The temperature of the ocean at the surface is not constant across all oceans. For example, the Arctic Ocean will have a much colder surface temperature than the Pacific.
temperature
The temperature of the ocean is 39 degrees below the surface.
The ocean water has a high amount of dissolved salts.
suface zone and thermocline zone
Surface zoneo
Surface Zone
infrared
Wind
The temperature of he oceans varies as the depth. the salinity and the latitude. The polar seas (high latitude) can reach -2 oC (28.4 oF) while the Persian Gulf (low latitude) as high as 36oC (96.8oF). The average temperature of the ocean surface waters is about 17oC (62.6oF). The deep ocean is another story. About 90 % of the total volume of ocean is found below the thermocline in the deep ocean. This deep ocean water is between 0-3 oC (32-37.5oF) As a result the average temperature of all the ocean waters (as a whole) approaches these temperatures.
In order for temperature to change the involved heat has to have some place to go. The water at the bottom of the ocean is surrounded by ground and other water that are already at the same temperature. Where can extra heat go to? At the surface the air transports heat up and away so ocean heat can leak out (or in) to the water.
The average temperature of the ocean's surface is from 30 to 60 degrees Fahrenheit in customary units.
If you were to measure reflected radiation then you would be measuring the temperature of the source of light (the sun)! So you need to look at the emmited radiation (measured during the night) to guage the temperature of the ocean's surface.