On the Uncertainty of Archive Hydrographic Data Sets

As the international hydrographic community continues to address the question of irreducible uncertainty in modern surveys, a similar question must be asked of archived vertical beam echosounder (VBES) and leadline data sets. The Office of Naval Research funded STRATAFORM project surveyed an area of the New Jersey shelf around 39$^circ$12' N 72$^circ$50' W using an EM1000 multibeam echosounder (MBES). This area is also covered by National Oceanic and Atmospheric Administration surveys from 1936 to 1938 (from early visual indicating fathometers) and 1975–1976 (VBES). The analysis shows that the earlier data are biased in deeper water, most probably because of “hydrographic rounding” or instrument limitations, and may be unrecoverable, but that the VBES data appear approximately unbiased. Estimates of uncertainty for a surface model generated from the archive data are constructed, taking into account measurement, interpolation, and hydrographic uncertainty (addressing the problems of unobserved areas and surface reconstruction stability). Comparison of predicted depths against the MBES data shows that the VBES-derived surface is consistent given the quoted uncertainty and that the uncertainty corresponds with appropriate hydrographic survey standards. However, spatial aliasing of the VBES surface is observed, which may be the limiting factor in the applicability of this data.