Using ground penetrating radar to detect people under rubble

Due to growing international tension, the topic of discovering buried people alive is becoming especially relevant. In addition, the risk of earthquakes and the quality of construction structures increase the urgency of searching for people under the rubble (Figure 1).

Ground penetrating radar, theoretically, is capable of detecting objects located under thick stones, bricks, concrete, etc. The following are the results of several model experiments demonstrating the capabilities of GPR.

First, a little theory. GPR, like any other radar, detects objects that differ in electrical properties from the environment, more precisely, in dielectric constant. Moreover, the higher the contrast (difference) in the dielectric constant of the object and the environment (K1 And K2), the easier it is for the georadar to detect the desired object. Since the human body consists mainly of water (K1=81), and the medium is air (K2=1), the proportion of reflected energy is 80%, which is quite a lot. In this regard, detecting a person in the air (even behind obstacles) is a relatively simple task.

For the purposes of this article, the study was carried out with ground penetrating radars of the Izh-Terra series, one of which is shown in Figure 2.

Main characteristics of the Izh-Terra georadar:

– signal type – continuous chirp, sweep period – 1 ms;

– frequency range: (50 – 1050) MHz;

– measurement frequency: up to 200 times per second with a time base of 500 ns;

– range resolution – 15 cm;

– radiated power: 0 dBm;

– operating temperature: minus 30⁰c – plus 30⁰c;

– storage temperature: minus 50⁰c – plus 50⁰c;

– continuous operation time: 3 hours;

– location reference: GPS/GLONASS;

– dimensions – cylinder with a diameter of 510 mm, a height of 100 mm;

– weight – 4.5 kg;

The study was carried out in two stages. At the first stage, the possibility of detecting a lonely person in an open area was assessed. The georadar was installed with a radiating surface perpendicular to the ground. Due to the wide radiation pattern of the antenna, there is no need for precise positioning of the GPR. We install approximately “by eye”. Next, turn on the device. To measure, just press one button, since the georadar does not require special settings.

After installing the georadar and turning it on, we leave. We leave without haste
for 15 seconds. Figure 3 shows the measurement results without
processing. The radargram contains many signals reflected from
the ground, stationary local objects and from a moving person. Displayed on the left
radio signal delay time caused by signal propagation to the target and
back, on the right – range (half the product of the signal delay time and
speed of light); below – time of the experiment. Fixed
Interfering reflections are eliminated by simply subtracting the average (Figure 4).

The main result obtained is the following: the practical maximum detection range of a person by ground penetrating radar is 30 meters.

At the second stage, the ability of the georadar to “see” through walls was assessed.
The experiment scheme is shown in Figure 5. The ground penetrating radar is leaning against the wall (Figure 6),
then the person moves through the rooms along the indicated trajectory. Walls of all rooms
concrete, ~20 cm thick. The walls contain metal reinforcement and wiring for
voltage 220 V.

In Fig. 7, during the first 4 seconds no movement occurs, so a picture without disturbance can be observed. The first 4 seconds are the reference area, this is what the radargram looks like in the absence of movement. When moving in rooms 1, 2, you can see two humps (hyperbolas), responsible for the movements “there” and “back”. In room 3, the humps expand and merge into one. The temporary distance between rooms 2 and 3 is a long transition (you need to take off and put on your shoes). Figure 8 shows the results of a similar experiment performed by a different experimenter.

Qualitatively extrapolating the results, we can assume the effectiveness of GPR at a distance of up to 15-20 meters with the number of walls up to 5. Such estimates are very conditional, since the probability of detection depends on the intensity of the object’s movement. I believe that it is possible to detect people by their heartbeat, but the distances are greatly reduced, the number of walls is no more than one, and for these purposes additional experiments are needed.

Conclusion. The ability to detect a moving person at a distance of up to 30 meters in open areas has been demonstrated. If there are brick or concrete walls (up to 5), a moving person can be detected at distances of up to (15-20) meters. In the work presented, the person moved quite intensely; I believe such movements are not typical for people under rubble.

Therefore, we can formulate advice for a person who finds himself under rubble: to be able to detect using the presented method, you do not need to move intensively, it is better to find a large metal object (frying pan, saucepan) and move it, so visibility will be much higher.

PS. As answers to frequently asked questions:

• Many people are put off by ground penetrating radars due to the high complexity of data processing and the lengthy learning curve of the devices. This article uses a ground penetrating radar that operates on the “plug and play” principle (does not require special settings), the georadar data has not been subjected to any special processing, all given radargrams are raw with simple subtraction of the average. As can be seen from the figures, no special processing is required. If necessary, the data can be subjected to additional processing; this option is available in the software supplied with the georadar.

• As for the safety of the method used, the emitted power of the georadar is one hundred times less than the power of a mobile phone in talk mode, and therefore the method is completely safe.