<s>
The	O
Umkehr	B-Algorithm
is	O
the	O
time	O
variation	O
of	O
the	O
ratio	O
of	O
the	O
scattered	O
intensity	O
at	O
two	O
different	O
wavelengths	O
.	O
</s>
<s>
The	O
Umkehr	B-Algorithm
effect	I-Algorithm
is	O
observed	O
when	O
measurements	O
are	O
made	O
with	O
ultraviolet	B-Application
spectrophotometer	O
of	O
the	O
ratio	O
of	O
the	O
zenith	O
sky	O
light	O
intensities	O
of	O
two	O
wavelengths	O
in	O
the	O
solar	O
ultraviolet	B-Application
when	O
the	O
sun	O
is	O
near	O
the	O
horizon	O
.	O
</s>
<s>
The	O
Umkehr	B-Algorithm
measurement	O
is	O
known	O
as	O
customarily	O
N-value	O
and	O
is	O
given	O
by	O
the	O
logarithm	O
base	O
10	O
of	O
the	O
ratio	O
of	O
cloudless	O
zenith	O
sky	O
intensities	O
at	O
two	O
different	O
wavelengths	O
scaled	O
by	O
a	O
multiplicative	O
factor	O
100	O
plus	O
a	O
constant	O
which	O
depends	O
on	O
instruments	O
and	O
extraterrestrial	O
radiation	O
.	O
</s>
<s>
Methods	O
for	O
deriving	O
vertical	O
distribution	O
from	O
the	O
umkehr	B-Algorithm
measurements	O
were	O
developed	O
by	O
Götz	O
,	O
Dobson	O
and	O
Meetham	O
in	O
1934	O
,	O
using	O
the	O
Dobson	O
ozone	O
spectrophotometer	O
developed	O
by	O
Gordon	O
Dobson	O
.	O
</s>
<s>
In	O
1964	O
Carlton	O
Mateer	O
provided	O
analysis	O
on	O
information	O
content	O
in	O
umkehr	B-Algorithm
measurements	O
.	O
</s>
<s>
This	O
reversal	O
(	O
Umkehr	B-Algorithm
)	O
or	O
inversion	O
implies	O
the	O
existence	O
of	O
maximum	O
of	O
ozone	O
concentration	O
at	O
some	O
level	O
in	O
the	O
atmosphere	O
.	O
</s>
