USGS Coastal & Marine Geology
Wong, F.L., Hamer, M.R., Hampton, M.A., and Torresan, M.E., 1996, Bottom Characteristics of an Ocean Disposal Site off Honolulu, Hawaii: Time-based Navigational Trackline Data Managed by Routes and Events: Redlands, California, Environmental Systems Research Institute, 1996 ESRI Users Conference Proceedings (cdrom), approx. 15 p.

GIS Analysis
Results and Conclusions
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The USGS conducted three surveys in Mamala Bay from 1993 to 1995 during which the following data were collected: bottom and sub-bottom geophysical profiles, sidescan sonar images, bottom video and still photographs, and physical samples. The goals of the surveys were to determine (1) the distribution of the dredged material, (2) the composition of the dredged material, (3) active sedimentary processes, and (4) how these processes are affecting the dredged material.

USGS 1994 survey tracklines. Navigational fixes on camera track. All data recorded during a survey include the time that the data were collected and specific information about the data-collection process. Examples of this information are survey line start/end times, time of core sampling, and beginning/ending times of camera lines. Using time of collection, the data are keyed to a master navigation log that contains the individual satellite (GPS) fixes (locations) or transponder signals (ranging) recorded at the time of the fixes. This log includes the time from the start of the survey (often departure from port) to the conclusion (return to port). Table 1 is an excerpt from the navigation log for the 1994 survey during which the bottom photographs were taken (Figure 3). The full log has a navigational fix every 10 seconds, which is a greater data density than is required for analysis of the photographs in this study. Table 1 has been desampled to include only 1-minute fixes. Figure 4 displays a small window of the survey area with time annotated along the tracklines.

Sample bottom photographs. Tables 2 and 3 are examples of the tabulations generated for each piece of data collected during the surveys. Table 2 records the deployment history of various pieces of equipment, that is, when pieces of equipment were turned on or off. These records cover discrete spans of time and are subsets of the complete survey time. The 1994 camera-survey segments are plotted in blue in Figure 3. Table 3 lists observations from still photographs, which were collected with a 35-mm underwater still camera loaded with 50-ft rolls of film (approximately 400 frames per roll). Shots were taken every 1.5 minute until the film was depleted (as long as 10 hours). Observations of bottom morphology and inferred current direction from each of the photographs were tabulated (Figure 5). Consecutive photographs showing the same characteristics were grouped into a single entry with the inclusive start and end times. Individual photographs showing features unlike the preceding or following ones in time sequence were entered as a single record with the same start and end time.


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