457 
Computer-calculated lake areas within the specified quad 
rangle provide a good example for use of the comparator. 
Tables 1 and 2 are retrieval listings that were limited to 
only those lakes with surface areas >2.0 km 2 within the 
quadrangle. Four lakes had areas >2.0 km 2 . The SLAR lakes 
were the largest 3 lakes in the area. 
Although usable in its present form, this computer lake 
system is not complete and can be refined in the future to 
provide more utility with greater simplicity. Three areas 
need additional attention. First, a method must be devised 
to merge master files from multiple overlapping Landsat 
scenes to enable extension of geographic coverage without 
duplication of lakes in the overlapping areas. Secondly, an 
algorithm should be developed to ease the updating lake data 
entry so that specific lakes on the lake file can be ac 
cessed and verified with a minimum of centroid position ac 
curacy, a maximum of data entry ease, and a minimum po 
tential for lake identity error. Finally, spectral thresh 
olds used to discriminate between water and land must be 
investigated further, and verification of computer-generated 
product accuracy, utility, and cost must be completed. 
SUMMARY 
A computer lake system was developed that uses computer 
compatible Landsat data to create a lake information file 
uniquely characterizing each lake in the file. The com 
puter-calculated latitude and longitude of the centroid for 
each lake provide a lake file with a geographic data base 
from which lakes can be retrieved for a defined area. 
Computer calculations of surface area, perimeter, and 
crenulation further characterize each lake. The lake file 
provides storage for additional information obtained about a 
lake from other sources. Retrieval of lakes on file can be 
accomplished through sorting and sieving (filtering) func 
tions defined by parameters of interest and values limited 
by comparators ( >, =, and <). When a geographic area 
containing lakes of interest is specified, the user-defined 
area is calculated and printed at the end of the listing. 
The sum of all lake surface areas in the listing is also 
printed for comparison with the geographic area in which 
they exist. 
This system has several potential uses. It could be used to 
consolidate aquatic data for dynamic retrieval. This can 
supplement or replace conventional means of lake data 
management and analysis. The system provides worldwide 
capability for rapid survey of lakes in relatively flat 
terrain and for monitoring their changes in time. Finally, 
it provides the capability for lake classification through 
sorting and filtering functions applied to the various lake 
parameters on file.