Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

1998: A YEAR OF INNOVATIONIN (THE)

Richard B. LangleyGeodetic Research LaboratoryUniversity of New Brunswick

Invited presentation at the Association of New Brunswick Land SurveyorsAnnual General Meeting, Fredericton, N.B., 23 January 1999

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

GPS Accuracy: Lies, Damned Lies, and StatisticsF. van Diggelen, Ashtech, Inc.

January

¥ Popular accuracy measuresÐ r.m.s. (vertical)Ð circular error probableÐ r.m.s. (horizontal)Ð R95 (horizontal 95%)Ð 2 d.r.m.s.Ð r.m.s. (3D)Ð spherical error probable

¥ Common misconceptionsÐ r.m.s. precisely equals 1 sigmaÐ 2 d.r.m.s. means Òtwo-dimensional r.m.s.ÓÐ 2 d.r.m.s. is exactly equivalent to a 95% probability levelÐ r.m.s. is perfectly comparable with a 68% probability levelÐ the error distribution really is Gaussian

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

January, contÕd.

Dimensions Accuracymeasure

Probability Typical usage(dimensions)

1 r.m.s. 68 vertical

2 CEP 50 horizontal

2 r.m.s. 63-68 horizontal

2 R95 95 horizontal

2 2 d.r.m.s. 95-98 horizontal

3 r.m.s. 61-68 3D

3 SEP 50 3D

Accuracy Measures

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

January, contÕd.0.

0

0.2

0.3

0.4

0.5

0.7

0.8

0.9

1.0

1.2

1.3

1.4 m

MeasuredTheoretical

Measured andtheoretical DGPShorizontal errorsfrom 2 million datapoints

CEP = 42 cmr.m.s. = 52 cmR95 = 91 cm2 d.r.m.s. = 104 cm

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

The UTM Grid SystemR.B. Langley, UNB

February

¥ Coordinates and Projections

¥ MercatorÕs WorldÐ Adopting the ellipsoid

¥ A Universal ProjectionÐ UTM

Ð The grid¥ British National Grid¥ 500 km squares → 100 km squares → x,y coordinates

¥ Tower of London: TQ 336805 or 33.6 km E, 80.5 km N of SW corner of TQ

Ð Military grid reference¥ UNB Gillin Hall ref. point: (WGS 84) 682,725 m E; 5,091,225 m N, zone 19T

= MGRS 19TFL8272591225

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

February, contÕd.

0°0' 0"

84°

80°

0mN andincreasingnorthward

10,000,000mNand increasingsouthward

500,

000m

E

~68

0,00

0mE

~32

0,00

0mE

Exa

ct s

cale

Exa

ct s

cale

Scale increases

Scale decreases

69°W

72°W

66°W

Sca

le fa

ctor

= 0

.999

6

UTM zone 19 extends from 86°to 72° west longitude. As withall UTM zones, the scale factoris 0.9996 on the central meridianand true (unity) on two slightlycurved lines approximately 180km to either side. The shape ofthe zone has been exaggeratedfor clarity.

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

Pseudolites: Enhancing GPS with Ground-based Transmitters

S. Cobb and M. O’Connor, Integrinautics Corp.

March

¥ What is a Pseudolite?

¥ Primary Pseudolite UsesÐ Code-based ranging augmentation

Ð Code-phase differential ranging

Ð Carrier-phase differential ranging¥ Ambiguity resolution

Ð Indoor pseudolites

¥ The Near-far ProblemÐ Signal pulsing

Ð P-code use

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

March, contÕd.

L 1Filter

MicrowaveVCO

LoopFilter

PLLDivider

C/A CodeGenerator

ReferenceTCXO

Mixer Antenna

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

Integrity Beacon Landing System

March, contÕd.

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

Cellular Telephone Positioning Using GPS Time Synchronization

R. Klukas, Cell-Loc, Inc. and G. Lachapelle and M. Fattouche, U. of C.

April

¥ E-911 Cell Phone PositioningÐ FCC requires horizontal cell phone position to 125 m d.r.m.s. by

2001

¥ TOA EstimationÐ A system to horizontally position cellular telephones using

analogue AMPS (Advanced Mobile Phone Service)

¥ System DescriptionÐ Time tagging with GPSÐ Full correlation with MUSIC (Multiple Signal Identification and

Classification)Ð Position estimation

¥ Field TestsÐ Simulations used approximately 40 sites within a Calgary cellular

network; field tests with 4 sites

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

April, contÕd.

45 MHz 455 kHzBaseband

signal

Lockdetect

Digitalsignal

processor

Basebandsignal

GPSpulse

PLLchip

50 10 km

4000

3000

2000

1000

0

–1000

Nor

thin

g (m

eter

s)

–1000 0 1000 2000 3000 4000

WinwoodSheraton

Renfrew

Franklin

(a) Easting (meters)

4000

3000

2000

1000

0

–1000

Nor

thin

g (m

eter

s)

–1000 0 1000 2000 3000 4000

WinwoodSheraton

Renfrew

Franklin

(b) Easting (meters)

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

The Effect of Weather Fronts on GPS MeasurementsT. Gregorius and G. Blewitt, Univ. of Newcastle upon Tyne

May

¥ Atmospheric Delay

¥ The Positioning EffectÐ Height error = 3 x tropo delay error

¥ What is a Weather Front?

¥ Delay Estimation Models

¥ Fronts and GPS PrecisionÐ Improving repeatability

Ð Vertical velocity

Ð The horizontal factor

¥ Remedies and PossibilitiesÐ Radiosondes, satellites (GPS/MET), data editing

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

May, contÕd.

0.5 - 1º

WARMAIR

COLDAIR

COLDAIR

War

m F

ront

al Z

oneC

old Frontal Zone

~500 km ~100 km ~100 km ~800 km

tropopause

ground surface

direction of motion

~ 1 km

RA

IN &

CL

OU

D R A I

N & C

L O

U D

drydry

~ 1

0 km

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

May, contÕd.

2.32

2.34

2.36

2.38

2.40

2.42

2.44

Time past 00:00 on 28 November 1996 (hours)

Tot

al tr

opos

pher

ic z

enith

del

ay (

m)

GPS estimates Front model: r.m.s. = 6.1 mm Standard model: r.m.s. = 11.6 mm

Cold surface frontWarm surface front

0 12 24 36 48 60 72

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

June

The NSTB: A Stepping Stone to WAASAndrew Hanson, Stanford University

¥ WAAS in PracticeÐ Reference stations

Ð Error models

¥ The Stanford Connection

¥ WAAS MetricsÐ Accuracy

Ð Integrity

Ð Availability

¥ Flight Testing

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

June, contÕd.

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

A Primer on GPS AntennasR.B. Langley, UNB

July

¥ Fields and Waves

¥ Antenna CharacteristicsÐ Axial ratio

Ð Impedance

Ð Standing Wave Ratio

Ð Bandwidth

Ð Gain pattern

Ð Ground planes

Ð Phase-centre variation

¥ Low Noise Preamp

¥ Transmission Lines

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

July, contÕd.

x

y

z

t

x

y

At a fixed point in space, theelectric field vector of a right-hand circularly polarized waverotates clockwise as seen fromthe wave’s source.

The electric and magnetic fields aretransverse to the direction ofpropagation, and the fields aremutually perpendicular.

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

July, contÕd.

Microstrip patch

Quadrifilar helix

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

RTK GPSR.B. Langley, UNB

September

¥ A Fix on Accuracy

¥ Carrier-phase PositioningÐ Post-processed

Ð Real time

Ð Correction message formats: RTCM SC-104

¥ RTK System Architecture

¥ The Data LinkÐ Propagation distances; path loss; viability

¥ RTK SolutionsÐ OTF

Ð GLONASS

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

September, contÕd.

Standalone

Static Stop and Go

Pseudokinematic Rapid Static

Kinematic

Post-processed Real-time

Differential

Surveying

Carrier Phase(RTK)

Pseudorange(DGPS)

Differential Standalone

Navigation

GPS Positioning

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

September, contÕd.

Reference station Rover

RTK Hardware

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

GPS MATLAB Toolbox ReviewA.K. Tetewsky and A. Soltz, Draper Laboratory

October

¥ What is MATLAB?

¥ The ToolboxesÐ GNSS Toolbox, Orion Dynamics and Control Corp.

Ð Constellation Toolbox, Constell, Inc.

Ð SatNav Toolbox, GPSoft LLC

Ð GPS Signal Simulator Toolbox, Navsys Corp.

¥ Simulation ChallengesÐ Scenario simulation; GPS measurement selection, navigation

accuracy, algorithm development; fault monitoring; readingrecorded data; total receiver simulation; presentation graphics

¥ Experiences

¥ Suggestions

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

October, contÕd.

Toolbox Overview

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

October, contÕd.

GPS Measurement Selection, Navigation Accuracy,and Algorithm Development

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

The GPS End-of-Week RolloverR.B. Langley, UNB

November

¥ GPS TimeÐ GPS Time = UTC + 13 seconds + δÐ Z Count

Ð Time of week

¥ The RolloverÐ Similar to Y2K problems

Ð On 21/22 August 1999, GPS Week 1023 is followed by Week 0

¥ Receiver EffectsÐ Currently marketed receivers shouldnÕt be affected

Ð For some, a firmware upgrade is available

Ð Noncompliant: wrong date, wrong satellite coordinates, refuse tocompute positions, long startup times, fail to lock onto satellites

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

November, contÕd.

0 1 2 403,199 0 1 2 0 1 2 0 1 2 0

X1 epochs

0 1.5 sec 3.0 sec 7 days

P epoch

14 days

Week 0 Week 1 Week 1023 Week 0

403,199 403,199 403,199

19.6 years

Week 2

P epoch P epoch P epochP epoch

The inherent, fundamental GPS timing unit is the 1.5-second repetition periodof the P-code’s X1 subcode. The P-code is reset every week or 403,200 X1epochs. The GPS week number count is reset every 1024 weeks orapproximately 19.6 years.

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

November, contÕd.

GPS Week Cycle Start of Week 0 End of Week 1023

1 January 6, 1980(44244)

August 21, 1999(51411)

2 August 22, 1999(51412)

April 6, 2019(58579)

3 April 7, 2019(58580)

November 20, 2038(65747)

Start and end dates of the first three GPS week cycles.

(The numbers in parentheses are the corresponding modified Julian dates.)

Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering, University of New Brunswick

1999