Seismic Reflection Surveys


Seismic reflection surveys use low frequency acoustic energy by rapidly releasing compressed air downwards (air gun signals) and receiving the reflected signals by a long horizontal array towed behind the vessel to estimate the properties of the seafloor and find oil and gas underwater.

Figure below shows the lofargram of six airgun shots in a row. The full airgun array (6600 inch3) is used in the first two shots. The later arrivals due to the bottom reflections are obvious in these shots. The source array has been powered down to firing a mitigation gun (small airgun, 40 inch3) in the last three shots (because a marine mammal was observed in the area). No airgun has been shot during the transition between firing a full array and a mitigation gun. The different amount of energy released by different airgun capacities is clear in this figure.

Figure 1: Lofargram of recorded signals in six shots.

Seismic reflection data contains a lot of information about the ocean bottom and water channel. In my research, I use the recorded signals to calculate the average speed of sound that acoustic wave requires to travel horizontally. This information can be useful for finding the location of the sound source.