<s>
Anomalous	B-Algorithm
propagation	I-Algorithm
(	O
sometimes	O
shortened	O
to	O
anaprop	B-Algorithm
or	O
anoprop	B-Algorithm
)	O
includes	O
different	O
forms	O
of	O
radio	O
propagation	O
due	O
to	O
an	O
unusual	O
distribution	O
of	O
temperature	O
and	O
humidity	O
with	O
height	O
in	O
the	O
atmosphere	O
.	O
</s>
<s>
Anomalous	B-Algorithm
propagation	I-Algorithm
can	O
cause	O
interference	O
to	O
VHF	O
and	O
UHF	O
radio	O
communications	O
if	O
distant	O
stations	O
are	O
using	O
the	O
same	O
frequency	O
as	O
local	O
services	O
.	O
</s>
<s>
Radar	B-Application
systems	I-Application
may	O
produce	O
inaccurate	O
ranges	O
or	O
bearings	O
to	O
distant	O
targets	O
if	O
the	O
radar	B-Application
"	O
beam	O
"	O
is	O
bent	O
by	O
propagation	O
effects	O
.	O
</s>
<s>
Other	O
ways	O
anomalous	B-Algorithm
propagation	I-Algorithm
is	O
recorded	O
is	O
by	O
troposcatters	O
causing	O
irregularities	O
in	O
the	O
troposphere	O
,	O
scattering	O
due	O
to	O
meteors	B-Language
,	O
refraction	O
in	O
the	O
ionized	O
regions	O
and	O
layers	O
of	O
the	O
ionosphere	O
,	O
and	O
reflection	O
from	O
the	O
ionosphere	O
.	O
</s>
<s>
Anomalous	B-Algorithm
propagation	I-Algorithm
can	O
be	O
a	O
limiting	O
factor	O
for	O
the	O
propagation	O
of	O
radiowaves	O
,	O
especially	O
the	O
super	O
refraction	O
.	O
</s>
<s>
The	O
position	O
of	O
the	O
radar	B-Application
echoes	O
depend	O
heavily	O
on	O
the	O
standard	O
decrease	O
of	O
temperature	O
hypothesis	O
.	O
</s>
<s>
Anomalous	B-Algorithm
Propagation	I-Algorithm
(	O
AP	O
)	O
refers	O
to	O
false	O
radar	B-Application
echoes	O
usually	O
observed	O
when	O
calm	O
,	O
stable	O
atmospheric	O
conditions	O
,	O
often	O
associated	O
with	O
super	O
refraction	O
in	O
a	O
temperature	O
inversion	O
,	O
direct	O
the	O
radar	B-Application
beam	O
toward	O
the	O
ground	O
.	O
</s>
<s>
After	O
sunrise	B-Application
,	O
the	O
inversion	O
disappears	O
gradually	O
and	O
the	O
area	O
diminishes	O
correspondingly	O
.	O
</s>
<s>
Anomalous	B-Algorithm
Propagation	I-Algorithm
is	O
different	O
from	O
ground	O
clutter	O
,	O
ocean	O
reflections	O
(	O
sea	O
clutter	O
)	O
,	O
biological	O
returns	O
from	O
birds	O
and	O
insects	O
,	O
debris	O
,	O
chaff	O
,	O
sand	B-Application
storms	I-Application
,	O
volcanic	O
eruption	O
plumes	O
,	O
and	O
other	O
non-precipitation	O
meteorological	O
phenomena	O
.	O
</s>
<s>
They	O
are	O
all	O
indicating	O
something	O
actually	O
there	O
and	O
either	O
relevant	O
to	O
the	O
radar	B-Application
operator	O
and/or	O
readily	O
explicable	O
and	O
theoretically	O
able	O
to	O
be	O
reproduced	O
.	O
</s>
<s>
AP	O
in	O
the	O
sense	O
of	O
radar	B-Application
is	O
colloquially	O
known	O
as	O
"	O
garbish	O
"	O
and	O
ground	O
clutter	O
as	O
"	O
rubbage	O
"	O
.	O
</s>
<s>
Doppler	B-Algorithm
radars	I-Algorithm
and	O
Pulse-Doppler	B-Algorithm
radars	I-Algorithm
are	O
extracting	O
the	O
velocities	O
of	O
the	O
targets	O
.	O
</s>
<s>
Since	O
AP	O
comes	O
from	O
stable	O
targets	O
,	O
it	O
is	O
possible	O
to	O
subtract	O
the	O
reflectivity	O
data	O
having	O
a	O
null	O
speed	O
and	O
clean	O
the	O
radar	B-Application
images	O
.	O
</s>
<s>
This	O
method	O
is	O
used	O
in	O
most	O
modern	O
radars	B-Application
,	O
including	O
air	O
traffic	O
control	O
and	O
weather	B-Application
radars	I-Application
.	O
</s>
