The "Frequency Domain" tab provides you with control over the curve fitting mechanism. By default curve fitting is only performed between the "Low Cut" and the "High Cut" frequencies (the primary controls) which are defined in the "Fit Well Log Curves" group on the "Design Controls" dialog. This curve fit is referred to as the "Principle" curve. Below the "Low Cut" and above the "High Cut" we force to horizontal with the value of the "Principle" at the "Low Cut" and "High Cut" points.

Whilst using these advance controls it is advisable to QC the resulting curve fit by always having the spectrum you are trying to fit and the composite curve fit visible on one of the SsbQt Main Window charts (by default the "Global" chart). Immediately you make a change to one or more of the "Frequency Domain" parameters you will see the change on your Main Window chart. Note it might not be possible to QC against a spectrum if no well data is available. Under such circumstances, you would need to supply the curve fit parameters manually or read them from file.

Within the "Curve Fitting" group there is a matrix of "Beta" "DC" and "F-Shift" for "Below principal", "principal" and "Above principal" curves. For each curve there is a combo control to the right which specifies the mode of curve fit. We will now consider each of these three curve and describe there mode of use.

Below principal: The default mode is "Force Horizontal". In this mode, the "Beta", "DC" and "F-Shift" are insensitive and cannot be used. The "DC" value displayed is the value of the "Principal" curve fit at the "Low Cut" point. The "Fit Independently" mode uses the same curve fit algorithm between 0 Hz and "Low Cut" as that used for the "Principal" curve fit. The displayed "Beta", "DC" and "F-Shift" are parameters from the independent fit. This mode frequently gives strange results and it usage is not normally recommended. The "Extrapolate Principal" mode allows the "Principal" curve to be extrapolated below the "Low Cut" back to 0 Hz. The "Set" mode allows you to manually set the sensitive "Beta", "DC" and "F-Shift" of the "Below principal" curve. However, the "Set" mode is not normally recommend.

principal: The "principal" curve is by far the most important curve hence its name.The default mode is "Curve Fit". Curve fitting is performed between the "Low Cut" and the "High Cut" frequencies defined in the "Fit Well Log Curves" group on the "Design Controls" dialog. The "Beta", is the key curve fit parameter and is also displayed on the "Design Controls" dialog. The "Set" mode allows you to manually set the sensitive "Beta", "DC" and "F-Shift" of the "Principal" curve.

Above principal: The default mode is "Force Horizontal". In this mode the "Beta", "DC" and "F-Shift" are insensitive and cannot be used. The "DC" value displayed is the value of the "Principal" curve fit at the "High Cut" point. The "Fit Independently" mode uses the same curve fit algorithm between "High Cut" and nyquist as that used for the "Principal" curve fit. The displayed "Beta", "DC" and "F-Shift" are parameters from the independent fit. This mode frequently gives strange results and it usage is not normally recommended. The "Extrapolate Principal" mode allows the "Principal" curve to be extrapolated beyond the "High Cut" up to nyquist. The "Set" mode allows you to manually set the sensitive "Beta", "DC" and "F-Shift" of the "Above principal" curve. However, the "Set" mode is not normally recommend.

There are two other "Advanced Controls" on the "Frequency Domain" tab "Type of Fit" and "Set From File...". The following described these controls:

Type of Fit: This radio button control allows you to select the type of fit algorithm. Possible values are "Least Squares" or "Robust". By default, the type of fit is "Least Squares".

Set From File...: This push button will pop up a files selector dialog allowing you to read a previously saved session file to load the "Beta", "DC", "F-Shift", curve fit "Low Cut" and curve fit "High Cut". If there is a session file associated with this SsbQt run either via "File->Open..." or "File->Save As..." then that session file will be the default. You can also use this mechanism to load the above parameters from Spectral Blueing V2.3.x saved files. However, it should be noted that it is not possible to load from SsbQt V2.90 session files as these parameters were saved in that version. This option is useful when no well data is available or you wish to use the same curve fit parameters from a previously saved session.

There is currently on one parameter in this group. The "Set Operator Energy = 1" checkbox item is here for backward compatibility with earlier versions of the Coloured Inversion software. This checkbox item allows the time-converted operator to be normalised. With this turned on, the amplitude values are adjusted so that the energy in the time converted operator is set to one.

This group is split into the sub-groups "Data Conditioning" and "Log Data Resampling"

Sub-group: Data Conditioning

For the spectral blueing result to have amplitudes, which have physical meaning, then it will be necessary to normalise the Reflectivity log spectral amplitude. This is achieved by compensating for the effects of the relative differences between the seismic and Reflectivity log gate lengths together with the relative differences between the seismic and Reflectivity log sample intervals.

Normalisation

Normalise: This checkbox item allows you to toggle on/off the normalisation facility.

Interval Source: This radio button control allows you to specify whether the Sample Interval or Design Gate is determined from Seismic or User. If the source is Seismic then the normalisation parameters are obtained from the sample interval and gate length of the seismic data. If the source is User then you need to additionally provide the Norminal Seismic Sample Interval (ms) and Norminal Seismic Design Gate (ms) see below.

Nominal Seismic Sample Interval (ms): This spinbox control allows you to specify the nominal seismic sample interval to be used for normalisation purposes. This control is active if User is set for the "Interval Source" radio button above.

Nominal Seismic Design Gate (ms): This line edit field allows you to specify the nominal seismic design gate length to be used for normalisation purposes. This control is active if User is set for the "Interval Source" radio button above.

Remove Linear Trend from Log Data

Detrend: This checkbox item allows you to turn on the de-trend facility. Here the linear trend within the Reflectivity Log can be removed before the generation of amplitude spectra. The figure below shows on the LH plot the de-trend lines on the input log data. The RH plot shows the same logs after linear trend has been removed.

Ramp End of Log Using Papoulis Windowing

Apply Ramps: This checkbox item allows you to turn on the apply ramps facility. This allows the ends of the input Reflectivity Log data to be ramped.

Ramp Length (ms): This input field value allows you to specify the ramp length in milliseconds.

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