dbmwspec dbin [-V -pf pffile -s spec_dir -jack -correct]
This program computes multitaper spectral estimates from seismic data in windows around selected times taken from the arrival table. It is intimately linked to the css3.0 schema and is designed as a batch program to process a large collection of seismograms in a single run. dbin is the input css3.0 database. Output is saved in this same database using the specdisc table.
The program keys on times associated with rows in an arrival table. It can process multiple phases in a single pass with multiple window definitions and/or resolution specifications to the multitaper routine. The basic algorithm works from a list of window definitions defined in the input parameter file (see below). Each window definition is defined relative to a named seismic phase (e.g. P, S, PcP, etc.).
This program blindly processes all channels of data and tags the output spectral estimates by the channel code with which they were originally associated. If data gaps occur within a requested window the program will use the largest data segment within that window to compute the spectral estimate.
The primary output of this program is a set of files indexed by the specdisc table. The specdisc is similar to wfdisc and defines a method for indexing spectral files. The output file names for spectra are derived from the parent waveform file name by adding an appendage of "_mwspec" to the name. For example, if the parent waveform dfile name was evid_20001.w the spectra for all data derived from this file would be contained in a file called evid_20001.w_mwspec. Multiple spectral estimates may be contained in one of these files with appropriate values of foff defined in the specdisc table just as multiple waveforms can be present in one file for a wfdisc table.
spectra_windows. This is an &Tbl parameter that defines the time window and smoothing properties to be used to compute the multitaper spectral estimates. The &Tbl{ and } should enclose a series of lines of the form:
phase start end tbwwhere phase is the name of the seismic phase to use to define the time window for each pick (e.g. P, S, etc.). start and end define the times relative to the pick time for this phase for the start and end time of the window respectively. tbw is the time-bandwidth product for the multitaper spectral estimate. Larger tbw values produce smoother, but lower resolution spectral estimates. Typical values are 4 or 8.
Here is a simple example:
spectra_windows &Tbl{ P -0.25 1.25 4 P -1.75 -0.25 4 }
This would produce two spectral estimates for each P phase defined in the arrival table. The first is a signal window that is defined to start 0.25 seconds before the P arrival time and run to 1.25 seconds after this time. The second entry is a preevent noise spectra from 1.75 to 0.25 seconds before the P arrival time.