Infrared Remote Sensing of Coherent Structures in an Estuarine River
Abstract
Coherent structures in rivers are generated by the interaction of the flow with bathymetric and shoreline features. These coherent structures produce surface signatures that can be detected and quantified using remote sensing instruments such as infrared (IR) cameras and microwave radars. Furthermore, the existing evidence suggests a number of relationships between coherent structures and flow characteristics that have the potential to allow flow parameters to be inferred from remote measurements. The Coherent Structures in Rivers and Estuaries Experiment, or COHSTREX is a five-year, multi-institutional collaboration to determine the extent to which the remotely-sensed signatures of coherent structures can be used to initialize and constrain predictive models for river and estuarine flows. Following a brief overview of COHSTREX, we report on the use of IR imagery to characterize and quantify the flow in the Snohomish River, in Everett, WA during the 2006 COHSTREX field campaign. Applications of IR techniques include using DPIV techniques to derive surface velocity and detecting coherent structures such as vortices and boils. Here we will focus on the finding that the thermal signature of boils generated by the flow over a submerged sill can be used to detect the presence of stratification due to an estuarine salt wedge. The boils were observed to have both warm and cold surface signatures depending on the phase of the tide. In the absence of stratification, the boil signature was warm relative to the surrounding undisturbed surface. A warm signature is consistent with disruption of the cool thermal boundary layer that is typically present at the surface of natural water bodies. When stratification was present, the boil signature was cool relative to its surroundings. Comparisons with in situ temperature and salinity measurements show that a cold signature is due to deep, colder water from the salt wedge being brought to the surface. We also found that near-surface diurnal heating due to solar radiation can significantly affect the thermal signatures of boils and other surface disruptions such as surface wakes. Our findings indicate that the thermal signature of coherent structures generated by flow over topography can provide information on the presence and degree of stratification.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.H14B..06J
- Keywords:
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- 1855 Remote sensing (1640)