Summer 2019

Airport security: the drone danger, and possible counter-measures

Following this issue’s feature on drones and the threat they present to aircraft safety, Gary Walker of Rohde & Schwarz (R&S) takes a look at possible counter-measures to these machines that might be used when these machines become a danger to safety around airports

Whether intentional or accidental, the rising tide of drone misuse is running in parallel with dramatic growth in the consumer drone market itself, notes R&S account manager Gary Walker. The availability of relatively inexpensive and easily operated drones presents a new challenge for the protection of public and private spaces, such as those around airports. The devices provide ample opportunity for misuse – and there is growing evidence that remote drone operators are taking advantage of that, he suggests.

Counter-measures using visual and sound detection are rarely the answer, as performance is limited by local interference, Walker considers. To be successful, detection systems should have high sensitivity, give early warning and not create false alarms. Even electronic detection is not enough: a complete system also requires a safe, reliable means of neutralising the threat.

The first challenge is to detect these small flying objects. Once detected, the intruder must be classified to determine whether counter-measures are necessary. A superior approach, he says, is to monitor and analyse the radio control signals sent between the drone and operator.

Solutions like that developed by R&S, says Walker, identify these signals, confirm their direction and, best of all, provide counter-measures that bring the drone down or send it back to base. The company’s ARDRONIS automatic radio-controlled drone identification system can take bearings on the remote controller even before a drone takes off. It alerts security personnel early on, so they can take appropriate action in a timely fashion.

ARDRONIS focuses on the detection and counter-measure of consumer drones. More than 90% of consumer drones communicate over the industrial, science and medical (ISM) bands, Walker points out, which are also used for telecommunications, including WLAN and Bluetooth radio systems. The most common options for remote drone control involve proprietary implementations of frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS) technologies.

FHSS/DSSS radio links are notoriously difficult to detect and disrupt, but ARDRONIS rises to the challenge thanks to its powerful online hopper analysis capabilities. It analyses a radio signal’s parameters such as hop length, symbol rate and modulation type, and then classifies the transmission system used.

Intercepting drone control signals delivers many advantages over alternative methods, such as radar, optical or acoustical detection, Walker continues. These advantages include:

  • Reliable detection with minimal false alarms. The system is not confused by non-drone flying objects, such as birds, balloons or kites
  • Earliest possible detection. ARDRONIS issues an alert as soon as a remote-control unit begins transmitting, allowing counter-measures to be deployed without delay
  • Direction finding/position fixing of drone operators. As ARDRONIS can detect a drone via its downlink signals and/or remote-control unit via its uplink signals, it can immediately determine the bearing of the drone operator Multiple direction finders then enable a rapid positional fix of the operator
  • Situational awareness. ARDRONIS not only detects all drones operating over a large monitored area, but in many cases can also indicate the type of drone by analysing its radio signature, and thus its threat potential. Downlink activities such as video transmission are also monitored
  • Signal disruption. ARDRONIS utilises a smart jammer that can effectively disrupt the radio link to a drone. This forces the drone into failsafe mode so that it either lands immediately or returns to its point of origin. Jamming is so selective that it does not affect other radio activities

ARDRONIS combines R&S’s competencies in antennas, direction finders and signal analysis solutions, Walker informs. Field-tested hardware, combined with a powerful detection algorithm, permits reliable interception of short-duration signals.

Under optimal conditions, its range is between 1 and 3km, depending on the drone and remote control transmit power, and on the local environment. A user-friendly operator interface lists the detected drones and their critical parameters. With optional direction-finding (DF) or position-fixing functionality, DF beams or location markers are used to display the detection results on a map.

ARDRONIS also permits data recording, including video footage transmitted to operators. Everything the system ‘sees’ can be archived, from individual detection results to entire radio frequency (RF) scenarios. This data can be valuable after the event, for example in supporting law enforcement processes.

Integrating drone monitoring and counter-measures

A drone that does not emit any radio signals, when programmed with a fixed flight path for instance, is not only undetectable by these methods, but its radio communications cannot then be disrupted to force it to turn back or land.

Comprehensive protection, including cover for these types of situations, is offered by integrating ARDRONIS into systems that include complementary additional sensors and effectors, allowing an escalation of counter-measures for “effective threat neutralisation”, says Walker.

The modular counter-unmanned aerial system GUARDION is a prime example, he says, combining technology from R&S, ESG and Diehl Defence.

GUARDION responds promptly to potential threats from consumer drones, helping users to assess the situation. Experience has shown that in order to detect and counter drones, several technologies must be applied. As a comprehensive multi-sensor and ‘multi-effector’ solution, GUARDION incorporates “sophisticated sub-systems that complement each other for maximum security”, Walker says.

“It leverages three leading German companies’ proven expertise in radar, radio detection and electro-magnetic counter-measures as well as sophisticated command and control systems,” he adds, describing it as a “versatile weapon that helps businesses, government authorities and critical infrastructures to protect against drone misuse”.