<s>
Remote	B-General_Concept
sensing	I-General_Concept
in	O
oceanography	O
is	O
a	O
widely	O
used	O
observational	O
technique	O
which	O
enables	O
researchers	O
to	O
acquire	O
data	O
of	O
a	O
location	O
without	O
physically	O
measuring	O
at	O
that	O
location	O
.	O
</s>
<s>
Remote	B-General_Concept
sensing	I-General_Concept
in	O
oceanography	O
mostly	O
refers	O
to	O
measuring	O
properties	O
of	O
the	O
ocean	O
surface	O
with	O
sensors	O
on	O
satellites	B-Application
or	O
planes	O
,	O
which	O
compose	O
an	O
image	O
of	O
captured	O
electromagnetic	O
radiation	O
.	O
</s>
<s>
A	O
remote	B-General_Concept
sensing	I-General_Concept
instrument	O
can	O
either	O
receive	O
radiation	O
from	O
the	O
earth	O
’s	O
surface	O
(	O
passive	O
)	O
,	O
whether	O
reflected	O
from	O
the	O
sun	O
or	O
emitted	O
,	O
or	O
send	O
out	O
radiation	O
to	O
the	O
surface	O
and	O
catch	O
the	O
reflection	O
(	O
active	O
)	O
.	O
</s>
<s>
All	O
remote	B-General_Concept
sensing	I-General_Concept
instruments	O
carry	O
a	O
sensor	O
to	O
capture	O
the	O
intensity	O
of	O
the	O
radiation	O
at	O
specific	O
wavelength	O
windows	O
,	O
to	O
retrieve	O
a	O
spectral	O
signature	O
for	O
every	O
location	O
.	O
</s>
<s>
Unlike	O
passive	O
instruments	O
,	O
active	O
remote	B-General_Concept
sensing	I-General_Concept
instruments	O
also	O
measure	O
the	O
two-way	O
travel	O
time	O
of	O
the	O
signal	O
;	O
which	O
is	O
used	O
to	O
calculate	O
the	O
distance	O
between	O
the	O
sensor	O
and	O
the	O
imaged	O
surface	O
.	O
</s>
<s>
Remote	B-General_Concept
sensing	I-General_Concept
satellites	B-Application
often	O
carry	O
other	O
instruments	O
which	O
keep	O
track	O
of	O
their	O
location	O
and	O
measure	O
atmospheric	O
conditions	O
.	O
</s>
<s>
Remote	B-General_Concept
sensing	I-General_Concept
observations	O
,	O
in	O
comparison	O
to	O
(	O
most	O
)	O
physical	O
observations	O
,	O
are	O
consistent	O
in	O
time	O
and	O
have	O
good	O
spatial	O
coverage	O
.	O
</s>
<s>
Since	O
the	O
ocean	O
is	O
fluid	O
,	O
it	O
is	O
constantly	O
changing	O
on	O
different	O
spatial	O
and	O
temporal	B-General_Concept
scales	O
.	O
</s>
<s>
Capturing	O
the	O
spatial	O
variation	O
of	O
the	O
ocean	O
with	O
remote	B-General_Concept
sensing	I-General_Concept
is	O
considered	O
extremely	O
valuable	O
and	O
is	O
on	O
the	O
frontier	O
of	O
oceanographic	O
research	O
.	O
</s>
<s>
The	O
high	O
variability	O
of	O
the	O
ocean	O
surface	O
is	O
also	O
the	O
deterministic	O
factor	O
in	O
the	O
differences	O
between	O
land	O
and	O
ocean	O
remote	B-General_Concept
sensing	I-General_Concept
.	O
</s>
<s>
Remote	B-General_Concept
sensing	I-General_Concept
is	O
actively	O
used	O
in	O
various	O
fields	O
of	O
natural	O
sciences	O
like	O
geology	B-General_Concept
,	O
physical	O
geography	O
,	O
ecology	O
,	O
archeology	O
and	O
meteorology	O
but	O
,	O
remote	B-General_Concept
sensing	I-General_Concept
of	O
the	O
ocean	O
is	O
vastly	O
different	O
.	O
</s>
<s>
The	O
temporal	B-General_Concept
variability	O
in	O
the	O
object	O
of	O
study	O
determines	O
the	O
usability	O
of	O
specific	O
data	O
and	O
the	O
applicable	O
methods	O
and	O
is	O
the	O
reason	O
why	O
remote	B-General_Concept
sensing	I-General_Concept
methods	O
differ	O
materially	O
between	O
ocean	O
and	O
land	O
surfaces	O
.	O
</s>
<s>
A	O
single	O
wave	O
on	O
the	O
surface	O
of	O
the	O
ocean	O
can	O
not	O
be	O
tracked	O
by	O
satellites	B-Application
of	O
today	O
.	O
</s>
<s>
Remote	B-General_Concept
sensing	I-General_Concept
enables	O
temporal	B-General_Concept
analysis	O
over	O
vast	O
spatial	O
scale	O
,	O
since	O
satellites	B-Application
have	O
a	O
constant	O
revisit	O
time	O
,	O
provide	O
a	O
wide	O
image	O
and	O
are	O
often	O
operational	O
for	O
multiple	O
consecutive	O
years	O
.	O
</s>
<s>
Remote	B-General_Concept
sensing	I-General_Concept
as	O
we	O
know	O
it	O
today	O
started	O
with	O
the	O
first	O
earth	O
orbiting	O
satellite	B-Application
Landsat	O
1	O
in	O
1973	O
.	O
</s>
<s>
In	O
1978	O
NASA	O
makes	O
the	O
next	O
step	O
in	O
remote	B-General_Concept
sensing	I-General_Concept
for	O
oceanography	O
with	O
the	O
launch	O
of	O
the	O
first	O
orbiting	O
satellite	B-Application
dedicated	O
to	O
ocean	O
research	O
,	O
Seasat	B-Algorithm
.	O
</s>
<s>
The	O
satellite	B-Application
carried	O
5	O
different	O
instruments	O
:	O
a	O
Radar	B-Application
altimeter	O
for	O
retrieving	O
sea	O
surface	O
height	O
,	O
a	O
microwave	O
scatterometer	O
to	O
retrieve	O
wind	O
speeds	O
and	O
direction	O
,	O
a	O
microwave	O
radiometer	O
to	O
retrieve	O
sea	O
surface	O
temperature	O
(	O
SST	O
)	O
,	O
an	O
optical	O
and	O
infrared	O
radiometer	O
to	O
check	O
for	O
clouds	O
and	O
surface	O
characteristics	O
and	O
lastly	O
the	O
first	O
Synthetic	O
Aperture	O
Radar	B-Application
(	O
SAR	O
)	O
instrument	O
.	O
</s>
<s>
Seasat	B-Algorithm
was	O
only	O
operational	O
for	O
a	O
few	O
months	O
but	O
,	O
together	O
with	O
the	O
Coastal	O
Zone	O
Color	O
Scanner	O
(	O
CZCS	O
)	O
on	O
Nimbus-7	O
,	O
proved	O
the	O
feasibility	O
of	O
many	O
techniques	O
and	O
instruments	O
in	O
ocean	O
remote	B-General_Concept
sensing	I-General_Concept
.	O
</s>
<s>
TOPEX/POSEIDON	O
,	O
an	O
altimeter	O
launched	O
in	O
1992	O
,	O
provided	O
the	O
first	O
continuous	O
global	O
map	O
of	O
sea	O
surface	O
topography	O
and	O
continued	O
on	O
the	O
possibilities	O
explored	O
by	O
Seasat	B-Algorithm
.	O
</s>
<s>
The	O
Jason-1	B-Algorithm
,	O
Jason-2	B-Algorithm
and	O
Jason-3	O
missions	O
continue	O
the	O
measurements	O
from	O
1992	O
to	O
today	O
to	O
form	O
a	O
complete	O
time-series	O
of	O
the	O
global	O
sea	O
surface	O
height	O
.	O
</s>
<s>
Also	O
other	O
techniques	O
hosted	O
on	O
Seasat	B-Algorithm
found	O
continuation	O
.	O
</s>
<s>
The	O
European	O
Space	O
Agency	O
(	O
ESA	O
)	O
further	O
developed	O
SAR	O
with	O
the	O
ERS-2	B-Algorithm
,	O
ENVISAT	B-Algorithm
and	O
now	O
Sentinel-1	B-Algorithm
missions	O
by	O
providing	O
larger	O
spatial	O
footprints	O
,	O
lowering	O
the	O
resolution	O
and	O
flying	O
twin	O
missions	O
to	O
reduce	O
the	O
effective	O
revisit	O
time	O
.	O
</s>
<s>
Optical	O
remote	B-General_Concept
sensing	I-General_Concept
of	O
the	O
ocean	O
found	O
continuation	O
after	O
the	O
CZCS	O
with	O
polar	O
orbiting	O
missions	O
ENVISAT	B-Algorithm
,	O
OrbView-2	O
,	O
MODIS	B-Application
and	O
very	O
recently	O
with	O
Sentinel-3	B-Algorithm
,	O
to	O
form	O
a	O
continuous	O
record	O
since	O
1997	O
.	O
</s>
<s>
Sentinel-3	B-Algorithm
is	O
now	O
one	O
of	O
the	O
best	O
equipped	O
missions	O
to	O
map	O
the	O
ocean	O
hosting	O
a	O
SAR	O
altimiter	O
,	O
multispectral	O
spectrometer	O
a	O
radiometer	O
and	O
several	O
other	O
instruments	O
on	O
multiple	O
satellites	B-Application
with	O
alternating	O
orbits	O
providing	O
exceptional	O
temporal	B-General_Concept
and	O
spatial	O
resolution	O
.	O
</s>
<s>
Sensors	O
on	O
remote	B-General_Concept
sensing	I-General_Concept
instruments	O
capture	O
radiation	O
,	O
which	O
can	O
be	O
translated	O
back	O
to	O
deduce	O
the	O
physio-chemical	O
properties	O
of	O
the	O
surface	O
.	O
</s>
<s>
A	O
sensor	O
on	O
a	O
satellite	B-Application
returns	O
the	O
composite	O
signal	O
for	O
a	O
certain	O
area	O
inside	O
the	O
footprint	O
called	O
a	O
cell	O
,	O
the	O
size	O
of	O
the	O
unique	O
cells	O
is	O
referred	O
to	O
as	O
the	O
spatial	O
resolution	O
.	O
</s>
<s>
A	O
satellite	B-Application
passes	O
over	O
the	O
same	O
location	O
consistently	O
through	O
time	O
with	O
the	O
same	O
interval	O
called	O
the	O
revisit-time	O
or	O
temporal	B-General_Concept
resolution	I-General_Concept
.	O
</s>
<s>
Sensors	O
can	O
not	O
have	O
both	O
a	O
very	O
high	O
temporal	B-General_Concept
and	O
spatial	O
resolution	O
so	O
a	O
tradeoff	O
has	O
to	O
be	O
made	O
specific	O
for	O
the	O
goal	O
of	O
the	O
mission	O
.	O
</s>
<s>
Sensors	O
on	O
satellites	B-Application
have	O
measuring	O
errors	O
,	O
caused	O
by	O
for	O
example	O
atmospheric	O
interference	O
,	O
geolocation	O
imprecision	O
and	O
topographic	O
distortion	O
.	O
</s>
<s>
Complete	O
derived	O
products	O
from	O
remote	B-General_Concept
sensing	I-General_Concept
often	O
use	O
simple	O
calculations	O
or	O
algorithms	O
to	O
transform	O
the	O
spectral	O
signature	O
from	O
a	O
cell	O
to	O
a	O
physical	O
value	O
.	O
</s>
<s>
Change	O
detection	O
leverages	O
the	O
consistent	O
temporal	B-General_Concept
component	O
of	O
remote	B-General_Concept
sensing	I-General_Concept
data	O
to	O
analyze	O
the	O
change	O
of	O
surface	O
properties	O
in	O
time	O
.	O
</s>
<s>
In	O
land	O
remote	B-General_Concept
sensing	I-General_Concept
change	O
detection	O
is	O
used	O
for	O
example	O
:	O
to	O
assess	O
the	O
impact	O
of	O
a	O
volcano	O
eruption	O
,	O
check	O
the	O
growth	O
of	O
plants	O
through	O
time	O
,	O
map	O
deforestation	O
,	O
and	O
measure	O
ice	O
sheet	O
melt	O
.	O
</s>
<s>
In	O
oceanography	O
the	O
surface	O
changes	O
more	O
quickly	O
than	O
the	O
revisit	O
time	O
of	O
a	O
satellite	B-Application
making	O
it	O
difficult	O
to	O
monitor	O
certain	O
processes	O
.	O
</s>
<s>
Change	O
detection	O
in	O
oceanography	O
requires	O
the	O
characteristic	O
to	O
change	O
continuously	O
like	O
sea	O
level	O
rise	O
or	O
change	O
spatial	O
scale	O
slower	O
than	O
the	O
revisit	O
time	O
of	O
the	O
satellite	B-Application
like	O
algal	O
blooms	O
.	O
</s>
<s>
Another	O
way	O
to	O
infer	O
change	O
from	O
only	O
1	O
acquisition	O
is	O
by	O
computing	O
the	O
dynamical	O
component	O
and	O
direction	O
from	O
a	O
static	O
image	O
which	O
is	O
leveraged	O
in	O
RADAR	B-Application
altimetry	O
to	O
deduce	O
surface	O
current	O
velocity	O
.	O
</s>
<s>
The	O
radiation	O
coming	O
from	O
the	O
earth	O
's	O
surface	O
with	O
a	O
wavelength	O
within	O
the	O
atmospheric	O
window	O
can	O
be	O
captured	O
by	O
a	O
passive	O
radiometry	O
sensor	O
at	O
satellite	B-Application
height	O
.	O
</s>
<s>
Phenomena	O
close	O
but	O
not	O
at	O
the	O
surface	O
like	O
diurnal	O
thermocline	O
formation	O
are	O
not	O
well	O
captured	O
with	O
satellites	B-Application
but	O
SST	O
can	O
still	O
be	O
of	O
tremendous	O
value	O
in	O
oceanography	O
.	O
</s>
<s>
Overall	O
satellites	B-Application
measure	O
the	O
SST	O
with	O
a	O
~	O
0.1-0.6	O
K	O
accuracy	O
dependent	O
on	O
the	O
sensor	O
and	O
only	O
experience	O
limited	O
issues	O
like	O
surface	O
slicks	O
.	O
</s>
<s>
The	O
currents	O
and	O
fronts	O
are	O
visible	O
in	O
SST	O
images	O
and	O
can	O
be	O
detected	O
using	O
edge	B-Algorithm
detection	I-Algorithm
via	O
high	O
pass	O
filters	O
or	O
kernel	O
transformations	O
to	O
study	O
the	O
dynamics	O
and	O
origin	O
.	O
</s>
<s>
Optical	O
satellites	B-Application
like	O
Sentinel-2	O
or	O
active	O
radiometers	O
like	O
Sentinel-3	B-Algorithm
and	O
MODIS	B-Application
can	O
capture	O
the	O
reflectance	O
of	O
the	O
ocean	O
surface	O
in	O
the	O
visible	O
and	O
near-infrared	O
spectrum	O
.	O
</s>
<s>
RADAR	B-Application
altimeters	O
send	O
microwave	O
pulses	O
to	O
the	O
surface	O
and	O
catch	O
the	O
reflection	O
intensity	O
over	O
a	O
short	O
time	O
period	O
measuring	O
the	O
two-way	O
travel	O
time	O
of	O
the	O
signal	O
.	O
</s>
<s>
Electromagnetic	O
radiation	O
travels	O
with	O
the	O
speed	O
of	O
light	O
thus	O
the	O
two	O
way	O
travel	O
time	O
gives	O
information	O
on	O
the	O
height	O
of	O
the	O
satellite	B-Application
above	O
the	O
surface	O
following	O
the	O
formula	O
.	O
</s>
<s>
To	O
deduce	O
the	O
sea	O
surface	O
height	O
from	O
the	O
satellite	B-Application
height	O
the	O
two-way	O
travel	O
time	O
has	O
to	O
be	O
corrected	O
for	O
dynamical	O
errors	O
,	O
the	O
atmospheric	O
conditions	O
and	O
the	O
local	O
geoid	O
height	O
.	O
</s>
<s>
is	O
the	O
height	O
of	O
the	O
satellite	B-Application
above	O
the	O
reference	O
ellipsoid	O
which	O
is	O
in	O
the	O
order	O
of	O
a	O
100km	O
and	O
is	O
known	O
with	O
a	O
cm	O
precision	O
.	O
</s>
<s>
is	O
the	O
height	O
of	O
the	O
satellite	B-Application
above	O
the	O
ocean	O
surface	O
and	O
is	O
the	O
quantity	O
measured	O
by	O
the	O
satellite	B-Application
with	O
cm	O
precision	O
.	O
</s>
<s>
As	O
a	O
solution	O
remote	B-General_Concept
sensing	I-General_Concept
analysts	O
use	O
the	O
Sea	O
Surface	O
Height	O
Anomaly	O
(	O
SSHA	O
)	O
which	O
only	O
requires	O
information	O
on	O
the	O
tidal	O
height	O
and	O
atmospheric	O
pressure	O
,	O
which	O
can	O
be	O
deduced	O
from	O
drifters	O
,	O
weather	O
programs	O
and	O
tidal	O
models	O
.	O
</s>
<s>
The	O
geoid	O
height	O
for	O
SSHA	O
retrieval	O
is	O
deduced	O
from	O
a	O
long	O
time-series	O
of	O
the	O
same	O
RADAR	B-Application
altimetry	O
data	O
.	O
</s>
<s>
The	O
SSHA	O
is	O
computed	O
by	O
subtracting	O
the	O
temporal	B-General_Concept
mean	O
of	O
the	O
SSH	O
or	O
Mean	O
Sea	O
Surface	O
(	O
MSS	O
)	O
from	O
the	O
current	O
SSH	O
with	O
so	O
that	O
:	O
</s>
<s>
The	O
dynamical	O
sea	O
surface	O
height	O
from	O
radar	B-Application
altimetry	O
provides	O
useful	O
insight	O
into	O
ocean	O
currents	O
.	O
</s>
<s>
If	O
assuming	O
geostrophic	O
balance	O
,	O
the	O
velocity	O
anomaly	O
and	O
direction	O
of	O
surface	O
currents	O
perpendicular	O
to	O
the	O
satellite	B-Application
overpass	O
can	O
be	O
computed	O
using	O
the	O
formula	O
:	O
</s>
<s>
RADAR	B-Application
altimeters	O
are	O
able	O
to	O
collect	O
data	O
even	O
in	O
cloudy	O
circumstances	O
but	O
only	O
cover	O
the	O
globe	O
up	O
to	O
latitudes	O
~	O
60	O
-	O
65°	O
.	O
</s>
<s>
Often	O
the	O
spatial	O
resolution	O
of	O
RADAR	B-Application
altimeters	O
is	O
not	O
too	O
high	O
but	O
their	O
temporal	B-General_Concept
coverage	O
is	O
tremendous	O
,	O
allowing	O
constant	O
monitoring	O
of	O
the	O
ocean	O
surface	O
.	O
</s>
<s>
RADAR	B-Application
altimeters	O
can	O
also	O
be	O
used	O
to	O
determine	O
the	O
specific	O
wave	O
height	O
and	O
estimate	O
wind	O
velocities	O
using	O
the	O
wave	O
form	O
and	O
backscatter	O
coefficient	O
of	O
the	O
pulse	O
limited	O
return	O
signal	O
.	O
</s>
<s>
There	O
can	O
be	O
numerous	O
limitations	O
with	O
the	O
sensors	O
and	O
techniques	O
used	O
by	O
remote	B-General_Concept
sensing	I-General_Concept
tools	O
when	O
it	O
comes	O
to	O
mapping	O
coastal	O
regions	O
.	O
</s>
<s>
Some	O
challenges	O
stem	O
from	O
issues	O
with	O
resolution	O
and	O
pixel	O
size	O
,	O
as	O
most	O
remote	O
imaging	O
satellites	B-Application
have	O
a	O
pixel	O
size	O
of	O
approximately	O
1	O
square	O
kilometer	O
.	O
</s>
<s>
This	O
presents	O
issues	O
with	O
analyzing	O
coastal	O
regions	O
in	O
the	O
desired	O
level	O
of	O
detail	O
as	O
most	O
coastal	O
processes	O
occur	O
on	O
a	O
spatial	O
scale	O
that	O
is	O
approximately	O
the	O
same	O
(	O
or	O
smaller	O
)	O
than	O
the	O
pixel	O
size	O
provided	O
by	O
remote	O
imaging	O
satellites	B-Application
.	O
</s>
<s>
Additionally	O
,	O
most	O
ocean	O
sensors	O
have	O
a	O
global	O
coverage	O
frequency	O
of	O
1-2	O
days	O
,	O
which	O
may	O
be	O
too	O
long	O
to	O
observe	O
the	O
temporal	B-General_Concept
scale	O
of	O
coastal	O
ocean	O
processes	O
.	O
</s>
<s>
Furthermore	O
,	O
remote	B-General_Concept
sensing	I-General_Concept
of	O
coastal	O
areas	O
has	O
faced	O
challenges	O
in	O
accurately	O
interpreting	O
the	O
color	O
of	O
the	O
ocean	O
.	O
</s>
<s>
The	O
satellites	B-Application
can	O
also	O
be	O
influenced	O
by	O
"	O
adjacency	O
effects	O
"	O
,	O
where	O
the	O
color	O
of	O
the	O
land	O
can	O
bleed	O
into	O
coastal	O
ocean	O
pixels	O
.	O
</s>
<s>
All	O
of	O
these	O
factors	O
can	O
make	O
it	O
increasingly	O
challenging	O
to	O
accurately	O
analyze	O
coastal	O
regions	O
from	O
remote	B-General_Concept
sensing	I-General_Concept
satellites	B-Application
.	O
</s>
<s>
Satellites	B-Application
,	O
while	O
the	O
core	O
of	O
remote	B-General_Concept
sensing	I-General_Concept
,	O
have	O
limitations	O
in	O
their	O
spatial	O
,	O
spectral	O
,	O
and	O
temporal	B-General_Concept
resolution	I-General_Concept
.	O
</s>
<s>
In	O
an	O
effort	O
to	O
combat	O
these	O
limitations	O
,	O
satellite	B-Application
remote	B-General_Concept
sensing	I-General_Concept
utilizes	O
interpolation	O
and	O
modelling	O
to	O
fill	O
in	O
the	O
gaps	O
.	O
</s>
<s>
The	O
use	O
of	O
UAVs	O
,	O
or	O
drones	O
,	O
as	O
a	O
remote	B-General_Concept
sensing	I-General_Concept
tool	O
can	O
provide	O
data	O
at	O
higher	O
resolutions	O
that	O
can	O
then	O
be	O
used	O
to	O
fill	O
in	O
the	O
gaps	O
in	O
satellite	B-Application
data	O
,	O
often	O
at	O
a	O
lower	O
price	O
than	O
satellites	B-Application
or	O
manned	O
aircraft	O
.	O
</s>
<s>
Notable	O
benefits	O
can	O
be	O
found	O
in	O
the	O
pixel	O
gaps	O
found	O
along	O
coastal	O
areas	O
in	O
satellite	B-Application
data	O
as	O
well	O
as	O
the	O
ability	O
to	O
conduct	O
observations	O
of	O
a	O
given	O
area	O
between	O
satellite	B-Application
passes	O
.	O
</s>
<s>
These	O
sensors	O
consist	O
of	O
multispectral	O
,	O
hyperspectral	B-Application
sensors	O
as	O
well	O
as	O
standard	O
visual	O
spectrum	O
,	O
high	O
definition	O
cameras	O
.	O
</s>
<s>
Satellites	B-Application
and	O
manned	O
aircraft	O
require	O
shore-based	O
facilities	O
or	O
ships	O
capable	O
of	O
supporting	O
take-off	O
and	O
landing	O
operations	O
.	O
</s>
<s>
There	O
are	O
some	O
limiting	O
factors	O
to	O
UAV	O
use	O
for	O
oceanic	O
remote	B-General_Concept
sensing	I-General_Concept
.	O
</s>
<s>
Furthermore	O
,	O
the	O
sensors	O
themselves	O
encounter	O
similar	O
challenges	O
to	O
the	O
sensors	O
mounted	O
on	O
satellites	B-Application
,	O
namely	O
in	O
alterations	O
to	O
oceanic	O
reflectance	O
in	O
coastal	O
zones	O
;	O
however	O
,	O
the	O
higher	O
resolution	O
provided	O
by	O
UAV	O
mounted	O
sensors	O
allows	O
for	O
a	O
more	O
diverse	O
assignment	O
of	O
pixels	O
,	O
reducing	O
the	O
blending	O
effect	O
of	O
terrestrial	O
and	O
aquatic	O
environments	O
and	O
reducing	O
the	O
amount	O
of	O
calculations	O
needed	O
to	O
account	O
for	O
reflectance	O
shifts	O
.	O
</s>
