Lecture 6 RADAR

Outlines of Lecture Introduction RADAR Frequencies RADAR Applications Types of RADAR

Introduction RADAR is stand for Radio Detection And Ranging and was developed prior to World War II. Today RADAR is extremely important in civil aviation. It is used by ATC to monitor and control numbers of aircrafts in airspace as well as by pilot for weather warning and navigation. Radar is an object detection system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft &ships. Radar uses include: Air traffic control: Precision approach and landing guidance to aircraft. Weather Forecasting / Severe weather detection Measuring ocean surface waves Police detection of speeding traffic Satellite

Radar Frequencies Radar operates on UHF and SHF - Super High Frequency (1 GHz - 30 GHz). RADAR systems are in SHF bands because: These frequencies are free from disturbance. Higher frequency, shorter wavelength, RADAR more effective.(shorter wavelengths are reflected more efficiently.) Super High Frequency SHF 3 GHz - 30 GHz 0.10m - 0.01m

RADAR Applications RADAR has a wide range applications including Ground RADAR : extensively used by ATC to separate aircrafts. Airborne Weather RADAR: used by pilots. It provide pilots with information regarding weather ahead.

Types of RADAR AWR (Airborne Weather Radar) Types of RADAR (RSR) En-Route Surveillance Radar TAR- Terminal Approach Radar (PSR & SSR) AWR (Airborne Weather Radar) SMR (Surface Movement Radar)

Ground RADAR

A) RADAR used by ATC Ground RADAR used by ATC are used to fix an aircrafts position which allows ATC to separate aircraft and guide the pilot. Three ground RADAR systems used by ATC include 1. En-Route Surveillance Radar (RSR) 2. Terminal Approach Radar (TAR) Primary Surveillance Radar (SSR) Secondary Surveillance Radar (SSR) 3. Surface Movement Radar (SMR) Surface Movement Radar (SMR): Short-range ground radar Terminal Approach Radar (TAR): Long-range ground radar Primary Surveillance Radar (SSR) Secondary Surveillance Radar (SSR) L-Band Radar This frequency band (1 to 2 GHz) is preferred for the operation of long-range air-surveillance radars out to 250 NM (≈400 km). Used by En Route Surveillance Radar-RSR S-Band Radar This frequency band (2 to 4 GHz) are used near airports to detect and display the position of aircraft in the terminal area with a medium range up to 50-80 NM (≈100 km). Used by Terminal Area Radar –TAR K- and Ka- Band Radars This frequency bands (18-40 GHz) provide short range, very high resolution data. Used by Surface Movement Radar-SMR

En-Route Surveillance Radar (RSR) En-Route Surveillance Radars (RSR) are long range radars which the signal goes to 300 NM. It operates with frequency between 1 to 2 GHZ. It used for airway surveillance to provide range and bearing of aircraft. **Surveillance: close observation, especially of a suspected spy or criminal.

2) Terminal Approach Radar (TAR) TAR is a high definition radio detection device which provides information on Identification Air speed Direction Altitude of aircraft It is use to assist ATC to track the position of aircraft in the air within the vicinity of the airport. Vicinity = Surrounding region / neighborhood.

2) Terminal Approach Radar (TAR) This radar gives the ATC a better or true picture of all aircraft flying in his control zone . Enable him to effect separation of aircraft to a finer degree than possible with information exchange by voice communication between the pilot and the controller.

2) Terminal Approach Radar (TAR) SSR PSR The need to be able to identify aircraft more easily and reliably led to another radar development  SSR -Secondary Surveillance was developed in the late 1960s. It was another form of radar surveillance that receives transmission reflections every few seconds. However, these reflections provide much more data than in primary surveillance. These reflections are digitized messages that report each aircraft's identifications and altitude. These information are transmitted back by the Aircraft’s Transponder on the 1030 MHz back to the ground SSR’s Antennae

a) Primary Surveillance Radar (PSR) HOW PSR works Primary Surveillance Radar (PSR) transmits a high power signal. When a signal strikes an object or target, some signal energy is reflected back and is received by the radar receiver. Radar operates on the 3,000 to 10,000 MHz frequency bands. (super high frequency SHF) Electromagnetic energy radiating outward from a source is reflected back by objects in its path. The time difference between transmission (trace) and reflection (echo) is measured giving an accurate indication of an objects distance. Distance, azimuth, and elevation can be used to fix the objects position in three dimensional space. Signal timing is critical to accuracy. (one microsecond error results in a distance error of almost 500ft.) As a result position accuracy is directly related to the accuracy of the timing device used. An enormous amount of energy must be transmitted in order for even a small amount to be reflected back. Radar must be very powerful as a transmitter and very sensitive as a receiver. This powerful transmitter would completely overpower the receiver. The problem is corrected by alternating the transmit and receive functions at very brief intervals (signal sharing) and at very high rates. (at a range of 40nm radar cycles between transmitting and receiving approx. 800 times/sec.) SHF waves are subject to line-of-sight limitations, which limit range and create problems with terrain masking. Radar has difficulty differentiating between different types of objects. It will show returns from aircraft, terrain, precipitation, flocks of birds, built up areas such as cities. -Primary Surveillance is a form of radar surveillance developed after World War II. It relies on the "skin effect," which is the reflection of the transmitted radar signal from the aircraft's metallic skins. Thus, air traffic controllers were able to observe the horizontal position of the aircraft. Determines the position of contacts by measuring and displaying reflected radio frequency signals from the contacts. The information is displayed to the user on an oscilloscope. (scope) Detects and reports reflections of aircraft, weather, flocks of birds, built-up areas, and terrain. It is a short range radar effective to 80nm. There is no way to tell one aircraft from another without having the pilots verify position.

a) Primary Surveillance Radar (PSR) RADAR receiver will plot the direction and the distance of the target (aircraft) from the radar station. Thus, the ATC could know the position of aircraft. through the RADAR display

Primary Surveillance Radar (PSR)

Advantages of PSR The advantage PSR is that it operates totally independently of the target aircraft. Means that no action from the aircraft is required for it to provide a radar return. But PSR only provide direction and distance of aircraft.

Disadvantages of PSR First, the signal can be interrupted by buildings, hills & mountains. Second, more power must be radiated to ensure returns from the target. Third, because of the small amount of energy returned at the receiver, reflected signals may be easily disrupted. This may cause the displayed target to 'fade‘ (not clear). Radar Performance Radar uses frequencies that are normally in the higher bands of the electromagnetic spectrum. Normally propagation follows a direct wave path. In general, the range of radar is therefore ‘line of sight.’ Radar is subject to certain factors, other than those of design, which affect its performance as follows: Atmospheric Conditions At the very high frequencies used, super refraction caused by inversions of temperature and/or humidity (Anaprop), may cause the direct wave range to be considerably increased. It is possible for echoes to return from a range greater than the design maximum range and to appear on the screen as false targets at any range. Sub refraction will cause poor radar performance at the upper range limits. Weather Rain and snow will attenuate the radar signal and will cause at least reduced performance and possibly even blind sectors. Target Size, Shape and Aspect As previously mentioned, the size and shape of the target will have a tremendous effect on its ability to reflect radar signals. How it appears to the radar is also important. A B747 head on is much harder to see than one that is side on and radar has the same difficulty with targets of differing size. By the same reasoning, a flat surface at right angles (to the direction to the radar aerial) will produce a much stronger return than a similar sized curved surface.

b) Secondary Surveillance Radar (SSR) HOW SSR works Secondary Surveillance Radar (SSR) transmits an interrogation signal which is received by the target aircraft. The aircraft transponder sends back a coded reply to the ground radar equipment. From the coded signal, information of the aircraft’s call sign, altitude, speed and destination. SSR requires an aircraft to be fitted with transmitter/receiver called as transponder. The SSR interrogates aircraft by means of pulse trains forming questions (interrogation mode). Aircraft transponder interpret these questions and transmit back the pulse train which are replies that contain information relate to questions (interrogation). SSR receivers capture these signals and transform them for analysis and processing. SSR is complement to the primary radar as it provide ATC with additional info about aircraft such as aircraft’s call sign, altitude, speed and destination. SSR requires an aircraft to be fitted with transmitter/receiver called as transponder. Secondary Radar The principles of operation of primary radar and some of the factors which affect a radar’s performance have been illustrated. Some of the effects can be minimised by using Secondary Radar techniques. The principle of measuring range from a time delay is still applicable, but the target plays an active role. The interrogating radar unit sends out a pulse (interrogation pulse). When this pulse is detected at the target, it triggers a transmitter to respond, sending a signal back to the interrogator. This signal will be stronger than an echo, will not be dependent on how well the target has reflected the energy and could be coded with additional information.

How SSR Works? -Secondary Surveillance was developed in the late 1960s. It was another form of radar surveillance that receives transmission reflections every few seconds. However, these reflections provide much more data than in primary surveillance. The transponder is a radio receiver and transmitter which receives on one frequency (1030 MHz) and transmits on another (1090 MHz). The ground secondary radar transmits 1030MHz signal. The aircraft radar receives on 1030MHz and transmits back 0n 1090MHz. The transponder reply is more powerful than the reflected radar signal allowing for far greater range. (250nm).

PSR VS SSR

SSR display

Secondary Radar Display What appear on secondary radar display? Aircraft Identity. Altitude Speed Direction/Destination Example MH092 FL280 585 Meaning: Flight Malaysian 092 cruising at 28’000ft with speed of 585knots

Advantages of SSR Requires much less transmitting power to provide coverage up to 200 to 250NM. Provides more information: aircraft’s identity (its code & call sign), indicates aircraft’s altitude, speed & destination. Reply signal is much stronger as it does not rely on returning reflected signals.

PSR Vs SSR PSR SSR Transmits a very high power radio frequency signal (600 kW for subang and 14 kW for KLIA) Received signal is the reflections of transmit signals when hitting aircraft Short coverage (60 nm to 80 nm) Provide aircraft direction and distance. Transmit low power radio frequency signal (1 kw) Received signal is a signal transmitted from aircraft transponder Long coverage (200 nm) Provide aircraft’s call sign, altitude, speed and destination.

3) Surface Movement Radar (SMR) SMR installed at airport (at top of ATC tower building). SMR provide a very accurate radar display in all weathers and conditions of visibility. SMR radar display can show all of airfield infrastructure including aircraft movements on runway, taxiway and apron.

3) Surface Movement Radar (SMR) It is designed to provide clear display of all aircraft on runway or taxiway so that ATC can ensure: runway are clear for take-off/landing guide aircraft to apron in order.

3) Surface Movement Radar (SMR)

3) Surface Movement Radar (SMR) The surface movement radar (SMR) allows the Air Traffic Controller to 'see' in real time the aircraft and vehicles movements into the airport control area. Surface movement radar can improve both safety and efficiency of airport traffic by providing the ground controller with a clear picture of the areas or under poor visibility conditions.

3) Surface Movement Radar (SMR)