These data show how different types of rocks resist the flow of electrical currents across Ireland. The rock types can then be mapped. The data were collected between 2005 and 2021.

Several surveys were merged to create this dataset.

(1) Tellus Northern Ireland 2005-2006

(2) Cavan-Monaghan, 2006

(3) Tellus Border, 2011-2012

(4) Tellus North Midlands, 2014-2015

(5) Block A1, 2015

(6) Block A2, 2016

(7) Waterford, 2016

(8) Block A3, 2017

(9) Block A4, 2017

(10) Block A5, 2018-2019

(11) Block A6, 2018-2019

(12) Block A7, 2019

(13) Block A8 2020-2021

(14) Block A9 2021

The data were collected using an airplane. The airplane flies at 60 m flight height along lines that are 200 m apart. Electromagnetic data are recorded at around 6 m intervals along the flight lines. The electromagnetic system mounted on the airplane sends an electromagnetic signal (at different frequencies) into the ground and records the response of the ground returning to the system receiver. The response changes depending on the type of rock or soil that the electromagnetic signal meets. For example, graphite has a high response value (meaning it is a low resistivity rock) while limestone has a low response value (it is a high resistivity rock).

The data are collected as points in XYZ format. X and Y are the airplane coordinates. Z is the different recorded data, which include electromagnetic responses and aircraft flight height. The XYZ data for each line contains thousands of points. The data from separate lines are merged to create a resistivity grid for each survey block. All the survey blocks are then merged to create a final resistivity grid for Ireland.

Colours are used to show resistivity ranges. Resistivity values are defined in ohm-metre units. Pinks and reds show the highest values. Greens and blues show lower values.

This is a raster dataset. Raster data stores information in a cell-based manner and consists of a matrix of cells (or pixels) arranged into rows and columns. The format of the raster is a grid. The grid cell size is 50 m by 50 m. This means that each cell (pixel) represents an area on the ground of 50 metres squared. Each cell has a value which is the average resistivity of all the points located within that cell.

The Tellus project is a national survey which collects geochemical and geophysical data across Ireland. It allows us to study the chemical and physical properties of our soil, rocks and water. It is managed by the Geological Survey Ireland.