BSA Flow Software Installation and User's Guide - CSI

Normalize The property Normalize is used to determine whether or not the estimated
autocorrelation function should be normalized. By default this property is set
to No/Off, but changing it to Yes/On the estimate will be normalized to give
the correlation coefficient instead of the correlation itself.
By definition the autocorrelation at lag-time zero should equal the variance
of the measured quantity, and the correlation coefficient ρ(τ) is defined as
the correlation R(τ) divided by the variance V:
( )
ρτ
( τ)
= R
V
In practice the estimated correlation at lag-time zero never matches the
variance exactly, and to avoid problems with this, the correlation coefficient
is estimated by dividing all correlation estimates with the value estimated at
lag-time zero:
( )
ρτ
( τ)
( )
R
≅ ⇒
R0
( )
ρ 0 ≡1
-This ensures that the correlation coefficient at lag-time zero equals one.
Input selection The property Input selection is used to select the data for which a
correlation estimate should be calculated. Clicking in the value field will
bring up the Select Channels dialogue in which the source-data is selected.
Please remember that the correlation object cannot handle more than one
arrival time. Multiple inputs (for example LDA1, LDA2 and LDA3) are thus
allowed only if they share a common arrival time (i.e. if coincidence filtering
has been performed prior to correlation calculation).
If several arrival times are available, only one velocity may be selected, and
the software will then automatically use the corresponding arrival time.
Output from the Correlation object
The Correlation object is a processing object as identified by the -icon in
the project explorer, and like all processing objects it performs calculations,
but does not itself present the results. To see the results you can create a
List-object as a child of the Spectrum object. (See Figure 6-64)
Figure 6-64 Output from the Correlation object
The minimum output from the correlation object is two columns as shown in
Figure 6-64, but if several inputs sharing a common arrival time have been
selected, more columns will be included, corresponding to several
correlations estimated at the same discrete lag-times.
6-68 BSA Flow Software: Options and Add-ons