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Fig. 11.19
The EMAP filter
using the Hunning window
(Torres-Verdin and Bostick,
1992)
WH
2
a
1
0
w
-1
-0.5
0
0.5
1
h
1
-0
3
dB
-5
b
-10
-15
0.1
20
dB
-20
-25
-30
-35
0.01
-40
0.01
0.1
1
10
Wk
x
W
=
Ch
eff
1
≤
C
≤
4
,
Z
xy
/
o
. It is strange, because we have to take into account the
scale of near-surface local inhomogeneities rather than the induction in the layered
host medium. Wouldn't it be more reasonable to take
W
where
h
eff
=
x
is the
characteristic dimension of static anomalies producing the geoelectric noise?
Next we consider an areal filtering technique applied by Berdichevsky and
Nechaeva (1975) and Berdichevsky et al. (1989b). In the simplest case, the two-
dimensional filtration of apparent resistivities
x
, where
A
can be performed discretely by
means of a rectangular window
W
x
×
W
y
formed by two box-functions,
B
x
(
x
) and
B
y
(
y
):
N
i
1
flt
A
(
x
o
,
y
o
)
=
A
(
x
i
,
y
j
)
B
x
(
x
i
−
x
o
)
B
y
(
y
j
−
y
o
)
,
(11
.
11)
j
