Know your surroundings
We are constantly surrounded by an immense number of electronic signals. They come from radio transmissions, data communication, TV broadcasts, mobile phones and radars just to name a few sources. Most of this communication is civilian but there is also a significant amount of signals with military origin in the air. In this article Saab's Hampus Delin explains what signals intelligence is all about.
Picking up and analysing these military signals is one way for a nation to gain crucial understanding of its surroundings. Are our neighbors transmitting more than usual, and more than can be explained by exercises? Has an air defence system, which was previously inactive, suddenly become active? This method of picking up signals is known as signals intelligence (SIGINT), which is a passive form of surveillance. Passive sensors used for SIGINT do not emit any signals; they just listen.
Creating a picture of 'the normal situation'
Registering and analysing different types of military signals allows a nation to get an overview of the normal behavior of signal traffic in the surrounding area. This creates a picture of the types, amount and behavior of signals you would normally expect to find there. If the normal picture changes, gradually or suddenly, you would want to understand the reason for the changes. These analyses can form the basis for military- and security related decision making.
Registering and understanding signals
All types of radio- and radar systems emit signals with a signature that is unique for that particular type. By registering the signatures, it is possible for a nation to build up a signature library, which connects every signature to a particular type of emitter.
There are millions of signals in the ether, and each one of them can tell us something. The challenge is not only picking them up but also understanding what they reveal, and then drawing the right conclusions.
Understanding the emitters
Analysing and positioning signals from vessels, aircraft or ground forces makes it possible to follow their movements, displaying them on a map in real time. And by comparing the signals’ unique signature to the signature library, it possible to determine which type of emitter the signal comes from and, in turn, identifying the type of vessel or aircraft emitting the signals.
Fusing the data
Saab’s experience of developing complex systems featuring passive sensors and data fusion goes back decades.
“Our system consists of advanced and sensitive sensors, combined with the capabilities and tools to sift through huge amounts signals and data, to extract what is interesting and relevant”, Hampus Delin says.
There are different types of passive sensors depending on what is the most pressing need. Typically, it is a compromise between picking up something very far away, or making sure you pick up everything all around you. The different sensors’ characteristics complement one another and are optimised for their specific tasks. This allows the user to pick up individual signals, even at great distances, and perform highly accurate measurements on them, or to get wide coverage of the complete radio frequency spectrum, and immediately detect communication- and radar signals.
To be able to draw correct conclusions, you also need the means to handle the collected information. For this reason, a system has robust and selective algorithms and methods for identifying and classifying radar and communication signals. These processes are automated, and a high degree of automation means the operator can focus on critical tasks while keeping the system continuously running with fewer staff during periods with low activity levels.
Detecting and identifying the adversary
In addition to the long-term strategic signals intelligence activities, passive sensors are also used for tasks with much shorter time-span, for example to detect and identify an attacking hostile aircraft. Traditionally, a radar system detects the hostile aircraft, passing its location and speed on to the nation’s own ground based air defence. But we can assume that these radar signals are quickly identified by the attacking aircraft’s own passive sensor system. This gives the opponent the possibility to steer the aircraft out of reach of the ground-based air defence, or to jam the radar’s signals electronically. Additionally, the radar station’s location is revealed, opening it up for an attack.
In a situation like this, passive sensors detect the hostile aircraft, by picking up the electronic signals the aircraft emit, radar, speech, or data communication. The passive sensors detects the hostile aircraft without the attacker understanding they are detected, and the air defense radars can stay silent, undetected, until they are really needed.
“Having different modern and efficient systems that pick up, understands and can make use all the signals that surround us, are a basic precondition for a nation’s capability of protecting itself against threats , be it in peacetime, crisis or during war”, Hampus Delin concludes.
Sirius is Saab's family of innovative and networked passive sensor systems based on common architecture and with a domain specific edge. It provides a complete synergistic capability for Intelligence, Surveillance and Reconnaissance – beyond the scope of individual sensors.
These systems provide armed forces and intelligence services around the world with the silent power required to turn signals into knowledge, whilst remaining undetected.