VERIPOS – specialists in positioning 31.03 · VERIPOS – specialists in positioning 31.03.2010....

www.veripos.comVERIPOS – specialists in positioning 31.03.2010

Surface Positioning Systems

Presentation Overview

Satellite Navigation

Increasing the AccuracyP i O iPresentation Overview

Augmentation Services

Network Infrastructure

Presentation Overview

Network Infrastructure

Operational Implementation

Solar ActivitySolar Activity


What is GNSS?

• Term Global Navigation Satellite System (GNSS) is used as a term for all satellite based navigation systemssatellite based navigation systems


Components of a GNSS?

SPACE-SEGMENTSPACE-SEGMENT

CONTROL-SEGMENT

USER-SEGMENT


Space Segment

• Network of orbiting satelliteset o o o b t g sate tes

• Satellites are merely radio transmitters

• Transmitting data to users (passive system)

P t f i t llit iti• Part of message is satellite position

• At any moment in time, satellite position is knownis known

• Each satellite broadcasts almanac of whole constellationwhole constellation

• Satellite transmissions very weak- need line of sight


line of sight

GPS Control Segment

• Responsible for overall satellite command and control• Maintaining exact orbits of each satellite


• Monitoring the integrity and accuracy of the system

User Segment

• User hardware used to decode the data from the satellites

• Includes antennas and GNSS receivers


• Includes antennas and GNSS receivers

The Global Positioning System

• Presently 30 operational satellites

• Global coverage, 24 hours a day, all weather conditions

• Satellites broadcast precise time and orbit information on L-band radio frequencies

• 6 orbital planes, 55° inclination

• 20,180 km above earth’s surface

• 11:58 Orbital Period


GPS SignalsData (code)L1: C/A-code (civil)L1: C/A code (civil)

P(Y)-code (military)L2: L2C-code (civil) [not on all satellites]

P(Y)-code (military)L5: TBC

Navigation Messageon L1 and L2

Carrier FrequenciesL1: 1575.42 MHzL2: 1227 60 MHzL2: 1227.60 MHzL5: 1176.45 MHz [future signal]


C i C d M

What happens at the satellite?

Carrier Code Message

S t llitSatellite

L1 L2 L5

Receiver

Carrier Code Message


Modulation

Carrier

CodeCode

ModulatedModulatedModulatedcarrierModulatedcarrier


De-Modulation

ModulatedcarrierModulatedcarrier

CodeCode

Carrier


Determining the range (distance) to the satellite…


What does the data look like?


Next step is to compute a position…

• Now we have enough data to compute a position for the user’s receiverreceiver

• A position consists of 3 components (XYZ or Lat, Long, Height) which will allows a user to position themselves on the Earth

• pseudorange ( ) is observed by the receiver

• broadcast ephemeris contains the satellite coordinates

SRPR

p(XS, YS, ZS) and the satellite clock offset (δtS) at the instant of satellite transmission

• signal propagation is modelled ( )

• Therefore, to determine the position of a receiver, ranges to at least four satellites are required in order to solve for the four

SRATMΔ

least four satellites are required in order to solve for the four unknowns:

• Coordinates (XYZ) for user’s location and receiver clock


( )offset (δτR) at the instant of signal reception

What are the errors in GNSS

• Errors in satellite navigation can be di id d i 2 b d i

O

C

True SV PosCalc SV Posdivided in to 2 broad categories:– Temporal – those that change with

time

I

T

– Spatial – those that change with location

• Furthermore errors can relate to:

M

Main Errors

Satellite orbit error (O)

• Furthermore errors can relate to:– The satellites

– The radio signal in space

we need to remove this

Satellite clocks (C)

Atmospheric effects

Signal delay due ionosphere (I)

– The receiver on the ground

Signal delay due ionosphere (I)

Signal delay due troposphere (T)

Signal reflections at user receiver (M)


Errors in user equipment

Increasing Accuracy

• GPS & GLONASS were primarily designed for navigation and timing

• Survey and Offshore community requires a higher level of accuracy

I d b hi d th h l ti iti i i DGPS• Increased accuracy can be achieved through relative positioning using DGPS (or DGLONASS) or Precise Point Positioning

• Relative positioning or Precise Point Positioning allows for the correction or reduction of GNSS error sources that contaminate a stand-alone GNSS positioningpositioning


Differential GNSS (DGNSS)

• Requires a number of precisely located reference stations where the t t h t llit i l l t d b i k dmeasurement error to each satellite is calculated by comparing known and

measured range

Errors remain similar for other GNSS users within several hundred kilometres of• Errors remain similar for other GNSS users within several hundred kilometres of reference station

• Error information is delivered to the user via satellite or terrestrial radio• Error information is delivered to the user via satellite or terrestrial radio broadcast

• Robustness is improved by using data from multiple reference stations andRobustness is improved by using data from multiple reference stations and multiple broadcasts

• As the distance between the user and reference station increases the accuracyAs the distance between the user and reference station increases the accuracy decreases, nominal accuracy is 1m within 1000Km and <3m within 2000Km of a station


DGPS Overview

R2R3

R1 Ref

R2 Ref R3 Ref

R1R3

ReferenceStation

R1 R2 R3R1 R2

GPSReceiver

CorrectionProcessor


High Accuracy DGNSS

• Accuracy improvements to the standard DGNSS solutions have been made through the following:through the following:

– More precise correction information using measurements approaching carrier phase accuracy

– Improved troposphere modelling– Removal of Ionosphere effects– Inclusion of satellite orbit corrections leading to reduced spatial de-correlationg p

• Other techniques include real time kinematic (RTK) systems:Other techniques include real time kinematic (RTK) systems:– Double differencing– Centimetre accuracy– Limited range due to transmission technique (e.g. UHF) and error de-correlation – RTK raw data or correction information lead to high-bandwidth requirements and

prevent operation over satellite links


Principles of Precise Point Positioning

• Apply calculated SV clock error correction to broadcast ephemeriscorrection to broadcast ephemeris value

• Apply satellite orbit corrections to Zpp y sate te o b t co ect o s tobroadcast orbit position

• Iono error is calculated using dual-

DzY

erroneous SV Position

Dx

frequency mobile GPS hardware

• Tropo delays minimised using model l id l i ti t d t

SV Position

plus residual error is estimated as part of the calculation process

• Measurement noise and multipath• Measurement noise and multipath minimised using carrier phase observable


PPP Mathematical Approaches

• DGPS or DGNSS typically uses Least Square mathematical technique for deriving positionderiving position

• For PPP the following 2 approaches are used:

K l Filt A h• Kalman-Filter Approach– use iono-free observable– filter over time to resolve carrier phase integer ambiguities– filter also used to resolve other residual errors (e.g. Tropo)– model to account for user dynamics

• Non Kalman-Filter Approach– uses iono-free observable– epoch-epoch calculation (no dynamic model required)epoch epoch calculation (no dynamic model required)– carrier phase integer ambiguities are estimated


PPP Convergence

• With Kalman-Filter approach convergence of the PPP solution isconvergence of the PPP solution is variable

• Convergence linked to change in l ti t llit trelative satellite geometry

– more observations and measurements help with estimation of parameterso pa a ete s

• Certain values are being estimated vary slowly over time (e.g. troposphere)troposphere)

• Convergence time can be reduced by using

– known start position– more accurate a-priori information– more satellites/observations


VERIPOS Overview


A i S iAugmentation Services


VERIPOS Services

• The VERIPOS augmentation services allow the errors in GPS (or other GNSS) to be cancelled or minimised, resulting in a more accurate position


Standard Service PerformanceVERIPOS-Standard (175Km baseline)

• The effect of the increasing baseline can be clearly seen although 2σperformance is well within service specification

Single station 2σ accuracy (0.51m) – baseline 170km (Aberdeen – Wick)

VERIPOS-Standard (670km baseline)

specification

• The main factors contributing to degradation include: non-cancellation of ionosphere and satellite orbit errors

Single station 2σ accuracy (0.99m) – baseline 670km (Aberdeen – Ijmuiden)

VERIPOS-Standard (2300Km baseline)

of ionosphere and satellite orbit errors as well as weakened geometry through reduction in commonthrough reduction in common satellites


Single station 2σ accuracy (1.75m) – baseline 2300km (Aberdeen - Marbella)

VERIPOS Services



Standard+ Performance• The plots represent the horizontal

position error in Veripos Standard p pand Standard+ solutions at a monitor site in Malongo. The reference station was located 1265Km distant at Port Harcourt. The de-correlating effect of the ionosphere, which can be clearly seen in the single frequencyseen in the single-frequency Standard solution, has been fully compensated in the Standard+ solution


VERIPOS Services



VERIPOS Ultra Service

The plots represent the horizontal and

vertical position errors in Veripos

Standard and Ultra solutions at a

it it i Si Th fmonitor site in Singapore. The reference

station used in the Standard solution

was located 322Km distant at Kemaman.


VERIPOS Services



VERIPOS - Standard HF

• available in Mexico and Brazil only

• complements satellite delivery especially where:

– atmospheric conditions can affect satellite

broadcast

– obstructions mask visibility to delivery satellites

– satellite low on horizon in high latitudes

• system is based upon L1 DGPS

• data transmitted on 2 independent frequencies

• operational range is 700km over sea-path

• normal system accuracy is 1-2m (2DRMS/95%)


VERIPOS Services



VERIPOS DGLONASS

GPS Only Solution GPS/GLONASS Solution


N k I fNetwork Infrastructure


VERIPOS System Architecture

broadcast to users

Network

Generate data

products

Uplink to comms

satellites

broadcast to users

Reference Station

Comms networks

Network Control Centre

Raw measurement data – via multiple Service redundant communications links Monitoring

~80 stations distributed

globally


Network Control Centre

• Process and disseminate data • Redundant Control Centres

• Monitoring integrity of comms network

• GNSS integrity monitoring

• Aberdeen NCC is manned 24/7

• Activation and deactivation of users


• Full control of all reference stations • Customer support

• 80 stations worldwide

• Fully redundant dual-frequency GNSS rx• Fully redundant communications networks


• Fully redundant communications networks• 7 x delivery satellites• 24-hour / 365 day global support

Delivery of Augmentation Data to User

• Geo-stationary Communications satellitesWide areas of coverage and highly reliable– Wide areas of coverage and highly reliable

– Redundant broadcast by transmitting on 7 L-Band Satellites

– 6 x High Power and 1 x Low Power L Band Satellites

– Low-power transmissions require directional antennas– Low-power transmissions require directional antennas

– High-Power transmissions require small omni-directional antennas

Hi h F t t i l di b d t• High-Frequency terrestrial radio broadcast– Operational range of 700km over sea

– Independent of third party systems

Di h t i ti f t llit– Diverse characteristics from satellite

– Does not require visibility to transmitters

• Other– Internet using RTCM NTRIP Protocol


O i l I l iOperational Implementation


Navigation and positioning for survey applications

• Seismic acquisition

• Hydrographic survey including route surveys and rig moves

C t ti d i l• Construction and pipe-lay

• Positioning of vessels and structures

• Requires sophisticated quality control processes and software, high levels of accuracy and redundancy to ensure high-quality dataquality data


Navigation and positioning for vessel station-keeping

• Dynamic positioning / mooring monitoring

• Requires simple to operate, robust stable positioning

St bilit f iti i t t th• Stability of position - more important than accuracy

• Other reference systems such as yacoustics, taut-wire means less dependence on satellite navigation –unless working in deep water

• Critical to vessel operation



Source: Managing Dynamically Positioned (DP) Operations - A Practical Approach - An Operator’s PerspectiveSuman Muddusetti & Tracy Harris - Shell International Exploration and Production Inc.

Typical Survey Vessel Configuration

Augmentation Data Link (1)Augmentation Data Link (2)

multiple

cula

tion

SW

(2)

calculated positionraw gnss observations

received augmentation data

position

solutions to

clients

navigation

suite

ted

mob

ile (1

)

PPP Solution

ated

mob

ile (2

)

DGPS Solution

augmentation data received of LP satellite

QC

/C

alW

UPS(1)

inte

gra

Inmarsat terminal UPS(2)

inte

graaugmentation data received of HP satellite

QC

/ C

alcu

latio

n SW

(1)

calculated positionraw gnss observations

multiple

position

solutions to

clients

navigation raw gnss observations

received augmentation data suite


Infrastructure Overview

• Satellite Beams



• Satellite Beams


F fFuture ofSatellite Navigation


Modernisation of Global Positioning System (GPS)

• Present GPS constellation has 31 satellites on orbit

• New signals – L2C, L5 and in the future L1C

• First signal that will be available to civilian users is the L2CL2C

– Tracking coded signal (as opposed to semi-codeless) = high SNR

– Better chipping rate provides better signal tracking

– More robust and accurate signal tracking when multipath present

– Pilot signal which carries no data meaning that receivers can acquire the signal under weak condition (e.g. RF interference or ionosphere scintillation)


© Boeing

GLONASS

• The Russian equivalent of GPS has been undergoing a revival with the launch of new satellites which has made the system a viable alternative to GPSof new satellites which has made the system a viable alternative to GPS

– Presently the system has 20 operational (healthy) satellites

Last 2 satellites launched in March 2009– Last 2 satellites launched in March 2009

– Improvements to geodetic reference frame and ground control segment = better accuracy

– Recently, the Russian government announced extra funding for GLONASS program (67 billion roubles)

• Looking to modernise the constellation

– New generation of satellites

– New civil signal at L3 and the possible change to code division multiple access for the L1 signal


Galileo

• At present the Galileo program is looking to place contracts with companies to implement the system (ground and space segment)

• At present 2 satellites are in orbit – Giove-A and Giove-B

• Advantages of the Galileo signals compared against the current GPS satellites:

– Power of signals will be greater by a factor of 2 = reduction in tracking noise

– Pilot signal (data-less)

Si l d l ti h ill lt i d ti f– Signal modulation schemes will result in reduction of tracking and multipath noise

– Robust coding scheme for nav bits to increase reliability of decoding (useful in presence of interference or with low signal power)


COMPASS

• Chinese launched satellite with SatNav capability named COMPASS (or Beidou 2)

• There is very little information in the public domain about the signal and data structures – no ICD has been published

• The current plan calls for a system to provide global positioning and navigation• The current plan calls for a system to provide global positioning and navigation– Constellation of 35 satellite (5 geostationary)– 10 SV’s to be added over next 2 years and be fully operational by 2015– Three frequency structures that operate at similar frequencies to GPS & Galileo


© Septentrio

Other Systems

• QZSS – Quasi-Zenith Satellite System– Japanese regional system– Designed to work with GPS– 3 SV’s with one satellite always available at an elevation

angle of 60° over Japan– Transmitting on L1-L2-L5 frequencies– First launch anticipated 2009, early 2010p , y

• IRNSS – Indian Regional Navigation Satellite System– Regional coverage for India– Consists of 7 SV’s (3 geostationary & 4 orbiting)– System completion anticipated in 2011/2012System completion anticipated in 2011/2012– Independent system offering 10m accuracy– Transmitting on L5 and S-band


Positioned for Success


S l A i iSolar Activity


Introduction

• Satellite Navigation is a key technology within the offshore oil and gas sectorthe offshore oil and gas sector

• Signals from the GNSS satellites travel through Earth’s atmosphere

– Ionosphere is one part of the atmosphere that affects the GNSS signals

Signals experience propagation delay– Signals experience propagation delay

• Ionosphere is the ionized uppermost part of the atmosphere

– ionization depends primarily on the Sun and its activity

• Regions predominately affected by ionosphericg p y y pactivity are along the geomagnetic equator and polar regions


Solar Cycle

• Solar activity rises and falls over an 11 year cycleyear cycle

– Can be shorter/longer

– Activity correlates with Sunspot Number

• The 11-year cycle is called a Solar Cycle

– Moved from Cycle 23 into Cycle 24

• The increase in solar activity directly affects the ionosphere through which the GNSS i l t t lGNSS signals must travel


Why Use Sunspot Number?• Satellite technology is used today to measure the

solar output from the sun, but…p ,

• Number of visible sunspots has been the historical measure of solar activity and that is why it is still used as a measurey


Sunspot Activity Progression – December 2008


Sunspot Activity Progression – December 2009


Sunspot Activity Progression – March 2010


Other Solar Effects

• During solar maximum, the sun generates a large number of energetic eruptions such aslarge number of energetic eruptions such as solar flares or Coronal Mass Ejections (CMEs)

• Increased fluxes of high-energy particlesIncreased fluxes of high energy particles released

• Disturbances in the solar wind interact with the Earth’s magnetosphere, causing geomagnetic storms

Solar FlareSolar Flare

Solar Eruption


Total Electron Content (TEC)

• The ionospheric delay is proportional to the Total Electron Content (TEC) of the ionosphere along the signal path

• TEC values will vary depending on solar activity & geomagnetic disturbances

• Increase in TEC values results in errors in GNSS range measurements

• Large variations in TEC occur along the geomagnetic equator & polar regions

Mid l tit d b ff t d b ti ti it


• Mid-latitudes can be affected by geomagnetic activity

Effect of Solar Activity on Positioning

• Increase in ionospheric activity which can introduce large errors/biases into

standard single frequency DGPS

– failure in the differential process to cancel the effects of the ionospheric

delay between the reference station and user

– L1 DGPS systems utilise the Klobuchar ionospheric correction modelL1 DGPS systems utilise the Klobuchar ionospheric correction model

transmitted in the GPS navigation message

• in areas of increased ionospheric activity the model does not reflect the true• in areas of increased ionospheric activity the model does not reflect the true

behaviour of the ionosphere as it is only updated periodically and has no

direct measurement of ionospheric delayp y

• Systems using dual frequency can measure the ionospheric delay and apply a correction to the GPS range minimizing this error


Scintillation

• Scintillation is another symptom of ionospheric activity

• Causes rapid fluctuations in the phase and amplitude of the satellite signal as it passes through small-scale irregularities in the ionosphere

• Effects of scintillation appear in different localised regions of the sky and thus only affect certain satellites at a time

T ff t d i i d f i till ti• Two effects occur during periods of scintillation– Amplitude scintillations can lead to periods of reduced signal levels at the GPS

antenna which results in an increase in the measurement noise within the code and carrier tracking loops

– Phase scintillations increase the dynamic stress on the carrier tracking loops which results in additional phase measurement jitter. p j

– Both effects result in an increase in pseudo-range measurement errors and under extreme conditions can lead to complete loss of signal lock

Not onl affects GNSS b t also L band data link


– Not only affects GNSS but also L-band data link

Positioned for Success


VERIPOS – specialists in positioning 31.03 · VERIPOS – specialists in positioning 31.03.2010....

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Transcript of VERIPOS – specialists in positioning 31.03 · VERIPOS – specialists in positioning 31.03.2010....