062 Radio Navigation.

Presentation on theme: "062 Radio Navigation."— Presentation transcript:

1 062 Radio Navigation

2 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

3 Radio Waves

4 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)

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

6 Frequency Bands

7 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

8 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

9 Diffraction Caused by sharp objects Greatest at low frequencies

10 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

11 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

12 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

13 Ionosphere

14 Skywave

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

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

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

18 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)

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

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

21 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

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

23 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)

24 Radar Aerials Energy is focused into a narrow beam

25 Radar Aerials Parabolic Aerial

26 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

27 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

28 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 degrees Receiver measures the frequency shift in the reflected signal

29 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

30 ADF/NDB ADF Automatic Direction Finder NDB Non Directional Beacon
Frequency band: KHz 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

31 Aircraft equipment

32 NDB Tracking

33 NDB Tracking

34 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

35 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!

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

37 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

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

39 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

40 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

41 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

42 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

43 CDI (course deviation indicator)

44 RMI (radio magnetic indicator)

45 EFIS

46 VOR approach chart

47 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)

48 ILS

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

50 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 feet

51 ILS Emission patterns

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

53 ILS

54 ILS on Primary Flight Display

55 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 MHz

56 ILS chart

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

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

59 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

60 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

61 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

62 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

63 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

64 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

65 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 = (μs)

66 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 = x 0,000750 2 = (m) = 112,5(km)

67 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

68 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

69 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

70 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

71 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

72 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 sec

73 Modes Mode A and C interrogation format

74 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

75 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

76 Mode S Over 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

77 TCAS (Traffic Collision Avoidance System)

78 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

79 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

80 TCAS Displays

81 Combined TCAS and SSR control panel

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

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

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

85 AWR Indicator Antenna Receiver/ Transmitter Control Unit

86 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)

87 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

88 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!

89 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

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

91 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

92 Area Navigation Systems (RNAV)

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

94 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

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

96 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

97 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

98 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;

99 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

100 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

101 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

102 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.

103 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

104 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

105 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!

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

107 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

108 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!

109 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

110 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

111 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

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

113 CDU Performance page Climb phase (A320): 36

114 CDU Performance page Approach Phase (A320): 37

115 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

116 EHSI Controller (A320) 39

117 Expanded Map or Arc Mode (A320)
40

118 Full Rose Map (A320)

119 Plan Mode (A320) 42

120 Expanded VOR/ILS (737)

121 Full Rose VOR/ILS (737)

122 Nav Mode (737)

123 Map Mode (737)

124 Center Map Mode (737)

125 Plan Mode (737)

126 PFD (Primary Flight Display)
49

127 50

128 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

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

130 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

131 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

132 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

133 Space Segment GPS L1 frequency: 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: MHz transmitting the P code for determing the ionospheric delays L3 frequency: 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

134 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

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

136 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!

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

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

139 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, seconds!

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

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

142 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

143 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

144 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

145 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:

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

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

148 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!

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

150 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)

151 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!

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

153 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

154 Differential GPS Satellite Based Augmentation System (WAAS)

155 Differential GPS European geostationary Overlay System (EGNOS)

156 Differential GPS EGNOS footprints and service area

157