<s>
Isoline	B-General_Concept
retrieval	I-General_Concept
is	O
a	O
remote	B-Application
sensing	I-Application
inverse	B-Algorithm
method	I-Algorithm
that	O
retrieves	O
one	O
or	O
more	O
isolines	O
of	O
a	O
trace	O
atmospheric	O
constituent	O
or	O
variable	O
.	O
</s>
<s>
When	O
used	O
to	O
retrieve	O
a	O
whole	O
field	O
,	O
it	O
is	O
a	O
general	O
,	O
nonlinear	O
inverse	B-Algorithm
method	I-Algorithm
and	O
a	O
robust	O
estimator	O
.	O
</s>
<s>
and	O
we	O
wish	O
to	O
validate	O
this	O
against	O
satellite	O
remote-sensing	B-Application
data	O
.	O
</s>
<s>
from	O
a	O
set	O
of	O
training	O
data	O
is	O
variable	B-General_Concept
kernel	I-General_Concept
density	I-General_Concept
estimation	I-General_Concept
.	O
</s>
<s>
most	O
collocation	B-General_Concept
procedures	O
,	O
</s>
<s>
and	O
constitutes	O
a	O
general	O
,	O
nonlinear	O
inverse	B-Algorithm
method	I-Algorithm
.	O
</s>
