Environmental study of Devils Lake, North Dakota, using landsat multispectral imagery.

Abstract

Landsat multispectral scanner (MSS) imagery was used to document environmental changes that have occurred in Devils Lake from 1973-1991. Devils Lake, a terminal lake located in northeast North Dakota, has glacial origins and is of special interest because of its fluctuating water level. The fluctuations are largely climatically controlled. Within recent years the water-level has risen to its highest elevation since the late 1800's, threatening to flood the city of Devils Lake and the surrounding area. Local citizens are interested in identifying a way to stabilize the water level so as to eliminate future flood threats. A technique to estimate the surface-area of Devils Lake was developed and applied. The surface-area estimation technique involves the creation of an infrared/red ratio to separate land and water surfaces within the images. This step is followed by reclassification and grouping of the surface areas of detectable water bodies.Finally the surface area is estimated by counting the number of pixels. For Devils Lake, comparison of the estimation results shows a good correlation with historical water elevation records taken at the lake. Other tasks undertaken were the detection of environmental changes within the lake and the surrounding area. Environmental changes observed include not only water-level fluctuations but also water quality changes in the bays of the lake. Strong winds were correlated with images illustrating the ability of the wind to stir into suspension the lake bottom sediments of shallow water areas. Standard as well as special image-enhancement techniques were used to note these changes. Standard false-color composite images were viewed chronologically to note changes on land as well.