Geovation地震处理软件-空间振幅平滑模块SPASM.pdf

CGGVeritas SPASM Spatial amplitude smoothing Source code changelist 84480 Last updated December 2010 1 FUNCTION 1 1 General This module equalizes an input seismic trace with respect to its NC 1 neighboring traces NC is the user defined number of input traces considered for amplitude comparisons spatial window This results in smoothing the amplitudes of the processed traces Equalization is performed on each set of NC traces on overlapping time windows The length of the time window is set by user defined parameters For a given input trace the average amplitude is computed for the NC neighboring traces on each time window This amplitude is compared with the median found on the NC traces or with the mean of the NC 1 neighboring traces if MOY is coded In the standard case the amplitude of the window center is multiplied by the coefficient where M is the median or average amplitude value and m is the amplitude value at the considered trace This means that the amplitude at the window center is replaced by the median or mean of the neighboring traces A linear interpolation is performed on coefficients between window centers There is no alteration of the general amplitude level of the section or of the distribution in relation to time As an option it is possible to replace the portions of a trace having anomalous amplitude values or to attenuate the noisy portions of the traces It is possible to apply SPASM processing on given frequency ranges with different Noise Attenuation parameterization with the RANGE coding geovation User GuideSPASM1 CGGVeritasSPASM 2 FUNCTION CALL 2 1 Description ColumnContents 1 3 7SPASM 15 16 Input buffer Contains the trace to be processed 23 24 Output buffer Contains the processed trace It must be different from the input buffer 31 80 Parameters 2 2 Parameters 2 2 1 Mandatory parameter Bc c Number of the post processing loop in which the buffer containing the output traces is available 2 2 2 Optional parameters Computation parameters ONE Att n If this parameter is coded processing is performed until the value of attribute Att n changes Att n must correspond to the header attribute on which the Y flag is set NEUTRAL Att n If this parameter is coded the traces whose attribute Att n equals 9999 are not processed Otherwise all the traces are processed Spatial window limits NCa a Number of traces used for amplitude comparisons and smoothing For a given input trace the program computes the average amplitude of the NC neighboring traces If the user defines an input spatial window composed of a traces the processed trace is at the center of the window and its trace number is set to whether a is an odd or even number Time window limits Lb b Length of the window used for amplitude comparisons Default 500 ADDd d Time in ms added to the mute time that is to attribute TR FNZ of the trace header to define the starting time of the equalization window or geovation User GuideSPASM2 CGGVeritasSPASM TI atti atti Name of the attribute defining the starting time of the equalization window Cannot be coded with ADD TF attf attf Name of the attribute defining the ending time of the equalization window Cannot be coded with ADD TAPERp p Taper in ms to apply before the start of the application window A coefficient of 1 is applied from the beginning of the trace up to the time of the first sample of TAPER TAPER works only if ADD TAPER Parameter specific to horizontal equalization MOY If this parameter is coded the amplitude of the processed trace is equal to the average amplitude of NC 1 neighboring traces By default the amplitude of the output trace the median amplitude of neighboring traces See Example 1 Parameters specific to noise attenuation The parameters in this section cannot be used with the MOY parameter See Example 2 Parameter defining the noise amplitude threshold CTk k Value of the computation coefficient defining the amplitude threshold value real that activates the noise attenuation option If this parameter is coded the program compares the amplitude of the window of the processed trace with the amplitude threshold value which is equal to k times the value of the median amplitude By default the noise attenuation option is not activated Limits k 0 See Section 3 1 Remarks p 5 Parameters defining the amplitude at the center of the processing window CMMp or CMIp p Amplitude coefficient value real number If the amplitude of the window of the processed trace is greater than k times the median amplitude value the amplitude at the center of the processing window is multiplied by where M is the median amplitude value and m is the amplitude value of the input trace Recommended values 0 001 p 1 000 See Section 3 1 Remarks p 5 If the amplitude of the window of the processed trace is less than or equal to k times the median amplitude value the amplitude at the center of the processing window is for the CMM parameter replaced by the median amplitude geovation User GuideSPASM3 CGGVeritasSPASM for the CMI parameter unchanged Limits For CMM option p 0 CMI and CMM cannot be coded together RANGE parameters The RANGE coding enables you to apply the SPASM processing in a given frequency range A maximum of 30 different RANGEs can be coded The different frequency ranges cannot overlap but can be continuous The frequencies outside the RANGE are output but are not processed See Example 3 General coding RANGE FMINm FMAXn TAPFREQf CTk CMMp or RANGE FMINm FMAXn TAPFREQf CTk CMIp where FMINm m Minimum frequency to processed FMAXn n Maximum frequency to processed TAPFREQf f Length of the transition zone where Hanning function will be applied to attenuate discontinuities on the boundaries of frequency RANGE Users are advised to be careful with the non default values being too small or too big they may not be helpful in removing the boundary artifacts By default n fmax fmin 0 1 CTk k Value of the computation coefficient defining the amplitude threshold value real that activates the noise attenuation option If this parameter is coded the program compares the amplitude of the window of the processed trace with the amplitude threshold value which is equal to k times the value of the median amplitude By default the noise attenuation option is not activated Limits k 0 See Section 3 1 Remarks p 5 CMMp or CMIp p Amplitude coefficient value real number If the amplitude of the window of the processed trace is greater than k times the median amplitude value the amplitude at the center of the processing window is multiplied by where M is the median amplitude value and m is the amplitude value of the input trace Recommended values 0 001 p 1 000 See Section 3 1 Remarks p 5 geovation User GuideSPASM4 CGGVeritasSPASM If the amplitude of the window of the processed trace is less than or equal to k times the median amplitude value the amplitude at the center of the processing window is for the CMM parameter replaced by the median amplitude for the CMI parameter unchanged Limits For CMM option p 0 CMI and CMM cannot be coded together CT CMM and CMI can be coded inside or outside the RANGE coding Parameters coded inside the RANGE coding are considered local to the RANGE and will be applied only in this RANGE Parameters outside the RANGE coding are considered global and apply to every RANGE which has no local value 3 RECOMMENDATIONS 3 1 Remarks An invalid input trace results in an invalid output trace Computation window length The length of the computation window must be a multiple of the sample interval If it is not the case it is rounded down to the lower multiple and a message is issued at analysis Noise attenuation option The values of the parameters CT amplitude threshold value and CMM or CMI must be carefully selected If the amplitude of the window of the processed input trace is greater than the amplitude threshold value k times the median amplitude value the program multiplies the amplitude ratio of the processing windo