Heat as a proxy tracer for gas exchange measurements in the field: principles and technical realization

An infrared technique to investigate the transfer processes across the aqueous
mass boundary layer is presented. This controlled flux technique (CFT)
uses heat as a proxy tracer for gases to allow for fast and local measurements
of the gas transfer rate. Three different ways of gas transfer velocity
measurements are investigated. The first one, the steady state method is a
straightforward way to probe the basic unknowns needed to directly compute
the gas transfer velocity k. The other two proposed techniques are
model based but also yield a deeper insight into the mechanisms of air-sea
gas exchange. The decay method works only in a lab environment while the
spatio-temporal temperature fluctuation method is well suited for both lab
and ocean measurements. The mathematical foundations of the underlying
models are introduced together with their practical application.