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Remote sounding of the atmosphere is a well-established method used extensively used extensively for operational weather forecasting and scientific research. Active or passive instruments carried on satellites (or aircraft) can measure profiles of temperature, pressure, trace gases, and particulate matter.

Is anything similar possible for a ship sailing on the ocean? What methods exist, in theory and in practice, to remotely sense a profile of temperature, density, salinity, etc., from the ocean floor to the ship? Or can such profiles only be obtained in-situ?

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There are a number of programs and instruments that sample the ocean autonomously. Examples of such programs are:

  • The ARGO program (http://www.argo.net/): Currently around 3000 floats are freely drifting in the ocean measuring temperature, salinity and in some cases velocity of the upper 1000-2000 meters of the ocean. The floats drift for around 10 days most commonly at 1000 or 2000 meters and then conduct a vertical profile to the surface where they transfer the data to a satellite.
  • RAFOS floats (http://www.whoi.edu/instruments/viewInstrument.do?id=1061): They map the ocean currents using the SOFAR channel (a horizontal layer in the ocean where sound speed is minimum).
  • Gliders (http://www.ioos.noaa.gov/glider/): A type of autonomous underwater vehicle (AUV) that uses buoyancy to control its vertical position in the ocean. They sample along predetermined routes and can be equipped with instruments to measure temperature, salinity, turbidity, velocity...
  • Other AUVs: Most other AUVs use propellers powered by rechargeable batteries and are able to carry a lot more instruments, but are limited to shorter missions.

Measuring oceanographic interior conditions remotely is much more challenging. While satellites provide data for sea surface (or near-surface) parameters, such as temperature (e.g., MODIS), salinity (SMOS & Aquarius), height (e.g., Jason 2) and color (SeaWiFS, MODIS), remote interior data are more challenging to acquire.

Seismic oceanography is a recently developed technique that uses multichannel seismic reflection to characterize the ocean interior. It provides continuous mapping of the finer structure associated with the thermohaline (temperature and salinity) structure of the ocean. One of the best examples is Holbrook et al., 2003 Science paper (sciencemag.org/content/301/5634/821.full). You can find more information in: steveholbrook.com/research/seismic_oceanography and www.utm.csic.es/so

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  • $\begingroup$ Thank you. I am aware of ARGO floats and NOAA gliders. As far as I know, both measure profiles in-situ, and do not answer my question. As for the SOFAR, isn't this just a Lagrangian kind of active measurement, where they float around and their position is determined through sounding? My question is if one could profile the ocean directly from the surface, without actually diving down with any instrument. $\endgroup$ – gerrit Apr 16 '14 at 16:46
  • $\begingroup$ Thanks for the additional pointers. That's much more the answer I'm looking for, perhaps you could adapt your answer around those? (I can't help to note that this seismic oceanographer is based in Wyoming, which I find quite amusing) $\endgroup$ – gerrit Apr 16 '14 at 18:10
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    $\begingroup$ @gerrit - The Wyoming connection is an interesting story. Steven Holbrook is a geophysist (quite well known), and discovered "seismic oceanography" essentially by accident. Basically, you'll often get subtle reflections up within the water column that we normally filter out as noise (or fish/floating stuff). Holbrook noticed a particularly bright and continuous reflection in the water column, filtered out everything below the seafloor instead, and took the result to an oceanographer to ask "what the heck is this?". And thus a field of study is born! :) $\endgroup$ – Joe Kington May 6 '14 at 21:39

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