Conventional source designature methods assume that the source wavelet is constant for all shots in a survey (and from one survey to the next). However, this is can be an invalid assumption. Minor perturbations in wave height, gun pressure, array geometry, and dropouts mean that the true source signature varies from shot to shot.
The Calibrated Marine Source (CMS) is the WesternGeco solution for performing an accurate shot-by-shot designature. Using Q-Marine technology, the recorded near-field responses for every gun in an array are used to generate an estimated wavelet (signature) in the far field for each shot - optionally at different take-off angles. Each shot record can then be deconvolved relative to the average far-field signature to provide a common vertical signature for every shot in the survey.
CMS is a deterministic method that provides control of the source spectrum, calculates signatures at angles other than vertical (important for optimal Directional Designature), and removes both relative differences due to source variations as well as absolute variations between surveys. Compensating for signature perturbations is a crucial part of stabilizing the seismic wavelet, benefiting both imaging and inversion processes (such as AVO inversion and rock property characterization).