Realization of time-domain ultra wideband ground-penetrating radar using high speed accumulation and interpolated sampling

• US 9,057,782 B2
• Filed: 08/17/2012
• Issued: 06/16/2015
• Est. Priority Date: 08/17/2012
• Status: Active Grant

• Current Assignee: Geophysical Survey Systems, Inc.
• Original Assignee: Geophysical Survey Systems, Inc.
• Inventors: Feigin, Jeffrey R.
• Primary Examiner(s): GREGORY, BERNARR E
• Application Number:
  US13/588,213
• Publication Number:
  US 20140049418A1
• Time in Patent Office: 1,033 Days
• Field of Search: 342/21, 342/22, 342/27, 342/28, 342/59, 342/82, 342 89-103, 342/175, 342/176, 342/179, 342192-197, 375/316, 375/340, 375/341
• US Class Current: 1/1
• CPC Class Codes: G01S 13/885 for ground probing prospecting or detecting using electromagnetic waves G01V3/12
• CPC Class Codes: G01S 7/2923 based on data belonging to a number of consecutive radar periods

Abstract

Embodiments of the disclosed technology use high-speed interpolated (interdigitated) sampling for the specific purpose of GPR (Ground-Penetrating RADAR). This technology solves several issues associated with high-speed sampling in GPR which included 1) dynamic range limitations, 2) regulatory compliance issues, 3) sampler core offset error, and 4) timing errors. High-speed interpolated sampling GPR is implemented using a high-speed ADC in combination with trigger logic (such as an FPGA) and a programmable delay generator. The FPGA or other trigger logic generates a series of randomly dithered trigger pulses. A variable delay generator (or “Vernier”) is synchronously controlled in order to produce the fractional timing. The timing of the pulses is randomly or pseudo-randomly dithered, and the phase of the interpolation is shuffled in order to avoid producing discrete spectral lines in the radiated RADAR signal.

Claims

1. A ground-penetrating radar transmitter and receiver comprising:

an analog to digital converter (ADC), trigger logic, and programmable delay generator;

said trigger logic generating a series of randomly dithered trigger pulses;

said analog to digital converter producing a continuous stream of digital samples from analog data;

a processor constructing a measurement waveform comprised of a plurality of interdigitated linearly sampled sequences based on output of said trigger logic and said analog to digital converter;

said processor further offsetting each said sequence of said plurality of sequences by a time frame whose modulus is smaller than the sampling period of a single sampled sequence of said plurality of sampled sequences; and

wherein

said measurement waveform is constructed from a plurality of iterations of constructing said interdigitated waveform from constituent sequences which form said interdigitated waveform;

said constructing is based on accumulation or averaging of said interdigitated waveforms; and

said accumulation or averaging incorporates interdigitated waveforms that were collected using equal representations of each core of said multi-core analog to digital converter (ADC), such that said ADC core'"'"'s interleaving error is canceled.

2. The ground-penetrating radar transmitter and receiver of claim 1 wherein said measurement waveform further comprises a plurality of combined individual interdigitated sequences, wherein each said linearly sampled sequence is acquired at a lower rate than is represented by said measurement sequence.

3. The ground-penetrating radar transmitter and receiver of claim 2, further

transmits a plurality of pulses into the ground at a location, each transmitted pulse of said plurality of pulses comprising a unique fractional delay corresponding to a position of phase of said interdigitated sequences.

4. The ground-penetrating radar transmitter and receiver of claim 3, wherein the sampling phase of each said sequence in said plurality of interdigitated linearly sampled sequences is collected in a randomized interdigitation order.

5. The ground-penetrating radar transmitter and receiver of claim 3, wherein the sampling phase of each said sequence in said plurality of interdigitated linearly sampled sequences is collected in a pseudo-randomized interdigitation order.

6. The ground-penetrating radar transmitter and receiver of claim 5, wherein each said sequence is sampled a single time in said plurality of combined individual interdigitated sequences.

7. The ground-penetrating radar transmitter and receiver of claim 3, wherein a discrete time filter is applied to said measurement waveform after construction of said measurement waveform.

8. The ground-penetrating radar transmitter and receiver of claim 3, wherein resultant transmit pulses of at least one single-sampled sequence are pseudo-randomly jittered with discretely quantized time steps equal to said unique fractional delay, such that said measured waveform is whitened.

9. The ground penetrating radar transmitter and receiver of claim 1, wherein an ADC core interleave phase of said ADC is adjusted by adding a fixed time delay equal to an integer multiple of the time sample period of each linearly sampled sequence of said plurality of linear sampled sequences, to every transmit pulse used to construct the composite of the interdigitated sequences.

10. The ground penetrating radar transmitter and receiver of claim 1, wherein said ADC core interleave phase is adjusted by utilizing system clocking whose fractional relationship results in composite measurement sequences that comprise alternating ADC core interleaving pattern error such that summation of an integer number of composite interdigitated sequences results in hardware ADC core interleave error cancellation.

11. A method of producing a waveform using a ground-penetrating radar transmitter and receiver, comprising the following steps:

obtaining a plurality of interdigitated linearly sampled sequences by transmitting a plurality of pulses into the ground using said transmitter;

using a processor or analog to digital converter to offset each said sequence of said plurality of linearly sampled sequences by a time frame smaller than the sampling period of a single-sampled sequence of said plurality of sampled sequences;

constructing a measurement waveform based on said plurality of interdigitated linearly sampled sequences and displaying said measurement waveform on a display;

wherein

constructing from a plurality of iterations of constructing said interdigitated waveform from constituent sequences which form said interdigitated waveform;

said constructing being based on accumulation or averaging of said interdigitated waveforms; and

said accumulation or averaging incorporates interdigitated waveforms that were collected using equal representations of each core of a multi-core analog to digital converter (ADC), such that said ADC core'"'"'s interleaving error is canceled.

12. The method of producing a waveform using a ground-penetrating radar transmitter and receiver of claim 11, further comprising a step of constructing a measurement sequence comprised of a plurality of combined individual interdigitated sequences;

wherein each said linearly sampled sequence is acquired at a lower rate than is represented by said measurement sequence.

13. The method of producing a waveform using a ground-penetrating radar transmitter and receiver of claim 12, further comprising a step of transmitting a plurality of pulses into the ground at a single location;

wherein each transmitted pulse of said plurality of pulses comprises a unique fractional delay corresponding to a position of phase of said interdigitated sequences.

14. The method of producing a waveform using a ground-penetrating radar transmitter and receiver of claim 13, wherein the sampling order of each said sequence in said plurality of interdigitated linearly sampled sequences is randomized or pseudo-randomized.

15. The method of producing a waveform using a ground-penetrating radar transmitter and receiver of claim 14, wherein each said sequence is sampled exactly one time in said plurality of combined individual interdigitated sequences.

16. The method of producing a waveform using a ground-penetrating radar transmitter and receiver of claim 13, wherein resultant transmit pulses of at least one single-sampled sequence are pseudo-randomly jittered with discretely quantized time steps equal to said unique fractional delay, such that said measured waveform is whitened.