Lecture 12 - Sensors for guidance, navigation, and control Flashcards
(38 cards)
What is celestial navigation?
Using time and angles between local vertical and known celestial objects to estimate the latitude and longitude of moving objects.
Radio navigation
Using radio frequency sources with known locations (Eg. GPS; reference nodes).
Inertial navigation
Relies on knowing initial position, velocity, attitude. Only form of navigation that doesn’t rely on external references.
What are the 2 components that make up an ILS?
Ground-based signal transmitters + onboard receiving equipment.
What is a localiser?
Ground-based array of transmitters: provides horizontal guidance relative to the centre line. Two signals transmitted from co-located antennae.
Receiver onboard measures difference between modulated signals (90Hz; 150Hz)
What is a glide slope?
Array of transmitters that provide vertical guidance until safe touchdown. GS signal transmitted on a carrier frequency.
Where are marker beacons on an ILS and what types are there?
At known distances. Lights, outer marker, inner maker.
Explain the control perspective of the GS on an ILS.
What does RADAR stand for?
Radio detection and ranging
How does RADAR work?
Distance between the reflecting objects and radar is determined by measuring running time of transmitted pulses.
Speed is constant and known (EM waves travel at speed of light [300,000 km/s]) and time is measured.
Radar flow chart
What do targets produce in Radar?
A diffuse reflection. Pulse is reflected in a wide number of directions. “Scattering”.
What is a duplexer?
Switches the antenna between the transmitter and receiver so that only one antenna needs to be used.
High-power pulses of the transmitter would destroy the receiver if energy was allowed to enter the receiver.
What is a receiver?
Amplifies and demodulates the received RF-signals. Provides video signals on the output.
How does primary survaillence radar operate?
What is required for long-range operations?
1 con of PSR?
Operates independantly of the target aircraft - no action from the aircraft is required for it to provide a radar turn.
Enormous amounts of power must be radiated to ensure returns from the target (especially at long ranges).
Returns may be easily disrupted, eg. due to rain.
2 facts about and 3 pros of secondary surveillance radar?
Relies on a “transponder”, where a unique, 4-digit “squawk” code is transmitted.
Target aircraft’s transponder responds to interrogation by the ground station by transmitting a coded reply signal.
Pros:
1. Strong signal received by ground station
2. Reduced power required to emit signal
3. Electronically-coded signals & additional info. can be transmitted
4 main ways to track aircraft?
Satellite comms.
Primary radar
Secondary radar
ACARS
What is ACARS?
Aircraft Communications Adressing and Reporting System
What is radar cross-section?
Measure of how detectable an object is by radar.
Exact definition of RCS (Radar Cross Section)
Hypothetical area that would intercept the incident power of the target which, if scattered uniformly, would produce the same echo power at the radar, as the actual target.
Wavelength equation
speed/frequency
AM and FM meaning?
Amplitude modulation
Frequency modulation
How is range measured and name 3 types of range measuring equipment.
Pulse emitted and round trip time for return of pulse is measured. This is converted into range.
Active radar, LIDAR, sonar sensors
What is LIDAR?
Light detection and ranging.
Optical remote sensing technology that can measure the distance to, or other properties of, a target by illuminating the target with a light, often using pulses from a laser.
