454 
dotted with lakes. If the 4.3% of the scene with 1,426 
computer-identified water bodies is representative of the 
Arctic Coastal Plain area the system might identify 
as many as 28,000 water bodies on the terrestrial 
estate contained within this 1 scene. 
Lake Calculations (Subroutine LCALC). Each lake com 
pletely contained within the scene area processed has had 
its centroid (center), area, perimeter, and crenulation 
calculated. The PIXGEO subroutine is called to convert the 
Landsat polar coordinates for the lake centroid to latitude 
and longitude through map projection algorithms. PIXGEO was 
developed by a number of people cooperating within the USGS 
Cartography Division of Reston, Virginia, and EROS Data 
Center Digital Image Processing Group at Sioux Falls, South 
Dakota. Preselected ground control points are used in NASA 
Goddard Space Flight Center and EROS Data Center software 
systems to produce geometrically corrected Landsat scenes. 
These corrected data make this lake system unique and par 
ticularly useful. A user will be able to obtain an EDIPS 
corrected computer compatible tape that, when fully proc 
essed, should be capable of lake basin centroid calcula 
tions that have latitude and longitude accuracies to 
+ 60 m (McCormach and Elliott 1980). A new subroutine 
being developed for geometric correction of Landsat IV 
scenes should provide more accurate positions with greater 
computer efficiency. These systems can provide a lake 
data file suitable for geographic retrieval of information 
at accuracies near those of inch to the mile or smaller 
scale map bases. The original centroid calculation is 
listed in decimal degrees for latitude and longitude. 
Decimal degrees are converted to degrees and decimal 
minutes for lake data retrieval, but the decimal degrees 
to 5 places for both latitude and longitude provide the 
unique identity for each lake. 
Area is the second most useful lake parameter calculated. 
Area is calculated in km 2 , accurate to 5 decimal places, to 
accommodate the resolution of a .00325 km pixel. Lake 
area is an easy, inexpensive, and useful parameter to cal 
culate . 
Perimeter is calculated through the rigorous and time- 
consuming process of following the perimeter samples around 
the computer generated lake shore. Removing this calcula 
tion from the program might save a significant amount of 
computer time, but this has not been tested. 
Crenulation is calculated from area and perimeter values to 
provide an index of shoreline development. A value of 
1.000 is the idealized smooth shoreline of a perfectly 
circular lake. The index value increases from 1.000 as the 
shoreline perimeter/crenulation increases. 
Additional lake surface characteristics, such as length and 
azimuths of major and minor axes, might be added to computer 
calculations in the future. At this time, storage space and 
computer cost have limited this system to centroid, area, 
perimeter, and crenulation. Perimeter and crenulation are 
not particularly important lake criteria but show the