<s>
Coastal	B-Algorithm
ocean	I-Algorithm
dynamics	I-Algorithm
applications	I-Algorithm
radar	I-Algorithm
(	O
CODAR	B-Algorithm
)	O
describes	O
a	O
type	O
of	O
portable	O
,	O
land-based	O
,	O
high	B-Algorithm
frequency	I-Algorithm
(	O
HF	O
)	O
radar	B-Application
developed	O
between	O
1973	O
and	O
1983	O
at	O
NOAA	O
's	O
Wave	O
Propagation	O
Laboratory	O
in	O
Boulder	O
,	O
Colorado	O
.	O
</s>
<s>
CODAR	B-Algorithm
is	O
a	O
noninvasive	O
system	O
that	O
permits	O
to	O
measure	O
and	O
map	O
near-surface	O
ocean	O
currents	O
in	O
coastal	O
waters	O
.	O
</s>
<s>
Moreover	O
,	O
using	O
CODAR	B-Algorithm
it	O
is	O
possible	O
to	O
measure	O
waves	O
heights	O
and	O
it	O
provides	O
an	O
indirect	O
estimate	O
of	O
local	O
wind	O
direction	O
.	O
</s>
<s>
CODAR	B-Algorithm
utilizes	O
a	O
compact	O
antenna	O
system	O
that	O
consists	O
of	O
crossed	O
loops	O
and	O
a	O
whip	O
for	O
receiving	O
and	O
a	O
whip	O
for	O
transmitting	O
radio	O
pulses	O
.	O
</s>
<s>
CODAR	B-Algorithm
is	O
capable	O
of	O
operating	O
in	O
virtually	O
all	O
weather	O
conditions	O
(	O
it	O
can	O
tolerate	O
temperatures	O
from	O
0°F	O
(	O
-18	O
°C	O
)	O
to	O
90°F	O
(	O
32°C	O
)	O
)	O
and	O
the	O
relatively	O
small	O
dimensions	O
of	O
the	O
antenna	O
system	O
allow	O
CODAR	B-Algorithm
deployment	O
even	O
in	O
highly	O
populated	O
and	O
rocky	O
coastal	O
areas	O
.	O
</s>
<s>
A	O
minicomputer	O
controls	O
the	O
radar	B-Application
and	O
processes	O
the	O
signals	O
and	O
the	O
operator	O
can	O
communicate	O
with	O
the	O
system	O
through	O
a	O
portable	O
keyboard	O
terminal	O
.	O
</s>
<s>
Measuring	O
surface	O
currents	O
is	O
the	O
primary	O
result	O
obtained	O
by	O
using	O
CODAR	B-Algorithm
.	O
</s>
<s>
In	O
general	O
,	O
however	O
,	O
in	O
their	O
long-range	O
mode	O
,	O
modern	O
CODAR	B-Algorithm
can	O
measure	O
out	O
to	O
100	O
–	O
200km	O
offshore	O
with	O
a	O
resolution	O
of	O
3	O
–	O
12km	O
.	O
</s>
<s>
A	O
single	O
CODAR	B-Algorithm
system	O
can	O
measure	O
only	O
the	O
component	O
of	O
surface	O
current	O
travelling	O
toward	O
or	O
away	O
from	O
the	O
radar	B-Application
so	O
,	O
to	O
determine	O
the	O
total	O
surface	O
current	O
vectors	O
,	O
it	O
is	O
necessary	O
to	O
use	O
at	O
least	O
a	O
two-system	O
setup	O
.	O
</s>
<s>
An	O
array	O
of	O
CODAR	B-Algorithm
sites	O
can	O
be	O
employed	O
to	O
obtain	O
regional	O
coverage	O
.	O
</s>
<s>
In	O
a	O
multiple	O
radar	B-Application
configuration	O
,	O
spacing	O
between	O
two	O
radar	B-Application
systems	I-Application
should	O
be	O
approximately	O
15	O
to	O
40km	O
for	O
long-range	O
open	O
ocean	O
mode	O
and	O
8	O
to	O
20km	O
for	O
“	O
higher	O
frequency	O
,	O
higher	O
resolution	O
,	O
shorter	O
range	O
”	O
mode	O
.	O
</s>
<s>
Typically	O
,	O
CODAR	B-Algorithm
data	O
are	O
averaged	O
over	O
one	O
hour	O
to	O
reduce	O
the	O
noisiness	O
of	O
the	O
sea	O
echo	O
.	O
</s>
<s>
CODAR	B-Algorithm
’s	O
measurements	O
are	O
interesting	O
for	O
both	O
military	O
and	O
civil	O
purposes	O
.	O
</s>
<s>
Also	O
,	O
data	O
obtained	O
by	O
using	O
CODAR	B-Algorithm
are	O
used	O
as	O
inputs	O
for	O
global	O
resource	O
monitoring	O
and	O
weather	O
forecasting	O
models	O
and	O
are	O
particularly	O
helpful	O
for	O
tidal	O
and	O
storm-surge	O
measurements	O
.	O
</s>
<s>
CODAR	B-Algorithm
operates	O
using	O
sky	O
transmission	O
of	O
waves	O
in	O
the	O
high	B-Algorithm
frequency	I-Algorithm
(	O
HF	O
)	O
band	O
(	O
3	O
–	O
30MHz	O
)	O
,	O
as	O
electromagnetic	O
waves	O
in	O
this	O
band	O
have	O
wavelengths	O
that	O
are	O
commensurate	O
with	O
wind-driven	O
gravity	O
waves	O
on	O
the	O
ocean	O
surface	O
.	O
</s>
<s>
As	O
the	O
ocean	O
has	O
a	O
rough	O
surface	O
,	O
when	O
a	O
high	B-Algorithm
frequency	I-Algorithm
signal	O
reaches	O
the	O
ocean	O
surface	O
,	O
a	O
portion	O
of	O
the	O
incident	O
energy	O
is	O
scattered	O
back	O
towards	O
the	O
source	O
and	O
the	O
receiver	O
measures	O
the	O
reflected	O
signal	O
.	O
</s>
<s>
This	O
backscattering	B-Algorithm
(	O
or	O
reflection	O
)	O
produces	O
an	O
energy	O
spectrum	O
at	O
the	O
receiver	O
,	O
even	O
if	O
the	O
energy	O
source	O
is	O
single-frequency	O
,	O
because	O
of	O
the	O
shape	O
and	O
motion	O
of	O
the	O
sea	O
surface	O
.	O
</s>
<s>
As	O
a	O
consequence	O
of	O
Bragg	O
’s	O
Scattering	O
Law	O
;	O
the	O
strongest	O
received	O
return	O
comes	O
from	O
ocean	O
waves	O
traveling	O
directly	O
toward	O
or	O
away	O
from	O
the	O
radar	B-Application
source	O
and	O
whose	O
physical	O
wavelength	O
is	O
exactly	O
one-half	O
as	O
long	O
as	O
the	O
transmitted	O
radar	B-Application
wave	O
.	O
</s>
<s>
That	O
is	O
;	O
the	O
scatter	O
velocity	O
along	O
the	O
line	O
between	O
the	O
hit	O
surface	O
and	O
the	O
radar	B-Application
.	O
</s>
<s>
Therefore	O
,	O
CODAR	B-Algorithm
measures	O
the	O
Doppler-induced	O
frequency-shift	O
(	O
along	O
with	O
the	O
distance	O
from	O
the	O
radar	B-Application
to	O
the	O
sector	O
and	O
directional	O
angle	O
)	O
to	O
provide	O
an	O
estimate	O
of	O
the	O
radial-component	O
of	O
wave-speed	O
in	O
the	O
sector	O
of	O
sea	O
surface	O
of	O
interest	O
.	O
</s>
<s>
In	O
order	O
to	O
measure	O
currents	O
,	O
the	O
CODAR	B-Algorithm
equipment	O
computes	O
three	O
components	O
:	O
</s>
<s>
The	O
signal	O
sent	O
from	O
the	O
CODAR	B-Algorithm
antenna	O
has	O
a	O
known	O
frequency	O
and	O
it	O
moves	O
at	O
the	O
speed	O
of	O
light	O
.	O
</s>
<s>
Exploiting	O
the	O
Bragg	O
’s	O
Law	O
,	O
CODAR	B-Algorithm
maximizes	O
the	O
scattered	O
HF	O
signal	O
,	O
given	O
that	O
the	O
resonance	O
will	O
only	O
occur	O
for	O
the	O
given	O
wavelength	O
:	O
</s>
<s>
As	O
the	O
CODAR	B-Algorithm
antennas	O
are	O
usually	O
placed	O
at	O
sea	O
level	O
,	O
the	O
angle	O
of	O
incidence	O
theta	O
can	O
be	O
assumed	O
to	O
be	O
zero	O
.	O
</s>
<s>
Therefore	O
,	O
these	O
waves	O
will	O
produce	O
a	O
scattered	O
signal	O
“	O
stronger	O
”	O
and	O
thus	O
easily	O
identifiable	O
,	O
which	O
is	O
measured	O
by	O
the	O
CODAR	B-Algorithm
system	O
.	O
</s>
<s>
CODAR	B-Algorithm
is	O
a	O
"	O
direction	B-Device
finding	I-Device
system	O
"	O
.	O
</s>
<s>
comparisons	O
with	O
surface	O
drifters	O
and	O
error	O
analysis	O
made	O
in	O
1979	O
indicate	O
that	O
CODAR	B-Algorithm
measures	O
surface	O
currents	O
with	O
at	O
least	O
10cm/s	O
accuracy	O
.	O
</s>
<s>
In	O
2010	O
,	O
retailers	O
of	O
modern	O
CODAR	B-Algorithm
equipments	O
guarantee	O
an	O
accuracy	O
typically	O
<	O
7cm/s	O
of	O
the	O
total	O
current	O
velocity	O
and	O
1	O
–	O
2cm	O
of	O
the	O
tidal	O
component	O
,	O
in	O
normal	O
environment	O
condition	O
.	O
</s>
<s>
CODAR	B-Algorithm
does	O
not	O
permit	O
to	O
measure	O
currents	O
and	O
waves	O
in	O
the	O
area	O
closer	O
than	O
2km	O
from	O
its	O
location	O
.	O
</s>
<s>
In	O
this	O
lapse	O
of	O
time	O
,	O
any	O
signal	O
backscattered	B-Algorithm
is	O
lost	O
.	O
</s>
<s>
CODAR	B-Algorithm
’s	O
resolution	O
cell	O
size	O
is	O
generally	O
bigger	O
than	O
5km2	O
.	O
</s>
<s>
As	O
discussed	O
before	O
,	O
for	O
a	O
given	O
look	O
angle	O
,	O
a	O
single	O
CODAR	B-Algorithm
station	O
permits	O
to	O
detect	O
only	O
the	O
component	O
of	O
flow	O
traveling	O
toward	O
or	O
away	O
from	O
its	O
location	O
.	O
</s>
<s>
Moreover	O
,	O
when	O
using	O
two	O
CODAR	B-Algorithm
stations	O
the	O
so-called	O
“	O
baseline	O
problem	O
”	O
can	O
affect	O
the	O
measurement	O
.	O
</s>
