Patent Application
20220350007
The present invention relates to the field of surveys by means of GPR (Ground Penetrating Radar) technique.
In particular, the invention relates to a method for sampling an Ultra Wide Band signal.
As known, the signals emitted and received by a GPR (Ground Penetrating Radar) sensor are of the Ultra Wide Band (UWB) type, i.e. they are characterized by a −10 dB band of at least 500 Hz, or a −10 dB equal to at least 20% of the center frequency on which this band is measured. Band at −10 dB is the difference between the highest and lowest frequency for which the power spectral density is 10 dB lower than the maximum.
The main limitation of the prior art for sampling, in the time domain, of UWB signals is given by the sampling rate of Analog-Digital converters (ADC). In fact, to receive a signal correctly, the converter must have a sampling rate equal to at least double the maximum frequency of the signal (Nyquist sampling theorem). Therefore, a very high speed A/D converter must be used for a UWB signal, i.e. with a sampling frequency that can be a few GHz and analogical band sufficient to meet the Nyquist condition.
With reference to
A first solution present in the prior art provides the acquisition of the signal by means of the so-called “equivalent-time sampling” or “stroboscopic sampling”, which consists in transmitting a multiplicity of consecutive pulses, and for each of these collecting only one sample at a time. An example of this method is shown in US2010195699.
Such acquisition method is typically characterized by a high sensitivity, or dynamic range (DR), i.e. the ratio between the maximum and minimum signals that can be received by the system.
In particular, the dynamic range can be defined as follows:
DR˜η*GAV*DRX
wherein
A greater dynamic range results in a greater ability of the GPR to detect very weak signals. Since this return signal is strongly attenuated by the ground, a high sensitivity of the receiver basically indicates the ability of the GPR to locate objects at greater depths.
However, the stroboscopic sampling has the disadvantage of requiring numerous consecutive transmissions for the correct acquisition and reconstruction of the signal.
In particular, the number of samples NS that have to be taken is dictated by the Nyquist condition:
N
S>2*TFS*fmax
wherein
Since, in the prior art, stroboscopic sampling involves the acquisition of only one sample at a time, the total time required for sampling the received signal is given by:
T
tot
=N
S*PRI=NS*1/PRF
wherein
Therefore, the aforesaid sampling method, in the face of good sensitivity, involves very long signal acquisition and reconstruction times, i.e. equal to at least NS times the transmission time of a pulse.
An alternative approach present in the prior art is the so-called “real-time sampling”, which allows a much faster acquisition than that in equivalent time, as it uses an A/D converter with a sufficiently high speed to correctly sample the UWB signal in a single transmission-reception of the radar pulse, therefore such as to respect the Nyquist condition on the maximum frequency of the received signal.
However, due to technological limitations, as the sampling rate increases, the ENOB value (and therefore the dynamic range) of the A/D converters decreases. Therefore, the sensitivity of GPR using this technology is much lower than that obtainable by sampling in equivalent time.
To overcome the aforementioned drawbacks, a hybrid solution (“pseudo-stroboscopic” or “pseudo real-time sampling”) is described in U.S. Pat. Nos. 8,884,807 and 9,057,782, which makes use of faster A/D converters than those used in equivalent time sampling, acquiring however a multitude of samples for each signal received.
However, even this hybrid solution requires a certain number of repetitions of the transmission of impulses, resulting in any case slower than real-time sampling.
It is therefore an object of the present invention to provide a method for sampling an Ultra Wide Band signal that allows the reconstruction of the signal in a much shorter time than equivalent-time sampling or pseudo-stroboscopic sampling, while ensuring a dynamic range that is not less than these methods, in order to guarantee the detection of objects at great depths.
It is also an object of the present invention to provide such a method that allows the possibility of further increasing the dynamic range of the system by means of the “stacking” technique.
It is also an object of the present invention to provide such a method that allows multi-channel GPR acquisition, i.e. through a plurality of GPR antennas, while maintaining the same efficiency of the single channel.
These and other objects are achieved by a method for sampling an Ultra Wide Band signal according to claims from 1 to 6.
Further characteristic and/or advantages of the present invention are more bright with the following description of an exemplary embodiment thereof, exemplifying but not limitative, with reference to the attached drawings in which:
With reference to
With reference also to
With reference also to
Depending on the dynamic range of the signal, and on the sampling requirements, the steps [304], [305] and [306] can then be repeated again with more than one secondary signal, dividing the full-scale of the signal into respective portions.
The method, according to the present invention, then provides the division of the full-scale of the signal into two or more portions, in order to sample the first portion without amplification and then proceed with the amplification and the sampling of the subsequent portions.
This allows the sampling of UWB signals in very short times with respect to the methods of the prior art while preserving a high dynamic range. In particular, the time required for the above method is proportional to the number of transmissions/receptions of the signal and, therefore, to the number of portions into which the full-scale of the signal is to be divided.
Furthermore, the method according to the present invention provides the possibility of repeating the steps of transmitting and receiving of both the primary signal and each secondary signal, with subsequent average of the signals, so as to be able to implement the “stacking” technique to further increase the dynamic range.
In particular, at least two sampling steps of the values of the primary signal and at least two sampling steps of the values of each secondary signal can be provided, to implement the “pseudo-stroboscopic” mode.
Furthermore, the method according to the present invention can provide prearranging a GPR antenna comprising n≥2 transmitters and m≥2 receivers, in order to allow a superimposed transmission/reception of signals by the transmitter/receiver couples.
In particular, in the exemplary embodiment of
In particular, at a time t1 there is a step of transmitting and receiving a primary signal from a first couple of transmitter/receiver, with following sampling of values of the primary signal, and at a time t2<PRI=1/PRF there is a step of transmitting and receiving an auxiliary primary signal by a second couple of transmitter/receiver, with following sampling of values of the auxiliary primary signal.
At a time t3=t1+PRI there is then the step of transmitting and receiving a secondary signal by the first couple of transmitter/receiver, with consequent amplification and sampling of values, and at a time t4=t2+PRI there is the step of transmitting and receiving an auxiliary secondary signal by the second couple of transmitter/receiver, with consequent amplification and sampling of values.
This way, it is possible to repeat the sampling steps of the primary and secondary signal, thus obtaining a number of overlapping signals to obtain a more accurate sampling, exploiting the PRI delay between the transmission/reception of two signals made by a transmitter/receiver couple. Typically, in fact, the time between one pulse and the next (PRI) is several orders of magnitude greater than the maximum delay identifiable by the radar (full-scale). For this reason it is possible to transmit and receive with multiple channels, placing them temporally separated.
With reference to
This is possible by using a common time reference for each transmitter or receiver element that makes up the system, and by setting an individual programmable delay for receiving the same signal between two or more different receivers.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102019000016562 | Sep 2019 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/058661 | 9/17/2020 | WO |
