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Surveillance
Published in Vincent P. Galotti, The Future Air Navigation System (FANS), 2019
SSR differs from PSR in that it operates in a request-reply mode whereby the ground equipment sends out a signal which, in turn, triggers a reply signal transmitted from the aircraft transponder, rather than relying on reflected signal returns from the aircraft. Because of a required action on the part of the aircraft, namely, the need for a transponder to reply, SSR is considered as being a dependent type of surveillance. The FANS Committee considered SSR as being a type of cooperative dependent surveillance (CIS), a phrase developed by the FANS Committee, however, since its inception, very little work has been done in the way of expanding on the concept of CIS for several technical and economic reasons. For the purposes of this text, therefore, SSR will be considered in the context of its traditional categorization, which is that of dependent surveillance. Overall, SSR offers several advantages over PSR.
Secondary Surveillance Radar
Published in Habibur Rahman, Fundamental Principles of Radar, 2019
SSR1 is a radar system used in ATC that makes use of a transmitter to interrogate a transponder-equipped aircraft, providing a two-way data link on separate transmitting and reply frequencies. The transponder is a radio receiver and transmitter pair, which receives on 1030 MHz and transmits on 1090 MHz. This radar not only detects and measures the position of aircraft, but also requests additional information from the aircraft such as its identity and altitude. Unlike primary radar systems that measure the bearing of targets using the detected reflections of radio signals, SSR is essentially a cooperative system that relies heavily on targets equipped with a radar transponder that replies to each interrogation signal by transmitting a response containing encoded data. Both the civilian SSR and the military IFF have become much more complex than their wartime ancestors, but remain compatible with each other, not to allow military aircraft to operate in civil airspace. Given its primary military role of reliably identifying friends, IFF has much more secure (encrypted) messages to prevent “spoofing” by the enemy, and is used on many types of military platforms including air, sea, and land vehicles. Today's SSR can provide much more detailed information, for example, the aircraft altitude, as well as enabling the direct exchange of data between aircraft for collision avoidance.
Air Traffic Control (ATC) surveillance environment
Published in Busyairah Syd Ali, Aircraft Surveillance Systems, 2017
The Secondary Surveillance Radar (SSR) sends out interrogation signals at 1030 MHz from the ground station to each aircraft within its range (200–250 NM) and then awaits a reply at 1090 MHz from the aircraft transponder. The aircraft’s transponder responds to interrogations, enabling the aircraft’s range and bearing from the ground station to be calculated independently by the SSR (ICAO, 2004b) (see Figure 2.3). The system provides an update rate of 4–12 seconds. The SSR requests two types of data from an aircraft transponder: Mode A/C or Mode S. Mode A data represents a four digit aircraft identity, while mode C data represents aircraft altitude (Wassan, 1994). Mode S is an enhancement of mode A/C by the addition of the selective addressing of targets by the use of unique 24-bit address. It also provides a two-way data link between the ground stations and the aircraft for information exchange (ICAO, 2007c).
Estimation of aircraft distances using transponder signal strength information
Published in Cogent Engineering, 2018
Mode C interrogations are broadcast from both approach control and Air Route Traffic Control Center (ARTCC) radar installations. These interrogations, as the principal component of Secondary Surveillance Radar (SSR), are broadcast from antennas that are collocated with primary radar, which is used by air traffic control computers to determine the azimuth and range of aircraft within the facility’s designated airspace. The most common type of radar installation is ASR-9; 135 of these systems are currently deployed across the United States. The ASR-9 antenna has a rotational speed of 12.5 rpm and therefore requires 4.8 s for a 360° scan of its associated airspace. Because an aircraft may be interrogated by multiple SSR interrogators, dependent on position, the timing of Mode C replies generated by the aircraft is stochastic in nature. However, if one assumes that an aircraft is within range of a single SSR site, the expected frequency of Mode C replies is 0.208 Hz.
A New Efficient Array Architecture for Small L-Band Secondary Surveillance Radars with Reduced Number of Elements
Published in Electromagnetics, 2022
Sayed Hesamoddin Najmolhoda, Mohammad Ali Khak, Mehdi Shirichian, Amirreza Nikfal, Reza Bayderkhani, Hadi Aliakbarian
Tracking and identifying any operational aircraft are highly consequential in preventing collisions in the sky. This task, which is the role of Aviation Traffic Control (ATC) systems, is performed with the help of Secondary Surveillance Radars (SSR). In contrast with primary radar, the clutter effect in SSR is negligible because of obtaining replies on a different frequency from the interrogations (Stevens 1985). Also, extra information can be obtained from the responses of the aircraft to this system. Other advantages of SSRs are their long-range coverage and low average power level (Stevens 1988).