The spectrum shows the sensitivity that LISA will obtain in its operating band, as well as spectral regions where various sources are predicted to be. The sensitivity below 3 mHz is dominated by spurious accelerations of the reference proof masses. The sensitivity from 3 mHz to 1 Hz reflects the shot noise limited performance of the interferometer. The sensitivity above 10mHz has a complex behavior caused by the interferometer arm length being greater than the wavelength of the gravitational waves.
In the region marked "Unresolved Galactic Binaries", gravity wave sources are so numerous that they will appear to LISA as an unresolved background.
The sensitivity anticipated for the most advanced version of LIGO, a 4km long ground based interferometer is also shown. LIGO began science operations in 2002, although with a much lower sensitivity.