Process_Description:
LANDSAT-TM images of the Salton Sea Basin offered the first preliminary look at possible areas where the shoreline was visible from space. Digital Ortho Quarter Quads were utilized in areas in which the shoreline was not visible from space and for increased accuracy of preliminary shoreline elevations.
Global Positioning Units were primarily used to collect control points at areas where shoreline evidence such as tufa deposits, differences in soil composition, or other geomorphic features were present. Using the GPS receiver, clusters of 180 geographic positions were collected for post-processing in the laboratory.
Post-processing involved differential correction and determination of a centroid within the point cluster. The control points were then plotted on 7.5-minute digital raster graphics (DRGs). Elevations of the control points were correlated with a digital elevation model (DEM) to produce a shoreline delineation at 11.9m asl.
Results
Of the fourteen control points taken, three were eliminated due to inconsistencies with GPS satellite telemetry. By differential correction, the remaining 11 control points achieved 95% locational accuracy. This process eliminates 95% of the error introduced by the Department of Defense on the GPS system and distortion from the ionosphere.
The 11.9m-contour was plotted on a LANDSAT-TM base image. The shoreline delineation for Mexico was not obtainable due to pending acquisition of digital elevation data for this region. To supplement this, a 10m contour was interpolated with the 11.9m contour used for the California side of Lake Cahuilla. The 11.9m-contour is consistent with the approximated shoreline elevation of Wilke and Waters.