Hydrophone/geophone sensor sensitivity - noise versus signal

Question

Today, a student asked this question, and I was unable to answer it in a way that was understandable and accurate - even for myself.

For seismic data acquisition projects, how are sensors able to 'hear' seismic signals in the midst of other much 'louder' and more ongoing ambient noise sources/events?

I understand that the spectral characteristics of ambient noise - be it a culmination of periodic and/or transient events - are usually much different than downgoing/upcoming recorded seismic signals (~15 - 100Hz). However, I'm unsure if the ability to 'see' through the noise at the acquisition stage is more of a sensor specification topic than some pre-processing filtering/gain action occurring real-time during recording.

Answer 1

Sound-generating wave action takes place only on the surface, and is usually less noisy than seismic events. I'm not sure what you mean by streamers, but I take it you mean ships. These man made sounds are loudest on the surface and much quieter in the depths, whereas with seismic noises it is the other way around, so the way to preferentially hear seismic sounds is to send your hydrophones deep. In any case, man made sounds are usually very transient and would not cause much interference. Shipping tends to stick to recognised routes, so you would place your hydrophones away from heavily used shipping lanes.