available for testing during the project, was not geomet 
rically corrected. Figure 2 is a reduced computer output 
from the identification system which was used to verify the 
lake identification for the eastern half of the area proc 
essed. Figure 2 shows the limits of the area processed and 
the quadrangle specified for lake information retrieval. 
The lakes and boundaries are skewed due to lack of geometric 
correction of this test area. Figure 3 is a 31 July 1977 
natural color aerial photograph over the same area and lakes 
in Figure 2. The capability for computer identification 
of surface water is illustrated by comparing Figures 2 and 
3. Although the data being compared were collected 2 years 
apart, and surface water conditions could differ, the simi 
larity between water bodies illustrated is manifest. 
Identification System 
Lake Identification (Program LAKEID). A fully processed 
computer compatible tape in the new EDIPS (EROS Data Center 
Digital Image Processing System) format was used in the 
processing. The data contained no ground control points; 
therefore, no geometric correction has been applied to the 
scene. Each sample or pixel making up a scene is 57 x 57 m 
and has an intensity stored for each of the 4 bands. The 
system has potential for recognizing and identifying lakes 
as small as 0.5 ha. Landsat multispectral scanner resolu 
tion is approximately 80 m. Water body identification was 
performed by thresholding at a value of 9 in band 7 (0.8 
to 1.1 jam) . All intensities < 9 are water and those > 9 
are land. Both the literature (Work and Gilmer 1976) and 
some simple tests indicate that a threshold of 9 is a good 
reflectance value for discriminating between land and water 
in band 7. The EROS Data Center's General Electric IMAGE 
100 System was used to vary this threshold to observe changes 
in water area discriminated for Alaskan arctic lakes. No 
change in areas was observed when the reflectance 
value was changed + 1, while less than 2% in area occurred 
with a change of ± 3 in reflectance values above and below 
the 9 threshold. Figure 2 illustrates the shape and size of 
lakes defined using the 9 threshold value. The shape and 
size of each discrete basin are defined by like numbered 
sample elements on this printout. Each sample that is 
identified as land is portrayed as a zero. The printout has 
been reduced to such an extent that the characters are 
illegible; therefore, the lake and pond shorelines contained 
within the quadrangle have been blackened by hand to better 
define each basin for this illustration. 
Utilizing the 9 threshold value, 1,426 separate water bodies 
were computer identified that were wholly contained within 
the area processed. The Meade River in the northwest corner 
was not continuous which provided some additional enumerated 
water bodies. Ponds smaller than 0.5 ha may not be identi 
fied and water bodies with less than 80 m separation are 
merged; thus, the number of computer-identified water bodies 
within this scene is probably less than what actually 
exists. This area represents 4.3% of the entire Landsat 
scene (Figure 1). Approximately 16% of the scene in the 
upper half consists of very large water bodies, including 
the Arctic Ocean with embayments and Teshekpuk Lake. The 
remaining 84% of the scene is the Arctic Coastal Plain, 
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