<s>
Hemispherical	B-Algorithm
photography	I-Algorithm
,	O
also	O
known	O
as	O
canopy	O
photography	O
,	O
is	O
a	O
technique	O
to	O
estimate	O
solar	O
radiation	O
and	O
characterize	O
plant	O
canopy	O
geometry	O
using	O
photographs	O
taken	O
looking	O
upward	O
through	O
an	O
extreme	O
wide-angle	O
lens	O
or	O
a	O
fisheye	O
lens	O
(	O
Rich	O
1990	O
)	O
.	O
</s>
<s>
Hemispherical	B-Algorithm
photography	I-Algorithm
has	O
been	O
used	O
successfully	O
in	O
a	O
broad	O
range	O
of	O
applications	O
involving	O
microsite	O
characterization	O
and	O
estimation	O
of	O
the	O
solar	O
radiation	O
near	O
the	O
ground	O
and	O
beneath	O
plant	O
canopies	O
.	O
</s>
<s>
For	O
example	O
,	O
hemispherical	B-Algorithm
photography	I-Algorithm
has	O
been	O
used	O
to	O
characterize	O
winter	O
roosting	O
sites	O
for	O
monarch	O
butterflies	O
(	O
Weiss	O
et	O
al	O
.	O
</s>
<s>
1996	O
)	O
,	O
impacts	O
of	O
hurricanes	B-Application
on	O
forest	O
ecology	O
(	O
Bellingham	O
et	O
al	O
.	O
</s>
<s>
1996	O
)	O
,	O
leaf	O
area	O
index	O
for	O
validation	O
of	O
remote	B-Application
sensing	I-Application
(	O
Chen	O
et	O
al	O
.	O
</s>
<s>
Hemispherical	B-Algorithm
photography	I-Algorithm
entails	O
five	O
steps	O
:	O
photograph	O
acquisition	O
,	O
digitization	O
,	O
registration	O
,	O
classification	O
,	O
and	O
calculation	O
.	O
</s>
<s>
Registration	O
,	O
classification	O
,	O
and	O
calculation	O
are	O
accomplished	O
using	O
dedicated	O
hemispherical	B-Algorithm
photography	I-Algorithm
analysis	O
software	O
.	O
</s>
<s>
The	O
lens	O
used	O
in	O
hemispherical	B-Algorithm
photography	I-Algorithm
is	O
generally	O
a	O
circular	O
fisheye	O
,	O
such	O
as	O
the	O
Nikkor	O
8mm	O
fisheye	O
lens	O
.	O
</s>
<s>
Full-frame	O
fisheye	O
are	O
not	O
suitable	O
for	O
hemispherical	B-Algorithm
photography	I-Algorithm
,	O
as	O
they	O
only	O
capture	O
a	O
full	O
180°	O
across	O
the	O
diagonal	O
,	O
and	O
do	O
not	O
provide	O
a	O
complete	O
hemispherical	O
view	O
.	O
</s>
<s>
Photograph	O
classification	O
involves	O
determining	O
which	O
image	O
pixels	B-Algorithm
represent	O
visible	O
(	O
non-obscured	O
)	O
versus	O
non-visible	O
(	O
obscured	O
)	O
sky	O
directions	O
.	O
</s>
<s>
Typically	O
this	O
has	O
been	O
accomplished	O
using	O
interactive	O
thresholding	O
,	O
whereby	O
an	O
appropriate	O
threshold	O
is	O
selected	O
to	O
best	O
match	O
a	O
binary	O
classification	O
with	O
observed	O
sky	O
visibility	O
,	O
with	O
pixel	B-Algorithm
intensity	O
values	O
above	O
the	O
threshold	O
classified	O
as	O
visible	O
and	O
pixel	B-Algorithm
intensity	O
values	O
below	O
the	O
threshold	O
classified	O
as	O
non-visible	O
.	O
</s>
