Technical Notes - Helicopter Electromagnetics

The Effect of Sun Spots on HEM Surveys

Question:

Is the Dighem system more sensitive to sun-spot activity than earthbound electromagnetic methods? This year the sun-spot activity is supposed to be very high.

Answer:

Sunspot activity is not a problem for frequency domain EM systems, because of the narrow frequency band of each channel. The magnetic oscillations caused by solar winds are very low frequency compared to the HEM frequencies. To the best of our knowledge, no HEM survey was stopped because of strong magnetic storms interfering with the EM data. (The Dighem system is much more sensitive than ground geophysical systems of similar scale.)

The sunspot-related magnetic storms do affect magnetic surveys, and require very good base station monitoring, and can even become so severe that magnetic surveys cannot be conducted.

Greg Hodges, Chief Geophysicist, 2000