I recently returned from a trip to Australia where I educated a bunch of Utility Locators in GPR. I did a presentation at a conference, a workshop, a 3 day bootcamp, and a coaching session. Throughout this amazing trip I had three people ask me the same question…which part of the hyperbola should I use to measure the depth of my target.

This is a super important questions since one of the most important benefits of GPR is its ability to measure depths, but this issue has some problems. One of the people (thanks Josh) whom I had this discussion with pointed out an article to me where the author asked 6 (I believe) different manufacturers where to mark the ground surface and the author received 6 different answers!!! WHAT??? That is nuts.

So who is correct?

The truth is that all of them could be correct. The way that I learned it was that you should measure the First Break. The initial part of the signal that indicates a reflection. So, that’s what I have done for as long as I can remember. But, you could measure it from any other place too. The key to correctly measuring depths to a target is to use consistent markers for where you measure your ground surface and where you measure your target.

The ground surface is your reference point anyway. So if you measure the peak amplitude of the central band for your ground surface…then you MUST measure the peak amplitude of the central band of your target. If you measure the First Break for your ground surface, then you MUST measure the First Break of your target. In either case you should end up with the same depths.

So where should you measure? It doesn’t really matter all that much as long as you remain consistent.

Leave a comment below about how you have measured depths until now.

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