Complementary Ground Observations
Just as it is important to complement the optical and radio observations from the ground with observations from space at submillimetre, infrared, ultraviolet, X-ray and gamma-ray wavelengths, so too is it important to complement the gravitational-wave observations made by the ground-based interferometers in the high-frequency regime (10 to 103 Hz) with observations in space in the low-frequency regime (10-4 Hz to 10-1 Hz).
Ground-based interferometers can observe the bursts of gravitational radiation emitted by galactic binaries during the final stages (minutes and seconds) of coalescence when the frequencies are high and both the amplitudes and frequencies increase quickly with time. At low frequencies, which are only observable in space, the orbital radii of the binary systems are larger and the frequencies are stable over millions of years. Coalescences of massive black holes (MBHs) are only observable from space. Both ground- and space-based detectors will also search for a cosmological background of gravitational waves. Since both kinds of detectors have similar energy sensitivities their different observing frequencies are ideally complementary.
(Extract from LISA: Detecting and observing gravitational waves, the Mission Summary of the Cornerstone Study Results, ESA brochure 164.)