Far-field Directional Source Signature Acquisition, Processing and Analysis: Taking a Janus-Helmholtz Transducer as an Example

Signature estimation is critical for source evaluation and data processing. Far-field measurement is an accurate way to deterministically finalize the process and more importantly to clarify the source directivity. Based on the position-fixed mode, a seismic survey is carried out in India Ocean in 2021 with a deep-towed Janus-Helmholtz transducer as the source. This work shows a full view of acquiring, processing and analyzing the far-field source signature. According to the source-receiver reciprocity theorem, an incidence angle of 7.4° ~ 87.8° is covered in this survey. In order to overcome the positioning uncertainty of the ultra-short baseline mode, a novel joint ray-tracing inversion approach is presented on the basis of the CTD derived sound velocity model. On the data processing side, a customized workflow is established to attenuate the complex sea-floor reflections. It is realized based on sparse f-k transformation and adaptive subtraction and is validated effective from both the shot gather and spectrum panel. Analysis indicates that the signature of the transducer is jointly affected by the input assignment and the system response. It is potential to tune the two factors to optimize the signature, e.g. widening its bandwidth. Moreover, strong directivity is observed in terms of waveform consistency, amplitude decay and energy distribution which challenges the point-source propagation theory. Missing of the directivity information may cause severe imaging issue as illustrated by the comparison between global and directional deconvolution. This work could be a good guideline for the future signature estimation and the so-based data processing and analysis.