Full waveform inversion of reflection seismic data for ocean temperature profiles

We show that ocean temperature profiles can be accurately recovered using only acoustic methods employed at the sea surface. Using a towed air gun array and a hydrophone streamer, thermohaline boundaries are ensonified at a suite of frequencies and angles, yielding travel time trajectories and reflectivities. These data are inverted via full waveform inversion to estimate sound speed and, subsequently, a temperature profile. The high lateral data density of the seismic technique offers the potential of acoustically derived temperature profiles to be used to constrain models of ocean mixing and internal waves. Results on realistic synthetic data show that sound speed can be recovered with arbitrary accuracy when using broadband data, with known source function and recording geometry. Application to field seismic data (corroborated by expendable bathythermograph) shows that even with a seismic acquisition system not specifically calibrated for seismic oceanography, temperature contrasts within the ocean can be recovered to within one degree Celsius.