How it works FAQ’s
We are frequently asked, “How can you possibly achieve subsurface penetration of up to 200m?” when the maximum scanning depth of all other Ground Penetrating Radars is limited to 10 to 20 metres. Surely this is not possible…..?
- It is correct that the commonly achieved depth penetration for “normal” GPRs in the market today across the world are just some 10m to 20m. Loza-Radar’s claim of greater competency – of a significant order of magnitude - would therefore appear to be an extraordinary claim! Below is our simple answer...
- Traditional GPR operates in the frequency range 100-500 MHz. The Loza-Radar research team and developers have, after many years of hard work, conceived of and designed an entirely different type of GPR.
- To achieve the extended depths with our GPR, the transmitting signal is moved to a lower frequency, being within a band of 1-50 MHz, and the peak power of the transmitter is increased by a factor of hundreds of thousands in relation to the traditional types of GPR.
We therefore find that...
The attenuation of the signal is heavily dependent on the frequency. The higher the frequency, the higher the attenuation. Graphically, the theoretical and experimental data, shows that this relationship is as follows:
The frequency range of traditional GPR attenuation can really be 5-10 or even 20 dB / m when scanning through wet clay. At frequencies of less than 10 MHz, the attenuation of the signal may be considerably less than 1 dB / m.
In assessing the power of the GPR’s signal, the correct assessment of decay in the environment with ohmic losses is:
a = 1.88 σ / (ε) 1/2.
To evaluate the dynamic range we use a formula for the "power” being;
db = 10 log (48x 106).
In order to evaluate various GPRs, it is common to compare the (a) peak voltage, (b) transmitter switched to the antenna, and (c) the minimum voltage that can register with the receiver. This measure might be called the "potential of the device." The formula for determining the potential (voltage ratio) differs from the formula for power:
dB voltage = 20 • lg (U1 / U0)
U1 - peak voltage of the transmitter (in this case 21 • 103),
U0 - the minimum voltage that can register the receiver (sensitivity), (in this case ~ 10 • 10-3 B).
The potential of the device will be equal to:
dB = 20 • lg (21 • 103/10 • 10-3) = 126 dB
With an attenuation in the order of 0,3 - 0,4 dB / m, we obtain an estimated depth penetration of about 400 meters. The resulting estimates should be divided by 2, since the GPR signal takes a “doubled” path; (a) from the surface to the reflector and then (b) back to the receiver.
As a result, the maximum depth of our 21 kW transmitter at frequencies of 1-10 MHz is circa 200 meters. In the case of surveying sub-surface lithologies that have uniformity from near surface, our depth-penetration markedly increases. The estimated sensing depths are empirically proved and verified on a regular basis by our many surveying teams, over ground that is “referenced” by way of drilling, trenching or where the stratigraphic record is obtainable.