Reducing the volume of a marine seismic source array can cause a significant reduction in the effect upon and interaction with marine fauna. Small sources are favourable in environmentally sensitive areas; however, the conventional understanding is that larger sources are required for improved signal-to-noise ratio and deep penetration. Results from a number of reduced source-strength tests suggest that this is only partly true; at the lower end of the seismic bandwidth, we can benefit from more power (we are governed by non-shot-generated noise), but for the majority of the seismic bandwidth, we can indeed accept less power (we are governed by shot-generated noise). We look at the system as a whole and use a 4C towed streamer that is towed deep. This amplifies the low frequencies and compensates for the lack of low-frequency signal from the smaller source array. This allows us to acquire data with a small source array (typically three or four times smaller than normal) while maintaining the data quality of a conventional towed-streamer system using a larger source array. The high-frequency limit of the conventional pressure only streamer is also overcome by the inherent notch filling of the 4C measurements.


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