Prof. Ludovico Biagi. Satellite Navigation and Monitoring

Transcription

1 Prof. Ludovico Biagi Satellite Navigation and Monitoring Navigation: trajectories control positions estimations in real time, at high frequency popular applications: low accuracy (10 m) required specific applications require better accuracy Monitoring: positions monitoring in time positions estimations for campaigns and time series analysis typically high accuracy required (10 cm -> 1 mm) GNSS provides navigation and monitoring From geodetic theory to geomatics methods

2 Γεωδαισια: Earth parcelling, Greek agricultural needs The science of measuring and mapping the Earth surface (Helmert (1800) definition): 1. determination of Earth gravity field and its linear functions, 2. determination of (precise) global, regional and local three dimensional positions, 2.a. measurement and modelling of geodynamical phenomena, 2.b. kinematic positioning and navigation.

3 The beginning of Geodesy Eratosthenes ( BC) First measure of the Earth radius ( 1% ε ) Angles by Sun observations directions and distance on Earth surface by camel travel time!

4 Physical geodesy Geoid: an assigned equipotential surface of the Earth gravity potential Geoid undulation (N): the height of the geoid wrt an assigned 'simple' surface (ellipsoid) Geoid undulation knowledge allows the conversion from ellipsoidal (h) to orthometric (H) heights

5 Geoid undulation is known with accuracy of few cm at the global scale

6 Positioning (our main interest) In the past (traditional): observations to the stars, terrestrial angles and distances measurements (topographic surveys) At the present: terrestrial surveys + GNSS observations

7 GNSS (Global Navigation Satellites Systems) Several constellations of artificial satellites around the Earth A receiver observes signal travel times from all the in-view satellites The satellites positions are known from ephemerides The travel times are converted to distances (d=ct) The observations are used to estimate the receiver position

8 Estimation principle 1 distance from 1 satellite

9 2 distances from 2 satellites

10 3 distances from 3 satellites

11 Measurement problems and errors Synchronization of satellites and receiver clocks Atmospheric delays Observation (electronic) noises Integer fixing è Different classes (cost) of receivers and data processing algorithms è Different classes of positioning accuracy

12 The spatial scale Global A constellation allows positioning everywhere at every time on the Earth Regional A constellation allows positioning in limited regions of the Earth

13 The constellations GPS, USA, first project in '60, development started '70 fully operating from 1995 GLONASS, Russia, first project and development in '70 (USSR) economical crisis and partial dismission from '90 to 2000 fully operating from 2011

14 The constellations BEIDOU/Compass, Cina, en.beidou.gov.cn first project in the '80, regional (Asia) coverage from 2011 a second project for a global coverage forseen for 2020 GALILEO, European Community, first project in the '90, slowered from 2000 to experimental satellites in orbit

15 Real time GNSS autonomous navigation 5-10 m accurate Instrumental cost:

16 Applications people, cars, boats, trains, planes,...: guidance and control Applications Industrial: route optimization, real time overview,.. Public security: critical transports, car/trucks theft,... Assistive technologies Recreational: hiking, sailing,...

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18 Relative kinematic and fast static positioning A reference and a rover GPS stations observe range differences: the rover position can be estimated with accuracies in the range 2-5 cm 1-2 m. Instrumental cost: (for the rover)

19 Accurate navigation applications Instrumental cost: Accuracies better than 1 m Applications cars, boats, trains, planes guidance and control in critical areas (construction sites, railways stations, airports,...) assistive technologies others: sport performance monitoring,...

20 Real Time kinematic: cadastral and cartographic surveying Instrumental cost: Required accuracies: 2-3 cm

21 Post-processed static surveys: geodetic monitoring Instrumental cost: for each receiver required accuracies better than few centimeters Local networks for structures / landslides /... control Regional permanent networks for local geodynamics Global permanent networks for global geodynamics

22 SLOMOVE ( experiment for landslide monitoring

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24 Permanent Networks A network of GPS stations continuously operating and observing range differences: accuracies up to some mm. Instrumental cost: for each station

25 Post-processed time series: movements... A four year time series for a station...

26 Global network for the determination of the Earth shape and its movements in time Estimated velocities of ITRF permanent stations

27 Survey type Notes Accuracy According to the receiver From 10 m Absolute kinematic types and new signals to 1 m in real time availability Absolute static in real time Relative kinematic in real time or post processing Static relative and post processing Still a research topic According to the receiver type and the distance between reference and rover By very long surveys 10 cm From 1 m to 2-5 cm Better than 1 cm

28 Needed tools Reference systems and frames Statistics for navigation and monitoring GNSS Satellites systems Signal propagation Observations equations Point positioning Relative positioning Geodetic post-processing Networks adjustment Real Time Kinematic

29 Course structure Lectures: 38 Hours All the above topics! Exercises: 12 Hours Laboratory: 12 Hours

30 Exercises Reference frames transformations Coordinates transformations Kalman filtering Leveling network adjustment Integer (cycle slip / ambiguities) fixing Geodetic network simulation and adjustment Analysis of coordinates time series Laboratories (3 slots of 4 hours) Static and RTK Survey Data post processing Network adjustment

31 Slides and teaching material (course webpage under the courses link) Time schedule and practical details See monthly timetable (course webpage) Exam written reports on exercises/laboratory + oral examination Professor: Ludovico Biagi, ludovico.biagi@polimi.it, office V2.9, 031/ Consulting hours: Tuesday, after the lecture