Surveillance Terminology

(Under Construction)

RADAR

RADAR is an acronym which stands for "RAdio Direction And Ranging." Radar is a method whereby radio waves are transmitted into the air and are then received when they have been reflected by an object in the path of the beam. Range is determined by measuring the time it takes (at the speed of light) for the radio wave to go out to the object and then return to the receiving antenna. The direction of a detected object from a radar site is determined by the position of the rotating antenna when the reflected portion of the radio wave is received. Note: although actually an acronym (and therefore properly capitalized), the word radar has become simply a noun in common usage and is, more often than not, un-capitalized. It is this approach which we have adopted on this site. Therefore, except where capitalization is important to a particular use of the term, we have opted to use lowercase rather than treat RADAR as an acronym.

Primary Surveillance Radar

Simply, RADAR as defined above. Primary surveillance radars are divided into three general categories: Airport Surveillance Radar (ASR), Air Route Surveillance Radar (ARSR), and Precision Approach Radar (PAR).

Airport Surveillance Radar

Approach control primary radar used to detect and display an aircraft's position in the terminal area. ASR provides range and azimuth information but does not provide elevation data. Coverage of the ASR can extend up to 60 miles.

 

 

 

 

Air Route Surveillance Radar

Air route traffic control center (ARTCC) primary radar used primarily to detect and display an aircraft's position while en route between terminal areas. The ARSR enables controllers to provide radar air traffic control service when aircraft are within the ARSR coverage. In some instances, ARSR may enable an ARTCC to provide terminal radar services similar to but usually more limited than those provided by a radar approach control.

 

 

 

 

Precision Approach Radar (PAR)

PAR is designed for use as a landing aid rather than an aid for sequencing and spacing aircraft. PAR equipment may be used as a primary landing aid or it may be used to monitor other types of approaches. It is designed to display range, azimuth, and elevation information. Two antennas are used in the PAR array, one scanning a vertical plane, and the other scanning horizontally. Since the range is limited to 10 miles, azimuth to 20 degrees, and elevation to 7 degrees, only the final approach area is covered.

 

 

Each PAR scope is divided into two parts. The upper half presents altitude and distance information, and the lower half presents azimuth and distance.

PARs are rare and most often found on military airfields, and not all military fields have them.

 

 

 

 

 

 

 

Secondary Surveillance Radar

Air Traffic Control Radar Beacon System (ATCRBS)

The ATCRBS, sometimes referred to as a secondary surveillance radar, consists of three main components:

• Interrogator: Primary radar relies on a signal being transmitted from the radar antenna site and for this signal to be reflected or "bounced back" from an object (such as an aircraft). This reflected signal is then displayed as a "target" on the controller’s radar scope. In the ATCRBS, the Interrogator, a ground−based radar beacon transmitter− receiver, scans in synchronism with the primary radar and transmits discrete radio signals which repetitiously requests all transponders, on the mode being used, to reply. The replies received are then mixed with the primary returns and both are displayed on the same radar scope. The interrogator ("secondary radar antenna") may be co-located with the primary antenna as shown here where it is mounted atop a primary ASR antenna, or may be installed alone.

 

• Transponder: This airborne radar beacon transmitter−receiver automatically receives the signals from the interrogator and selectively replies with a specific pulse group (code) only to those interrogations being received on the mode to which it is set. These replies are independent of, and much stronger than a primary radar return. The transponder in the image at right is highlighted within a general aviation aircraft radio stack.

 

 

 

 

• Radar scope: The radar scope used by the controller displays returns from both the primary radar system and the ATCRBS. These returns, called targets, are what the controller refers to in the control and separation of traffic.

The job of identifying and maintaining identification of primary radar targets is a long and tedious task for the controller. Some of the advantages of ATCRBS over primary radar are:

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

A part of the ATCRBS ground equipment is the decoder. This equipment enables the controller to assign discrete transponder codes to each aircraft under his/her control. Normally only one code will be assigned for the entire flight. Assignments are made by the ARTCC computer on the basis of the National Beacon Code Allocation Plan. The equipment is also designed to receive Mode C altitude information from the aircraft.

Airport Surface Detection Equipment − Model X (ASDE−X)

Airport Surface Detection Equipment Model X (ASDE−X) is a multi−sensor surface surveillance system the FAA is acquiring for airports in the United States. This system will provide high resolution, short−range, clutter free surveillance information about aircraft and vehicles, both moving and fixed, located on or near the surface of the airport’s runways and taxiways under all weather and visibility conditions. The system consists of:

• A Primary Radar System. ASDE−X system coverage includes the airport surface and the airspace up to 200 feet above the surface. Typically located on the control tower or other strategic location on the airport, the Primary Radar antenna is able to detect and display aircraft that are not equipped with or have malfunctioning transponders.
• Interfaces. ASDE−X contains an automation interface for flight identification via all automation platforms and interfaces with the terminal radar for position information.
• ASDE−X Automation. A Multi−sensor Data Processor (MSDP) combines all sensor reports into a single target which is displayed to the air traffic controller.
• Air Traffic Control Tower Display. A high resolution, color monitor in the control tower cab provides controllers with a seamless picture of airport operations on the airport surface.

The combination of data collected from the multiple sensors ensures that the most accurate information about aircraft location is received in the tower, thereby increasing surface safety and efficiency.

Transponder Modes

Mode A, B, C

Mode C

Some transponders are equipped with a Mode C automatic altitude reporting capability. This system converts aircraft altitude in 100 foot increments to coded digital information which is transmitted together with Mode C framing pulses to the interrogating radar facility. The manner in which transponder panels are designed differs, therefore, a pilot should be thoroughly familiar with the operation of the transponder so that ATC may realize its full capabilities.

Adjust transponder to reply on the Mode A/3 code specified by ATC and, if equipped, to reply on Mode C with altitude reporting capability activated unless deactivation is directed by ATC or unless the installed aircraft equipment has not been tested and calibrated as required by 14 CFR Section 91.217. If deactivation is required by ATC, run off the altitude reporting feature of your transponder. An instruction by ATC to STOP ALTITUDE SQUAWK, ALTITUDE DIFFERS (number of feet) FEET," may be an indication that your transponder is transmitting incorrect altitude information or that you have an incorrect altimeter setting. While an incorrect altimeter setting has no effect on the Mode C altitude information transmitted by your transponder (transponders are preset at 29.92), it would cause you to fly at an actual altitude different from your assigned altitude. When a controller indicates that an altitude readout is invalid, the pilot should initiate a check to verify that the aircraft altimeter is set correctly.

Pilots of aircraft with operating Mode C altitude reporting transponders should exact altitude/ flight level to the nearest hundred foot increment when establishing initial contact with an ATC. Exact altitude/flight level reports on initial contact provide ATC with information that is required prior to using Mode C altitude information for separation purposes. This will significantly reduce altitude verification requests.   

 

Mode 1, 2, 3

Mode 1

 

Mode 2

 

Mode 3

Military Mode 3 is identical to Civilian Mode A

Mode S

ADS

Multilateration

Interrogator

Transponder

ASDE

AMASS