The purpose of this web-app is to facilitate investigations regarding filter design in the context of user specified impedance or reflectivity profiles. Kallweit and Wood demonstrated that an Ormsby filter with a high cut slope of two octaves exhibits minimal sidelobe energy. As the high-end slope increases, the sidelobes become stronger. This web-app allows the user to compare the effects of sidelobes generated with a two-octave high end slope against the sidelobes generated with two other user-defined filters.
This approach is based largely on that work done by Bob Kallweit and Larry Wood, and presented by them in 1977 during a technology meeting at Amoco in Houston, Texas and published in 1982. The concepts introduced by them continue to be very useful in today's world of seismic analysis and interpretation.
Their original 1977 material is available in pdf form, via a FreeUSP web document. It was examined in more detail by Partyka in 2006.
The application described here, enables the user to examine their own data in a similar way. The input data can comprise either time/impedance or time/reflectivity pairs, with time measured in milliseconds. It can be regularly sampled, as is the case with log data, or may be an irregularly sampled model. It is entered directly via a text box on the input form .
The user can choose to filter either amplitude or reflectivity, with the additional option of creating a comparison of impulse responses.
Further required parameters are the two values of the low cut side of the filters and the range of values for the fourth filter corner that are to be tested. Two different high cut slopes (difference in Hz between the third and fourth corners) can be chosen. Whilst testing the range of filters with these choices of high side slope; should the third corner be less than the low side first and second corners then these are adjusted to the third corner value.
After filtering, the results can be downloaded as '.csv' format files.
The layering model and filter parameters are defined in the form that is displayed when Sidelobes, below is selected. Initially, this form is populated with an example set of values demonstrating the format for describing the model.