Proceedings of the U.S. Geological Survey (USGS)
Sediment Workshop,


Harpers Ferry West Virginia.

A subset of a color infrared photograph from the first mission of the National Aerial Photography Program (NAPP) was used to create the image on the cover of the workshop binder. This photograph was collected on April 11, 1988 from an altitude of approximately 20,000 feet to yield a nominal source scale of 1:40,000. A color print was scanned at 150 dpi and reproduced using a Hewlett Packard Scanjet 4c and Colorlaserjet 5M printer*. The scale of the image as provided on the cover is approximately 1:11,000.

The source photograph was collected between 10:30 A.M. and noon. Shadows were cast to the northwest. Bright red areas in the image depict locations of green vegetation. Bright white areas indicate cleared land, bare soil, or man-made features such as roads or buildings. The two railroad lines, pylons from the old railway, and several road bridges crossing the rivers are easily recognized.

Of particular note are the differences in sediment load for various water features, as captured in this image. For example, the higher turbidity of the Potomac River, flowing from the North, is evidenced by its light blue color. Meanwhile, the Shenandoah River is much darker in color, indicating a relative lack of sediment which scatters and reflects light. Similarly, ponds near recently cleared fields exhibit a bright blue hue (in the north central edge of the image) while those in more heavily vegetated areas (in the southeast corner) remain a deep black as absorption of light in the infrared is high in the absence of sediment. The mixing of Potomac and Shenandoah river waters is visible. The influence of features affecting flow, such as rapids and rough river edges, are also shown by the distribution of Shenandoah and Potomac waters downstream.

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