Signals, Instruments, and Systems W11. Localization Techniques & Traditional and Advanced Instruments for Environmental Monitoring

Transcription

1 Signals, Instruments, and Systems W11 Localization Techniques & Traditional and Advanced Instruments for Environmental Monitoring

2 Outdoor Positioning Systems

3 Selected Outdoor Positioning Techniques GNSS: GPS Differential GPS (dgps) Assisted GPS (agps) Acustic Positioning Systems

4 Global Navigation Satellite System (GNSS) a system of satellites that provide autonomous geo-spatial positioning with global coverage allows small electronic receivers to determine their location to within a few meters using time signals transmitted along a line-of-sight by radio from satellites NAVSTAR-GPS (U.S.) developed in 1973 by the U.S. Department of Defense fully operational in 1994 Originally: 24 satellites Currently: ~31satellites in orbit and healthy GALILEO (Europe) October 2011: first 2 operational satellites launched expected completion in 2019 (27 operational + 3 spare satellites) New feature: Search & Rescue (SAR) GLONASS (Russia) development began in 1976 in the U.S.S.R. 24 satellites by 1995 quickly fell into disrepair back to full constellation since October 2011 only current alternative to GPS BeiDou (China) 1 st generation: 3 satellites offering navigation services to Chinese costumers since nd generation: 35 satellites by 2020 Currently: 10 satellites

5 Global Positioning System

6 Global Positioning System Originally 24 satellites (including three spares) orbiting the earth every 12 hours at a height of km. Monitor station satellites: Monitoring the satellites from a number of widely distributed ground stations Master station analyses all the measurements and transmits the actual position to each of the satellites Satellites user (at 50 bits/s): Time of transmission Ephemeris data: position of the satellite at any point in time Position of other satellites

7 Global Positioning System We now have: From ephemeris: absolute position of satellite From time of transmission + receiver clock: range to satellite = ( ) r t t c receive transmit Solving for the position: 3 unknowns require 3 equations xs1 xs 2 xs 3 y y y S1 2 3, S S, y z S1 z S 2 z S3 S1 S 2 S3 x z r r r Remaining problem: clock accuracy Very expensive and accurate clock on satellite Very cheap and inaccurate clock on receiver Solution: use 4 th satellite and use time error e t_receive as 4 th unknown. Improving accuracy: Using more than 4 satellites ( receive transmit ) r treceive r = t t c e = e c xs1 xs 2 xs3 xs 4 x y S1 y S 2 y S 3 y S 4 y,,, z S1 z S 2 z S 3 z S 4 z rs 1 rs 2 rs 3 rs 4 t Position information from 2 satellites

8 Global Positioning System Error sources: Atmospheric effects (dispersion) Path length through atmosphere Ionosphere Humidity (Troposphere) Multipath Buildings in cities High mountains Canyons Outdated ephemeris data Updated every 2 hours Relativity Time dilation Gravitational frequency shift Eccentricity effects Artificial Selected Availability, artificial time varying error Disabled Unfavorable geometry (GDOP)

9 Differential GPS Position accuracy: typically from a few m to a few tens of cm

10 Assisted GPS Position uses additional network resources to locate and use satellites in poor signal conditions improves start-up performance (time-of-first-fix TTFF) used extensively in GPS-capable cellular phones u-blox, GPS Essentials of Satellite Navigation Compendium, 2009

11 Underwater localization systems Underwater sensing nodes: Autonomous underwater vehicles (AUVs) Glider Drifter Underwater navigation: GPS does not work underwater! Alternative: Use GPS on surface Use surveyed acustic beacon network when submerged

12 Indoor Positioning Systems

13 Selected Indoor Positioning Systems Laser-based indoor GPS Ultrasound (US) + radio frequency (RF) technology Infrared (IR) + RF technology Vision-based overhead system Impulse Radio Ultra Wide Band (IR-UWB)

14 Laser-Based Indoor (KPS) fixed mirrors laser module rotating mirror slave unit master unit mirror 1 mirror 2 mirror 3 photodiodes on slave unit sense pulses fixed mirrors project 3 consecutive planes that scan the work space angles α and β computed from t α, t β and T motor

15 Laser-Based Indoor (KPS) Performance: a few mm in position over 5x5 m arena, Hz, a few degrees in orientation Position available on the robot without com (GPS-like) Line-of-sight method Tested in 2D but extensible in 3D (2 laser base stations)

16 Ultrasound + Radio Technology The cricket (le grillon) Principle: All devices are the same except for a unique ID US emitter + data radio US pulse emission is synced with a radio broadcast Receiving node receives radio and US pulse ( t t ) v = d US RF SOS node1, node2 Position computation: Set of crickets set of ranges = constraints Each node uses all available ranges Each node solves for the position of all crickets

17 Infrared + Radio Technology Principle: belt of IR emitters (LED) and receivers (photodiode) IR LED used as antennas; modulated light (carrier 10.7 MHz) RF chip behind, measured RSSI Measure range & bearing of the next robot; can be coupled with RF channel (e.g ) for heading assessment Can also be used for 20 kbit/s com channel [Pugh et al., IEEE Trans. on Mechatronics, 2009]

18 Infrared + Radio Technology Performance summary: Range: 3.5 m Update frequency 25 Hz with 10 neighboring robots (or 250 Hz with 2) Accuracy range: <7% (MAX) Accuracy bearing: < 9º (RMS) Possible extension in 3D, larger range (but more power) and better bearing accuracy with more photodiodes (e.g. Bergbreiter, PhD UCB 2008, dedicated asic, up to 15 m, 256 photodiodes, single emitter with conic lense)

19 SwisTrack single-camera setup multi-camera setup Tracking objects with one (or more) overhead cameras Active, passive, or no markers Open source software

20 SwisTrack Absolute positions, available outside the robot/sensor Major issues: light, calibration Price per camera: CHF to Accuracy ~ 1 cm (2D) Update rate ~ 20 Hz # agents ~ 100 Area ~ 10 m 2

21 IR-UWB Ubisense fixed external sensors emitter tag formerly known as pulse radio low energy, large bandwidth pulses do not interfere with narrowband signals

22 IR-UWB Ubisense Tracking UWB tags Absolute positions, available outside the robot/sensor Multiple antennas Battery for 5 years Accuracy 15 cm (3D) 6-8 GHz UWB channel Update rate 40 Hz / tag Price: EUR base system # agents ~ EUR 70.- / additional tag Area ~ 1000 m 2

23 Traditional and Advanced Instruments for Environmental Monitoring On-going Mobile Sensor Network Project

24 OpenSense Community-driven, large-scale air pollution measurement in urban environments Mobile sensors (parasitic, uncontrolled mobility) on public transportation vehicles Sensorscope Static wireless sensing and communication infrastructure Permasense

25 Motivation Urban population will double in next decades > 50% of world population already lives in cities rural population expected to stagnate or drop Urban air pollution 2% of all deaths (1.2 million people) 0.6% of burden of disease (DALY) World Urbanization Prospects, U. N Global Health Risks, WHO 2009

26 Motivation Air pollution is highly locationdependent traffic chokepoints urban canyons industrial installations Fine resolution air quality data is needed! Enabling research in: Human exposure Air Pollution Engineering Urban Planning Environmental Justice Public Policy Public service & education enable private users to make informed decisions raising popular awareness

27 Traditional Air Monitoring Systems Sparse networks of ground stations Example: Switzerland s NABEL ( Station locations 16 stations specially selected sites urban with traffic urban residential suburban rural, etc. resolution: high temporal low spatial Ozone concentration Mission: monitor air pollution on national level & gauge impact of environmental policies Public data access:

28 Traditional Air Monitoring Systems Satellite-based remote sensing Examples: Measurements of Pollution in the Troposphere (MOPITT on Terra satellite) Ozone Measurement Instrument (OMI on Aura satellite) Features: daily scans large coverage homogeneous quality sensitive to cloud coverage low resolution

29 Proposed System mobile sensor network parasitic mobility: anchored to existing mobility sources public transport - vehicle energy supply - predictable mobility - single point maintenance low-cost, light-weight chemical sensors (CO, CO 2, NO 2, O 3 ) intelligent integration & control to mitigate demanding constraints

30 Proposed System NANO SENSING SYSTEM From many wireless, mobile, heterogeneous, unreliable raw measurements INFORMATION SYSTEM to reliable, understandable and Web-accessible real-time information TERA mobile nodes static nodes Nabel station Zürich GPRS GPS sensor network control optimization of data acquisition information dissemination

31 Value of Dense Measurements Traditional approach Few stations Low resolution interpolated estimates of pollutant concentrations across massive regions Recent results Massive deployment of stations (150) at street-level (2008/2009 New York City Community Air Quality Survey) Pollutants of interest heavily concentrated along roads with high traffic densities

32 Challenges Global questions: More data, more noise, but also more redundancy Can we produce better quality data? Case study for other environmental phenomena: Radiation, noise, energy Research directions: Wireless Sensor Network control When/Where to sample? What/To whom to transmit? Sensor Node design Sampling System Localization Software & hardware architecture Mechanical integration Community sensing privacy protection trustworthiness of data, relevance of data gathered and information produced Modeling sensor, device and mobility models air quality models privacy, trust & activity models

33 Gas Sampling System Problem: Chemical sensors have very slow dynamics (example: Telaire 6613 CO2 sensor step response <2min) Open sampling Closed sampling sensors directly exposed to environmental measurand Benefits: simple & slim solution continuous sampling Drawbacks: no absolute concentration values noisy signal (sensitive to environment variations: pressure, humidity) Typical response: sensors exposed to measurand inside controlled chamber 3-phase strategy Benefits: absolute measurements noise due to environment filtered Drawbacks: complex & bulky non-continuous sampling Typical response: [Lochmatter 2010] [Trincavelli 2010] Idea: Combine these two approaches to get the benefits of both systems.

34 Gas Sampling System Current deployment open passive active controlled flow [Lochmatter et al. 2010] closed unclean air clean air [Gonzalez-Jimenez et al. 2011] Smart sampling module possibly hybrid single/multi-chamber wind sensing Anemometer [Lochmatter et al. 2010]

35 Localization Robust localization prerequisite for adaptive control exploits commercial state of the art u-blox LEA-6R GPS + dead reckoning (DR) module augmentation with additional sensor modalities (compass, accelerometer, gyro) GPS only GPS + DR

36 On TL bus no 601 Deployment Status Lausanne 1 mobile plus 2 prototype stationary stations Measured parameters NO2, CO (2 sensors), Humidity, Temperature, CO2 (only mobile station), GPS Power Solar panel (stationary stations) Bus power (mobile station) Data Transmission via GPRS to a central NABEL station on Cesar Roux since June 2011 testing mechanical & electronic integration since September 2011 NABEL roadside station necessary for sensor calibration Outlook: 20 new stations to be deployed over the summer (new more modular architecture)

37 Deployment Status Zürich 5 mobile plus 1 static station Measured parameters CO, O3 (2 sensors), Humidity, Temperature, Accelerometer (only mobile station), GPS Communication: GPRS, WLAN On top of Tram NABEL station in Dübendorf 1 st since July additional nodes since April 2012 Originally calibrated O 3 sensor: correct trend, but wrong absolute value. Calibration required.

38 Open Data Access Lausanne Zürich

39 Books Additional Literature Week 11 Weston J. and Titterton D, Strapdown Inertial Navigation, IET, 2005 Siegwart R. and Nourbakhsh I. R., Introduction to Autonomous Mobile Robots, MIT Press, Borenstein J., Everett H. R., and Feng L. Navigating Mobile Robots: Systems and Techniques, A. K. Peters, Ltd., Everett H.R., Sensors for Mobile Robots, Theory and Applications, A. K. Peters, Ltd., u-blox, GPS Essentials of Satellite Navigation Compendium, 2009, available online: