Amplitude Adjustment Steps

This section documents the processing steps available for Amplitude Adjustment. Processing steps currently available are:

AVA Calculator

Usage:

The AVA Calculator step computes traditional Amplitude Versus Angle (AVA) operations using estimates of AVA intercept (A) and gradient (B)

Input Links:

1) Seismic data in any sort order (mandatory).

Output Links:

1) Seismic data in same sort order as input (mandatory).

Reference:

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Example Flowchart:

Step Parameter Dialog:

Parameter Description:

Intercept (A) – If seleceted, compute AVA Intercept.

Gradient (B) – If seleceted, compute Gradient.

A * B – If seleceted, compute AVA Intercept and AVA Gradient and multiplies both.

B/A – If selected, compute the division between the AVA Gradient with the AVA Intercept.

B * sign(A) – If selected, compute the AVA Gradient and multiplies it by the signed AVA Gradient.

(A+B)/2 – If selected, computes the average between AVA Intercept and Gradient.

(A-B)/2 – If selected, bomputes the difference between AVA Intercept and Gradient and divides by two.

AB Rotation –  If selected, sums AVA Intercept and Gradient after inpute traces being rotated by the Phase rotatation angle (degrees).

Phase rotatation angle (degrees) – Enabled if AB Rotation is selected. Enter constant angle in degress used to rotate the phase of each trace.     

Amplitude Equalization

Usage:

The Amplitude Equalization step allows you to balance the RMS values of your data traces to a constant specified RMS level. You can also clip your data at a specified level. You can specify the data window to use in calculating the RMS amplitudes, the output RMS and clipping levels, and the method of amplitude equalization, which may be either trace constant or record constant.

Input Links:

1) Seismic data in any sort order (mandatory).

Output Links:

1) Seismic data in same sort order as input (mandatory).

Reference:

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Example Flowchart:

Step Parameter Dialog:

 Parameter Description:

Equalization window start (ms) — Enter the start time in milliseconds of the window to be used in calculating the trace amplitude. {=>0}

Window length (ms) — Enter the length in milliseconds of the window to be used in calculating the trace amplitude. {>0.0}

RMS level — Enter the output RMS level of the data window specified. {>0.0}

Clipping level — Enter the clipping level of the trace data. {>0.0}

Method: Specify whether to apply the equalization on a trace by trace basis or to maintain relative amplitudes and level the RMS value of the entire record.

Trace constant equalization — If selected, your data will be equalized on a trace by trace basis.

Record constant equalization — If selected, your data will be equalized on a record by record basis, which will depend on the sort order of the input data.

Apply moveout to equalization window — If checked, the equalization will be performed after linear moveout at the specified velocity. The window start time will shift by: delta time = offset/velocity.

Linear moveout velocity — Enabled in Apply moveout to equalization window is checked. Enter the constant moveout velocity. {>0.0}

Amplitude Versus Angle

Usage:

The Amplitude Versus Angle step allows you to map seismic reflection information in the biangular domain using various methods to interpret the amplitude values. You may also define the velocity field, select the ray tracing type, specify the angle range, and choose the velocity curve fit type.

Input Links:

1) Seismic data in any sort order (mandatory).

Output Links:

1) Seismic data in any sort order (mandatory).

Reference:

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Example Flowchart:

Step Parameter Dialog:

Parameter Description:

Method: Select an approximation to the Zoeppritz equation that will be used to interpret the amplitude values.  The Shuey method is accurate out to approximately 30 degrees, whereas the Aki and Richards method can be considered accurate out to 40 degrees.

Shuey — If selected, the Shuey approximation will be used.

Aki and Richards — If selected, the Aki and Richards approximation will be used.

Gardner exponent — Enter the value to be used for the exponent in the Gardner equation. The value may be set to 0.0 and the default (0.25) only applies if the Aki and Richards method is selected.

Velocity field definition: Define the velocity field to be used.

Use velocity field from data file — If checked, the velocity field will be used from the data file.

Use velocity field from seismic file — If checked, the velocity field will be used from the seismic file.

Use constant velocity — If checked, a constant velocity will be used.

Constant velocity — If Use constant Velocity is checked, enter a constant velocity.

Scale input velocities by (%) — Enter a percentage to scale input velocities. {1.0 = 100%}

Ray tracing type: Define the ray tracing method used in the estimation of propagation angles.

Straight ray — If selected, rays will be traced using a straight ray algorithm.

Perturbed ray — If selected, rays will be traced using a perturbed ray algorithm.

Curved ray — If selected, rays will be traced using a curved ray algorithm.

Eikonal ray — If selected, rays will be traced using an eikonal ray algorithm.

Angle range: Define the minimum and maximum angles used in the calculation of AVA attributes.

Minimum angle — Enter the minimum angle.

Minimum angle — Enter the maximum angle.

Velocity curve fit type: Define the procedure to interpolate velocities between time-velocity pairs specified in the linked velocity file.

Polynomial fit — If selected, velocities will be interpolated with a polynomial interpolator.

Spline fit — If selected, velocities will be interpolated with a spline interpolator.

Angle Gather

Usage:

The Angle Gather step produces angle domain common image gathers, allowing you to specify the angle range to calculate AVA attributes. You may also define the velocity field, select the ray tracing type, and choose the velocity curve fit type.

Input Links:

1) Seismic data in any sort order (mandatory).

Output Links:

1) Seismic data in any sort order (mandatory).

Reference:

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Example Flowchart:

Step Parameter Dialog:

Parameter Description:

Angle range: Define the minimum and maximum angles used in the calculation of AVA attributes.

Minimum angle — Enter the minimum angle.

Minimum angle — Enter the maximum angle.

Velocity field definition: Define the velocity field using the check boxes.

Use velocity field from data file — If checked, the velocity field will be used from the data file.

Use velocity field from seismic file — If checked, the velocity field will be used from the seismic file.

Use constant velocity — If checked, a constant velocity will be used.

Constant velocity — Enter a constant velocity.

Scale input velocities by (%) — Enter a percentage to scale input velocities. {1.0 = 100%}

Ray tracing type: Define the ray tracing method used in the estimation of propagation angles.

Straight ray — If selected, rays will be traced using a straight ray algorithm.

Perturbed ray — If selected, rays will be traced using a perturbed ray algorithm.

Curved ray — If selected, rays will be traced using a curved ray algorithm.

Eikonal ray — If selected, rays will be traced using an eikonal ray algorithm.

Velocity curve fit type: Define the procedure to interpolate velocities between time-velocity pairs specified in the linked velocity file.

Polynomial fit — If selected, velocities will be interpolated with a polynomial interpolator.

Spline fit — If selected, velocities will be interpolated with a spline interpolator.

Apply Gain

Usage:

The Apply Gain step allows you to apply gain function curves to your seismic data. Any or all source, receiver, offset or gain card data may be applied. Gain curves may also be applied from the data file. Additionally, gain may be applied by entering dB/second. Gain curves are specified as time – dB pairs and are linearly interpolated to each location along the line. A constant gain multiplier may also be applied to the data.

Input Links:

1) Seismic data in any sort order (mandatory).

2) Source Gain Corrections cards (optional).

3) Receiver Gain Corrections cards (optional).

4) Offset Gain Corrections cards (optional).

5) Gain Curves cards (optional).

Output Links:

1) Seismic data in same sort order as input (mandatory).

Reference:

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Example Flow chart:

Step Parameter Dialog:

Parameter Description:

Apply source gain corrections — If checked, source gain corrections will be applied to the seismic data from a source gain correction auxiliary file.

Apply receiver gain corrections — If checked, receiver gain corrections will be applied to the seismic data from a receiver gain correction auxiliary file.

Apply offset gain corrections — If checked, offset gain corrections will be applied to the seismic data from an offset gain correction auxiliary file.

Apply gain curves from data file — If checked, gain curves will be applied to the seismic data from a gain curves auxiliary file.

Apply dB/sec gain — If checked, gain will be applied to the data in decibels per second.

dB/sec gain — Enter the gain in decibels per second.

Constant gain multiplier — Enter a constant gain multiplier by which value each trace data sample will be multiplied.

Apply any gain specified — If selected, apply specified gain to the seismic data.

Remove any gain specified — If selected, remove specified gain from the seismic data.

Automatic Gain Control

Usage:

The Automatic Gain Control step allows you to apply up to five sliding window gain functions to each data trace. You specify the number of gated windows, the overlap between the gated windows, and the start time and length of each gate. The calculated gain functions may be output to an optional seismic file, which allows you the option to remove the AGC functions prior to subsequent processing steps.

Input Links:

1) Seismic data in any sort order (mandatory).

Output Links:

1) Seismic data in same sort order as input (mandatory).

Reference:

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Example Flowcharts:

 Step Parameter Dialog:

Parameter Description:

Number of operators — Enter the number of operators to design and apply on each trace. Each trace will be divided into this number of time gates (windows). {1,5}

Overlap between gates (ms) — Enter the overlap between gates in milliseconds. Longer overlap between gates results in a smoother transition between the gated windows. {=>0}

Output type: Select the type of output after applying this processing steps.

Data after application of AGC — If selected, output the seismic reflection data after the AGC.

Gain functions only — If selected, output only the gain functions that might be applied to the seismic data using Apply Gain processing step.

Start time (ms) — Enter the start time in milliseconds for each gate. {=>0.0}

Length (ms) — Enter the operator length in milliseconds for each gate. {=>0.0}

Equalize RMS amplitudes — If checked, the trace RMS amplitude prior to AGC and after AGC will be the same.

Clipping

Usage:

The Clipping step is used to remove high-amplitude sample values from the input data and replace them with a user supplied threshold sample value. The largest positive and largest negative acceptable sample amplitudes are provided by the user. Values outside of this range are replaced by the threshold value.

Input Links:

1) Seismic data in any sort order (mandatory).

Output Links:

1) Seismic data in same sort order as input (mandatory).

Reference:

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Example Flowchart:

Step Parameter Dialog:

Parameter Description:

Clipping upper value — Specify the largest acceptable positive value.  Positive values larger than the clipping upper limit are replaced with the clipping upper limit.

Clipping lower value — Specify the largest acceptable negative value.  Negative values greater than the clipping lower limit are replaced with the clipping lower limit.

Offset Amplitude Corrections

Usage:

The Offset Amplitude Corrections step allows you to correct the amplitude values of your seismic reflection data with the offset. You need to specitfy a function of gain with the offset.

Input Links:

1) Seismic data in any sort order (mandatory).

2) Offset Gains cart data (mandatory).

Output Links:

1) Seismic data in same sort order as input (mandatory).

Reference:

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Example Flowchart:

Step Parameter Dialog:

Parameter Description:

Define Window: Define window configuration where the correction is going to be applied. The window may be defined within a constant time gate, and/or by applying a linear moveout and/or by limiting the traces in the calculation by the offset.

Used fixed window to build pilot — If checked, the pilot window is defined within a time gate.

                Design window start time (ms) — Enter the start time for the design window.

                Design window stop time (ms) — Enter the end time for the design window.

Apply Linear moveout to design window — If checked, apply a linear moveout to the design window with a constant velocity as defined in Linear moveout velocity.

Linear moveout velocity (m/s) — Enter velocity to apply the linear moveout to the design window.

Offset limt traces in design window — If checked, the traces considered to the design window are limited by offset.

                Minimum offset — Enter the minimum offset to be considered in the design window.

                Maximum offset — Enter the maximum offset to be considered in the design window.

Offset gain calculations: Define parameters related with the gain calculation.

Offset bin size — Enter bin size to compute offset gain.

Minimum hit count per bin — Enter minimum hit count per bin.

Random Noise

Usage:

The Random Noise step estimates the signal level then generates random noise to add to the data at a specified Signal to Noise ratio. It is useful for creating noise in model data.

Input Links:

1) Seismic data in any sort order (mandatory).

Output Links:

1) Seismic data in same sort order as input (mandatory).

Reference:

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Example Flowchart:

Step Parameter Dialog:

Parameter Description:

Signal amplitude estimation mode: Estimate signal amplitude either on a single channel or on multi channel.

Signal-channel — If selected, use a single channel to estimate the signal amplitude.

Multi-channel — If selected, use multi-channel to estimate the signal amplitude.

Signal amplitude estimation type: Select the type of signal amplitude estimation.

RMS amplitude —  Signal amplitude is estimated by RMS amplitude.

Average magnitude — Signal amplitude is estimated by average magnitude.

Max magnitude — Signal amplitude is estimated by maximum magnitude.

Power — Signal amplitude is estimated by the power of amplitude.

Average amplitude — Signal amplitude is estimated by average amplitude.

Max amplitude — Signal amplitude is estimated by maximum amplitude.

Signal-to-noise ratio — Enter the desired signal to noise ratio.

Spherical Divergence

Usage:

The Spherical Divergence correction step is designed to compensate for the decrease in seismic amplitude as a wavefront propagates away from the source location.  The Spherical Divergence Correction step allows you to apply a gain to the data traces based on the equation:

Gain = T_Multiplier * (Time ** T_Exponent) * V_Multiplier * (Velocity(Time) ** V_Exponent).

The T_Multiplier and the V_Multiplier are constant gain factors and the T_Exponent and the V_Exponent vary the gain with time. Multipliers of one (1) and an exponent of two (2) are commonly used for the spherical divergence correction since energy from a point source dissipates in proportion to the square of distance traveled.  To apply the spherical divergence correction as a function of both time and velocity, you must supply the optional velocity function. Otherwise, the velocity terms in the above equation will be ignored and the spherical divergence correction will only be applied as a function of time. You also have the option to apply the inverse spherical divergence correction function to your data.

Input Links:

1) Seismic data in any sort order (mandatory).

2) Velocity field card (optional).

Output Links:

1) Seismic data in same sort order as input (mandatory).

Reference:

Claerbout, Jon F., 1985, Fundamentals of Geophysical Data Processing: Blackwell Scientific Publications.

Example Flowcharts:

Step Parameter Dialog:

Parameter Description:

The Gain equation for the following definitions is:

Gain = T_Multiplier * (Time ** T_Exponent) * V_Multiplier * (Velocity(Time) ** V_Exponent).

Time correction:  Define parameters related with spherical correction based on time.

Time multiplier — Enter the time multiplier in the gain equation.

Time exponent — Enter the time exponent in the gain equation.

Velocity correction: Define parameters related with spherical correction based on velocity.

Use velocity field for gain correction — If checked, spherical correction is applied based on a velocity field.

Velocity multiplier — Enter the velocity multiplier in the gain equation.

Velocity exponent — Enter the velocity exponent in the gain equation.

Apply inverse function — If checked, an inverse spherical divergence correction will be applied to your data.

Use normalize gain function — Normalize the gain function to be applied.

Surface Consistent Gain Corrections

Usage:

The Surface Consistent Gain Corrections step calculates source and receiver amplitude variations in a surface consistent manner. Gain curves must be specified for source and receiver.

Input Links:

1) Seismic data in any sort order (mandatory).

2) Source Gain Corrections cards (mandatory).

3) Receiver Gain Corrections cards (mandatory).

Output Links:

1) Seismic data in same sort order as input (mandatory).

2) Source Gain Corrections cards (optional).

3) Receiver Gain Corrections cards (optional)

4) Offset Gain Corrections cards (optional).

Reference:

Taner, M. T., and Coburn, K. W., 1980, Surface consistent estimation of source and receiver response functions: 50 th International  Meeting of Soc. Expl.Geophy., Expanded Abstract.

Example Flowchart:

Step Parameter Dialog:

Parameter Description:

Design window:

Use window definition file — If selected, the pilot area is defined with a Window Definition card.

Use fixed window to build pilot — If selected, the pilot area is defined within a fixed time gate.

Design window start time (ms) — Enter the window starting time in ms.

                Design window stop time (ms) — Enter the window ending time in ms.

Apply linear moveout to desing window — If checked, the window is defined variable based on a linear moveout with the velocity defined in Linear moveout velocity.

                Linear moveout velocity — Enter the linear moveout velocity in m/s.

Offset limit traces in design window — If checked the window definition is limited by a Minimum and Maximum offset values.

                Minimum offset — Enter the minimum offset in field units to build the window.

Maximum offset — Enter the minimum offset in field units to build the window.

Surface consistent amplitude decomposition:

RMS error for termination —

Compute log amplitude —

Remove linear trend at each interation —

Compute source term —

Output source gain corrections —

Compute receiver term —

Output receiver gain corrections —

Compute offset term —

Output offset gain corrections —

Compute Structure term —

Trace Header Amplitude Math

Usage:

The Trace Header Amplitude Math step use used to modify sample values using mathematical operations on trace header fields.  Any of the trace header fields can be used.

Input Links:

1) Seismic data in any sort order (mandatory).

Output Links:

1) Seismic data in same sort order as input (mandatory).

Reference:

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Example Flowchart:

Step Parameter Dialog:

Parameter Description:

Operations: Select the mathematical operation that will modify the seismic amplitude values based on value specified on a user-defined header.

Add header to — add header value to each seismic amplitude value.

Subtract header from — subtract header value to each seismic amplitude value.

Multiply by header — multiply each seismic amplitude value by header.

Divide by header — divide each seismic amplitude value by header.

Power of header — compute the power of each seismic amplitude value by an exponent as defined in header.

Header Field — Select the trace header field that will modify the seismic amplitude values.

Example:  If the Multiply by header operator is selected and the Header field is set to offset, then the sample values in each input trace will be multiplied by the value of offset in the corresponding trace header.

Windowed AGC

Usage:

The Windowed AGC step step allows you to apply window gain functions to each data trace based on user-defined windows. You specify the number of windows by setting the start time and length of each gate. The calculated gain functions may be output to an optional seismic file, which allows you the option to remove the AGC functions prior to subsequent processing steps.

Input Links:

1) Seismic data in any sort order (mandatory).

Output Links:

1) Seismic data in same sort order as input (mandatory).

2) Gain functions (optional).

Reference:

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Example Flowchart:

Step Parameter Dialog:

Parameter Description:

Output gain functions — If checked, output the gain functions to a gain functions card. This allows removing the AGC effect later on the processing flow.

Number of Windows — Define number of different windows where the AGC is going to be applied. Each window is defiend by its starting time and length, both in ms.

Windowed Trace Balance

Usage:

The Windowed Trace Balance step step allows you to balance the seismic amplitudes within user-defined windows based on RMS amplitude or Mean amplitude within each window

Input Links:

1) Seismic data in any sort order (mandatory).

Output Links:

1) Seismic data in same sort order as input (mandatory).

Reference:

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Example Flowchart:

Step Parameter Dialog: