Radar is a useful tool with familiar uses such as detecting aircraft and observing weather. It also has some less known applications, such as a technology known as ground-penetrating radar (GPR). Despite the difficulty of sending and receiving radio waves through solid objects, with the right equipment it’s possible to build a radar that works underground as well.
GPR is used often for detecting underground utilities, but also has applications in other fields such as archaeology and geology. For those people in these fields, a less expensive GPR was the priority of a group presenting at a 2017 National Institute of Telecommunications of Poland conference (pdf warning). The presentation goes into specific detail on how to build a GPR for around €600, much less than commercial offerings.
The presentation begins by highlighting the basics of GPR, then details the hardware bill of materials for the transmitting circuit, receiving circuit, and the DC power supplies. It also details the theory behind the software needed to get the circuit running properly, and has code as well. The processing is done on a 32-bit Mbed platform, and the rest of the GPR is built with easy-to-source components as well.
It’s always good to see useful hardware projects that bring costs of traditionally expensive equipment down to the grasp of average people. Even traditional radar systems are now available for hundreds of dollars, and we’ve even seen attempts at other GPR systems before as well.
Thanks to [Stefan] for the tip!
Still looking for that Nazi Gold Train eh?
https://en.wikipedia.org/wiki/Nazi_gold_train
not only train…
https://thechive.com/2015/05/18/19-real-life-lost-treasures-that-have-yet-to-be-found-19-photos/
From a geophysics perspective, the best way to search for that would be an aerial gravimetric survey.
You’re telling this to people who are making their own janky GPR’s. You think we have the cash for that?! :P
Anybody who knows where I can find the firmware for the MBed? It’s not in the PDF.
Time Team here I come!
Excellent write up, but no testing data to show if the design is effective… Also how did they design those antennas?
They look like standard off the shelf highly directional log periodic PCB antennas (e.g. https://www.wa5vjb.com/products1.html ). If you read through the linked pdf, it is mostly COST parts used.
sorry COTS (Commercial off-the-shelf)
They’re bow tie antennas, which are very wideband. You need to understand that being in contact with the ground reduces the wavelength of all frequencies (like the impedance of stripline). Might be 3:1 over typical ground.
I’ve built 40 foot antennas which worked down to about 1.5 MHz.
We have 3D images of mine tunnels down 150 feet.
MAY we contact through email ?
That depends who you are and what you’re up to.
Sonofodinragnar14@gmail.com
I would greatly appreciate plans for this. We just bought a house from the late 1800s that historically has info on tunnels below the house used to smuggle slaves to Canada yes Even tho slavery was abolished.. many still had to run north to truly start a new life and did till the early 1930s. I don’t wanna just go digging everywhere and after buying and restoring a historic home I don’t have 14k to drop on gpr just for this..
The antenna appear to be log-periodic ( not bow-tie), broad band.
Why, so they are.
After fooling around with log periodic and yagi antennas aimed at the ground, we found that antennas work one way in free space and completely differently when pointed at the ground, a small multiple of a wavelength away. It detunes your short elements (at the point) and your signal might go up, not into the ground. The dielectric constant of the air-ground interface is what causes it.
If you pull them far enough away from the ground so they don’t detune, you get a big ground bounce. So bow ties laying right on the ground seem to be the smoothest match.
Hello,
I run a GPR company in Canada and would like to talk to you about building a low frequency antenna (30mHz to 60mHz). Can we connect?
I’ll send a message on your company website. Ours was at
http://www.sc-radc.com/home/personnel/vandamme-html if you’d like to see some of the stuff I’ve played with over the years.
I am interested in DIY inexpensive and basic if that is even realistic. I would be willing to compensate you for the ability to create one for personal use. How can I contact you?
First, explain what you’re looking for, how deep, what kind of soil/rock, what resolution you want, and how long you need to use it. It might be better to hire somebody to find a pipe or tank one time.
The hard part is the software. It’s like a sonogram that gives 3D images in different density mediums. They all have limits. Have you read the Polish PDF writeup referenced in the article?
The FMCW setup is very similar to G. Charvat’s design described in Small and Short-Range Radar Systems. A dual chip pulsed radar was published in http://jmfriedt.free.fr/rsi_strobo_fabian.pdf with the pulse generator further investigated in http://jmfriedt.free.fr/gpr2018.pdf. Equipment cost is negligible, the time spent developing is not and might justify some of the cost beyond the raw material !
See you at gnuradio french days ;)
EUROPEAN GNU Radio days @ https://gnuradio-fr-19.sciencesconf.org/
That PCB tho… yikes.
It’s 1.3-2.6GHz… expensive Minicircuits plumbing modules screwed together, it’s basically identical to Greg Charvat’s MIT radar.
I’ve never heard of somebody making PCBs with AZ1518 photoresist and a mask aligner before… that sounds super expensive to make a chip mask in the yellow room just to make a PCB.
The true challenge of a ground penetrating radar is not the transmitter/receiver- it is the processing- the focusing algorithms that allow you to figure out the size, shape, depth, and composition of things without having to interpret hyperbolas or simple time domain stripcharts. I was building/testing/field testing with virtually the same technology(*) (**) in the early 90’s and the vast majority of the interpretation methods are the same 25 years later. Collecting the data is maybe 2% of the effort, and the methods have long been solved.
(*) Keith Sturgess, Matthew Bennett, Marc Ressler, Ted Grosch, Army Research Laboratory Ultra-Wideband Boom-SAR: System Overview and Minefield Detection and Recognition Results, presented at the Symposium for the Application of Geophysics to Engineering and Environmental Problems (SAGEEP ‘95) April 24 – 27, 1995 in Orlando, Florida.
(**) Lynn Happ, Marc A. Ressler, Keith Sturgess, Matthew Bennett, Lawrence Carin, and S. Vitebskiey, Army Research Laboratory ultrawide-band testbed radar and comparisons of target data with models, Proc. SPIE Int. Soc. Opt. Eng. 2496, 42 (1995)
So what is the solution? Is there open source software that can turn these signals into a 2d image or 3d model?
Now I can find velociraptor skeletons just like Dr Grant!
Utilities is still a thing because finding water leaks is a pain.
Dont see any rf filters in signal chain – dynamic range will be poor asfk. But anyway its good project for learning students.
Depending on your country and regulations, 1.3-2.6 GHz seems like a big wide chunk of spectrum that you can’t legally use.
You’re stepping on GPS, aircraft navigation radar, radio astronomy and a host of other things.
UWB (UltraWideBand) regulations will allow stepping on other bands as long as signal power level is below “noise” level.
Those are underground?
Would expect low frequencies would work much better than 2 gig. What’s the lowest frequency that can be used for unlicensed use?
Would FMCW be suitable for working in the 500Mhz range to get more depth? Obviously it would change the specs on the components and filters.
A GPR is so fascinating to read about. Thinking about all the things that are still buried deep in the ocean, is just exciting. Excellent write up!
Keep in mind that GPR has quite significant limitations in conductive surfaces such as clay soil, wet soil, and salt water will cause significant signal attenuation.
Can this be used to find water reservoirs underground or it only for detecting objects of other densities?
It detects transitions between two materials of different dielectric value, for example, the boundary between clay and sand, or concrete and rebar, ice and water, or concrete and air pockets.
Can this find Jimmy Hoffa?
Yes, if he’s a different conductivity and dielectric constant than the surrounding ground. GPR looks for differences in the RF propagation characteristics, like any radar.
Ok, stupid question from someone who has been working in RF for the last 30 years:
How can this possibly work? You are launching a low-power wave directly into absorbent / reflective earth, and looking for some sort of return? I would guess all that you are seeing is the atmospheric conditions above your angle of incidence. To make a much simpler analogy, imagine pointing a bright flashlight into a dirty mirror, and looking for reflections. How can you pernitrate the earth with anything in the MHz range? It seems to me that this would best be served with large acoustical impulses into the dirt, exactly how the oil prospectors do it?
Sonar works, but sometimes you don’t want to make so much noise. And sonar has the same problems as GPR.
GPR works just like radar in air. RF does penetrate into the ground, and it does reflect off features that are different than the surrounding medium. The attenuation is much greater than air, and it works both ways, so you are greatly limited in range. But the attenuation varies with frequency, so you can penetrate deeper with lower frequencies. But … the resolution is proportional to bandwidth, so at lower frequencies your resolution gets worse. Also, antennas get bigger and/or less efficient at lower frequencies and higher bandwidths. If you are looking for a tank 3 feet down, or a salt dome 500 feet down, you use different frequencies.
Another big problem is isolation. If you use an FMCW radar, and your transmitting antenna is near your receiver, you need a lot of dynamic range to cancel out the transmitted signal from your received signal, so you can see those targets waaaay down in the mud (electrically, and physically). If you use a pulsed radar, you need a short enough pulse to do this cancellation, so you need a higher power or PRF, but there’s limits on that too.
Simple pulsed radars are used to find buried tanks, pipes, and the like. Ground contact is commonly used to reduce ground bounce. Designing antennas for these is not fun. They are electrically shortened by the effective dielectric constant of the ground/air half plane (kind of like stripline). So pointing a long log periodic down is not going to work right. Bow ties flat on the ground are good, but for wide bandwidth they need to be electrically long. Loaded dipoles are easier to move around but inefficient.
It’s an engineering problem. If you are looking for smaller targets, deeper, through a more dissipative or dispersive medium, sooner or later you run out of dBs, and money to buy A/D converters.
It was mentioned that GPR is often used for finding underground utilities. Is this something that would be helpful before you begin digging in your yard? We are wanting to build an underground pool, and want to make sure we don’t hit any water lines in the process. I will have to let my husband know about GPR, and see what he thinks.
In most places there are laws that require you to contact utilities to see what’s buried where; they will come and mark them. I’d expect you’re not doing the digging yourself, so make sure your pool installer does this. It will cost you time and money, but the fines are high if you don’t. And if you hit a sewer, water, power, or internet line, that would be very bad.
Finding a thin pipe buried below the frost line with GPR is possible but don’t count on it. Plus, renting a radar and somebody who knows how to run it is not cheap. If it’s something you or a previous homeowner put in, better to start digging (carefully) and see what turns up. You might run across an old well or septic tank. I found a foundation for a building that was gone by 1900. Do some detective work, looking for clues like old pipes coming out of the ground or oddly settled ground. Use a metal detector if you have one; much cheaper than a GPR.
hello, what a nice job,
I want to have access to the full document so that I can try to manufacture ..
where can I find the information?
thanks in advance!
The PDF referenced in the writeup above contains complete hardware and software descriptions.
You could spend a lot of time building and programming, according to the data given in the article. But since you’d end up with a UHF band system you might have only a couple feet of penetration. It might be enough to find a shallow buried tank in dry ground. If you’re looking for a tunnel down say ten feet, you’ll need to run at less than VHF, and then your resolution will suffer. You might be better off with a sonar. Or just drill some thin pipes in the ground with a pressurized water drill head and see if you find some voids in suspicious places.
Can you show us how to build one step by step with parts list and instructions, PCB gerbal files? Thank you.