PROCESS FILTER Parameters, alphabetically: addwb dbdrop fillen fno ftype interp levs lno minpha pass sets window winlen Document Date: 22 April 2005 Process FILTER applies a frequency filter to every trace. Filters available are: (see parameter FTYPE) Time domain (convolutional) zero phase time varying bandpass Frequency domain zero phase bandpass Frequency domain minimum phase Low pass Butterworth Frequency domain notch Time varying filtering is performed by applying different time domain filters to different parts of the trace. The different parts of the trace are called windows. The portion of the trace between windows are merged by ramping (linear). The merge zone thus contains data that has been filtered by different filters and then added together after being ramped. The weights of the windows can be different, however then the merge zone will contain more of one type of filter than the other. e.g. F1 F2 F3 .......... .......... . . . .......... . . . .. . . . . . . . . . Up to 5 windows may be given, each with a different window level, and may be spatially varied by shot or rp or by hanging the windows on the water bottom. Time varying filters are available only on time domain filters. All parameters that remain constant for a set of shots (rps) may be described in a parameter set FNO to LNO. Windows between two parameter sets are calculated by linearly interpolating between LNO of one set and FNO of the next set. Only the time windows (sets) are spatially varied. The filter (pass) remains constant even though the application window (sets) vary. Parameter INTERP may be used to turn spatial interpolation off. Each parameter list must be terminated with the word end. The entire set of filter parameters must be terminated by the word END. THE PARAMETER DICTIONARY --- --------- ---------- FNO - The first shot (or rp) to apply the filter(s) to. Shot (rp) numbers must increase monotonically. Preset=1 LNO - The last shot (rp) number to apply the filter(s) to. LNO must be larger than FNO in each list and must increase list to list. Default=fno SETS - Start-end time pairs defining the windows of a time varying filter. Times are in seconds and may be negative when hanging the windows from the water bottom. A maximum of 5 windows may be given. Only available on time domain filters. Preset= delay to last time. e.g. sets 0 3.0 3.3 6.0 PASS - For time domain (convolution filtering or FTYPE 99): A list of passbands. A passband is a set of two frequencies between which the data will be passed. Frequencies outside the passband will be cut. Pass is an approximate number but very sharp sloped filters can be obtained by increasing the filter length. Up to 5 passbands may be given. - For frequency domain bandpass filters (ftype 0 and 20) The two corner frequencies of the passband. The slopes of the filter are given via DBDROP. - For low pass or high pass filters (ftype 1 and 2 ): The cutoff frequency. - For notch filters (ftype 3 and 23): The two corner frequencies between which the frequencies will be cut out (filtered out). Required. e.g. pass 10 70 FILLEN - The length of each time domain filter. The number of points to use in the convolution. Up to 5 filter lengths may be given. An odd number of points should be used since the filters are symmetrical. Short filters (25 points) may run fast, but the filter shape becomes poor. Short filters do not filter low frequencies well. Preset = 25 25 25 25 25 e.g. fillen 39 LEVS - The amplitude level of each window described by sets. Each window may have a different level. Each level must be >0. Up to 5 levels may be given. PRESET= 1. 1. 1. 1. ADDWB - When given a value of yes, the windows given via sets will be added to the water bottom time of the trace. (Water bottom times may be entered via process wbt). Preset=no FTYPE - Filter type. Time varying filter is permitted with time domain filtering only. Add parameter MINPHA for minimum phase filters. = 0, John Shay's frequency domain zero phase bandpass. = 1, John Shay's frequency domain low pass. The corner frequency is the first value of parameter PASS. = 2, John Shay's frequency domain high pass. The corner frequency is the first value of parameter PASS. = 3, John Shay's frequency domain notch. = 10, Low pass 3 pole Butterworth filter. = 20, Warren Wood's frequency domain zero phase bandpass. = 23, Warren Wood's frequency domain notch. = 99, Time domain (convolutional) zero phase time varying. These are VERY fast filters. Preset = 99 e.g. ftype 0 DBDROP - Decibel drop per octave. The slope of the filter response in db/octave. Valid with FTYPE 0, 1, and 3 Preset = 48. e.g. dbdrop 6 WINDOW - The type of window to apply before computing the fft. = hamm, Hamming = hann, Hanning = bart, Bartlett (triangular) = rect, rectangular (box car - no window) = blac, Blackman = ebla, exact Blackman = blha, Blackman-Harris Preset=hann e.g. window rect WINLEN - The window length, in seconds. A window length of zero causes the entire time domain gate to be windowed. A non zero length indicates that winlen data will be modified at both ends of each data gate. Preset = 0. e.g. winlen .2 MINPHA - A yes/no switch indicating that the filter should be a minimum phase filter rather than zero phase. Valid for ftype 0, 1, 2. The switch is set by any no-zero value. Preset = no e.g. minpha yes INTERP - A yes/no switch indicating whether spatial interpolation should be done or not. Normally all shots/rps and traces are filtered, but this can be overridden with INTERP NO. Traces not specified in an fno/lno list will not be filtered with INTERP OFF. Preset = yes e.g. interp no END - Terminates each parameter list. Copyright (C) 1980 The Regents of the University of California ALL RIGHTS RESERVED. Written by Paul Henkart, May 1980Go to the list of seismic processes. Go to SIOSEIS introduction.