Ganymede is the largest moon in our Solar System, and unique in producing its own magnetic field, as well as possibly possessing a subsurface ocean. The measurements from the only spacecraft that visited the moon, Galileo, provided two models for the internal field- a dipole and quadrupole model or a dipole and induction model. The focus of the initial 3 close flybys of the JUpiter ICy moons Explorer (JUICE) mission is to differentiate between the two signals and confirm the existence of an ocean. We begin with an analysis of the JUICE and Galileo trajectories in different reference frames and predict the induction signal using the time-varying field of Jupiter. A comparison between the induction and quadrupole signatures for Galileo flybys shows that the former seems more likely. Finally, we present and discuss the importance of the 3 JUICE flybys to observe the induction field and hence confirm the ocean.