- Natural electrostatic field of the Earth - an example of double grass circleKoppel, Tarmo; Haldre, HeldurEarth's Fields and Their Influence on Organisms : International Conference at Birštonas, June 15-18, 2017 : abstracts and materials2017 / p. 89-93
- Radiowaves' standing waves could be mistakenly interpreted as Hartman linesKoppel, Tarmo; Haldre, HeldurEarth's Fields and Their Influence on Organisms : International Conference at Birštonas, June 15-18, 2017 : abstracts and materials2017 / p. 54-60
- Spatial distribution of the Earth's magnetic field in the nature - example measurements at Elva reservoirKoppel, Tarmo; Haldre, Heldur; Priiman, R.Earth's Fields and Their Influence on Organisms : International Conference at Birštonas, June 15-18, 2017 : abstracts and materials2017 / p. 61-65