I have had several people reach out lately that were frustrated when dealing with GPR manufacturers and distributors. They asked about multi-frequency systems, and had several different manufacturers that indicated they made multi-frequency gpr systems but each manufacturer had a completely different type of system.
In this video I go over some basic terminology and review different types of systems to help YOU, the user, navigate the confusing GPR jargon.
1) A pulse radar is one that puts out a discreet signal over a short period of time. Once the signal is produced, the receiver begins to record data for a defined amount of time. This is helpful for making estimates about depths. The antenna used have a central frequency and actually put out a range of frequencies approximately +- 50%. So a 400 MHz antenna will produce a range between about 200 and 600 MHz. Multiple of these antenna can be fit into the same system (such as a 700 MHz and a 250 MHz) so the GPR actually records data from two separate antenna with two separate central frequencies at the same time.
2) Ultra-wide band radar is also a pulse radar system, but the engineering of it allows the system to produce a much wider range of frequencies. These antenna still have a central frequency, but the range is far greater than +- 50%. With this ultra wide range, the user can define a sub-range of frequencies that he or she wants to analyze.
3) Continuous wave stepped frequency (CWSF) is a system that does not produce a pulse (a short burst of energy), but rather continuously produces electromagnetic signals. However, the continuous production of signals is cycled through a series of different frequencies. When the receiver records returning signals, then it can distinguish what the frequency of the returned signal is and can work out when it was produced by the transmitter.
So which one is a multi-frequency? It almost doesn’t matter. You could make a case that each one of these are however it doesn’t do anyone any good! So the best way to move forward is to restrict the use of the term to one thing. My personal use of the term multi-frequency is reserved for systems that have multiple pulse radar antenna on the same system, each with a different central frequency.
This is NOT a knock on CWSF or UWB. CWSF produces multiple frequencies, but why not make it clear that it has one antenna that cycles through these. For UWB, just say it is a UWB and offer the end user the information about maximizing its use through effective band pass filtering.
SO users, hold the manufacturers feet to the fire when inquiring about equipment. And manufacturers, be upfront and transparent about what you are selling. If you call it multi-frequency, then fine, but also tell the potential customer exactly why you are saying that.
If you use GPR and didn’t know how this worked, then you should get further training. Check out our upcoming webinars, classes, and live workshops at LearnGPR.com.
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