Mixed Dune Types

    This Landsat 7 Enhanced Thematic Mapper Plus (ETM+) image of the western part of the Sand Hills north of Lake McConaughy shows several dune types.  It was acquired September 21, 1999. Note this false color composite image depicts vegetation as green.  By September 21st  the only green vegetation would be cool-season grasses, alfalfa, and trees.  Corn would be mature. Note the lines of green vegetation in the interdunal areas and the many small lakes and wetlands. 

    The long dunes in the upper portion of the image are what H.T.U. Smith referred to as transverse-linear dunes.  They are now referred to as barchanoid-ridge dunes as they are composites of many crescentic barchans that have grown together. Individual crescent-shaped barchan dunes can be found in the lower-center part of the image.  They have two horns  pointed downwind from the the ancient prevailing northwest wind. Lake McConaughy (bottom) provides perspective for size comparison to the dunes. It is approximately 25 miles long. 

    Some of the smaller dune forms are not apparent  to the untrained eye with satellite imagery.  However, high altitude aerial photographs provide close detail. See the next page.. 

Landsat ETM+, 9.21.99 - click here for a more detailed view

image data

    Landsat 7 travels in a sun-synchronous orbit 705 km above earth's surface.  Its image swath is 185 km and resolution is 30 m for most bands.  This scene and others like it can be found at the Earth Explorer website hosted by the US Geological Survey.

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