Historically, many data processing techniques assumed that raypaths could be described as vertical in all situations. Increasingly, however, we must recognize the limitations of this assumption and account for the horizontal propagation of the seismic wavefield (e.g., by incorporating anisotropy into our time and depth migration algorithms).
Directional designature builds on the detailed knowledge of far-field signatures enabled by Calibrated Marine Source (CMS) to apply a source designature that stabilizes the seismic wavelet over all emergence angles and preserves frequency content at target depth.
Starting with a common vertical signature for every shot (as generated by CMS), a far-field signature is computed for each emergent angle. Finally, this signature is deconvolved against every emergent angle in the seismic record to output the common vertical signature. The result is to convert the seismic signature of all datasets to the vertical ideal, and as such gives enhanced amplitude fidelity for data recorded at high offset-to-depth ratios.
Directional designature creates a common signature for every emergent angle for every shot in a survey. It is a prerequisite for calibrated AVO and inversion workflows, as well as other angle-dependent processes such as 3D demultiple (3D SMP).
The same principles for directional designature apply equally to the seismic wavelet recorded at the receiver. By applying an equivalent correction, we are able to remove the receiver dependency on angle of arrival.