modsel

NAME

SYNOPSIS

DESCRIPTION

modsel estimates the amplitude distribution across a CDP by fitting isotime amplitudes through linear regression to the polynomial defined by the 3-term Shuey equation and selects different outputs modes through the magnitude of the intercept (B0), the magnitude of the gradient (B1), relations between the magnitude of B0 and B1, or the Coefficient of Determination (R^2) statistic. Output is in the form of CDP data in which the only non-zero samples correspond to events meeting the selection criteria.

The details of the operation of this program are fully described by Crider et al, 2001. The basis equation for the least squares regression is given by (for the 3-term fit)

R(t,theta)=B0(t)+B1(t)*sin^2(theta)+B2(t)*tan^2(theta)*sin^2(theta)

where theta is the offset-dependent incident angle at time t and "^2" denotes squaring. The coefficients B0, B1, and B2 are computed by minimizing the difference between the observed amplitude values and the values predicted by R(theta). Once the coefficients are computed, the "theoretical" R(theta) may then be computed for the given angle field.

Reflectivity modes are extracted from the data by specifying certain criteria for B0 or B1, both B0 and B1, or limits on the "goodness of fit" statistic R^2. If data do not pass the specifications, the output is zero'd. In this manner, for example, only values with R^2 greater than .5 can be output, or only events for which B0 is less than some small value. The reverse can be obtained by simply subtracting the output from the input or by setting the residual flag (-sre).

Note: when running inside XIKP the 0 connector is for the input data, the 1 connector is for the output data, and the 3 connector is for the RMS P-velocity.

Program modsel gets its data and parameters from command line arguments. These arguments specify the input data and velocity files, the output data set, and other computation limitations.  

Command line arguments

-N ntap

Enter the input data set name immediately after typing -N. This input file should include the complete path name if the file resides in a different directory. Example -n/b/tsp/dummy tells the program to look for file 'dummy' in directory '/b/tsp'. (Default = stdin). Note: when running inside XIKP the 0 connector is for the input data, the 1 connector is for the output data, and the 3 connector is for the RMS P-velocity.

-O otap

Enter the output data set name immediately after typing -O. Specify the full path to write the file to a directory other than the current working directory. (Default = stdout ). Note: when running inside XIKP the 0 connector is for the input data, the 1 connector is for the output data, and the 3 connector is for the RMS P-velocity.

-v RMS velocity file

Enter the name of the file containing the RMS velocities corresponding to the input data set, one velocity record for each CDP. This is typically the output from program VELIN or program VOMIT. (Default = NONE. This parameter is REQUIRED when the input is X-T domain. It will otherwise be ignored). Note: when running inside XIKP the 0 connector is for the input data, the 1 connector is for the output data, and the 3 connector is for the RMS P-velocity.

-rs start record

Enter the sequential number of the record on which to begin processing. All data prior to this record will be skipped and not output. (Default = first)

-re end record

Enter the sequential number of the record on which to end processing. All data following this record will be skipped and not output. (Default = last)

-as mininum angle

Enter the minimum incident angle, in degrees, to limit the data values used in the weighted stacks. Data corresponding to incident angles less than this value are ignored. (Default = 0 degrees)

-ae maximum angle

Enter the maximum incident angle, in degrees, to limit the data values used in the weighted stacks. Data corresponding to incident angles greater than this value are ignored. (Default = 45 degrees)

-md ray tracing mode for X-T input

Enter the flag to indicate the type of ray-tracing solution desired. A value of 0 gives a straight ray solution. A value of 1 gives a curved ray solution. A value of 2 give a perturbed curved ray solution ein the smooth curved ray solution is "perturbed" in accordance with the true input velocity function. (Default = 1).

-at A-T Domain flag

If this flag is present, the input data are assumed to be in the A-T domain and the angles computed and stored in the trace headers by ANGST will be used for the regression procedure. (Default = no, the input data are assumed to be in X-T domain.)

-rj Reflectivity Selction mode

If this parameter is 0, all events are reconstruced from the regression parameters; if 1, selection of output is based on B0 restrictions only; if 2, selction is based on B1 restrictions only; if 3, selection is based on both B0 and B1 restrictions; and, if 4, selection is based on R^2 restrictions only. (Default = 0)

-t1 Intercept Threshold

Enter the maximum acceptable ratio, as a fraction, between each B0 and the temporal average of B0. All events for B0/<B0> greater than this ratio are zeroed on output. (Default = 0.5)

-t2 Gradient Threshold

Enter the maximum acceptable ratio, as a fraction, between each B1 and the temporal average of B1. All events for B1/<B1> greater than this ratio are zeroed on output. (Default = 0.5)

-rsqm R^2 restriction

Enter the minimum acceptable value of R^2. Events for which the R^2 is less than this value are zero'd on output. (Default=0.6)

-sre Save Residual Flag

If this flag is set, the differnece between the input and the data selected according to specified criteria is output. (Default = No).

-? Enter the command line argument '-?' to get online help. The program terminates after the help screen is printed.

-h Same as -?, except a list of the output traces is also printed. The program terminates after the help screen is printed.  

SEE ALSO

REFERENCES

Aki, K. and Richards, P.G., 1980, Quantitave Seismology: Theory and Methods, Freeman, San Francisco.

Crider, R.L., Thomsen, L.A., and Beaudoin, G.J., 2001, Selection of Seismic Modes Through Amplitude Characteristics, U.S. Patent #6,263,284, July 17, 2001

AUTHOR

COPYRIGHT

Index

NAME

SYNOPSIS

DESCRIPTION

Command line arguments

SEE ALSO

REFERENCES

AUTHOR

COPYRIGHT