The Tellus high-resolution three – in- one airborne survey (Magnetics, Electromagnetics and Radiometric) is a national airborne geophysical survey managed by the Geological Survey, Ireland. To date over 260,000 line km of electromagnetic data (both FDEM and TDEM) have been collected, although the majority of this data has been four frequencies (912, 3005, 11962 and 24510 hertz) FDEM data flown at a nominal survey altitude of 60 m. The data has been collected over an extensive area over variable geological conditions. This report describes the high resolution Tellus Frequency Domain Electromagnetic method (FDEM) including;