A turbulence data reduction scheme for autonomous and expendable profiling floats

Abstract. Autonomous and expendable profiling float arrays such as deployed in the Argo Program require the transmission of reliable data from remote sites. However, existing satellite data transfer rates preclude complete transmission of rapidly sampled turbulence measurements. It is therefore necessary to reduce turbulence data onboard. Here we propose a scheme for onboard data reduction and test it with existing turbulence data obtained with a newly developed version of a SOLO-II profiling float. The scheme invokes simple power law fits to (i) shear probe voltage spectra and (ii) fast thermistor voltage spectra that yield a fit value plus a quality control metric. At roughly 1 m vertical interval resolution, this scheme reduces the necessary data transfer volume 240-fold to approximately 3 kB for every 100 m of a profile (when profiling at 0.2 m s^-1). Turbulent kinetic energy dissipation rate ε and thermal variance dissipation rate χ are recovered in post-processing. As a test, we apply our scheme to a dataset comprising 650 profiles and compare its output to that from our standard turbulence processing algorithm. For ε, values from the two approaches agree within a factor of two 87 % of the time; for χ, 78 %. These levels of agreement are greater than or comparable to that between the ε and χ values derived from two shear probes and two fast thermistors, respectively, on the same profiler.