Tracker (radar)

In radar systems in air traffic control or in military surveillance systems, a tracker is a component that combines individual position reports from the radar ("plots") into complete flight tracks ("tracks") and thus enables the behavior and movement patterns of the observed objects to be recognized .

The tracker is usually implemented as software and uses mathematical models, such as the Kalman filter or the alpha-beta filter , for the state estimation in order to estimate the actual position, direction of movement and speed of an aircraft as precisely as possible, taking into account To achieve measurement errors.

functionality

In civil or military airspace surveillance, all-round search radars (so-called "fan-beam" radars) are typically used to search the assigned surveillance area for aircraft . For the functional principle of these devices s. Radar . These radar systems usually have rotating antennas that scan the surveillance area at a frequency of one revolution per 10 seconds ("scan cycle"). If the scanning beam hits an object, the position of the object is sent from the radar device to the tracker. The position information is usually composed of the angular position of the antenna at the time at which the object was discovered and the distance of the object to the radar, which can be calculated based on the transit time of the radar pulse to the object and back.

In older systems, this position information was displayed directly on the Plan Position Indicator console . A practical problem that arose for the airspace surveillance was that the position information is only individual points (plots) on the console. Especially with high aircraft density, the PPI consoles displayed entire clouds of individual points, the position of which changed every 10 seconds (with points from the previous cycle still "glowing", so that a certain history was recognizable).

The clear assignment of which point belongs to an aircraft, which point represents a false signal and v. a. which point belongs to a point in the previous scanning cycle (and thus describes a moving object) would hardly be feasible even for experienced users given today's air traffic situation. Particularly in the case of high traffic density, the clearest possible assignment is important, since this is the only way to recognize flying objects, calculate their flight route and avoid possible collisions.

A tracker is a computer system that supports exactly this purpose: the position data is fed into the tracker in each scanning cycle. This then calculates the most probable assignment of a position point to measuring points from previous scanning cycles (“association”) and thus builds up “traces of flight” from the points of the previous cycles; these traces of flight thus describe the previous path of a flight object and thus allow observation of its behavior, i.e. H. its current position, its speed and its flight direction.

In practical use, further information is simultaneously associated with the flight object and shown on a display. For example, signals that are received via the secondary radar and can contain, for example, the (civilian ICAO-AICD) identification code of the aircraft, military identifiers (NATO-IFF) or additional information on the position. This information can be further merged by means of corresponding flight plan inquiries, so that a complete and constantly available situation report is created.

Basic Models (Alpha-Beta Filters / Kalman Filters)

The tracker software uses mathematical estimation models to build the flight tracks, which make it possible to assign a plot to a flight track with less delay (latency), taking into account systemic inaccuracies and random measurement errors. Typically, these models are based on simple observations of the movement of the flying objects. The basic principles are briefly described below:

Areas of application

The tracking of objects is always important where the direct cooperative contact between the moving objects and with a control center can be disturbed, e.g. B. in coastal surveillance, airspace surveillance and perimeter surveillance.

Civil applications

Internationally, air surveillance is carried out in all countries and, where there are coasts, coastal surveillance is carried out. The task in air and sea traffic has police-like traffic control functions. Ground-based functions are increasingly being replaced by on-board functions. Then each vehicle carries out its own tracker functions and generates a situation report of the surroundings in the moving vehicle. Tracker functions are used in modern system definitions of the IMO and the ICAO as fallback protection for cooperative systems.

Navigation in closed areas

Accurate navigation is important in large open areas. There are tracking systems for this purpose, which overlay map information with order information and movement information and, through tracking, support the optimization of one's own movement and avoidance of collisions with other objects.

Military application areas

Military applications assume a threat perspective that arises from the traditional paranoia of states and the modern hubris of interest groups.

In some countries, air surveillance and coastal surveillance are subordinate to the military command. This does not change the task at hand in air and sea transport.

• Monitoring of flying objects
• Tracking of attacking air targets in the air defense (fire control) (see tracking in the real sense)
• Tracking of artillery shells to determine the location of the artillery (artillery location)
• Estimation of the possible impact of ballistic missiles

Artillery location

Artillery pieces and artillery rockets (see e.g. Katyusha (rocket launcher) ) represent a considerable threat potential in armed conflicts due to their sometimes enormous destructive power; this applies both to direct armed conflict in the field and to attacks on the civilian population.

Due to their long firing range (> 30 km) and their mobility, massive attacks from several guns and different geographical positions on a target can be carried out largely without the possibility of advance warning. In addition, the gun emplacements operating far behind the lines can hardly be made out. In particular, the mobility of the usually self-propelled guns considerably limits the possibilities of aerial reconnaissance.

Artillery locating radars detect approaching missiles and determined by "tracking" their flight path ( trajectory ) with sufficient accuracy. The estimation of the trajectory enables a short-term prognosis of the probable point of impact and a tracing of the projectile back to its launch position, i. H. the indirect location of the gun position. This data can then in turn be passed on to your own staff as target data.

Special technical difficulties arise from the fact that artillery projectiles are much smaller than aircraft, for example, and are therefore more difficult to detect. Since tracking has to be carried out relatively close to the ground, there is also a relatively high level of disruptive factors (terrain overshadowing, ground reflection (clutter), interference from birds, flying objects, other radar systems, etc.), which places special demands on the filters.

A high density of flying objects (projectiles, rockets, drones, etc.) in the battlefield under observation represents a particular complexity for the tracking algorithms with regard to the assignment of current position measurements to trajectories. In order to obtain sufficiently accurate estimates of the trajectories under these conditions In particular, high update rates and a special radar control are necessary, which is why radars with electronic beam pivoting (so-called phased array radars ) are mainly used for artillery location .

In addition to radar tracking, tracking methods using (passive) acoustic sensors or optical sensors are also in use.

Modern systems are able to combine the measurements from different sensors, or "merge" them (see multi-sensor tracking). This can involve both the integration of passive sensors and the integration of several measuring systems (so-called "sensor items") in order to achieve more robust and less error-prone estimates on the one hand and, on the other hand, by analyzing flight behavior and the Projectile stabilization to determine additional information (e.g. about the type of ammunition).

In addition to pre-warning and target location, artillery location systems are also used to monitor and coordinate one's own artillery, i.e. H. for fire control, used.

Web links

• Phased Array Radar
• Artillery location radar COBRA (PDF; 120 kB)
• From page 15 Radar tracker examinations (PDF; 1.54 MB)
• Real-time flight tracking

Individual evidence

1. ↑ Archived copy ( Memento of the original from September 15, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
2. ↑ Umberto Eco: The narrative structures in Ian Fleming and Hans Christoph book: James Bond or the small bourgeois in arms , in: Jochen Vogt (Ed.): The crime novel. Poetics - Theory - History. UTB for Science, Volume 8147. Fink, Munich 1998, 581 pages, ISBN 3-8252-8147-7 (UTB) & ISBN 3-7705-3226-0 (Fink).