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Let us come back to Fig. 3.13. In a model with the two-dimensional regional
background,
ske
2. So, applying
the Cantwell-Bibby-Brown method, we determine the principal directions of the
phase tensor that coincide with principal directions defined by Bahr's formula. Here
the Cantwell-Bibby-Brown and Bahr methods give the identical results.
In the general case of the three-dimensonal asymmetric regional background,
ske
w
CBB
=
0
,
ske
w
B
=
0 and
1
=
,
2
= +
/
2. Here we determine the principal
directions of the phase tensor by the formula that is identical to Bahr's formula, but
introduce a correction
w
CBB
=
0 and
1
= −
,
2
= − +
/
w
CBB
for the regional background asymmetry. It is
simply evident that such a correction makes sense if
=
ske
considerably exceeds errors
in the phase measurements With small
we can neglect the asymmetry and resort
to the two-dimensional (or axially symmetric three-dimensional) approximation of
the regional background.
Evidently, the Caldwell-Bibby-Brown method may be viewed as a three-
dimensional generalization of the Bahr method.
