Before satellites were used to study the ocean, we had to rely on information collected by ships, buoys, tide gauges, and such. This is all covered about two web pages over, so I won't go into details here. THE GYRE Picture a ship that's not even one kilometer long trying to study all of the ocean. It would take forever to cover that much territory. Satellites on the other hand use solar energy once they are launched into orbit.
Satellites can sometimes be damaged by particles from the sun, so there are hazards.
We still need data collected from ships, buoys, and gauges so we can compare them to the satellite data for accuracy. There are still some things about the ocean that a satellite can't tell us. Perhaps, you will be the scientist of the future who develops an instrument for satellites that will tell us all we want to know. All of these measurements are used to get a clear picture of what is happening in the ocean. The models also use measurements made from ships and drifting buoys.