I believe that the earth is 71% water (sea) and 29% land. Don't know if I got the figures right, but if this is so I have the following question(s).
1. How much of the sea bed is explored and how certain can oceanographers know exactly what is on the deep sea bed.
2. Does oceanographers have the ability today to see what is on the sea bed in the deep oceans of the entire 71% area - the same way the earth is mapped with a satellite.
3. Also what lies below the deep sea ocean bed?
West Miramar, Florida
Very little of the sea bed has been "explored" in the sense of somebody going down and taking a look at it and retrieving samples, certainly less than 1%. An example of the mysteries of the deep and how there may be more interesting things to be discovered are the so-called deep sea vents discovered in the late 70s which contain whole ecosystems (e.g., tube worms) powered by the heat from the vents (in turn due to their proximity to the super hot mantle beneath the crust) and not by the sun. There is also abundant evidence for the existence of giant squid but no one has seen a live one except for perhaps a few fleeting snapshots.
As far as what the sea floor is made of, oceanographers extrapolate from known areas and types using well understood geological principles, but they are still extrapolations. A lot of work has been done exploring sea floor deposits of minable minerals, such as manganese nodules but the prospecting is very expensive and, again, only a tiny portion of the sea floor has been sampled. Areas with high potential don't necessarily get explored because of the cost (and the business decision of cost vs. potential revenue).
On the other hand, the topography (elevations) of the sea floor has been much more thoroughly studied, in large part by satellites. Your mention of satellites is, I think, in reference to non-ocean land features. By measuring the perterbations to the satellites orbit, the gravimetric properties (loosely, the density and volome of sea floor materials) under the orbit can be measured. Note that this has a coarser spatial resolution (100 meter ?) than direct samplng.
As far as measuring the high resolution topography of the ocean floor, in analogy to satellites mapping the land surface, sonars are the system of choice (vs. photography). While sonar technology is very advanced, including use of synthetic aperture sonar to give high resolution with broad coverage, again it is a very expensive proposition to map out the ocean bottom, especially the deep ocean which constitutes most of the ocean. For this reason, mostly coastal regions and some deep areas (eg., Gulf of Mexico) have been systematically mapped.
Just like the surface crust comprising the land we walk on, the sea floor is also part of the surface crust. Below this is the mantle which is very hot and consists of molten rock (terms used loosely; molten means minerals are hot enough to flow; think lava). Like on the land surface, molten material can come up though the crust to become deposited (like volcanoes). Examples include the mid-Atlantic ridge and the Hawaiian Islands.