It carefully measures the time for the radio signal to go down and back. When we divide the time by two and multiply by the speed of light we get the distance from the satellite to the ocean surface. This is the altimeter range in the picture. The Jason MIcrowave Radiometer listens to the radio waves produced by the ocean surface, by clouds, and by water vapor in the atmosphere. It uses these signals to calculate the amount of water vapor in the atmosphere.
Water vapor slows the signal from the altimeter.
This causes the altimeter to calculate that the ocean surface is further away than it really is by about 10 cm. This is a small error but we need to remove it. The laser retroreflector array has mirrors that reflect laser beams aimed at the satellite from lasers on the ground. The reflected laser light is used to measure the position of the satellite so that scientists on Earth can know where Jason is above the Earth and how high it is. TRSR measures the position of the satellite by tracking the signals from GPS satellites and ground systems simultaneously.