Geological Survey, Ireland is pleased to announce the publication of a report titled 'Variability in the Tellus Waterford Test-line FEM data'. This report takes data flown from a series of repeat flights, flown at different times along the airborne geophysics test-line in Co. Waterford between 2019 and 2021. The report investigates the variability and repeatability of Tellus airborne frequency-domain electromagnetic (FEM) data. 

FEM data examined consisted of 20 flights, flown over a 4.4km line close to the town of Bunmahon in county Waterford, with a nominal flight clearance of 60 m recording four frequency EM data. Along with the variability of the recorded data, an appraisal of 1D inversion resistivity models, the effect of Principal Component Analysis filters on FEM data variability, as well as the signal footprint are also discussed. The primary control observed on the variability of the 12 and 25 kHz FEM responses is variability in flight clearance, while the 0.9 and 3 kHz EM responses is less sensitivity to flight-clearance.  The dominant cause of variability in the 0.9 and 3 kHz EM responses is interpreted to be variability in the cultural noise signal recorded on each of the twenty repeat flights.

The report will hopefully improve our understanding of the Tellus FEM data and how we can merge and interpret it. It also assists in the development of inversion models for the data.

The report can be accessed from the Geological Survey Ireland publications page.