Thermal remote sensing of tidal flat bathymetry and circulation

Tidal flats exhibit strong thermal gradients due to mixing water masses, solar heating and latent and sensible heat flux. During a pilot experiment in August 2008, the thermal signal of the Skagit Bay tidal flats in northwest Washington State was measured using airborne and tower-based long-wave infrared imaging. A small network of in situ temperature loggers recorded water column and sediment temperatures. The strong temperature difference observed between the water and the exposed flat sediments revealed the tidal flat bathymetry as the tide flooded and ebbed. Waterlines identified in the thermal imagery and in situ tide measurements will be used to generate large-scale (kilometer) and small-scale (meter) scale bathymetry maps over the braided network of channels and shoals of the flats. In addition, the surface extent and evolution of the relatively warm freshwater plume from the Skagit River is traceable in the thermal images as it extends into the colder Puget Sound seawater. The circulation of the river plume over the changing tide and on complex bathymetry will be explored via airborne thermal mapping and combined with in situ thermometry of the water column. The larger goal of this work is to eventually produce gross circulation and bathymetry maps over an annual cycle to provide a broad framework for understanding the geomorphology and hydrodynamics in this dynamic system.