It has often been said that we know more about the backside of the Moon then our own ocean's bottom. Sadly this is true. The Moon and Mars have both been mapped at much higher resolution then the 75% of the earth’s surface represented by the world's ocean basins.
https://www.kva.se/en/kalendarium/thamsk-forelasningocean-mapping-exploring-the-secrets-of-the-deep