Estimation of turbulent fluxes from remotely sensed SAR imagery

Recent research has been done during the last decade by number of scientists suggesting that there is a great potential to use space-borne SAR imagery for estimation turbulent fluxes in the Marine Atmospheric Surface Layer during thermally unstable stratification. The UNIS experiment in Longyearbyen, Svalbard (Norway) was an attempt to obtain a comprehensive set of data on wind and temperature fluctuations over open water surface to determine how robust these methods of estimation turbulent fluxes from satellite imagery are.

Instrumentation for the UNIS experiment included a three-axes sonic anemometer mounted at 6.0m level, 10 thermocouples each mounted on a 4.0 m mast and slow response "profile" measurements of wind and temperature mounted on three different (2.18, 4.05, 10.0) levels. During the UNIS experiment seven days of tower measurements have been used to investigate the turbulent structure of the Marine Atmospheric Surface Layer and validity of the SAR derived turbulent fluxes technique. By using these measurements and remotely sensed SAR data a method for calculation turbulent fluxes from SAR imagery is suggested and validated against these insitu- measurements.

Two approaches for deriving boundary-layer turbulence and stability statistics from the SAR measured backscatter statistics are applied. The first approach calculates the stability correction term and the turbulent fluxes by applying Monin-Obukhov and mixed layer similarity theories, as well as mean and standard deviation of SAR derived wind fields. The second approach do the same job through applying the so-called inertial-dissipation method, which builds on a correct parameterization of the Turbulent Kinetic Energy budget to these SAR derived wind fields.

The SAR derived heat and momentum fluxes estimated through these two approaches are compared against each other and against the directly measured insitu- fluxes. Finally, the feasibility of applying of these two models to SAR derived wind fields are being investigated in depth.