Streamer depth versus vessel and seismic interference noise

Abstract

For marine seismic surveying it is commonly assumed that the noise level decreases with depth. In addition, recent advances in broadband seismic have shown that greater receiver depth is beneficial in preserving low-frequency data. However, in a heavily trafficked ocean, noise from other ship including seismic interference is a counteractive process in which the noise actually increases with depth. Normal modes can be used to explain and predict the ship noise and seismic interference noise level. We find that weather noise is dominant below a frequency around the first mode's cutoff frequency (around 6 Hz), ship noise is dominant from that frequency to the upper end of the useful seismic frequency band (80 Hz). In this paper, we use a unique dataset where the streamer was towed at 8, 45 and 60 m depth in three passes over the same area in the North Sea. The water depth is 135 m on average. We observe that the noise level at 45 and 60 m depth is about 1.6 times stronger than that at 8 m. After isolating the seismic vessel noise, we find that the air gun energy is up to 46 dB stronger than the noise from the seismic vessel. However, the ocean is an effective medium to transmit sound waves, the total noise from all the ships within several hundred kilometers radius can reduce the data quality.

Current and future multicomponent towed streamer design

“…Firstly, the signal to noise ratio of the raw data is significantly higher for hydrophone data. Secondly, hydrophone noise velocity shows less variability due to tension along the streamer and lastly, its frequency bandwidth is narrower with waterborne shipping noise being usually dominant above 20 to 30 Hz (Muyzert et al 2007, Dao andLandrø 2017). Part of the higher frequency waterborne noise is also filtered because of the array response, that however comes together with some high incidence signal filtering (Martin et al 2000).…”