Field Results from a Second-Generation Ocean/Lake Surface Contact Heat Flux, Solar Irradiance, and Temperature Measurement Instrument—The Multisensor Float

Abstract

This paper describes results from two field programs that support development of a wave-following surface contact multisensor float (MSF) designed to simultaneously measure net surface heat flux, net solar irradiance, and water temperature. The results reported herein compare measurements from a second-generation design (circa 1998) against directly measured radiative fluxes as well as turbulent fluxes derived using both eddy correlation and bulk aerodynamic methods. The reference flux data are collected using instrumented towers, buoys, and research vessels. Comparisons show that MSF net surface fluxes and net solar irradiance are in generally good agreement with values that are measured or derived using standard instruments and methods, having root-mean-square differences less than approximately 15%. MSF near-surface bulk water temperature measurement shows good agreement with similar measurements from a drifting buoy. MSF measurement of water surface temperature is not definitively determined, although results suggest it may be a good measure of skin temperature at night. MSF flux measurement occurs from within the aqueous conductive sublayer and so does not use turbulence models or parameterizations. At this time, results are most reliable in low wind conditions (2 m s?1 ≤ U10 ≤ 7 m s?1) and relatively calm seas. In higher winds and more active seas, the imperfect surface drifting and wave-following characteristics of the second-generation system limit its performance. More fundamentally, perturbation to the aqueous conductive sublayer and modification of near-surface turbulence structure by the MSF may also limit flux measurement accuracy under certain conditions.