Webinar: Basics of Ground Penetrating Radar (GPR) usage with a drone

The webinar was designed to learn the capabilities of a Ground Penetrating Radar (GPR) mounted on a drone.

The introduction webinar provided answers to questions:

  • Why mounting a GPR on a drone?
  • Is GPR+drone better than the conventional application?
  • Does a GPR+drone system acquire qualitative data?

Answers provided by UgCS Support team to questions asked during the webinar:

  • Q: What experiences do you have with the Air traffic law and other laws in connection with GPR on a drone?
    A: Hi, we have checked existing rules in the US/Canada and Europe. With our existing solution which allows us to remotely turn on and off the GPR antenna and fly very low (1m AGL) we are complying with the existing law.
     
  • Q: Do you configure the GPR/Antenna perpendicular or parallel to the acquisition line?
    A: Perpendicular.
     
  • Q: Do you have any case study to detect tunnels that are used by the human traffickers running up to 3 or sometimes 5 m below the borderlines by using GPRs?
    A: At the moment we don't have such a case study, but we know that it is possible to detect underground tunnels if they are enough big for people.
     
  • Q: What's the device behind you in the video?
    A: It is a DJI M600 Pro drone with a Zond-12e Drone 500A GPR system (orange antenna).
     
  • Q: Is it guaranteed that you CANNOT see anything under a clay layer?
    A: In most cases - yes. But at the end of the dry season sometimes you can detect something.
     
  • Q: Follow up on clay question: The reason why we can't see below clay is because of the water the clay absorbs?”
    A: Because wet clay has good conductivity and absorbs EM wave energy very effectively.
     
  • Q: Regarding uneven terrain, does the antenna need to be parallel to the ground?
    A: Yes, it is better that a GPR antenna is parallel to the surface.
     
  • Q: What is the Field of View of the GPR?
    A: It depends on the frequency, type of antenna, soil composition. We provide a "footprint" calculator to the customers.
     
  • Q: At which operation altitude of the drone do you still achieve a 50% penetration depth of the GPR?
    A: Altitude (or the distance between the antenna and the surface) should be less than the length of EM wave in the air corresponding to the center frequency of the antenna.
     
  • Q: These frequencies have to meet the government's limitations, right?
    A: You need to have a certified GPR antenna if you are speaking about the US and Canada. We have certified our RadSys Zond-12e 500A antenna in both countries. You also need to register the GPR antenna in local FCC or IC (for Canada) office.
     
  • Q: Penetration given from drone at what height?
    A: Altitude (or the distance between the antenna and the surface) should be less than the length of EM wave in the air corresponding to the center frequency of the antenna.
     
  • Q: What is the brand of the GPR you are using?
    A: Radarteam and RadSys.lv. Technically we can integrate any light enough antenna.
     
  • Q: At what flight altitude those depths of investigation have been computed?
    A: We usually suggest to fly 1 - 4 m high over the surface. It depends on several factors as the GPR antenna you use, and the target size you are looking for.
     
  • Q: Is your software able to fly the antenna parallel to the ground?
    A: Our system allows to keep constant distance from surface. But we don't have kind of gimbal to keep antenna parallel to the surface.
     
  • Q: What bandwidth to the comparisons of antennas table?
    A: Please, see antennas specs here: www.industrial.ugcs.com and scroll down to the end of page.
     
  • Q: As you are flying very low, it's impossible to work on a field with bushes or high grass?
    A: With hi-frequency antennas - yes (in most cases). But in case of dry sandy soil, for example, you can have good penetration from few meters even with 500Mhz antenna.
     
  • Q: Follow up question to regulations: are these antennae FCC and IC compliant for US and Canadian laws?
    A: Zond-12e 500Mhz is certified in the US/Canada. All other antennas are not certified.
     
  • Q: Do you use a Gimbal? How do you have the GPR Parallel to the ground?
    A: We do not use Gimbal. The GPR is mounted with special mountings under the drone to be parallel to the ground.
    You can see pictures in our website: www.industrial.ugcs.com
     
  • Q: Did you work with Mala company out of Sweden?
    A: No at the moment.
     
  • Q: Does software make comparison among the data of different flights on the same flight missions (same altitude, same route)?
    A: You can use GPR-Slice for that.
     
  • Q: Hi, does your software do topographic correction to the gpr data?
    A: Yes. We log GPR data with coordinates/altitude from autopilot, and Prism2 software supplied with our systems can do topographic correction.
     
  • Q: Is the antenna rigidly affixed to the UAV? In other words, if I am flying across a hillside with a 30° slope, can I change the mount angle of the antenna so it is parallel to the surface slope?
    A: We supply mountings with fixed orientation of the antenna. For some particular conditions it is quite easy to make customized mountings - it is just 4 aluminum tubes.
     
  • Q: What is the max altitude that the GPR can be useful?
    A: It depends on many factors, first of all frequency of antenna, type of soil, size of objects what you want to detect. But in any case it is something between 1m and few meters.
     
  • Q: Being so close to the ground how does it deal with the tree in the flight path?
    A: We don't have collision prevention sensors. So operator should monitor the flight.
     
  • Q: Does the data logger automatically imports the GPS data into the radar team's radargram?
    A: Yes. We save the data in the same SEG-Y format.
     
  • Q: Is it possible to make topographic models with this technique, and what is the accuracy?
    A: You can do the same what you can do in the case of terrestrial GPR surveys.
     
  • Q: Are you able to use the GPR-drone system for search and rescue missions above forests?
    A: NO. It is absolutely impossible. Unfortunately, we can forget about any idea to do GPR surveys from above forests - but it is a VERY popular request.
     
  • Q: If flying an automated survey using the onboard M600 GPS data for real-time terrain following at 1-2m AGL, how do you account for accuracy variability of the actual M600 height AGL which can vary by +/- 1-2 m from what is reported from the drone? (The M600 can say it's flying level when it's actually 1+ meter above or below that reported altitude AGL.)
    A: We use a radar altimeter to keep constant altitude over the surface.
     
  • Q: But if I fly over a Slope with 20° can I change the angle of the GPR with your setting?
    A: We don't have a gimbal, in theory, you can make some custom mountings for such work. But from our experience, 20 degrees slope is not a problem for collected data.
     
  • Q: How difficult is installing the radar/changing the payload?
    A: First installation and system setup will take a couple of hours. After that changing payload will take 5 to 15minutes.
     
  • Q: Do you have an example of real in-flight data? A recording of an actual flight?
    A: More data samples HERE.
     
  • Q: If we install a laser altimeter to the drone, the height detected will be ground or tree or grass?
    A: With laser altimeter, you will detect the first object in front of the laser beam. It can be a grass stem as well. We have implemented radar altimeter which helps to have a more smooth drone flight.
     
  • Q: Can we use it for roads, to measure the asphalt, gravel, the composition of the road?
    A: Yes, you can use it for measuring the composition of the road. Please write an email to us!
    You can write: oskars@ugcs.com
     
  • Q: Does wind impact the results (i.e. from the buffeting of the drone and GPR during flight disturbing the drone during its flight path) and how is this dealt with? Are the recommended wind speeds in which it is not advised for the drone with GPR to be used?
    A: In very windy weather you will get noisy data. The recommended maximum is 5m/s and no gusts.
     
  • Q: Is the pitch (during flight) affecting the GPR data?
    A: Almost no. More important is not to fly in windy conditions with gusts.
     
  • Q: How do we read the results? Do we need a special app or program to analyze the results?
    A: We supply Prism 2 software for data analyzing: http://radsys.lv/en/products-soft/prism2.5+software/
     
  • Q: The price of a system say for 150 antenna?
    A: Please ask oskars@ugcs.com for the prices.
     
  • Q: How far apart are the flight lines? Can the distance be increased if you fly higher?
    A: Distance between lines calculated using our "footprint calculator". The higher altitude allows increasing the distance between survey lines but on the cost of penetration.
     
  • Q: Do you have an example dataset to compare the same GPR system ground - and drone-launched? Is there any impact of the radio link to the drone visible in the GPR data?
    A: Yes - please ask adobrovolskiy@ugcs.com for samples. Usually, there is no interference with 2.4Ghz datalinks of drones with GPR. But if you will use 433Mhz or similar you can experience interference.
     
  • Q: How do high grass\small bushes effects penetration depth and resolution?
    A: The penetration depth and quality of data affected by the height of the flight. So if there is high vegetation at some level you will not be able to get good quality GPR data.
     
  • Q: Could I let a gimbal installed when I install the GPR?
    A: No, GPR antennas are quite big.
     
  • Q: Does ur ugcs data logger mark on prism automatically? If no, how do you do it?
    A: Automatically - in waypoints.
     
  • Q: What is the minimal size of objects you can see for instance with the 500MHz antenna? (In sand if you need an example) Is it more or less similar than with ground data?
    A: In dry sand for 500Mhz if the distance between surface and antenna is 0.6m, depth 1m, minimum size of detectable object is 16 cm. The same rules apply as in the case of terrestrial surveys.
     
  • Q: What's the cost of GPR?
    A: Please ask oskars@ugcs.com for the prices.
     
  • Q: Which version UGCS should be used for GPR survey?
    A: The latest version with additional software and hardware (SkyHub) to control GPR and set up terrain following.
     
  • Q: Can GPR be used in forested areas, such as the tropics?
    A: From above forest? NO.
     
  • Q: What material was the pipelines made of?
    A: Steel, 70cm diameter.
     
  • Q: Can you detect the bedrock below the soil layer?
    A: Yes, but it depends on the bedrock depth and the GPR antenna you have chosen.
     
  • Q: So this system is only suitable for clear area (without grass) as we need fly only few m from ground?
    A: Grass is OK. Recommended altitude depends on the frequency of GPR and varies from 0.6m till a few meters.
     
  • Q: How do you know the diameter of the pipe? Does it have any relationship?
    A: In the gas pipes survey we had information about pipes before the survey.
     
  • Q: Does the shape of hyperbola or similar shape formations in the software dependent on the structure detected ?
    A: Yes, the hyperbola shape is different with different objects detected. You need a good experience to say what structure possibly is detected.
     
  • Q: How can we create a 3D read-out of the data and use it in CAD or GIS software?
    A: You can use GPR-Slice software to generate 3D from GPR data.
     
  • Q: Have you been able to detect nonmetallic pipelines?
    A: Yes, of quite a big diameter, at least 1/4 of a wavelength of GPR center frequency in the air.
     
  • Q: Can you roughly measure the objects detected using this data?
    A: Yes, the same as in the case of terrestrial surveys, rough estimation is possible.
     
  • Q: If you're doing the ground following, what happens over rugged terrain? Also, in the images, the ground looks very bumpy. Why?
    A: In the images you see, the ground level is smooth. You need to look at 0 m level on the left side of the Prism 2 software.
     
  • Q: When flying over a water body, what is the flight height above water surface? What is the water depth limitations? What is teh depth of penetration into water body floor?
    A: We are flying 1,5-2m over the water. The maximum depth in freshwater we can reach is 15m for 52Mhz antenna.
     
  • Q: For freshwater, you mean we can detect the depth of the water similar if we use echo-sounder for the bathymetric survey?
    A: Yes.
     
  • Q: Is geohammer free? If no, how much?
    A: Yes, free.
     
  • Q: Why is there a zig-zag in the reflection positions? Antenna/GPS lag?
    A: Yes. We are working on a compensation algorithm.

  • Q: Fx drainage pipes will be air-filled plastic pipes. I understand that we should be able to detect them because of the contrast between air and soil - correct?
    A: Yes, but the diameter of the empty plastic pipe should be big enough.
     
  • Q: How do bushy vegetation and small branches affect the system? Is it possible to see anything below small bushes or high grass?
    A: It is possible to see under vegetation, but you need to be able to fly very low 1- 4m usually.
     
  • Q: Are the drone and the GPR electronically integrated to each other?
    A: Our onboard computer is integrated with both autopilot and GPR.
     
  • Q: Is the top pipeline deeper?
    A: Both pipes are on the same absolute level, but there was some slope in the survey area.
     
  • Q: Have you ever done any study over glaciers? Is it possible to fly higher in those cases?
    A: Yes, in Greenland past summer. Over ice/snow you can fly higher. With the low-frequency antenna, you will get useful data even from 10-15m.
     
  • Q: Do you use an accurate GPS or only the GPS from the M600 to get the Coordinates from the GPR Profile?
    A: We use GPS coordinates from DJI M600 Pro. It is possible to use PPK receiver to get more precise coordinates in the data during the post processing.
     
  • Q: You mention the RadSys Zond 500 is FCC certified. Is it approved by FCC for use greater than 1 meter above ground surface?
    A: It is certified as all other GPR systems, you have to follow all standard restrictions to use GPR in US. Maximum distance between antenna and surface 1m, and it should be functions to switch off radar remotely. All that is implemented in our system.
     
  • Q: Where you flying higher on this survey over snow ?
    A: In Greenland, you can see ice profiling data from Zond-12e 500Mhz, flight altitude 5m, HERE 
     
  • Q: Are these systems designed specifically and only for the DJI M600 Pro, or are they platform independent and could be mounted on any drone capable of carrying the payload
    A: Hi, you can use it with custom built drones with DJI A3 autopilot and also you can check different Pixhawk based drones as example Avartek Boxer Hybrid: http://avartek.fi
     
  • Q: Is it possible to fly on hilly land like scree?
    A: Here you can see our solution flying in those conditions: https://youtu.be/YJeyzx8LzAg
     
  • Q: I'm not very familiar with the SEG-Y format; is the metadata for waypoint marks and GPS info an open standard compatible with GPR-SLICE? Or something more proprietary for Prism2?
    A: Our customers use GPR-slice, they can import data with coordinates, but marks are a proprietary extension. You can use Prism2 or Geohammer to split files to separate profiles before import to GPR-Slice.
     
  • Q: Are lines the layers on the snowpack? Or just noise or irregularity?
    A: In the Greenland sample? It is layers of snow of different age I think.
     
  • Q: How many missions and how many flight hours is the double grid pattern?
    A: 5 flights as I remember, ~80 minutes of flight time [in Greenland sample]
     
  • Q: Can locate strata layers-with material of different densities. Such as rock outcroppings in the sand, or a clay layer under the sand?
    A: We can locate different materials in the soil if they have different dielectric permittivity values. Rocks in sand and clay under the sand layer are possible to detect.
     
  • Q: What are the costs for the various antennas?
    A: Please ask oskars@ugcs.com for the prices.
     
  • Q: Just out of curiosity, did they recover the plane?
    A: No. They are looking for money to do that.
     
  • Q: With beta version of UgCS GeoHammer can we use non-seg-y files?
    A: No. But we published Geohammer in source codes. So you can help us to implement support for more formats. We planned to implement the import of GSSI format.
     
  • Q: Can you show some migration?
    A: You can try using our samples: https://files.ugcs.com
     
  • Q: Can GPR measure soil water content?
    A: Yes. At least we have papers with the description of methodology. 
    Please ask oskars@ugcs.com
     
  • Q: Is it required a special configuration or equipment to adapt a GPS antenna to the UAV?
    A: You can use standard DJI M600/M600Pro to carry GPR. We supply SkyHub onboard computers for GPR data recording and radar and laser altimeters with necessary software and mountings and cables.
     
  • Q: Is there a way to maintain constant vertical when terrain is rugged (i.e. flat flight)?
    A: Do you mean tilt and roll angles = 0? It is impossible for UAV, but usually variations of till/roll angles are <5 degrees in case of calm weather (when drone is flying with the speed up to 3m.s)
     
  • Q: Is this able to be used in the US? I have heard there are frequency restrictions.
    A: Zond-12e 500Mhz certified in US/Canada.
     
  • Q: Why GPR signal loses penetration depth if on drone? Air shouldn’t be a perfect resistive?
    A: Yes, but the density of energy is decreased as 3rd power of the distance from the antenna.
     
  • Q: I'd like to see a migration of data, can you show this?
    A: You can try using our samples: https://files.ugcs.com
     
  • Q: Are any data available comparing ground-based GPR to drone-based GPR operated at different heights (same profile, same GPR system)?
    A: Here: https://files.ugcs.com - you can find GPR data collected from 2 till 7 meters AGL over gas pipes. But we didn't do a ground survey here.
     
  • Q: How do you get the true vertical reference for anything you find (i.e. height of top of pipe in WGS84)
    A: The same method as in case of terrestrial surveys.
     
  • Q: How does UgCS deal with tall objects encountered during flight… avoiding a collision when close to the ground?
    A: We don't have collision prevention sensors. So operator should monitor the flight.
     
  • Q: With that, it all connects to the UAV Systems? (i.e. the UGCS window shows the signal quality and UAV route)
    A: Do you mean right now [during webinar]? no - it is simulation mode.
     
  • Q: Do you know of any GPR missions using a swarm of drones?
    A: We have operated 2 drones with GPR simultaneously in Greenland.
     
  • Q: Ok, so in the real acquisition is not real-time visible the GPR Trace?
    A: By default operator will see the current trace twice per second, it is because of limitations of the DJI data link. It is possible to deliver almost real-time data down to the ground, but it will require separate datalink with high throughput.
     
  • Q: As I understand, the inclination of the GPR antenna depends on the flight direction and speed, correct? What are typical inclinations and is this measured/saved continuously so that I could be corrected during data processing?
    A: Correct. You will have all drone attitude information in a log file for every trace. You can ask adobrovolskiy@ugcs.com for the samples of log files together with data.
     
  • Q: How does GPR react to water bodies, small rivers, or ponds?
    A: In case of low-frequency systems it is possible to do bathymetric surveys. Samples are here: https://files.ugcs.com