9.1 Loading VSP Waveform data
VSP waveform data can be loaded from files in either LDF format or SEGY format. The process of loading and displaying LDF and SEGY files is similar to LAS files discussed above.
One minor complication with LDF files and SEGY files, is that these files do not contain any information on the Company name or Well name inside the file. Therefore, this information has to be specified upon load, and a window will appear before loading to capture this information. If other data has already been loaded, then the existing Company and Well names will be offered as choices.
And another complication with SEGY files, is that this format was not designed to support VSP data and a standard method of saving VSP data has never been determined. So different companies have adopted different ways to use SEGY format with VSP data. In most cases, the waveform traces will be loaded correctly, but the waveform headers which contain the depths, coordinates and other pertinent information may not be loaded correctly. Some common types of SEGY VSP files known to the author are listed as options, and the SEGY file type needs to be selected prior to the file being loaded. Extra types of SEGY files can be considered upon notification to the author.
An option to preview the SEGY file headers prior to loading the data is available, to assist in determining the best method to load the SEGY data.
The QuickView plot will only show a depth-time plot. The waveforms can be viewed from the Log Plot panel.
When an LDF or SEGY file is loaded, an attempt is made to determine what type of waveform data it is. Common types are X, Y or Z component waveform.
The "waveform type" information cannot be found inside an LDF or SEG-Y file, and it is guessed from information found in the filename. For example, if the filename ends with a "Z", or has "_Z" anywhere in the filename, it will classified as a Z component. This classification can be seen after the data-list listing.
If the classification has not been determined, or is incorrect, then it should be corrected. This can be done by right-clicking on the filename, select "waveform type", then select the appropriate value as shown below.
Confirming the correct waveform type is important for some later processing steps, since it will assist in quickly finding the correct waveform files for certain processing options.
The polarity of a waveform trace can be flipped by holding down the shift key and clicking on a waveform trace.
9.2 VSP Waveform Processing
Similar to the Log Processing described above; when a waveform file has been selected, the VSP Processing tab on the far right will become enabled. Click on this tab to bring up the VSP Processing window.
Waveform processing option that have been implemented include, Butterworth filter, FIR filter, Hilbert Transform, Frequency Spectrum, Q-Analysis, 3-C rotations and transit time picking. The transit time picking algorithm will be expanded to include extra options in a future release.