Theoretical study on multi-level source design.

This paper studies aspects that influence the de-ghosting performance of marine multi-level sources based on a modified Johnson model. The normalized squared error between actual signature and its corresponding ghost-free signature is introduced to evaluate the multi-level source design. The results show that optimum depth combinations and volume combinations exist in the design. However, there is also some flexibility in the volume combination which makes it possible to optimize with respect to residual bubble oscillation. By considering both operational aspects and performance, we propose that three or four levels in a multi-level source are reasonable. Compared to a horizontal source, a multi-level source can be designed to reduce the notch effect, strengthen the down-going energy and improve the energy transmission directivity. Studies of the influence of depth and firing time deviations indicate that a multi-level source is more stable than a normal horizontal source in an operational environment. [ABSTRACT FROM AUTHOR]