Lesson Notes By Weeks and Term v4 - SHS 2

Lesson Video

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Performance objectives

• Define ground-based surveillance systems.
• Identify different types like Radar, ADS-B, and MLAT.
• Summarize how these systems enhance flight safety.
• Discuss the advantages and disadvantages of these systems.

Lesson summary

This lesson introduces the fundamental ground-based surveillance systems used in aviation to monitor and manage air traffic. In Ghana, as air travel from airports like Kotoka International Airport (KIA), Kumasi, and Tamale increases, ensuring the safety of aircraft in our skies is more important than ever. The Ghana Civil Aviation Authority (GCAA) relies on these surveillance systems to see, identify, and guide aircraft, preventing collisions and ensuring an orderly flow of traffic. Understanding these systems is crucial for any student interested in becoming a pilot, air traffic controller, or aviation engineer.

Lesson notes

What is Aviation Surveillance?

In simple terms, aviation surveillance is the process of knowing where aircraft are in the sky or on the ground. It is the "eyes" of Air Traffic Control (ATC). The main purpose is to maintain a safe distance (separation) between aircraft to prevent accidents. "Ground-based" means the primary equipment used to "see" the aircraft is located on the ground. Key System 1: Primary Surveillance Radar (PSR) How it Works: PSR is the most basic form of radar. It works on a simple principle of echo. A large rotating antenna on the ground sends out a powerful pulse of radio energy into the sky. This energy travels outwards. If it hits an object (like an aircraft), a small fraction of that energy is reflected back towards the antenna. This reflected energy is called an "echo". The PSR antenna receives this faint echo. The system calculates two things: Range (Distance): By measuring the time it took for the pulse to travel to the aircraft and back. Since radio waves travel at the speed of light, this calculation is very fast and accurate. Bearing (Direction): By noting the direction the antenna was pointing when it received the echo. What ATC Sees: On the controller's screen, the aircraft appears as a simple dot or "blip" of light. Analogy: Imagine you are in a large, dark room and you shout "Hello!". You can tell where the walls are by how long it takes for the echo to come back to you and from which direction you hear it. You know *something* is there, but you don't know *what* it is. Key Feature: PSR is a non-cooperative system. It does not require any special equipment on the aircraft. It can detect any aircraft, bird, or even intense weather, as long as it's large enough to reflect the radio waves. Limitations: It does not know the aircraft's identity (e.g., flight number). It does not know the aircraft's altitude (height). The signal can be affected by weather ("clutter"). Key System 2: Secondary Surveillance Radar (SSR) How it Works: SSR was developed to overcome the limitations of PSR. It is a cooperative system. The SSR ground station sends out an "interrogation" signal (like asking a question). An aircraft equipped with a device called a transponder receives this signal. The transponder automatically replies with a coded message containing important information. The ground station receives this reply. Information in the Reply: The transponder's reply includes: Identity: A unique 4-digit "squawk" code assigned by ATC. Altitude: Sourced from the aircraft's own instruments. Sometimes, other information like speed. What ATC Sees: On the controller's screen, the aircraft "blip" now has a data block next to it, showing its flight number, altitude, speed, etc. Analogy: Instead of just shouting in the dark room, you now call out, "Is anyone there with the name 'Kofi'?" And a voice replies, "Yes, this is Kofi, and I am standing on a chair!" You get much more detailed information. Key Feature: SSR is cooperative. The aircraft must have a functioning transponder to be seen by SSR. Most modern aircraft are required to have one. Key System 3: Automatic Dependent Surveillance-Broadcast (ADS-B) How it Works: ADS-B is a cornerstone of modern surveillance. It is a revolutionary technology. Automatic: It works automatically without any action from the pilot or ATC. Dependent: It *depends* on the aircraft's own navigation systems, primarily the Global Positioning System (GPS), to determine its precise position. Broadcast: The aircraft continuously *broadcasts* its information (like a radio station) for anyone with the right receiver to hear. Process: The aircraft's GPS receiver determines its latitude, longitude, altitude, and velocity. This information is packaged into a digital message. The aircraft's ADS-B transmitter broadcasts this message once or twice per second. A network of simple ground-based receivers picks up these broadcasts and sends the data to ATC centres. Advantages over Radar: More Accurate: GPS-based position is generally more accurate than radar. Faster Updates: Information is updated almost in real-time. Cheaper Infrastructure: The ground stations are much cheaper to install and maintain than large radar antennas. This makes it easier to provide coverage in remote areas. More Information: Can broadcast more detailed information, like the pilot's intended flight path. Key Feature: The aircraft tells the ground where it is, rather than the ground having to find the aircraft. Key System 4: Multilateration (MLAT) How it Works: MLAT also uses the signals from an aircraft's transponder, but in a very clever way. It's often used to supplement SSR or in areas where radar is not effective, like on the airport surface. A network of at least four simple ground receivers is set up around an area (e.g., an airport). These receivers all listen for the signals broadcast by an aircraft's transponder (the same signals used by SSR). Each receiver records the *exact* time it received the signal. Because the receivers are in different locations, the signal arrives at slightly different times. This tiny difference is called the Time Difference of Arrival (TDOA). A central computer analyses the TDOA from all receivers and uses complex geometry (hyperbolic triangulation) to calculate the aircraft's precise 3D position. Analogy: Imagine a lightning strike. You see the flash instantly, but you hear the thunder a few moments later. If you and your friends are standing in different parts of a field, you will all hear the thunder at slightly different times. By comparing when each of you heard it, you could pinpoint where the lightning struck. MLAT does this with radio signals. Key Use: Excellent for accurately monitoring aircraft and vehicles on airport taxiways and runways, helping to prevent ground collisions at busy airports like KIA.

Guided Practice (With Solutions)

Question 1: An air traffic controller at Kotoka International Airport sees two "blips" on their screen. Blip A is just a dot. Blip B has a data tag next to it showing "GHA751, FL350" (Ghana International Airlines flight 751 at 35,000 feet).

Evaluation guide

• Present a summary of ground -based surveillance systems .
• Talk for Learning: Through a question and answer session , learners share views on ground -based
• conceptual
• understanding