Heat Transfer and Wave Measurements in the Baltic Sea: Principle, Setup and Plan for SOPRAN II

Heat is used as a proxy tracer for gases to study the transport processes
across the sea-surface interface to obtain a detailed insight into
the diffusive and turbulent processes controlling the transport. A carbon
dioxide laser forces a periodically varying heat flux density onto
the water surface and the amplitude damping and phase shift of the
sea surface temperature is measured from infrared image sequences.
The transport process can be treated by linear system theory and the
relation between the input signal (periodically varying surface flux density)
and the output (surface temperature) is estimated. Within the
framework of the SOPRAN initiative three field experiments in the
Baltic Sea were conducted. The locally derived heat transfer rates are
scaled to gas transfer rates, which are in good agreement with empirical
gas transfer wind speed relationships for moderate winds speeds.
At high wind speed, the transfer rates are lower, which is explained
by the fact that heat transport is insensitive to bubble-mediated gas
transfer, i.e. it measures only a part of the transfer process directly at
the water surface.