Hood Canal - Seepage Map - Non-overlapping Images


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Thermal infrared mapping of groundwater, small streams, and ephemeral creeks in Lynch Cove, Hood Canal, Washington

Instructions: Click on an image location (black dots) and a small image with both the thermal infrared and visible band images will be displayed. Click on the image to get a larger image. In the thermal infrared image, the coolest water, which appears as bright cyan, is that from groundwater seeps, small streams, and ephemeral creeks flowing across the sun warmed beach and into the warm surface waters of Lynch Cove.

EXPLANATION
	Thermal Infrared Image
	Ground Water or Stream present

Background:
The input of nutrients into Lynch Cove and, lower Hood Canal, by groundwater seeps, small streams, and ephemeral creeks may play a significant role in the nutrient loading of this low dissolved oxygen system. In situ measurements of ground water seepage rates are very limited and may not adequately represent the large spatial variability of outflow, and cannot provide detailed information of horizontal mixing and transport patterns. As a result, the groundwater processes important to understanding hypoxia are poorly known.

To determine the spatial variability and relative intensity of these sources, the USGS Washington Water Science Center teamed with the University of Washington Applied Physics Laboratory to obtain thermal infrared images of the Lynch Cove and lower Hood Canal shoreline at or near low tide. The cool water emerging from seeps and in streams, flowing across the exposed, sun warmed beach is readily evident in the images.

Image acquisition took place on September 2, 2008 at approximately 11:45 am PST, when the tide at Union was about +2.5 ft. The imaging system consisted of an ICI 320x240 pixel microbolometer with a 19? field-of-view that measures long-wave infrared radiation at 8-12 ?m. The ICI thermal camera is sensitive to changes in temperature of 0.1 ?C, which is adequate to observe the fine surface-temperature structure in seawater, where variations of 0.5? to several degrees Celsius are typical. An un-calibrated, visible band RGB (red, green, blue) camera (Lumenera 1392x1040 pixels with 30? field-of-view) was also mounted in the system to record color images for later reference, and could be used to qualitatively assess the relative abundance of near surface phytoplankton blooms and turbidity. The location and orientation of each image was measured by a GPS, digital compass, and accelerometers, logged once per second on a laptop and combined later for geo-registration.

This survey yielded 1500 scenes of the shore line and the majority displayed some evidence of cool, or fresh, water flowing into Lynch Cove. On the map the black dots are the locations of the images and a dot is surrounded by green if there was a cool water signature on the beach. Each image was referenced to a uniform temperature scene from the middle of Lynch Cove, to provide a common reference, and each TIR image was colorized to accentuate the cool signatures. The coldest temperature differences, < -0.5 C are shown by the bright cyan color, this shifts to black as the temperature differences approach +0.5 C. Temperature differences > 0.5 are mapped to a grey scale where white corresponds to +5.0 C.