I have on various occasions used the statement that we know the surface structure of Mars in greater detail than that of the sea floor on our on planet, and I understand that it is still true overall, but oceanographers are now working to close that gap in our knowledge. Just over 100 years after bathymetry, the science of measuring the depth of the oceans, and thus the topography of the sea floor, began in earnest, experts now met to lay out plans for future progress in exploring what's under the water. This knowledge is important not just for seafarers and fishing industries, but also for the safety of landlubbers in the face of sea level rise and tsunamis.
Read all about it in my latest feature:
How deep are the oceans?
Current Biology Volume 26, Issue 11, pR445–R447, 6 June 2016
permanent link to full text and PDF download
The combination of advanced sonar and satellite technology can produce high-resolution 3D models of seascapes like this one in the Caribbean. However, for much of the sea floor, there is still insufficient data. (Source: http://pubs.usgs.gov/of/2004/1400/).