Analysis of circulation patterns in Grays Harbor, Washington, using remote sensing techniques

Abstract

The objective of this investigation was to analyze surface circulation patterns in Grays Harbor, Washington, during flood and ebb tide, using National Aeronautics and Space Administration (NASA) aerial photographs and thermal‐IR imagery and low altitude aerial photographs of uranine dye drogues. The application of Landsat‐1 and passive microwave imagery was evaluated but did not prove useful. Water temperature, salinity, and suspended sediment data and the results of hydraulic model studies were used to verify and supplement interpretations from the photographs and imagery. Circulation maps prepared from the thermal imagery were most comparable to circulation patterns observed in the Grays Harbor hydraulic model. The thermal imagery was also useful in mapping nearshore mixing zones and warm water sources, and it showed temperature variations of 4°C between water masses within the harbor and 5–7°C between the water and adjacent tidal flats and land. Current velocities estimated using photographic measurements of sequential dye drogue positions were comparable at some locations to velocities previously measured by in situ current meters and in the hydraulic model. The use of remote sensing techniques in conjunction with ground truth data and hydraulic model results, when available, provides a more complete perspective of estuarine processes than is available by using conventional shipboard surveys alone.