Abstract

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Over the past decade, we have used infrared imagery to investigate a variety of air-sea interaction processes such as the cool skin effect, heat and gas transfer, and wave breaking. Most recently, we have been investigating the degree to which infrared imagery can be used to characterize and quantify river flow. To my surprise and delight, the riverine environment is rich with infrared signatures that provide new and intriguing examples of thermal phenomena such as the cool skin and warm layer effects. By understanding these phenomena in the context of the hydrodynamics of an estuarine river, infrared techniques can provide quantitative information about flow parameters such as stratification, surface velocity, and bottom characteristics.

The Coherent Structures in Rivers and Estuaries Experiment, or COHSTREX, is a five-year, multi-institutional collaboration to determine the extent to which the infrared signatures of coherent structures can be used to initialize and constrain predictive models for river and estuarine flows. In our first major field campaign in 2006, we used a combination of tower-based and airborne measurements. The tower provided a long-dwell time but had limited spatial coverage while the aircraft provided large area coverage but with limited temporal sampling. To combine the advantages of both approaches, we have developed an airborne platform based on a helikite (helium-filled kite) and a combination of electro-optical and infrared cameras mounted in a stabilized turret, which is made for UAV applications. The helikite provides a field of view of O(100 m) and virtually continuous dwell time.

In this talk, I will provide an overview of the COHSTREX experiment and highlight some of our recent findings using infrared imagery. The results include inferring the presence of stratification due to an estuarine salt wedge, comparison of the bulk-skin temperature difference from the TOGA-COARE model with differences across thermal wakes of small boats, and using Digital Particle Imaging Velocimetry to derive surface velocities. I will also describe the development and application of the helikite system, including recent measurements of the thermal signature of boils in the absence of stratification.

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