[1] The two sets of waves are then combined to form an interference pattern such as that produced by two separate aerials.
[4] Sea interferometers are drift instruments, that is, they are fixed and their pointing direction changes with the rotation of the Earth.
[4] A sea interferometer also has double the sensitivity of a pair of detectors set up to the same separation.
Wind waves on the water surface and variable atmospheric refraction adversely affect the signal, and the curvature of Earth must be taken into account.
[2] These difficulties can be overcome by observing for extended periods, and calibrating the instrument on sources of known position.