12th Conference on Interactions of the Sea and Atmosphere


Air-sea interaction effects on microwave propagation over the sea during the rough evaporation duct (RED) Experiment

Kenneth D. Anderson, Space and Naval Warfare Systems Center, San Diego, CA; and P. Frederickson and E. Terrill

Prediction of microwave frequency signal propagation over a wind-roughened sea relies on a thorough knowledge of its interaction with the sea surface, the mean profiles of pressure (P), humidity (Q), temperature (T), wind (U) and their turbulent fluctuations (p, q, t, u). Yet, within the marine surface layer, these mechanisms are not sufficiently understood nor has satisfactory data been taken to validate models. The RED experiment was designed to provide first data for validation of both meteorological and microwave frequency propagation models in the marine surface layer for rough surface conditions including the effects of surface waves.

Over the ocean, "smooth-rough" surface similarity theory is often applied to construct profiles of P, Q, T, and U in the surface layer. In this context, the "rough" boundary layer is derived from empirical relations where ocean wave characteristics are neglected. For seas where wind speeds are less than 10-15 m/s and wave age near unity, there is excellent agreement for both meteorological and microwave propagation theory and measurements. However, recent evidence indicates that even small waves perturb P, Q, T, and U profiles throughout the surface layer. Indirect evidence of surface induced distortion of P, Q, and T profiles via modeling of the vertical microwave refractivity profile (i.e., the evaporation duct) is indicated by analyses of previous microwave signal propagation experiments.

The RED experiment was conducted offshore of the Hawaiian Island of Oahu in late summer, mid-August to mid-September, of 2001. R/P FLIP, moored about 10 km off of the NE coast of Oahu, hosted the primary meteorological sensor suites and served as the terminus for the propagation link. Two meteorological buoys provided additional support. One buoy was located approximately 5 km west of R/P FLIP and the other was located approximately 15 km south, nearly mid-path on the microwave propagation link. Wind speed never exceeded 10 m/s. Significant wave height and wave age rarely exceeded 2.5 m and 1 respectively.

Analysis of the microwave data show a very good agreement between modeling, using the observed meteorological data to predict received signal levels, and the observed signal levels with standard deviations of the differences ranging from 2 dB to 5.7 dB. However, with the low winds and wave heights observed during RED, the effects of surface waves are not readily isolated.

extended abstract  Extended Abstract (344K)

Supplementary URL: http://sunspot.spawar.navy.mil/red

Session 9, RED SEAS Experiments
Thursday, 13 February 2003, 8:30 AM-2:15 PM

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