Radar

Surveillance Systems

• Use of radio waves transmitted into air • Waves reflected by an object in path of beam

are returned • Range determined by measuring time (SOL) for

wave to go out to and return to receiving antenna.

• Direction determined by position of rotating antenna when reflected wave received.

Limitations • Amount of reflective surface determines size of radar return. • Radio waves normally travel in continuous straight lines unless:

– "Bent" by atmospheric phenomena (temperature inversions) – Reflected or attenuated by dense objects (heavy clouds, precip, ground

clutter) – Screened by high terrain – Stationary/slow moving targets eliminated by moving target indicator

(MTI) • Radar energy reflected blocks aircraft at same range and weakens

or eliminates display of targets at greater range.• Aircraft flying tangential may not be displayed. • Low altitude aircraft screened by terrain or below radar (earth

curvature) • First priority vertical, lateral, or longitudinal separation between IFR

aircraft • VFR limited by traffic and workload

Air Traffic Control Radar Beacon System (ATCRBS)

Secondary surveillance radar, three main components:

1. Interrogator. ground based unit transmits (scans) in synch with primary radar and transmits discrete radio signals to all transponders to reply.

2. Transponder. airborne unit receives signals from interrogator and selectively replies with a specific pulse group (code) only to those interrogations being received on mode to which set. Replies are independent of, and much stronger than a primary radar return.

3. Radarscope. displays both primary radar system and ATCRBS.

Advantages of ATCRBS

• Reinforcement of radar targets. • Rapid target identification. • Unique display of selected codes.

part of ATCRBS ground equipment is decoder. enables controller to assign discrete transponder codes to each aircraft.

• Beacon (transponders) and MTI combat ground clutter and weather

• Some Locations Secondary-Radar-Only

4-5-3. Surveillance Radar

• Two general categories: – Airport Surveillance Radar (ASR) provides

short-range coverage in general vicinity of airport to handle terminal area traffic. Can also be used as an instrument approach aid.

• Air Route Surveillance Radar (ARSR). – long-range radar for large areas.

4-5-4. Precision Approach Radar (PAR)

• A landing aid that displays range, azimuth, and elevation info

• Two antennas— one scanning a vertical plane, and the other scanning horizontally.

• Range is limited to 10 miles, azimuth to 20 degrees, and elevation to 7 degrees, only the final approach area is covered

4-5-5. Airport Surface Detection Equipment - Model X (ASDE-X)

• Provides high resolution, short-range, clutter free surveillance info about aircraft and vehicles, both moving and fixed, located on or near surface of airport's runways and taxiways

4-5-6. Traffic Information Service (TIS)

• Provides info to cockpit via data link, similar to VFR radar traffic advisories over voice radio.

• Improves safety and efficiency of "see and avoid" flight through an automatic display that informs pilot of nearby traffic and potential conflict situations.

• Assists pilot in visual acquisition of these aircraft. • Employs enhanced Mode S radar system, to "uplink" information to

suitably-equipped aircraft • Provides estimated position, altitude, altitude trend, and ground

track information– Up to 8 intruder aircraft within 7 NM, +3,500 and -3,000 feet vertically of

client aircraft – Indicates target a threat within 34 seconds – Does not display an precise distance. – Data derived from ATC radar uplinked to client aircraft on each radar

scan (nominally every 5 seconds).

TIS Proximity Coverage Volume

Terminal Mode S Radar Sites

Concepts & Capabilities

• Intruder aircraft must have operating transponder (Mode A, C or S).

• Provides following data on each intruder aircraft: – Relative bearing information in 6-degree increments. – Relative range in 1/8 NM to 1 NM increments (depending on

range). – Relative altitude in 100-foot increments (within 1,000 feet) or

500-foot increments (from 1,000-3,500 feet) if intruder has Mode C

– Estimated intruder ground track in 45-degree increments. – Altitude trend data (climbing/descending >500 fpm) if intruder

aircraft has Mode C. • A max of eight (8) intruders may be displayed; if more

than eight "most significant" intruders are uplinked. • Closest proximity and/or greatest threat to TIS client.

Status Messages • Alert. Identifies a potential collision hazard within 34 seconds. • TIS Traffic. TIS traffic data is displayed. • Coasting. TIS display more than 6 seconds old. indicates missing

uplink from ground. When TIS info more than 12 seconds old, "No Traffic" status indicated.

• No Traffic. No intruders meet proximate or alert criteria. may exist when TIS system functional or may indicate "coasting" between 12 and 59 seconds old (see (c) above).

• TIS Unavailable. No ground system is available. Displayed when TIS uplinks missing for 60 sec.

• TIS Disabled. The pilot has not requested TIS or has disconnected from TIS.

• Good-bye. The client aircraft has flown outside of TIS coverage.

NOTE-

• Depending on avionics mfgr, some messages not available to pilot.

• client aircraft and display is oriented "track up," (12 o'clock the top)

• Rings indicate 2 and 5 NM. • Each intruder depicted by symbol positioned at

approximate relative bearing and range from client. – Circular symbol near center indicates an "alert"

intruder– diamond symbols indicate "proximate" intruders.

Limitations

• Does not relieve pilot responsibility to "see and avoid" other aircraft

• Shall not be for avoidance maneuvers during IMC or other times when there is no visual contact with the intruder aircraft.

• No recommended avoidance maneuvers are provided for, nor authorized, as a direct result of a TIS intruder display or TIS alert.