Note that odd values of topography (e.g., -2001m) are constrained by actual soundings while even values (e.g., -2000m) are predicted from gravity. Therefore one can extract the locations of the ship sounding.
Smith, W. H. F., and D. T. Sandwell, Global seafloor topography from satellite altimetry and ship depth soundings, Science, v. 277, p. 1957-1962, 26 Sept., 1997.
Gravity References:
Sandwell, D. T., R. D. Müller, W. H. F. Smith, E. Garcia, R. Francis, New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure, Science, Vol. 346, no. 6205, pp. 65-67, doi: 10.1126/science.1258213, 2014.
Sandwell, D. T., and W. H. F. Smith, Global marine gravity from retracked Geosat and ERS-1 altimetry: Ridge Segmentation versus spreading rate, J. Geophys. Res., 114, B01411, doi:10.1029/2008JB006008, 2009.
Sandwell, D. T., E. Garcia, K. Soofi, P. Wessel, and W. H. F. Smith, Towards 1 mGal Global Marine Gravity from CryoSat-2, Envisat, and Jason-1, The Leading Edge, 32(8), 892-899. doi: 10.1190/tle32080892.1, 2013
-10.1
359.5 360
-13
(Any values between -360 and 360 are acceptable)
Also, these files can get quite large, so you may have to divide the area up into smaller chunks.
The selection area must be less than 20 degrees in longitude and latitude.