Acoustically induced cavity cloud generated by air-gun arrays—Comparing video recordings and acoustic data to modeling

Abstract

For seismic air-gun arrays, ghost cavitation is assumed to be one of the main mechanisms for high-frequency signal generation. Ghost cavitation signals are weak for seismic frequencies (<300 Hz) and do not contribute to seismic reflection profiling. In the current experiment, the ghost cavity cloud is monitored by a high-speed video camera using 120 frames per second. This is, as far as the authors know, the first convincing photographic evidence of ghost-induced cavitation. In addition to video recording, acoustic signals were recorded with a sampling rate of 312.5 kHz using broadband hydrophones suspended 17 m below the array. The pressure drop around the source array is estimated using air-gun modeling followed by a phenomenological modeling of the growth and collapse of each vapor cavity. The cumulative effect of cavity collapses is modeled based on linear superposition of the acoustic signals generated by individual cavities. The simulated acoustic ghost cavitation signal and the corresponding cavity cloud show good agreement with the field data.