Michal Simko and Martin Valovsky of SEC Technologies describe and explain field trials of an active stand-off detection in various conditions

The ability to sense chemicals at large distances is a big deal. But as we found out, making sense of the data for the end user is even bigger. Sitting in a small trailer at Dugway Proving Ground in Utah in 2018, night after night for two weeks, collecting the data – little did we know how much our device, our approach, and our understanding of what we see would change.

The Falcon 4G, standing in front of the trailer and lasing its pulses of various wavelengths through the chamber short of a mile away from us, was collecting data. We were very confident as we viewed the results. We became even more confident of our technology months later when we received the comparison of our data with the referee system inside the chamber.

The Falcon 4G: a brief history
Technology-wise, this was not our first rodeo – as the previous generation of our active stand-off detector was already in use by the CBRN Unit of the Slovak Army. However, it was the first time we reevaluated in such comprehensive trials that lasted for two weeks.

The Falcon 4G is based on the same technology as its predecessor DDCWA. It is also using DIAL (Differential absorption LIDAR), with the main distinctions being a wider spectrum of wavelengths, (finally) an eye-safe laser, a better reach, and a smaller field of view.

Today in 2022, the product we have and sell is still called Falcon 4G, but only the shape and technological heart are common with its cousin that was ‘fighting’ with simulants and interferers at Dugway four years ago. When it comes to long-range detection, only a couple of customers had Falcon 4G on their wish list in 2018.

At present, the Falcon 4G proudly serves in NATO and non-NATO armies. Mounted on helicopters and vehicles, it helps to discover clandestine labs and to secure ships before entering ports, and it supports various infrastructures by detecting gas leaks.

The customers and the market were the expected driving force of many of the changes Falcon has undergone in its development over recent years. For us, the unexpected force were professionals from various institutions around the world who often turned out to have a better understanding of what the end user would utilise.

Adjusting to change
The last but very important force for change has been Mother Nature – who has surprised us with some really tough but very real conditions so many times. Improving on algorithms, the ROC curve, and the false alarm rate with various interferers and sensitivity in tough environments, we have tackled anything that Nature can throw at us in the hot Middle East or the cold North.

We have adjusted our power management to be able to work off a car battery, be connected to any power grid on the planet, or off any generator the army uses. These are just a few examples of the upgrades we have carried out. Perhaps the most notable change would be using a multi-line approach to increase confidence levels.

As it goes in our business, we cannot speak about the customers and institutions we work or have worked with. But we can present to you a few noteworthy trials we have undergone and can share publicly: a small number of tests under various conditions. We have picked only those that were conducted together with a third party as an observer.

Stand-off detection techniques
There are various optical techniques available for stand-off detection. The principle is always the same. Due to their physical properties, gases absorb infrared radiation. The ability of any stand-off detection technique to recognise these absorption spectra determines the performance of the system.

The key element in realistic scenarios is to reduce the impact of atmosphere, water vapours and impurities. In general, there are two principial ways of stand-off detection. The first technique relies on infrared radiation from the environment that is fluctuating, unknown and weak. The second technique relies on an artificial source of infrared radiation.

Active stand-off detection
As mentioned previously, we focused on the DIAL technique using two synchronised tunable and pulsed CO2 lasers (eye-safe and undetectable). The set-up with two independent lasers allowed us to sample with a higher sampling frequency. The key element is the utilisation of two independent tunable CO2 lasers.

Field trials
In this section, we will present results from four various trials. All four scenarios have specific challenges. The table below shows the summary of the key parameters of all four scenarios.

Winter conditions
Stand-off detection techniques are strongly impacted by ambient temperatures. In this trial, the goal was to obtain performance data in winter conditions. During winter the humidity is relatively low, and temperatures are below 0°C.

Both trials started with control measurements prior to the release, confirming ‘clear air’ and no false positives with a subsequent release of SF6. And in both trials various concentration levels were successfully detected.

Rainy conditions
Rain washes down chemical clouds from vapours to liquid forms and thus significantly decreases the concentration of chemical clouds. Typically, rainy conditions create a significant obstacle for stand-off detection systems. High humidity and water droplets limit the performance and chemicals fall rapidly in vapour concentration.

As Falcon 4G can avoid wavelengths absorbed by water and has enough energy to pass through light rain, even this trial was successful. Releases of chemicals and measurements by the Falcon 4G lasted for little more than an hour with constant light rain and low temperatures throughout the trial.

The DIAL system used in this trial successfully detected the released substances separately as well as those mixed in the cloud. Using a DIAL system with CO2 lasers allows us to mitigate the impact of high humidity due to its spectral accuracy.

Despite low temperatures and slow evaporation, the DIAL system successfully detected all three chemicals released. Even almost 100% humidity and constant drizzle of rain did not cause any problems with detecting all chemicals individually as well as those mixed in the cloud.

Narrow space
For their optimal performance, stand-off detectors require a good view to collect enough optical signal. Narrow spaces limit the received optical signal and thus generally limit the sensitivity and detection range of such a system.

The measuring path was chosen with a focus on limits that only reality can create for CBRN reconnaissance. There was only a very narrow passage between the detector and the release site, not wider than approximately 2 mRad. There was a very narrow space between trees and vegetation: a unique scenario that seems impossible at first sight.

The first scenario began with chemical reconnaissance. Several scans were conducted without any alarm, showing a clear path and with no dangerous substances present. SF6 released from the bottle lasted for 30 seconds. At the same time, the DIAL system was scanning the pre-set path continuously.

Roughly seven seconds later after opening the bottle, SF6 was detected and identified in all subsequent measurements– with the average concentration culminating at 0.01608 mg/m3. Once the SF6 had already blown away and flown off down the hill, 0.75 l of liquid ammonia (25% concentration) was dispersed in the tent on a soft paper to evaporate. The first detected concentration was 0.04321 mg/m3.

Subsequent scanning revealed a concentration of ammonia culminating at 0.05256 mg/m3. With ammonia still present, the second release of SF6 within the tent was performed. The DIAL system successfully detected both chemicals in the cloud 2.6 km away and through the narrow passage.

Long distance
We love using SF6, as due to its weight it resembles the behaviour of CWAs that are also heavier than air. At the same time, SF6 is easily identifiable on the FTIR (Fourier-transform infrared spectroscopy) spectrum. Also, even while this is not the same for an active system, we decided to add methanol, ethylene, TEP (triethylphosphate) and many other chemicals for our long-distance testing to simulate other realistic characteristics.

For the DIAL detector used during this particular trial we used methanol mixed with SF6 (released not at the same time). The releases were conducted in an urban scenario with various interferers present in such an environment. The whole measuring path was within the city itself. The release was also conducted on a busy road during the rush hour, with exhaust fumes clearly present.

The key challenge in such an environment is to combat the impact of these interferers. During this trial, 350 g of SF6 and 1,000 ml of methanol were released. But prior to that, ‘clear air’ was confirmed by Falcon.

The future
We could describe the various abilities of existing stand-off systems that look plausible if discussed out of context. But once you bring distance and detection into the picture the only thing that matters is if you can really detect. Isn’t the primary role of long-range stand-off detector to detect? To detect at long range? Sounds odd to even ask. And what if you add the parameter of ‘any conditions’? The Falcon 4G has many more improvements up its sleeve before it becomes the next-generation Falcon 5G. We are looking forward to being challenged and to current and future cooperations with our customers, along with potential customers and our competitors. We look forward to making the best long-range stand-off detector even better.

Image:
Field trial environment, release site and cloud size.
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