These data show the magnetic field strength of different rock types 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. Magnetic data are recorded at around 6 m intervals along the flight lines. The magnetometer system mounted on the airplane records the magnetic field strength of the rocks. The magnetic field changes depending on the type of rock beneath the aircraft. Iron rich rocks (for example, basalt) are strongly magnetic and have a strong magnetic field, while rocks with low iron content (for example, limestone) are weakly magnetic.

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

Colours are used to show magnetic field anomaly ranges. The values are defined in nanoTesla 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 value 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.