Li-Fi for marine surveys

Li-Fi stands for light fidelity which is a play on Wi-Fi (wireless fidelity or wireless network). This interesting technology could change how data is collected in geophysics.

Geophysics in most applications uses tools to image the interior of the earth. These tools measure some property of the earth like gravity or magnetic field strength. The success of any geophysics survey is limited by the technology used. There are entire companies that just focus on developing better technology for certain types of surveys. It is amazing how complex the instruments have become. One good example of this is seismic surveys conducted in the ocean.

Seismic surveys are used to characterize the subsurface geology. A source is used to make vibrations that travel through the subsurface and bound off of the geologic structures. The receivers record the bounced around waves.

A towed seismic source and receiver array.

The traditional method to conduct surveys is to tow the source and receivers behind a boat. The streamers (lines of receivers) can be kilometers long! This makes it difficult to keep straight lines. Another method used is ocean bottom cables.

Ocean bottom cables waiting to be laid on the ocean floor. 

These cables are laid down by a boat around the area of interest. They are usually put down in parallel lines. These are better than the towed array but the lines cannot be placed underneath an oil platform which is usually where the survey needs to be conducted. Enter ocean bottom nodes (OBN). OBN are geophones that are completely detached from any cable. Inside the cylinderical shape is every instrument needed, batteries, and a way to record the data.

An ocean bottom node from CGGVeritas.

These are placed on the ocean floor by a remotely operation underwater vechicle (ROV). They stay on the ocean floor until the survey is complete which is sometimes months. Then the ROV comes by and picks them up. Once they get back to the surface the data is downloaded from their memory.

A cartoon of an ROV placing nodes on the ocean floor.

The bad part of OBN is that you have to wait until the nodes are back on the surface to see the quality of the data. Problems could occur and you wouldn't know until the whole survey is complete. Better data is always the goal and with the high cost of these surveys it would help if the data could be streamed up to the boat or to the ROV. How might this be accomplished?

There is a idea out there to use light to transmit data exactly like how your wireless internet streams data to your computer or a radio tower communicates with your phone. Harald Haas, a professor from University of Edinburgh, explains and demonstrates the principle in the TED video below.

The basic idea is that an LED light can be turned off and on extremely fast so fast that humans can't see the variation. The light on equals a one and the light off equals a zero. So binary code is being transmitted by the light. The receiver takes that information and turns it into a video or a text or an email. The method still has a ways to go for everyday use with phones or internet but it is looking promising for communicate between nodes and ROVs. The ROV's light could be used to download data from the nodes. This is still just a futuristic idea but it could be a way to make a geophysical tool even more efficient and valuable for surveys.

How do you think data could be retrieved from ocean bottom nodes? Have you heard of any crazy technology that might change the way information is gathered?