	O
.	O
</s>
<s>
The	O
Doppler	B-Application
width	O
,	O
or	O
Doppler	B-Application
spectrum	O
width	O
,	O
is	O
the	O
standard	O
deviation	O
of	O
the	O
spectrum	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
measured	O
volume	O
contains	O
more	O
than	O
one	O
hydrometeor	O
population	O
,	O
which	O
leads	O
to	O
two	O
or	O
more	O
modes	O
in	O
the	O
Doppler	B-Application
spectrum	O
because	O
of	O
the	O
different	O
terminal	O
velocities	O
.	O
</s>
<s>
A	O
rapid	O
change	O
in	O
Doppler	B-Application
width	O
in	O
combination	O
with	O
the	O
mean	O
Doppler	B-Application
velocity	O
can	O
also	O
be	O
used	O
to	O
separate	O
two	O
hydrometeor	O
population	O
.	O
</s>
<s>
Since	O
the	O
air	O
motion	O
in	O
the	O
atmosphere	O
affects	O
the	O
Doppler	B-Application
width	O
,	O
this	O
parameter	O
provides	O
information	O
about	O
turbulence	O
within	O
the	O
measured	O
volume	O
.	O
</s>
<s>
Up	O
-	O
and	O
downdrafts	O
slow	O
down	O
the	O
terminal	O
fall	O
velocities	O
and	O
can	O
decrease	O
or	O
increase	O
the	O
Doppler	B-Application
width	O
.	O
</s>
<s>
The	O
knowledge	O
of	O
the	O
actual	O
wind	O
components	O
in	O
the	O
atmosphere	O
can	O
be	O
used	O
to	O
correct	O
the	O
Doppler	B-Application
spectrum	O
,	O
so	O
that	O
the	O
retrieved	O
microphysical	O
parameters	O
can	O
be	O
improved	O
and	O
the	O
uncertainties	O
decreased	O
.	O
</s>
<s>
The	O
skewness	B-General_Concept
parameter	O
of	O
the	O
Doppler	B-Application
spectrum	O
describes	O
the	O
asymmetry	O
of	O
the	O
spectrum	O
with	O
respect	O
to	O
a	O
symmetric	O
Gaussian	O
distribution	O
.	O
</s>
<s>
Therefore	O
,	O
a	O
positive	O
skewness	B-General_Concept
value	O
indicates	O
that	O
the	O
peak	O
is	O
located	O
to	O
the	O
left	O
with	O
respect	O
to	O
the	O
mean	O
.	O
</s>
<s>
A	O
negative	O
skewed	B-General_Concept
spectrum	O
has	O
its	O
peak	O
on	O
the	O
right	O
side	O
with	O
respect	O
to	O
the	O
spectrum	O
mean	O
.	O
</s>
<s>
In	O
this	O
way	O
,	O
the	O
shape	O
of	O
a	O
Doppler	B-Application
gives	O
information	O
on	O
changes	O
of	O
cloud	O
microphysics	O
or	O
of	O
dynamical	O
changes	O
within	O
the	O
measured	O
volume	O
.	O
</s>
<s>
The	O
higher	O
the	O
elevation	O
of	O
the	O
radar	B-Application
is	O
,	O
the	O
higher	O
are	O
the	O
dynamical	O
influences	O
on	O
this	O
parameter	O
.	O
</s>
<s>
Because	O
wind	O
shears	O
lead	O
to	O
a	O
broadening	O
of	O
the	O
Doppler	B-Application
spectrum	O
width	O
,	O
they	O
can	O
lead	O
to	O
rapid	O
changes	O
in	O
skewness	B-General_Concept
as	O
well	O
.	O
</s>
<s>
To	O
be	O
able	O
to	O
relate	O
the	O
change	O
in	O
skewness	B-General_Concept
of	O
the	O
Doppler	B-Application
spectrum	O
,	O
the	O
Doppler	B-Application
width	O
should	O
be	O
cross-checked	O
as	O
well	O
.	O
</s>
<s>
If	O
the	O
radar	B-Application
measurements	O
are	O
done	O
vertically	O
,	O
the	O
skewness	B-General_Concept
of	O
the	O
Doppler	B-Application
spectrum	O
gives	O
information	O
about	O
measured	O
cloud	O
microphysics	O
.	O
</s>
<s>
The	O
horizontal	O
wind	O
within	O
the	O
measured	O
volumes	O
cause	O
only	O
a	O
shift	O
of	O
the	O
whole	O
spectrum	O
within	O
the	O
Doppler	B-Application
domain	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
spectrum	O
is	O
shifted	O
along	O
the	O
Doppler	B-Application
velocity	O
axis	O
but	O
it	O
did	O
not	O
influence	O
the	O
broadening	O
of	O
the	O
spectra	O
.	O
</s>
<s>
The	O
kurtosis	B-Error_Name
of	O
the	O
Doppler	B-Application
spectrum	O
also	O
relates	O
to	O
its	O
curve	O
.	O
</s>
<s>
Since	O
the	O
measure	O
is	O
dominated	O
by	O
the	O
extremes	O
,	O
kurtosis	B-Error_Name
can	O
give	O
information	O
about	O
the	O
spectrum	O
tail	O
weight	O
,	O
helping	O
to	O
describe	O
the	O
spectrum	O
better	O
.	O
</s>
<s>
If	O
a	O
Doppler	B-Application
spectrum	O
is	O
exactly	O
normally	O
distributed	O
,	O
then	O
its	O
kurtosis	B-Error_Name
equals	O
3.0	O
.	O
</s>
<s>
If	O
in	O
general	O
the	O
kurtosis	B-Error_Name
is	O
>3	O
,	O
then	O
the	O
spectrum	O
is	O
called	O
leptokurtic	O
,	O
or	O
leptokurtotic	O
.	O
</s>
<s>
It	O
can	O
be	O
assumed	O
that	O
the	O
Doppler	B-Application
spectrum	O
is	O
dominated	O
by	O
one	O
single	O
particle	O
population	O
that	O
leads	O
to	O
a	O
strong	O
and	O
narrow	O
peak	O
,	O
which	O
in	O
some	O
(	O
but	O
not	O
all	O
)	O
cases	O
is	O
indicated	O
by	O
high	O
kurtosis	B-Error_Name
.	O
</s>
<s>
If	O
the	O
spectrum	O
has	O
kurtosis	B-Error_Name
<3	O
then	O
it	O
is	O
called	O
platykurtic	O
,	O
or	O
platykurtotic	O
.	O
</s>
<s>
The	O
shape	O
of	O
such	O
a	O
spectrum	O
(	O
in	O
some	O
cases	O
)	O
may	O
have	O
a	O
lower	O
,	O
wider	O
peak	O
around	O
the	O
mean	O
and	O
thinner	O
tails	O
,	O
but	O
it	O
can	O
also	O
be	O
infinitely	O
peaked	O
,	O
so	O
kurtosis	B-Error_Name
is	O
not	O
a	O
good	O
measure	O
of	O
"	O
peakedness.	O
"	O
</s>
<s>
Examples	O
of	O
such	O
shapes	O
can	O
be	O
found	O
in	O
the	O
kurtosis	B-Error_Name
wiki	O
entry	O
.	O
</s>
<s>
The	O
Doppler	B-Application
radar	B-Application
kurtosis	B-Error_Name
analysis	O
started	O
quite	O
recently	O
,	O
so	O
there	O
are	O
still	O
few	O
scientific	O
publications	O
dealing	O
with	O
this	O
parameter	O
.	O
</s>
<s>
An	O
example	O
can	O
be	O
found	O
in	O
Kollias	O
et	O
al.	O
,	O
where	O
kurtosis	B-Error_Name
is	O
used	O
to	O
interpret	O
Doppler	B-Application
spectra	O
and	O
to	O
understand	O
the	O
microphysical	O
changes	O
that	O
it	O
represents	O
.	O
</s>
<s>
Polarimetric	O
methods	O
are	O
considered	O
to	O
be	O
a	O
powerful	O
tool	O
in	O
the	O
remote	O
sensing	O
of	O
the	O
atmosphere	O
,	O
and	O
particularly	O
in	O
radar	B-Application
observations	O
of	O
clouds	O
and	O
precipitation	O
.	O
</s>
<s>
Polarimetric	O
techniques	O
have	O
been	O
well	O
developed	O
for	O
operational	O
use	O
in	O
weather	B-Application
radar	I-Application
networks	O
such	O
as	O
American	O
NEXRAD	B-Algorithm
and	O
European	O
OPERA	O
,	O
and	O
,	O
currently	O
,	O
are	O
being	O
implemented	O
in	O
ground	O
based	O
and	O
airborne	O
cloud	O
radars	B-Application
.	O
</s>
<s>
Another	O
potential	O
of	O
polarimetric	O
measurements	O
of	O
cloud	O
radars	B-Application
is	O
the	O
estimation	O
of	O
ice	O
crystals	O
habit	O
that	O
is	O
one	O
of	O
the	O
main	O
problems	O
in	O
remote	O
observations	O
of	O
mixed-phase	O
clouds	O
.	O
</s>
<s>
The	O
assumed	O
shape	O
of	O
ice	O
crystals	O
is	O
considered	O
to	O
be	O
the	O
main	O
source	O
of	O
errors	O
in	O
size	O
and	O
number	O
concentration	O
retrievals	O
based	O
on	O
vertical	O
combined	O
lidar	O
and	O
radar	B-Application
observations	O
.	O
</s>
<s>
Furthermore	O
,	O
in	O
the	O
existing	O
numerical	B-General_Concept
weather	I-General_Concept
prediction	I-General_Concept
models	O
the	O
assumed	O
shape	O
defines	O
the	O
depositional	O
growth	O
rate	O
of	O
ice	O
particles	O
and	O
the	O
area-mass-terminal	O
velocity	O
relations	O
of	O
ice	O
crystals	O
.	O
</s>
<s>
Most	O
of	O
the	O
existing	O
pulse	O
cloud	O
radars	B-Application
operate	O
in	O
the	O
LDR-mode	O
.	O
</s>
<s>
In	O
this	O
mode	O
,	O
a	O
radar	B-Application
transmits	O
a	O
horizontally	O
polarized	O
radiation	O
and	O
receives	O
horizontal	O
and	O
vertical	O
components	O
of	O
the	O
scattered	O
radiation	O
in	O
co-polarized	O
and	O
cross-polarized	O
channels	O
,	O
respectively	O
.	O
</s>
<s>
The	O
ratio	O
of	O
the	O
power	O
in	O
the	O
cross-polarized	O
channel	O
over	O
the	O
power	O
in	O
the	O
co-polarized	O
channel	O
,	O
named	O
as	O
linear	O
depolarization	O
ratio	O
,	O
is	O
the	O
polarimetric	O
variable	O
obtained	O
by	O
cloud	O
radars	B-Application
of	O
this	O
type	O
.	O
</s>
<s>
Often	O
cloud	O
radars	B-Application
have	O
two	O
receiving	O
units	O
,	O
which	O
allows	O
simultaneous	O
measurements	O
of	O
the	O
orthogonal	O
components	O
of	O
the	O
received	O
signal	O
.	O
</s>
<s>
Some	O
cloud	O
radars	B-Application
have	O
only	O
one	O
receiving	O
unit	O
and	O
measure	O
the	O
orthogonal	O
components	O
consequently	O
,	O
with	O
pulse-to-pulse	O
switching	O
of	O
the	O
receiving	O
channel	O
.	O
</s>
<s>
Many	O
of	O
operational	O
cloud	O
radars	B-Application
with	O
LDR-mode	O
are	O
pointed	O
vertically	O
together	O
with	O
other	O
remote	O
sensing	O
instruments	O
in	O
order	O
to	O
retrieve	O
microphysical	O
properties	O
of	O
cloud	O
particles	O
.	O
</s>
<s>
LDR	O
,	O
measured	O
by	O
vertically	O
pointed	O
cloud	O
radar	B-Application
,	O
is	O
used	O
for	O
the	O
detection	O
of	O
the	O
melting	O
layer	O
(	O
also	O
denominated	O
as	O
)	O
and	O
clutter	O
filtering	O
.	O
</s>
<s>
The	O
application	O
of	O
LDR-mode	O
for	O
the	O
shape	O
classification	O
in	O
scanning	O
cloud	O
radars	B-Application
is	O
limited	O
by	O
its	O
high	O
sensitivity	O
to	O
the	O
orientation	O
of	O
scatterers	O
.	O
</s>
<s>
Some	O
cloud	O
radars	B-Application
operate	O
in	O
the	O
SLDR-mode	O
,	O
that	O
is	O
a	O
modification	O
of	O
traditional	O
LDR-mode	O
.	O
</s>
<s>
In	O
this	O
mode	O
the	O
antenna	O
system	O
of	O
the	O
radar	B-Application
is	O
rotated	O
by	O
45°	O
,	O
i.e.	O
</s>
<s>
In	O
contrast	O
to	O
LDR-mode	O
,	O
SLDR-mode	O
is	O
less	O
sensitive	O
to	O
the	O
particles	O
orientation	O
and	O
,	O
therefore	O
,	O
it	O
is	O
used	O
in	O
cloud	O
radars	B-Application
for	O
the	O
classification	O
of	O
ice	O
crystals	O
.	O
</s>
<s>
Determination	O
of	O
ice	O
crystals’	O
habit	O
by	O
ground	O
based	O
cloud	O
radars	B-Application
requires	O
elevation	O
scanning	O
and	O
is	O
based	O
on	O
analysis	O
of	O
the	O
angular	O
changes	O
of	O
the	O
polarimetric	O
variables	O
.	O
</s>
<s>
Polarization-agile	O
cloud	O
radars	B-Application
use	O
pulse-to-pulse	O
switching	O
between	O
horizontal	O
and	O
vertical	O
polarization	O
state	O
of	O
the	O
transmitted	O
wave	O
.	O
</s>
<s>
CDR-mode	O
cloud	O
radars	B-Application
transmit	O
a	O
circularly	O
polarized	O
wave	O
and	O
receive	O
co-polarized	O
and	O
cross-polarized	O
components	O
.	O
</s>
<s>
As	O
the	O
cloud	O
radars	B-Application
sample	O
the	O
atmosphere	O
,	O
they	O
measure	O
the	O
backscatter	B-Algorithm
signal	O
produced	O
by	O
different	O
hydrometeor	O
types	O
(	O
cloud	O
droplets	O
,	O
drizzle	B-Application
,	O
rain	O
drops	O
,	O
ice	O
particles	O
,	O
snow	O
,	O
etc	O
.	O
)	O
</s>
<s>
All	O
these	O
targets	O
have	O
different	O
vertical	O
velocities	O
and	O
shapes	O
,	O
and	O
therefore	O
the	O
Doppler	B-Application
spectra	O
and	O
LDR	O
can	O
be	O
used	O
to	O
distinguish	O
between	O
targets	O
.	O
</s>
<s>
In	O
the	O
figure	O
below	O
,	O
an	O
example	O
of	O
the	O
cloud	O
radar	B-Application
measurements	O
in	O
Potenza	O
is	O
shown	O
,	O
where	O
using	O
the	O
information	O
given	O
by	O
the	O
different	O
parameters	O
,	O
an	O
identification	O
of	O
targets	O
can	O
be	O
done	O
:	O
</s>
<s>
The	O
radars	B-Application
operate	O
continuously	O
at	O
these	O
sites	O
in	O
Oklahoma	O
,	O
Alaska	O
and	O
the	O
tropical	O
western	O
Pacific	O
Ocean	O
,	O
and	O
are	O
designed	O
to	O
function	O
for	O
at	O
least	O
ten	O
years	O
with	O
minimal	O
manned	O
attention	O
.	O
</s>
<s>
Since	O
the	O
late	O
2000s	O
,	O
a	O
meteorological	O
35.5GHz	O
Ka-band	O
commercial	O
cloud	O
radar	B-Application
(	O
)	O
designed	O
by	O
in	O
collaboration	O
with	O
the	O
is	O
in	O
the	O
market	O
.	O
</s>
<s>
,	O
a	O
network	O
of	O
stations	O
for	O
the	O
continuous	O
evaluation	O
of	O
cloud	O
and	O
aerosol	O
profiles	O
in	O
operational	O
NWP	B-General_Concept
models	O
,	O
assimilates	O
their	O
data	O
,	O
as	O
well	O
as	O
data	O
acquired	O
by	O
other	O
instruments	O
in	O
the	O
various	O
sites	O
with	O
this	O
purpose	O
.	O
</s>
<s>
Outside	O
of	O
these	O
networks	O
,	O
some	O
research	O
sites	O
are	O
also	O
operating	O
cloud	O
radars	B-Application
.	O
</s>
<s>
continuously	O
at	O
3.2	O
and	O
9mm	O
for	O
the	O
study	O
of	O
insects	O
migrations	O
,	O
while	O
a	O
35GHz	O
cloud	O
radar	B-Application
is	O
operating	O
in	O
Cabauw	O
(	O
the	O
Netherlands	O
)	O
.	O
</s>
