Sea interferometry

A radio detecting antenna is placed on top of a cliff, It acts as a second aerial twice the height of the cliff below the first. The interference patterns for a sea interferometer commence sharply as soon as the source rises above the horizon, instead of fading in gradually as for a normal interferometer. Since it consists of just one detector, there is no need for connecting cables or for preamplifiers. A sea interferometer also has double the sensitivity of a pair of detectors set up to the same separation. Sea interferometry greatly increases the resolving power of the instrument. ==Data quality==

The quality of data obtained by a sea interferometer is affected by a number of factors. Wind waves on the water surface and variable atmospheric refraction adversely affect the signal, and the curvature of Earth must be taken into account. These difficulties can be overcome by observing for extended periods, and calibrating the instrument on sources of known position. ==Discoveries==

Among the discoveries made using sea interferometry are that sunspots emit strong radio waves and that the source of radio wave emission from Cygnus A is small (less than 8 arcminutes in diameter). The technique also discovered six new sources including Centaurus A. ==References==