Sparsely Referenced Environment of Bristol Bay, Alaska

• Main Authors: Ltjg Meghan Mcgovern, Weston Renoud, Dr. Robert, A. Mcconnaughey
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2009
• Subjects: Arctic; Alaska
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.492.8374; http://www.thsoa.org/hy09/0513A_02.pdf

The Bristol Bay region is a prime example of an area with vast economic and environmental significance but with minimal modern bathymetric data and poor spatial coverage of vertical reference stations. This significantly limits the accuracy of data essential to commerce, ecosystems, recreation, and research. This case study used a 2008 multibeam trackline survey of Bristol Bay to make a qualitative evaluation of Post Processed Virtual Reference Stations (PPVRS), Precise Point Positioning (PPP), single station tides, and discrete tidal zoning as methods for vertical transformation. Having few measured separations between the Mean Lower Low Water (MLLW) tidal datum, the International Terrestrial Reference Frame 2005 (ITRF05), and the GEOID06 model in Bristol Bay, the data were processed to compare ‘mean-difference ’ trends rather than quantitave values, in order to highlight quality and isolate errors within each process. Limitations were found in all processes, but PPP introduced the least error and is presented as the preferable choice to survey to ITRF05 in this region of Alaska. Since the method relies exclusively on precise satellite correctors, it does not introduce the inherent limitations of using the distant references that all other methods will use. However, since tides are not locally observed in most offshore surveys, and since land-based tidal observations and zoning are limited, a MLLW to ellipsoid or geoid separation is not known. This means that PPP data is accurate and robust, yet impractical for charting unless tidal observation is recorded onsite. As survey priorities begin to include arctic waters, where offshore water levels are not necessarily deep, PPP should be considered for use in conjunction with offshore water level gauges to measure the MLLW to ellipsoid and geoid separation.