An oceanographic satellite carries instruments which take measurements of the ocean. Several instruments have been developed to make different oceanographic measurements. The temperature of the sea surface can be measured using an instrument called a radiometer . Active instruments send pulses of energy to the Earth to take measurements.
Passive instruments measure the energy which is given off by the Earth.
Using the following information, try to figure out which instrument is active and which is passive. Imagine that you are standing on the flat roof of a building. If you bounce a tennis ball on the roof, the ball will return to you quickly. However, if you bounce the ball on the ground directly below the roof, it will take longer for the ball to return to you. In fact, the higher the roof, the longer it will take for your ball to return.