Document Type
Conference Proceeding
Publication Date
2003
Department
Marine Science
Abstract
The widespread use of multibeam sonar systems has brought to the forefront many developments to handle the tremendous amounts of data collected. One of the valuable quality assurance tools available for hydrographic data is that of analyzing depths where two tracklines cross. In contrast to the single-beam echosounding case, where crossing tracks result in single overlapping footprints, multibeam sonar crossing tracks involve the analysis of a multitude of redundant data points. The earliest (pre-GPS) multibeam crossing track analysis tools were used to improve georeferencing, shifting tracks to achieve spatial correlation at all intersections. Now, with georeferencing handled by GPS and other sensors, crossing track comparisons are important quality management tools. This paper describes an automated means of evaluating data quality from multiple multibeam crosschecks.
The current tools available at the Naval Oceanographic Office require executing a string of six programs to evaluate a single crosscheck. A typical survey area has hundreds of crossings when crosscheck lines are run at 10 times the development line spacing. Software was written that ingests a set of multibeam trackline files in Generic Sensor Format (gsf), determines the intersections and automatically grids and analyzes the crossing data. Two crosscheck analyses are performed. The first analysis determines a single quality indicator for each crosscheck, based on statistics run for residual depth differences of gridded data. This quality indicator is compared against a threshold, and the results are displayed. The user can easily determine any unexpected quality trends in the data. A trackline file whose quality indicators exceed the threshold for multiple crosschecks merits further investigation and analysis.
The second analysis compares each crosscheck beam by beam. This analysis is based on the increase in depth uncertainty with increasing beam angle, which is characteristic of multibeam sonar, primarily due to roll and sound speed profile uncertainties. For each crosscheck, a profile of the depth discrepancies is generated between the center (nadir) beam data from one trackline compared to the entire ping from the other trackline and vice versa. The results identify whether or not the overall comparison from the first analysis is driven by beam-dependent uncertainties.
Recommended Citation
International Hydrographic Organization Special Publication 44, 4 th Edition, April 1998, Pub. International Hydrographic Bureau, Monoco, France (http://www.iho.shom.fr). Guide to the Creation and Interpretation of the Comparative Data Products, John E. Hughes Clarke, Ocean Mapping Group, Dept. Geodesy and Geomatics Engineering University of New Brunswick, Canada, http://www.omg.unb.ca/~jhc/uschc97/comp_interp.html#sun_interp. Cooperative Research and Development Agreement between COMNAVMETOCCOM and Interactive Visualization Systems, Agreement Number NCRADA -CNMOC-00-005, Signed 8/31/2000.