New Processing Methodologies for Cross Check Analysis and Observed Water LevelsCorrections in Surveying

Current field surveying procedures for conducting cross check analysis and generating
observed water level corrections (tides). These procedures are standards in the field, but
require extra steps by the surveyor either before or after the survey. The Naval Oceanographic
Office (NAVOCEANO) has developed new approaches to reduce or eliminate the need for these
extra steps, while maintaining modern error standards.
Today’s multibeam surveys contain overlap between adjacent lines. NAVOCEANO has
developed a method of using the overlap to provide a continuously updated difference layer
that we use as a basis for cross check analysis and observed water levels (tides).
Performing a cross check analysis using the difference layer removes the need to run
special lines. This saves survey time and allows the survey crew to run more lines and generate
more coverage. In addition, since we are using consecutive lines, our method allows for a
continuous cross check analysis of the data.
A secondary benefit of our method is the creation of observed tides. If overlap areas
are collected within significant timespan, the difference layer can be used to generate values
for observed tides based on the change in the data. When tabulated the result is an
approximate tide chart for the overall area. While this method does not result in the creation of
constituents and/or a datum, application of sections of observed tides allow for the derivation
of both.
By generating and analyzing a difference layer created from the overlap area of
consecutive lines within a survey, we can reduce the need for additional cross check lines and
observed tides can be found and corrected without the need for tide gauges or constituents.
We believe application of these methods will result in higher quality data and more efficient
surveying.