What is HDR?

March 25 2022

HDR stands for High Dynamic Range and is a term used for GPR equipment with the ability to record extreme amplitude values and yet also very small variations within that range. This is made possible partly by using real-time sampling technology. The benefit of HDR technology is that it delivers a very clear, low-noise, broad-frequency signal. The practical benefits are that GPR data become extremely sharp, with very high-resolution, and achieve a good penetration depth with respect to the central frequency used.

Ground penetrating radar is regarded as ultra-wideband (UWB) equipment. UWB refers to the very broad range of frequencies produced and recorded by the antennas. All manufacturers of GPR equipment aim to create antennas delivering a signal with as wide a frequency range as possible since this benefits both the quality and the ‘usefulness’ of the data (in terms of the resolution and depth capability). There are several different approaches to deliver a signal with the broadest possible range of frequencies: multi-frequency antennas built with traditional, non-HDR, technology is a common way and continuous wave stepped-frequency (SFCW) systems is another. Typically, both approaches tend to make GPR equipment more complicated and expensive, and may deliver noisier data and limited dynamic range to customers. HDR is a more modern way to efficiently deliver affordable, high-quality, increased bandwidth data to GPR users.

Traditional GPR antennas take some time to collect a full trace with, say, 512 samples (the smallest building blocks of the trace). This is because the antenna has a repetitive sampling process: one pulse from the transmitter is needed for each sample captured in the receiver, thus summing up to 512 cycles of firing a pulse and recording a sample.

With a HDR antenna, each cycle consists of one pulse from the transmitter and many readings (samples) at the receiver end. This semi-real-time sampling system will therefore be much more efficient than a traditional solution. If comparing a complete set of 512 samples in a trace, collection time can be cut by a factor of 200-400.

This time saving in data collection can then be used to stack each sample more often and by that improve the signal-to-noise ratio and by that produce clearer data.

Another positive effect of the HDR technique is the antenna bandwidth. When you lower the noise floor, you also increase the bandwidth of the antenna and access additional parts of the signal spectrum. On the high frequency side, this will provide you with better resolution and, on the low frequency side, give you better depth penetration.

What is HDR?

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