The propagation of hydromagnetic plasma waves throughout the magnetosphere is controlled by the plasma density. I have adapted an existing magnetoseismic technique to create profiles of the plasma density in this region. This technique compares the arrival times of waves at several satellites located throughout the outer magnetosphere. The arrival times are controlled by the density, tomographic inversion is used to calculate the plasma density. This technique has been validated using synthetic data. The results obtained with real measurements from multiple satellites are qualitatively compared to the phenomena suggested by geomagnetic activity indices, where a plasmasphere plume has likely formed. This result shows that plasma density can be determined using satellites currently in orbit.