062 Radio Navigation

Properties Of Radio Waves Electro-Magnetic (EM) Radiation Two components, an electrical (E) field parallel to the wire and a magnetic (H) field perpendicular to the wire Polarisation Plane of the electric field Dependent on the plane of the aerial Vertical aerial → vertically polarized wave

Radio Waves

Radio Waves Period Frequency (f) The lenght of time it takes to generate one cycle of radio wave Signified by the greek letter tau (τ) Measured in microseconds (μs) Frequency (f) f = 1/τ Expressed in Hertz (Hz)

Radio Waves Wavelength (λ) C=speed of light (300 000 000ms or 162000nm) λ = c/f Example: If period is 0.2μs what is the wavelength?

Frequency Bands

Radio Propagation Theory How the radio waves pass and travel through different materials and atmosphere (Troposphere and Ionosphere) Determines the use of a particular frequency band

Refraction Speed of the wave is changed when passed through a material → bending Any change of the density of the medium a radio wave passes through or over will produce a similar effect Greates at low frequencies

Diffraction Caused by sharp objects Greatest at low frequencies

Reflection Is most likely when the wavelength is compatible with the target size (same size or smaller) Depends also on the density and the angle they hit the materials

Attenuation Loss of power in a wave Atmospheric attenuation is greatest at high frequencies Surface attenuation is greatest at high frequencies Ionospheric attenuation is greatest at low frequencies

Propagation paths Non-ionospheric Ionospheric Surface wave 20KHz-50MHz (used 20 KHz-2Mhz) Space wave >50MHz Ionospheric Skywave 20KHz-50MHz (used 2-30MHz) Satellite (UHF, SHF) Ducting <20KHz

Ionosphere

Skywave

Modulation Adding information to a carrier wave Transmission of audio, data, determination of bearing in VOR…

Keyed Modulation Simplest way to put information onto carrier wave Short and long bursts of energy Morse code

Amplitude Modulation (AM) Amplitude of the audio frequency (AF) modifies the amplitude of the radio frequency (RF) Simple and cheap

Amplitude Modulation Produces two sidebands (upper and lower) as well as the carrier wave Single Sideband (SSB) Removing one of the sidebands and the carrier wave → saves power and bandwidth and also better signal to noise ratio (less interference)

Frequency Modulation (FM) The amplitude of AF modifies the frequency of the RF

Phase Modulation Phase of the carrier wave is modified by the input signal With a digital signal → phase shift keying (GPS and MLS)

Antennae Two basic types: Half wave dipole Radiates in all directions Ideal dipole is half or quarter the wavelength Cone of silence in the overhead

Marconi (quarter wave aerial) Better aerodynamic qualities → used in aircraft

Directivity Adding parasitic elements to the aerial (reflector and directors) → strong beam along the plane of the aerial. Negative side is unwanted sidelobes (ILS, SSR and primary radar)

Radar Aerials Energy is focused into a narrow beam

Radar Aerials Parabolic Aerial

Phased array antenna (Slotted) Radar Aerials Phased array antenna (Slotted) Slots are fed with the radio energy → narrow beam similar to a parabolic deflector Beam is narrower than from a parabolic reflector Smaller/reduced sidelobes Lesser power requirement Improved resolution

Doppler Radar Continuous measurement of Doppler shift → ground speed and drift angle Completely self-contained Is usable worldwide Is most accurate overland Less accurate over the sea

Principle of Operation Relative motion between a transmitter and receiver → frequency shift (also known as Doppler shift or Doppler effect) Depression angle of array is 60-70 degrees Receiver measures the frequency shift in the reflected signal

Airborne Doppler Slotted waveguide antenna Technique of using opposing beams → Janus array Janus array indicates drift and also reduces errors from pitch, roll and vertical speed changes If a Doppler system unlocks → ceases to compute ground speed and drift

ADF/NDB ADF Automatic Direction Finder NDB Non Directional Beacon Frequency band: 190-1750KHz in the LF and MF bands, considered as MF aid ADF Automatic Direction Finder Airborne part of the equipment Loop and dipole antenna NDB Non Directional Beacon Ground part of the system

Aircraft equipment

NDB Tracking

NDB Tracking

Factors affecting ADF accuracy Static interference Precipitation static Collision of water droplets and ice crystals with the aircraft Thunderstorms Night effect Introduction of skywave when D-region disappears Worst around dawn and and dusk

Factors affecting ADF accuracy Station interference Should be considered during night time Coastal refraction Radio waves speed up over water refraction Quadrantal Error Lack of failure warning system in most systems!

VOR (VHF Omnidirectional Range) Used with: Marking of airways Sid and Stars Holding point Approach procedures

The principle of operation 30 Hz frequency modulated omni-directional reference signal 30 Hz amplitude modulated variable phase directional signal (30 revs/sec rotating) Aircrafts VOR receiver measures the phase difference Phase difference is 0 degrees when aligned to magnetic north from a VOR Phase difference is same as the radial

Transmission details VHF band between 108.0 – 117.95MHz 40 channels between 108.0 – 112MHz shared with ILS so that for example 108.0, 108.05, 109.4, 109.85 are VOR frequencies (Even decimal digits) 120 channels between 112 – 117.95 with 50kHz spacing

Identification 3 letter aural morse approx. 7groups/minute, at least every 10 seconds. May also be in voice form. Monitoring Automatic site monitor scans: bearing change exceeding 1degrees, reduction of signal >15%, a failure of monitor Removes the ident or switches of the beacon Standby transmitter comes on-line and during this period there is no ident

Errors and Accuracy The ICAO accuracy requirement is ±5 degrees Site error: caused by uneven terrain near the transmitter (monitored to ±1 degrees of accuracy) Scalloping or Bends: caused by terrain and buildings at the limits of a beacon´s range Airborne equipment: maximum allowed aircraft equipment is ±3 degrees

Doppler VOR (DVOR) Second generation VORs Bearing accuracy is improved and reduces site error Reference signal is AM and variable signal is FM The phase relationship at the aircraft is the same

VOR Airborne Equipment The aerial: Whip type for slow speed aircraft and blade type for high speed The receiver: navigation unit The indicator: CDI (course deviation indicator), RMI (radio magnetic indicator) or EFIS equipped aircraft with different possibilities to display information

CDI (course deviation indicator)

RMI (radio magnetic indicator)

EFIS

VOR approach chart

ILS (Instrument Landing System) Existence over 40 years Still the most accurate landing aid Guidance to horizontal and vertical planes Provides visual instructions in the cockpit to follow the glidepath and centerline (localiser)

ILS

ILS frequencies Localiser Glidepath Frequency pairing Operates in the VHF band between 108 and 111.95MHz to provide 40 channels Glidepath Operates in the UHF band between 329.15 and 335MHz to provide 40 channels Frequency pairing The GP frequency is paired with the localiser with automatic frequency selection

DME paired with ILS channels Frequency paired with an ILS DME paired with an ILS is zeroed to the threshold Protected only within the ILS localiser service area up to 25000 feet

ILS Emission patterns

ILS coverage Localiser extends from the transmitter: 25nm within plus or minus 10 degrees from the centreline 17nm between 10 - 35 degrees from the centreline Glidepath extends from the transmitter: 10nm in sectors of 8 degrees in azimuth on each side of the centre-line

ILS

ILS on Primary Flight Display

Factors affecting range and accuracy ILS multipath interference Large reflecting objects aircrafts, vehicles and fixed structures within the radiated signal coverage Weather Snow and heavy rain attenuates the ILS signals Fm broadcast FM frequencies just below 108MHz may overspill into te radio navigation band 108-117.975MHz

ILS chart

MLS (Microwave Landing System) Was designed to replace ILS Precision approach and landing system Allows 3D fixing 200 channels SHF band 5031 – 5090MHz

MLS Aircraft can choose their own approaches (STOL, Helicopters) Built In DME Compatible with conventional LOC and GS instruments

Principle of Operation Time Division Multiplexing (TDM) Time referenced scanning beam (TRSB) in Azimuth and Elevation Measures the time interval in microseconds between reception the ”to” and ”fro” scanning beams The azimuth transmitter is at the upwind end of the runway The elevation transmitter is at the downwind end of the runway

Radar Principles Stands for Radio Detection And Ranging Developed prior to World War 2 Pulsed and continuous wave technicues Used by ground based radars and in airborne systems

Primary Radar Secondary Radar Types of Pulsed Radars Uses pulses of radio energy reflected from a target Secondary Radar Transmits pulses on one frequency but receives on a different frequency Utilises an interrogator and a transponder

Radar Applications Air Traffic Control Monitor and vector Surveillance Radar Approach (SRA) or a Precision Approach Radar (PAR) Control and monitor on ILS let-downs, or in during airfield instrument approaches Provide information regarding weather for example storm clouds

Air/Ground navigational systems Radar Applications Air/Ground navigational systems Secondary Surveillance Radar Distance Measuring Equipment (DME) Doppler Radar Airborne Weather Radar Depict the range and bearing of clouds Indicate the areas of the heaviest rain and turbulence Calculate the height of the cloud Ground mapping

Propagation characteristics required: Radar Frequencies Propagation characteristics required: Minimal static Minimal atmospheric attenuation Line of sight propagation VHF band and higher: Free from external noise and static Narrow beams for good range and bearing resolution Shorter pulses Shorter wavelengths are reflected more efficiently

Pulse Technicue Transmission radio energy in very short bursts The duration of the pulse is equal to the pulse length or width Pulse Recurrence Period (PRP) is the time interval between two pulses Pulse Recurrence Frequency (PRF) is the number of pulses in one second (PPS) Example. If the PRF is 100 PPS what is PRP? PRP = 1/100 = 0,01s = 10 000(μs)

Distance Measurement – Echo Principle Timing the interval between instant of the pulse´s transmission and its return as an echo Example. If the time delay between transmission and echo is 750μs? Distance = 300 000 000 x 0,000750 2 =112 500(m) = 112,5(km)

Pulse Radar Maximum Range Relationship to PRF Radar is designed in to a certain distance Each pulse must be allowed to travel to the most distant object planned and back → it has to wait before sending a new pulse A low PRF for long range radars Max theoretical range (in metres) = c/2xPRF

Pulse Radar Minimum Range At very short ranges the beginning of the returning pulse can arrive before the the tail end of the pulse has been transmitted It is controlled by the pulse width Minimum range (in metres) = c x pulse length 2

SSR (Secondary Surveillance Radar) Interrogator and transponder (transmitter/receiver) Advantages of SSR over primary radar Less transmitter power Not dependent on aircraft´s echoing area Clutter free and does not rely on echoing pulses Positive aircraft identification (code and call sign) Track history, speed, altitude and destination Can indicate on a controller´s about a possible emergency/distress

SSR Display Displayed in combination with the primary radar on the same screen Includes: the callsign or flight number, pressure altitude or flight level, ground speed and destination

SSR Frequencies and Transmissions Ground station interrogates on 1030 MHz and receives on 1090 MHz Aircraft receives on 1030 MHz and transponds omnidirectionally on 1090 MHz

Modes Mode A – to identify Mode C – altitude reporting Ground station interrogates by sending trios of pulses P1, P2 and P3 Interval between P1 and P3 is 8μsec in mode A and 21μsec in mode C Altitude is always referenced to 1013,2mb Extra SPI (Special Position Identification) causes the return on the radar screen to bloom 20-25sec

Modes Mode A and C interrogation format

Special Codes 2000 Aircraft entering an FIR from an area where no code has been assigned 7500 Unlawful interference, hijacking or unlawfu interception 7600 failure of two way communications 7700 Emergency

Errors and Disadvantages of SSR Fruiting: if aircraft are in range of two interrogators they may reply to both FRUIT (False Replies Unsynchronized with Interrogator Transmissions or alternatively False Replies Unsynchronized In Time). Garbling: if aircrafts are closer together than 1,7nm and nearly at the same bearing they may produce overlapping replies Only 4096 identification codes in Mode A

Mode S Over 16 700 000 individual aircraft addresses Uplink/downlink data over the horizon Reduction of voice communications via the data link Height readout to the ground controllers in 25ft increments

TCAS (Traffic Collision Avoidance System)

Principle of Operation Secondary radar principle using the normal SSR frequencies of 1030 MHz and 1090 MHz Air to Air Two protective three dimensional bubbles around the aircraft TA (Traffic Advisory) RA (Resolution Advisory) advice/instructions in vertical plane TCAS1 only TA´s TCAS2 TA´s and RA´s

Aircraft Equipment A Mode equipped aircraft will be visible on a TCAS equipped aircraft but only TA´s C Mode equipped aircraft will give RA´s on TCAS equipped aircraft due to height information S Mode transponder equipped aircrafts will mutually resolve manouvres

TCAS Displays

Combined TCAS and SSR control panel

Airborne Weather Radar (AWR) To provide information regarding weather and for navigation Requires interpretation by the pilot

AWR Can be displayed on a dedicated unit or show on the EFIS navigation display (ND)

AWR Component Parts Transmitter/Receiver Antenna, which is stabilised in pitch and roll Indicator Control unit

AWR Indicator Antenna Receiver/ Transmitter Control Unit

AWR AWR Main Functions Detect the size of water droplets Determine the height of cloud tops Map the terrain Provide a position fix (range and bearing)

Principle of Operation Primary Radar Echo principle to depict range Searchlight principle to depict relative bearing Antenna Parabolic or Flat Plate for producing both: Pencil shaped (conical) and Fan shaped (cosecant) Stabilised in pitch and roll with the information from the IRU´s or by it´s own gyro

Principle of Operation Radar Beam Pencil beam: 3 - 5ᴼ wide, used for weather and longer range mapping ( over 60nm) Fan shaped: for short range mapping Beam width = 70 x wavelength/antenna diameter Example: wavelength 3cm with 45 cm antenna Beam width = 70 x 3/45 = 4,7ᴼ Narrower beams with shorter wavelengths and bigger antennas!

Principle of Operation Radar frequency We want to detect the large water droplets and wet hail (about 3cm across) → severe turbulence Typical frequency is about 9 GHz (9375 MHz +/- 30MHz in commercial systems) λ = 300m / 9375 = 3,2cm

Colour coding Color Return Strength Rainfall Rate Black Very Light or No returns Less than 0.7mm/hr Green Light returns 0.7-4 mm/hr. Yellow Medium returns 4-12 mm/hr Red Strong returns Greater than 12mm/hr Magenta Very strong returns Greater than 25mm/hr

Calculating Approximate Cloud Height Example: Determine the altitude of the cloud tops: Range 45nm, tilt 3 degrees, beamwidth 4 degrees and aircraft at FL360 Height = Range x 100ft x (TILT – BEAMWIDTH/2) = 45 x 100ft x (3 – 4/2) = 4500ft → cloud tops of 40500ft

Area Navigation Systems (RNAV)

RNAV Achieved by: VOR/DME ILS/MLS LORAN GNSS INS/IRS ADC Time

RNAV Benefits of RNAV: more direct flight path saves fuel, time and environment increase in the route capasity by using the all available airspace Reduction in separation minima Reduction in the number of ground navigation facilities 17

Types and Levels of RNAV B-RNAV: position accuracy to within 5nm on 95% of occasions Mandatory for all aircrafts carrying 30 passengers or more in Euro-control P-RNAV: position accuracy to within 1nm on 95% of occasions 18

Types and Levels of RNAV Three levels of RNAV: 2D RNAV: LNAV (lateral) 3D RNAV: LNAV and VNAV (lateral and horizontal) 4D RNAV: LNAV, VNAV and Time

Required Navigation Performance (RNP) B-RNAV (RNP5) Inputs from: DME/DME VOR/DME IRS or INS (for up to 2 hours of last radio or on ground update) GPS P-Rnav (RNP1) Inputs from: DME/DME VOR/DME GPS IRS

RNAV Equipment Minimum requirements for RNAV equipment: - Display present position in latitude/longitude or as distance/bearing to selected waypoint - Select or enter the required flight plan through the control and display unit (CDU) - Review and modify navigation data for any part of a flight plan at any stage of flight and store sufficient data to carry out the active flight plan; - Review, assemble, modify or verify a flight plan in flight, without affecting the guidanceoutput;

Minimum requirements for RNAV equipment: - Execute a modified flight plan only after positive action by the flight crew - Where provided, assemble and verify an alternative flight plan without affecting the active flight plan - Assemble a flight plan, either by identifier or by selection of individual waypoints from the database, or by creation of waypoints from the database, or by creation of waypoints defined by latitude/longitude, bearing/distance parameters or other parameters

Minimum requirements for RNAV equipment: - Provide automatic sequencing through waypoints with turn anticipation. Manual sequencing should also be provided to allow flight over, and return to, waypoints - Display cross-track error on the CDU - Provide time to waypoints on the CDU - Execute a direct clearance to any waypoint - Fly parallel tracks at the selected offset distance; offset mode should be clearly indicated - Purge previous radio updates

Minimum requirements for RNAV equipment: - Assemble flight plans by joining routes or route segments - Allow verification or adjustment of displayed position - Carry out RNAV holding procedures (when defined) - Make available to the flight crew estimates of positional uncertainty, either as a quality factor or by reference to sensor differences from the computed position - Conform to WGS-84 geodetic reference system; and - Indicate navigation equipment failure

Simple 2D RNAV First generation of radio navigation systems allowing the flight crew to select a phantom waypoint RNAV panel and select a desired track to fly inbound to the waypoint.

Simple 2D RNAV Flight Deck Equipment The control unit allows the flight crew to: Tune the VOR/DME station used to define the phantom waypoint Define the phantom waypoint as a radial and distance from the selected VOR/DME station Select desired track to follow inbound to the phantom waypoint Select between an en-route mode and approach mode of operation and the basic VOR/DME mode of operation

Simple 2D RNAV Navigation computer, VOR/DME navigation Computes the navigational problems by simple sine and cosine mathematics Navigation computer input Actual VOR radial and DME distance from selected vor station Radial and distance to phantom waypoint Desired magnetic track inbound to the phantom waypoint

Simple 2D RNAV Navigation computer output Desired magnetic track to the phantom waypoint shown on the CDI on the course pointer Distance from present position to the phantom waypoint Deviations from desired track as follows: In Enroute mode full scale deflection on the CDI is 5nm In approach mode full scale deflection on the CDI is 1/4nm In VOR/DME mode full scale deflection of the CDI is 10 degrees System is limited to operate within range of selected VOR/DME station!

Limitations and accuracy Each waypoint has to be inside of DOC Slant range error in DME (if facility close to track)

FMS (Flight Management System) Consists of FMC (flight management computer) and various inputs of other aircraft systems Ability to monitor and direct both navigation and performance of the flight Controls: Autopilot/Flight Director System (AFDS) Autothrottle/thrust LNAV/VNAV Contains performance and navigation database Navigation database is updated in 28 day cycle 29

FMS Navigation database VOR/DME station data (three letter ICAO identifier) Waypoint data (five letter ICAO identifier) SID an STAR data Holding patterns Airport runway data NDB stations (alphapetic ICAO identifier) Company flight plan routes Navigation database is write protected!

FMS Performance database V1, Vr and V2 speeds Aircraft drag Engine thrust characteristics Maximum and optimum operating altitudes Speeds for maximum and optimum climb Speeds for long range cruise, max endurance and holding Maximum ZFM (zero fuel mass), maximum TOM (take-off mass) and maximum LM (landing mass) Fuel flow parametres Aircraft flight envelope

FMS Kalman Filtering Combines the short term accuracy of the IRS with the long term accuracy of the external reference IRS position is the most accurate after the position update on the runway treshold Initially the IRS is the most accurate but when the flight is progressing, the external reference will become the most accurate

Typical Flight Deck Equipment Fitted on FMS Aircraft CDU (control display unit) Means of communication with the FMC together with AFDS (Autopilot Flight Director System) 34

CDU Flight Plan Page: Shows route and predictions Enables directs, changing the route and adding constraints 35

CDU Performance page Climb phase (A320): 36

CDU Performance page Approach Phase (A320): 37

EHSI (Electronic Horizontal Situation Indicator) Displays navigational, radar and TCAS information Inputs to EHSI: IRS FMC VOR, DME, ILS and ADF TCAS and AWR 38

EHSI Controller (A320) 39

Expanded Map or Arc Mode (A320) 40

Full Rose Map (A320)

Plan Mode (A320) 42

Expanded VOR/ILS (737)

Full Rose VOR/ILS (737)

Nav Mode (737)

Map Mode (737)

Center Map Mode (737)

Plan Mode (737)

PFD (Primary Flight Display) 49

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GNSS (Global Navigation System) Two operating systems: NAVSTAR Global Positioning System (GPS) Global Orbiting Navigation Satellite System (Glonass) European Galileo is under development (some satellites has been launched) WGS84 (World Geodetic Survey of 1984) is the ICAO standard for aeronautical positions 51

Glopal Positioning System (GPS) Currently two modes of operation: SPS (Standard positioning service) for civilian users PPS (Precise positioning service) for authorised users

The GPS Segments Space Segment Control Segment User Segment Satellites Master control station in colorado springs and monitor stations (Hawaii, Kawajalein, Diego Garcia and Ascension Islands) User Segment 53

Space Segment GPS Consists of 24 satellites (21 active and 3 spare) in 6 orbital planes The orbits average height is 10898Nm (20180km) The orbital planes have an 55 degree inclination to the equator The orbital period is 12 hours Observer will have 5 to 8 satellites in view at least 5 degree above horizon 54

Space Segment GPS Satellites have 3 or 4 atomic clocks of caesium or rubidium standard with an accuracy of 1 nanosecond A satellite will be masked (not selected in navigation) if it is less than 5 degrees above horizon The satellites broadcast pseudo random noise (PRN) codes of one millisecond duration on two frequencies and a NAV and a SYSTEM data message. Each satellite has its unique code 55

Space Segment GPS L1 frequency: 1575.42 Mhz transmits the coarse acquisition (C/A) code repeated every millisecond and the precision P code repeats every seven days.The navigation and system data message is used by both the C/A and the P codes L2 frequency: 1227.6 MHz transmitting the P code for determing the ionospheric delays L3 frequency: 1381.05 MHz has been allocated as second frequency for non-authorised users. It has been available from 2007 and its use is the same as the L2 frequency 56

Space Segment GPS C/A code for civilian users and P code for military and approved civilian users and foreign military users at the discretion of the US DOD. The P code is designated as the y code when the anti- spoofing measures are implemented

Control Segment Comprises of: Master Control Station Schriever Air Force base, 20 km south of Colorado Springs Monitoring Stations

User Segment All the GPS receivers! Several types of receivers Sequential receivers: One or two channels and scan the Satellites sequentially Multiplex receivers: Single or twin channel but scan the Satellites quickly Multi-channel receivers: Monitor several satellites simultaneusly Are used in aircrafts!

GPS Position Determination Position determination with two satellites (in a 2-dimensional world):

GPS Position Determination 2D position determination with 2 satellites and a receiver clock error:

GPS Position Determination A clock error of 1/100 seconds would lead to an error in position of a 3000km! To achieve an accuracy of 10m, the runtime of the signal must be precise to 0,00000003 seconds!

GPS Position Determination 2D position determination with 3 satellites and corrected clock error:

GPS Position Determination We need three satellites for determination of our position in 2d For 3D we need four satellites!

GPS Errors Selective Availability (SA) Introduced by the US DOD in 1995 Deliberately degraded the accuracy of the fixing on the C/A Code USA withdrew SA at 00:00 on 01 May 2000 Downgraded the accuracy derived from the C/A code to about 100m Was achieved by adding random errors to the satellites clock time

GPS Errors Ephemeris Errors Satellite clock error Errors in the satellites position caused by the gravitational effects of the sun, moon, planets and solar radiation Checked every 12 hours Maximum error 2,5m Satellite clock error Checked at every 12 hours Maximum error 1,5m

GPS Errors Ionospheric Propagation Error Ionosphere causes radio energy to be slowed down Known also as ionospheric delay With two frequencies we can minimise the error! Most of the significant errors in satellite navigation systems Maximum error for single frequency operation is 5m

GPS Errors Tropospheric Propagation Error Variations in pressure, temperature, density and humidity affect the speed of propagation Minimised with the use of two frequencies Maximum 0,5m Atmosphere:

GPS Errors Receiver noise error Internal noise Maximum 0,3m Multipath Reception Maximum 0,6m

GPS Errors Geometric Dilution of Precision (GDOP) Good geometrial alignment Bad geometrical alignment

GPS Errors Effect of aircraft manouvre May result the lost of satellite signal Optimum position for the antenna is on top of the fuselage close to the aircraft's center of gravity!

System Accuracy ICAO Requirement for SPS: Vertical +/-13m Horizontal +/-22m Time 40 nanoseconds

Differential GPS (DGPS) Dgps is a means of improving the accuracy of GPS by monitoring the integrity of the satellite data and warning the user of any errors which occur. Three kinds of DGPDS currently in use or under development: Air Based Augmentation System (ABAS) Ground Based Augmentation System (GBAS) Satellite Based Augmentation System (SBAS)

Differential GPS Air Based Augmentation System (ABAS) Called as RAIM Receiver Autonomous Monitoring By combination of five satellites it can discard a faulty one With six satellites it can discard one satellite and still continue RAIM!

Differential GPS Ground Based Augmentation A Local area DGPS implemented through a local area augmentation system (LAAS)

Differential GPS Satellite based augmentation system (SBAS) Three systems under development which will cover a large area of northern hemisphere The USA Wide Area Augmentation system (WAAS) declared operational in 2003 The European Geostationar Overlay System (Egnos) declared operational in 2004 The Japanese Multi-functional Transport Satellite Augmentation System (MSAS) expected to become operational in 2010

Differential GPS Satellite Based Augmentation System (WAAS)

Differential GPS European geostationary Overlay System (EGNOS)

Differential GPS EGNOS footprints and service area