Ocean temperature can be mapped remotely using sound propagation timing

Evidence

In the ocean, the speed of sound increases about 4 m/s for every 1°C increase in temperature. Variable temperature in the ocean therefore results in variable sound speed, which has the dual effect of refracting waves and making them arrive sooner or later according to the temperatures through which they have passed. In the 1970s, Walter Munk and Carl Wunsch suggested the idea of ocean acoustic tomography: measuring the temperature of the ocean remotely over large areas and at great depths if desired by sending sound long distances underwater to receiving hydrophones. Sounds are created hundreds of kilometers away from receiving stations, and ray tracing is used to help deduce the temperature profile of the water between the source and the receiver. Depending on the temperature profile, there may be many ways rays can travel from the sound source to the receiver, and generally each path will arrive at a different time and will have passed through different parts of the ocean. This technique is an important part of global earth monitoring of climate change. — Eric J. Heller, Why You Hear What You Hear- An…, 218

Categorization

• QUESTION: How does ocean acoustic tomography compare in spatial resolution to satellite-based sea surface temperature measurement? Wondering what its practical limits are.
• XREF: Connects to the chapter’s core theme of refraction and ray tracing as tools for inverse problems — echoes how seismic and medical imaging also infer medium properties from wave travel times.
• SEED: Article angle: how a climate-monitoring method works by abusing the very ocean properties climate change alters — measuring global warming via the speed of sound itself.