The Naval Research Laboratory's Air-Sea Interaction Blimp Experiment

Abstract

The rationale is given for a unique experiment in which microwave scatterometer and surface flux measurements are to be made from a blimp to develop an improved scatterometer model function. A principal goal of the effort is to obtain a more accurate understanding of the relationship between the surface fluxes and the microwave power backscattered from the surface of the ocean. The limitations of previous overwater surface flux and scatterometer measurements are reviewed. The accuracy of various flux measurement techniques are compared. Evidence shows that if direct surface flux measurements are to be accurate to better than 20%, the measurements should be made at an altitude of about 5 m to 10 m from a platform that is free of flow distortion. The improved surface flux measurements are required to test proposed scatterometer theories and to determine whether the radar backscatter is principally a function of surface stress or wind speed. It is concluded that scatterometer measurements accompanied by eddy-correlation technique flux measurements must be made from a platform that is highly mobile and which enables the measurements to be made over a variety of oceanic conditions. To meet these requirements, the Naval Research Laboratory is undertaking a series of air-sea interaction experiments in which a sonic anemometer and other flux measurement instrumentation are suspended 60 m beneath a blimp flying at an altitude of 70 m while multiple scatterometer measurements are made from the blimp's gondola. Experiments are planned for a wide range of oceanic environments beginning off the central east coast of the United States in 1990.