A little variation in the EM61 response may not be problem
if looking for large response targets. However, when looking for smaller targets, baseline measurements must have as little variation as possible. So why are your EM61 readings varying more than+/-1.5 mV?
Good question! I don’t know. That’s for you to discover. Variances as small as +/- 1.5 mV can happen for a number of reasons. Have you performed all of Geonics Quality Control tests? If not, start there! Certain sources of noise might not be so obvious. Have you checked your pants… shoes… body… for any metal? Are your cables securely connected to the proper port? Did you test the cables for any dreaded shorts? Was the equipment nulled in an area free of metal? Did you try shutting the machine off and restarting it? Did you allow the equipment to warm up before panicking?
I could go on asking questions but it’s up to you to take some quality time and troubleshoot the situation. Follow the Geonics Quality Control Tests and you will eliminate your inconsistent readings.
“But I have performed all of these quality control tests and I am still not collecting consistent readings during a Static Background Test!”
Well now, it can only be one thing- noise. There are many different types of noise that can affect an EM61 response. However, assuming that the EM61 is in a stationary position and free of any metal, ambient noise is most likely the culprit. Although rare, magnetic storms can affect the EM61 response. Ruling out a magnetic storm, an operator may find that radar, power lines, and navigation (GPS) equipment are common sources of ambient noise that affect the EM61 response. Look around, do you see any nearby power lines? While power lines and navigation equipment are easy to identify, radio waves can be harder to discern. Are there any broadcast stations, airports, or military bases nearby? Maybe, maybe not.
If you suspect that radio waves are interfering with your readings, move the EM61 five to ten miles away, and perform the Static Background Test again. If you’re readings are more consistent, chances are that radio waves were affecting your readings. Unfortunately, unless there is a way to stop the transmission of ambient noise, you may be out of luck!