Mr.Samniang SuttaraB.Eng. (Civil), M.Eng. (Survey)

Topcon Instruments (Thailand) Co.,Ltd.

E-Mail : gps@topcon.co.th

Tel. 08-1821-1297

Satellite Surveying

Global Navigation Satellite System

What is GNSS ?

ADVANTAGEADVANTAGE

- Accuracy from meter to millimeter- Everywhere- Everytime- One system coordination- Many user segment- No expenses

- Accuracy from meter to millimeter- Everywhere- Everytime- One system coordination- Many user segment- No expenses

• NAVSTAR GPS (Global Positioning System) By USA.

• GLONASS (GLObal NAvigation Satellite System or GLObalnaya NAvigatsionnaya Sputnikovaya Sistema) By Russian.

• GALILEO By The European Space Agency (ESA)

• COMPASS By China.

GNSS Provider?

• Launched: 1978• 24 Satellite Constellation

• Launched: 1982• Current Satellite Constellation: 18• Planned Constellation: 24

USA

Russia

E.U.• Test Satellite Launched: Dec. 2005• Current Satellite Constellation: 2• Planned Constellation: 30 Satellites

Constellation TechnologyConstellation Technology

Constellation TechnologyConstellation Technology

COMPASSCOMPASS

1. GPS Satellites

Satellites

2. GLONASS Satellites

Satellites

3. GALILEO Satellites 4. COMPASS Satellites

Number of Satellites 24 (24) 24 (27)

Launch Vehicle Proton k/DM-2 Delta 2-

7925

Satellite Per Launch 3 1

Orbital Planes 3 6

Orbit Inclination 64.8

55

Orbit Altitude 19100 km 20200 km

Orbital Period 11 h 15 min 11 h 58 min

Ephemerides Pos/Vel/Acc Keplerian

Reference Ellipsoid PZ90 WGS84

Carrier Freq. L1 1602.5625 - 1615.5 MHz

1575.42 MHz

Carrier Freq. L2 1246.4375 – 1256.5 MHz

1227.60 MHz

C/A-code(L1) 0.511 MHz 1.023

MHz

P-code(L1,L2) 5.110 MHZ 10.23

MHz

GLONASSGLONASS GPS

• 24 Satellites, 3 active spares

• 6 Orbital planes inclined at 55 degrees

• 1 orbit = 11 hours 58 min.

• 20,200 kilometers height

The The GPS Space Segment Space Segment

The GLONASS Space The GLONASS Space SegmentSegment

• 24 Satellites, 3 active spares

• 3 Orbital planes inclined at 64.8

degrees

• 1 orbit = 11 hours 15 min.

• 19,100 kilometers height

GNSS Comparison

All the satellite signals are received

GPSGPSGLONASSGLONASSGALILEOGALILEO

Increasing satellites of number

GPSGPS

GLONASSGLONASS

GALILEOGALILEO

1. Space Segment

Constellations of satellites.

2. Control Segment

Monitor and control stations for tracking and managing satellites.

3. User Segment

Receivers designed to receive, decode and process satellite data.

GPS Components

Control Control SegmentSegment

Space Space SegmentSegment

User User SegmentSegment

Bi-directional Information

Information in one direction

System OverviewSystem Overview

KWAJALEIN

DIEGOGARCIA

ASCENSION

HAWAII

COLORADO SPRINGS (MCS)

Control Stations

The User Segment

The User Segment

The User Segment

Receiver Types

1. Navigation receiverDistance measured with C/A code

Receiver Types

2. Geodetic or Surveying receiver

Absolute Positioning (Point Positioning)Absolute Positioning (Point Positioning)

Relative Positioning (Baselines-Vector)Relative Positioning (Baselines-Vector)

SOLUTION:SOLUTION: DX, DY, DZ DX, DY, DZ

SOLUTION:SOLUTION: X,Y,ZX,Y,Z

Positioning

How Does GPS Work?

GPS Receiver calculates position by one of GPS Receiver calculates position by one of the following methods:the following methods:

a) Pseudo-Range Measurementsa) Pseudo-Range MeasurementsLess AccuracyLess Accuracy

With codesWith codes-C/A code (300 m.)C/A code (300 m.)-P code (30 m.)

Distance are measured in GPS Positioning

a) Pseudo-Range Measurements

Receiver

RangeRange

Range

Ran

ge

Range = (Time Taken for signal to reach Receiver from Satellite) x (Speed of light = 3*108 m/s)

How Does GPS Work?

GPS Receiver calculates position by one of GPS Receiver calculates position by one of the following methods:the following methods:

b) Carrier-Phase Measurementsb) Carrier-Phase MeasurementsMore AccuracyMore Accuracy

By signal carriers phase-L1 carriers (19 cm.)-L2 carriers (24 cm.)

Distance are measured in GPS Positioning

b) Carrier-Phase Measurements

Receiver

RangeRange

Range

Ran

ge

Range = (Whole no. of Wavelengths from Satellite to Receiver) + (Fractional Part of Wavelength)

1. Satellite - Orbit = 5 m.

- Clock = 1 m.

2. Signal Propagation – Ionospheric (Dual freq) = cm.- dm.

- Troposheric = dm.

- Multipath = 5 m.

3. Receiver - Observation noise = 1-10 m.

- Hardware delay = m.

- Antenna phase center = mm.- cm.

Errors in GPS Survey

After that...a Geoid (Helmert, 1884)

Geoid

Ellipsoid

Helmert Geoid model accounts forDeflection of the vertical

Earth History

GEOID (MSL)

ELLIPSOID

TERRAIN

Geoid • Ocean surface free of disturbances (Helmert, 1884).• Equipotential Surface of the Earth’s Gravity Field.

EllipsoidGeometric representation of the Earth Surface.

Earth Surface Representation

GEOID (MSL)

ELLIPSOID

TERRAIN

h= Ellipsoidal height

H= Orthometric height

N = Geoid Undulation

N=h-H

Heights

h N

H

How EGM works ?-EGM96-EGM2008

Orthometric Heights

X (Greenwich Meridian)

Z (CIO)

Normal to Ellipsoid

North

East

Up

Station

Y

ECEF Coordinate System (X,Y,Z)Topocentric System (N,E,U)Geographic Coordinates (b,l,h)

Coordinate System

• Static Survey

• Fast or Rapid Static Survey

• Kinematic Survey

• Real Time Kinematic (RTK) Survey

- Single base

- Network RTK (VRS, MAC, FKP)

Field Methods Survey

GPS Only

GPS & GLONASS

Mission Planning

• VDOP =standard deviation in vertical

• HDOP =standard deviation in horizontal position(2D)

• PDOP =standard deviation in position(3D)

• TDOP =standard deviation in Time

• GDOP =standard deviation in position(3D) and time

Dilution of Precision (DOP)

(Geometrical)

Poor Poor GeometryGeometry

Dilution Of Precision (DOP)

DOP = σ /σ0

σ = positioning accuracy

σ0 = observation(pseudorange) accuracy

Good Good GeometryGeometry

Static Survey

Static GPS+ Survey

Process data

Fast Static

The RTK Concept

• Radio Technical Commission for Maritime Services (More than twice as long of a message format)

• Compact Measurement Record

RTCM vs. CMR

VRS Network

VRS Network

VRS Network