GPS 101 For Land Surveyors with GNSS Updates!!!!!

Transcription

1 GPS 101 For Land Surveyors with GNSS Updates!!!!!!!!!! New$York$State%Association! Of"Professional+Land+Surveyors! Annual&Conference!2014 Presented by Joseph Paiva - CEO January 2014

2 GPS 101 For Land Surveyors with GNSS Updates NYSAPLS Conference January 2014 Joseph V.R. Paiva CEO - Objectives! What the technology is! How it works! How to apply the technology! Better advantages and limitations! Learn improvements in GPS/GNSS on the horizon 2014 J.V.R. Paiva & GeoLearn, LLC 1

3 1 What GPS (and GNSS) is and not What GPS Is! Designed as navigation system! Military applications! All-weather! World-wide! 100 m horizontal positioning (initially)! Provides information on space and time 2014 J.V.R. Paiva & GeoLearn, LLC 2

4 GPS Was Not Designed To! tell someone else where the GPS device is! position with cm or mm accuracy! be coupled with GPS receivers used at other locations! be used in surveying 2014 J.V.R. Paiva & GeoLearn, LLC 3

5 The System Each satellite in posigrade orbit Two orbits per day Each satellite about 1700 kg 7.25 m 2 of solar panel each Arrives 4 min earlier each day Space Segment 24 satellites in constellation (nominally) 6 planes with 55 rotation each plane has 4 satellites Very high orbit 20,183 km (12,545 miles) for accuracy, survivability and coverage 2014 J.V.R. Paiva & GeoLearn, LLC 4

6 Delta II Launch Status! ftp://tycho.usno.navy.mil/pub/gps/gpsb2.txt 2014 J.V.R. Paiva & GeoLearn, LLC 5

7 Currently! 31 satellites (Mid January 2014)! 0 BLOCK I: SVN 1 11, launched Feb 78 Oct 85! 0 BLOCK II: SVN 13 21, launched Feb 89 Oct 90! 8 BLOCK IIA: SVN 23 38, launched Nov 90 Nov 97! 12 BLOCK IIR: SVN 42 61, launched Jan 97 Nov 04! 7 BLOCK IIRM: SVN 48 57, launched Sep 06 Aug 09! 4 BLOCK IIF: SVN 62 66, launched May 10 May 13 Other details! Design life of Block II/IIA 7.3 years; each has four atomic clocks: two Cesium (Cs) and two Rubidium (Rb)! Design life of Block IIR 7.8 years; each has three Rb atomic clocks.! BLOCK IIR-M transmit a second civil signal (L2C) on the L2 frequency! SV 49 broadcasts L5 (experimental)! IIF broadcasts L J.V.R. Paiva & GeoLearn, LLC 6

8 Why GNSS?! Stands for Global Navigation and Satellite Systems! GLONASS, Soviet built, now Russian system has been in existence since 1982 (1 st satellite) and is fully operational beginning 1995, but with some outages! Galileo has launched first two experimental satellites (GIOVE-A and GIOVE-B) in 2006 and 2008 by European Space Agency (ESA) GLONASS! 24 Satellites when fully operational (24 operational currently, spares and 1 in flight test phase)! All satellites use same code but different frequencies for each! Two antipodal satellites share same frequency! More resistant to interference! Spotty reliability record 2014 J.V.R. Paiva & GeoLearn, LLC 7

9 GLONASS! 21 sats in orbit (mid-jan 11)! 0 sats in commissioning phase! 5 sats in maintenance! 1 in decommissioning phase! Satellite orbit time: 11 h 15 m! Global'naya Navigatsionnaya Sputnikovaya Sistema [ : ] GLONASS Benefits! More satellites is always better! However different datum and time standard! Need one satellite just to make the transfer! So need a minimum of two to get any real improvements! Huge benefit in areas with limited sky view 2014 J.V.R. Paiva & GeoLearn, LLC 8

10 Coverage GLONASS Satellite Global Navigation Satellite System 2014 J.V.R. Paiva & GeoLearn, LLC 9

11 ! Similar to GPS Galileo! Different services; some will be for a fee! Galileo In-Orbit Validation Element (Giove-A and Giove-B first test satellites), now four more IOV satellites much closer to operational satellites! 30 satellites including 3 in-orbit spares when operational! Scheduled fully operational date? Galileo 2014 J.V.R. Paiva & GeoLearn, LLC 10

12 Other GNSS! Chinese Regional Satellite Navigation System Compass (Beidou)! Regional; 2-dimensional! 2-way comms required! Beidou 2 in planning! 30 MEO and 5 GEO satellites! Quasi-Zenith Satellite System (Japan)! Japan/Asia coverage (augmentation)! First QZSS launches 2009; 3 sats total Even more GNSS! IRNSS: Indian Regional Navigational Satellite System to be completed Seven satellites placed in Geostationary orbit 2014 J.V.R. Paiva & GeoLearn, LLC 11

13 General 2 way the systems & techniques work Satellite Signal Structure Carrier L1 L2 Frequency MHz MHz Wavelength 19 cm 24 cm Code Modulation C/A-code - P(Y)-code P(Y)-code NAVDATA NAVDATA C/A - Coarse Acquisition Code P - Precise Code (Y-Code when encrypted) NAVDATA - Satellite health, satellite clock corrections, and ephemeris parameters J.V.R. Paiva & GeoLearn, LLC 12

14 Satellite Signal Structure Code C/A P Chip Rate 1.023Mbit/s 10.23Mbit/s Repeats every 0.001s 7 days (37 wk) Contains information on Time, Position, Atmosphere & Satellite ID and Ephemeris Satellite Signal Structure Carrier C/A-code P-code NAVDATA Received Signal 2014 J.V.R. Paiva & GeoLearn, LLC 13

15 IIR-M Carrier L1 L2 Frequency MHz MHz Wavelength 19 cm 24 cm Code Modulation C/A-code C (M & L) P(Y)-code P(Y)-code NAVDATA NAVDATA C/A - Coarse Acquisition Code C Civil Code P - Precise Code (Y-Code when encrypted) NAVDATA - Satellite health, satellite clock corrections, and ephemeris parameters. II-F Carrier L1 L2 L5 Frequency MHz MHz MHz Wavelength 19 cm 24 cm 25 cm Code C/A-code C (M & L) Civil Code Modulation P(Y)-code P(Y)-code NAVDATA NAVDATA C/A - Coarse Acquisition Code C Civil Code P - Precise Code (Y-Code when encrypted) NAVDATA - Satellite health, satellite clock corrections, and ephemeris parameters J.V.R. Paiva & GeoLearn, LLC 14

16 ECEF Coordinate System +Z ECEF X = m Y = m Z = m Z X Y -Y +X Segments Ground Space User Your location is: 37 o N 122 o W Global Positioning System 2014 J.V.R. Paiva & GeoLearn, LLC 15

17 Control segment! 5 Monitor Stations (Hawaii, Kwajalein, Ascension Island, Diego Garcia, Colorado Springs)! 3 Ground Antennas, (Ascension Island, Diego Garcia, Kwajalein)! Master Control Station (MCS) at Schriever AFB in Colorado. Code Ranges Pseudorange = Δ Time C Travel Time 2014 J.V.R. Paiva & GeoLearn, LLC 16

18 GPS by Trilateration Distance D = Speed of Light x Time D Calculating Position 11,000 miles Intersection of two spheres is a circle 12,000 miles 2014 J.V.R. Paiva & GeoLearn, LLC 17

19 Edge view of circle of intersection What is Measured? GPS Observables Code Ranges Carrier Phases (1) Autonomous (2) Differential Position Relative Position 2014 J.V.R. Paiva & GeoLearn, LLC 18

20 GPS Modernization! Current satellites (Blocks IIA, IIR and IIR-M)! Modernized II-F, III! Modernization adds L2C: L2 CM (civil moderate) and L2 CL (civil long)! Remember the original configuration was C/A on L1 only and P on L1 and L2 Block IIR-M 2014 J.V.R. Paiva & GeoLearn, LLC 19

21 Modernization Continued! L2C chip rate is Kbps! CM 10,230 chips at 20 ms rep rate! CL 767, 250 chips at 1.5 s rep rate! Also added with modernization L5! Potential interference at L2! L5 added mainly for safety-of-life issues! Higher power GPS III system! Authorized by Congress in 2000! New ground stations and new satellites with additional nav signals for both civilian and military users! L2 (L2C) has moderate (10,320 bits 20 ms) and long (767,250 bits codes! CM has 25 bit/s nave message! CL has approximately 24 db greater correlation protection (i.e. ~250 times stronger) that L1 C/A! All on current L2 frequency! Accuracy improvements for all users 2014 J.V.R. Paiva & GeoLearn, LLC 20

22 Fascinating note! M-code block III satellites beginning with 2014 launches will have an additional antenna with spot (several 100 km diameter) in addition to the full Earth broadcast! This M-code is not available to civilians Safety of Life (L5)! On the aeronautical radionavigation services band, freq: MHz)! About twice as powerful signal than L1 or L2 (transmitted power)! Wider bandwidth to yield 10 times processing gain 2014 J.V.R. Paiva & GeoLearn, LLC 21

23 L1C! On the current L1 frequency! First satellite with this signal will be launched 2014! Better tracking features! Enables greater civil interoperability with Galileo L1 Retroreflectors!! NASA has request that Block III space vehicles carry laser retroreflectors! Why? Enables tracking independent of radio signals. This allows easier breakdown to separate ephemeris errors from clock errors 2014 J.V.R. Paiva & GeoLearn, LLC 22

24 Satellites by block NAVSTAR Global Positioning System satellites Block I Block II Block IIA Block IIR Block IIRM Block IIF Block IIIA Satellites by block Block Launched Operational Not usable Retired LaunchFailures Block I Block II Block IIA Block IIR Block IIRM Block IIF Total J.V.R. Paiva & GeoLearn, LLC 23

25 Orbital slots Slot Plane A B C D E F (35) (27) (49) Parentheses indicate satellite out of commission GPS III Late News! The Lockheed Martin prototype of the nextgeneration GPS satellite, the GPS III, recently proved it was backward-compatible with the existing GPS satellite constellation in orbit! GPS Block IIIA or GPS III is the next generation. Lockheed Martin will produce the first eight satellites. The USAF plans to purchase up to 32 such satellites! First satellite in the series is GPS IIIA J.V.R. Paiva & GeoLearn, LLC 24

26 Techniques 3 for surveying & mapping Carrier Phases 2014 J.V.R. Paiva & GeoLearn, LLC 25

27 The Integer Ambiguity Receiver measures partial wavelength when it first locks on partial, circularly polarized phase is read like a clock N λ$ Range Receiver counts successive cycles after this λ φ $ Receiver does not know whole number of wavelengths (behind that first partial one) between it and SV Carrier Phase Results Measured Reduced Baseline or Vector (cm precision) Az = 212 o HDist = m Δ Ht = m OR Δ X = m Δ Y = m$ Δ Z = m 2014 J.V.R. Paiva & GeoLearn, LLC 26

28 Reference Ellipsoid a = semi-major axis b = semi-minor axis (a b) Flattening f = a H φ latitude λ longitude H ellipsoidal height WGS-84 Ellipsoid a = m b = m 1/f = a b λ" φ" GPS Mapping & Surveying Techniques! Differential GPS (DGPS)! Real-Time Differential GPS (DGPS)! Static Surveying (CP)! Kinematic Surveying (CP)! Real-Time Kinematic Surveying (CP)! Post-processed mapping! Route location, setting out utilities! Control! Precise topographic mapping! Setting out 2014 J.V.R. Paiva & GeoLearn, LLC 27

29 Static Surveying Static Survey Benefits! Long baselines! Highest accuracy! Only way to bring in survey-level control! But do not do single shots! Know what an independent observation is 2014 J.V.R. Paiva & GeoLearn, LLC 28

30 Kinematic Example Static Initialization Kinematic Example 2014 J.V.R. Paiva & GeoLearn, LLC 29

31 Kinematic Example 10:00 10:30 Loss of Lock! Fixed Initialization w/ Static Baseline Kinematic Example 2014 J.V.R. Paiva & GeoLearn, LLC 30

32 Topographic Survey Overview of RTK 2014 J.V.R. Paiva & GeoLearn, LLC 31

33 Integer Resolution 19 CM Real-Time Kinematic Surveying 2014 J.V.R. Paiva & GeoLearn, LLC 32

34 For Survey Integrity! Post-process RTK whenever possible! Your own! Private services! Public services! Differential! RTK! RTN real time network Base Stations 2014 J.V.R. Paiva & GeoLearn, LLC 33

35 Differential Corrections Differential GPS Benefits! Higher positioning accuracy than autonomous! Ideal for reconnaissance! Also many natural resource surveys! Adequate for many mapping and GIS applications! Pre-surveying 2014 J.V.R. Paiva & GeoLearn, LLC 34

36 Real-Time DGPS Real Time DGPS Benefits! Real-time, so can navigate to a point with greater certainty! Good for corner location, corner search! Preliminary surveys! Searching for utilities 2014 J.V.R. Paiva & GeoLearn, LLC 35

37 WAAS! One of many Wide Area Differential GPS systems! Implemented by/for FAA to improve safety of air navigation! Broadcasts RTCA format message from geosynchronous satellites! 1-2 m positioning feasible! Similar systems: MSAS (Japan); EGNOS (Europe); Gagan (India) WAAS satellite locations Satellite Name & Details Galaxy 15 Anik F1R Inmarsat-4 F3 NMEA / PRN NMEA #48 / PRN #135 NMEA #51 / PRN #138 NMEA # 46 / PRN #133 Location 133 W W 98 W 2014 J.V.R. Paiva & GeoLearn, LLC 36

38 Satellite elev & azimuth! For elevation angles, go to Example: In Utica, approx. altitude to Anik is 31 (azimuth 223) ; for Galaxy: 15 (az 247 ); for Inmarsat-4-f3: 35 (az 212 ) WAAS coverage J.V.R. Paiva & GeoLearn, LLC 37

39 SBAS! Can improve system accuracy, reliability, and availability! Integration of corrections into positioning! Corrections may include additional error information: clock drift, ephemeris, ionospheric delay, etc.! Some may provide additional SV information to be integrated in the calculation process A short list! WAAS United States FAA! EGNOS European Space Agency! WAGE US DoD for military and authorized receivers only! MSAS Japan's Ministry of Land, Infrastructure and Transport (JCAB)! StarFire John Deere! OmniSTAR DGPS System Fugro! The Quasi-Zenith Satellite System (QZSS) Japan! GPS and GEO Augmented Navigation (GAGAN) India 2014 J.V.R. Paiva & GeoLearn, LLC 38

40 Overall similarities! SBAS designs and implementations may vary widely! Term refers to any satellite-based augmentation system! Under the International Civil Aviation Organization (ICAO) rules a SBAS must transmit a specific message format and frequency which matches the design of the United States' Wide Area Augmentation System Channels! Channels used to mean actual number of satellite signals receivable! GLONASS and Galileo require different front ends (radios)! However, digital signal processing can be done with similar channels and are switchable! SBAS generally receive GPS-like signals at front-end 2014 J.V.R. Paiva & GeoLearn, LLC 39

41 Understanding 4 errors and biases General Error Sources! Systematic errors called biases! Can originate at satellites! Can originate at receiver! Can be from signal propagation 2014 J.V.R. Paiva & GeoLearn, LLC 40

42 ! Ephemeris! Selective Availability! Clock errors Satellite Errors! Rx clock! Multipath! Antenna phase center! Rx measurement noise Receiver Errors 2014 J.V.R. Paiva & GeoLearn, LLC 41

43 ! Ionosphere! Troposphere Propagation Errors In Addition! Constellation geometry! The elevation vs. altitude problem! Miscellaneous errors 2014 J.V.R. Paiva & GeoLearn, LLC 42

44 Multipath Reflections off buildings, trees, ground, water, fences, etc. Direct Signal Reflected Signal Satellite Geometry Poor satellite geometry (high DOP) Good satellite geometry (low DOP) 2014 J.V.R. Paiva & GeoLearn, LLC 43

45 Geometry Considerations! PDOP, HDOP and VDOP should be looked at periodically! Before surveying look at values! But remember shading can change what you expected so look at it while surveying too! Vertical positioning is always a poor intersection vertical accuracy worse than horiz by multiplier of 1.5 to 2 Dilution of Precision! DOP (generic term)! PDOP (position)! HDOP (horizontal position)! VDOP (vertical position)! TDOP (time)! GDOP (time and position) 2014 J.V.R. Paiva & GeoLearn, LLC 44

46 Elevation vs. Altitude! GPS altitude is height above WGS-84 ellipsoid! Elevations are height above mean sea level (orthometric height)! Sea level, unlike the ellipsoid is a non-smooth undulating surface! In US geoid separation can be up to 100 m Ellipsoid, Geoid, Topography Mass Excess Local Topography Ellipsoid Mass Deficiency Geoid 2014 J.V.R. Paiva & GeoLearn, LLC 45

47 Coordinate Systems! GPS measures in WGS-84 Cartesian! Surveyor could be using SPCs, UTMs, other systems! Converting from native GPS system to surveyor s system can be fraught with errors (and mistakes) Error and Bias Review! Systematic errors called biases! Can originate at satellites! Can originate at receiver! Can be from signal propagation 2014 J.V.R. Paiva & GeoLearn, LLC 46

48 Ephemeris Errors! Satellite position from eph good to about 1.6 m, but has been observed to be as large as 20 m! Differencing gets rid of this error (mostly) especially with short baselines Baseline Error Estimation ESVpos Baseline Ebaseline = SVrange Where E baseline is the error in the surveyed GPS baseline E SVpos is the ephemeris error for satellite position Baseline is the length of the surveyed baseline, and SVrange is the range to the satellite (~20,000 km) 2014 J.V.R. Paiva & GeoLearn, LLC 47

49 Alternatives to Broadcast Ephemeris! International GNSS Service (IGS) post-mission precise orbits! Ultrarapid half orbit (3 hr)! Rapid orbit (17 hr)! Final orbit (13 days)! 5-10 cm SV position accuracy but vary in satellite clock accuracy! Also JPL, NRCan and others Ionospheric Effects - Short Baseline * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * < 10 KM 2014 J.V.R. Paiva & GeoLearn, LLC 48

50 GPS for Elevations or Heights! Geoid models! More granularity as time goes by! Associates geoid undulation value with grid points on Earth s surface! System can automatic do two-way interpolation and add correction to ellipsoidal height Caveats for GPS-derived Elevations! Develop check system! Do not bet the farm on it! Use your good judgment! Best to blend other methods if GPS will be used! Don t forget that geoid model or not, that vertical component delivered by GPS is the weakest 2014 J.V.R. Paiva & GeoLearn, LLC 49

51 Altitude Reference Ellipsoid: A smooth, mathematically defined model of the earth's surface. Geoid: A surface of equal gravitational pull (equipotential) best fitting the average sea surface over the whole globe. MSLE HAE Earth's Surface Ellipsoid Geoid Geometric Relationships Topographic Surface H e h N Geoid H = Ellipsoid Height h = Orthometric Height N = Geoid Undulation Ellipsoid H = h + N e = Deflection of the vertical 2014 J.V.R. Paiva & GeoLearn, LLC 50

52 Coordinate Systems! GPS measures in WGS-84 Cartesian! Surveyor could be using SPCs, UTMs, other systems! Converting from native GPS system to surveyor s system can be fraught with errors (and mistakes) Calibration/Localization/ Transformation! Calibration performs one function: It converts GPS (WGS-84) measurements into local coordinates 2014 J.V.R. Paiva & GeoLearn, LLC 51

53 The Calibration! In the order they are applied:! Datum Transformation! Plane Projection. (Possibly derived)! Horizontal (Plane) Adjustment! Rotation! Scale! Translation! Vertical (Height) Adjustment Importance of Calibration! We would like to survey in local coordinates! We would like to stake out in local coordinates! We also need to account for: Survey network noise A height adjustment 2014 J.V.R. Paiva & GeoLearn, LLC 52

54 Datum Transformation Three Parameter Datum Transformation (Translation in X, Y, Z) Seven Parameter Datum Transformation adds 3 Rotations (Rotation X, Y, Z) Plus Scaling Y Z Y Z X X Field operations 6 and applications 2014 J.V.R. Paiva & GeoLearn, LLC 53

55 GPS Things to Worry About / 1! Base station location (ha!)! Antenna height! Accessories, accessories, accessories! Effect of geoid Optical plummet Antenna pole bubble Antenna cables Antenna pole straightness Tripod stability Tribrach bubble Antenna pole height! Phase and range measurement errors! Atmospheric attenuation of signal! Phase center errors Don t Forget! How to traverse and triangulate! Redundant baselines as you bring in control! Avoid wagon wheel surveying! Think about how to monitor RTK performance! RTK doesn t solve any and every survey problem 2014 J.V.R. Paiva & GeoLearn, LLC 54

56 Bringing in Control Static Observation RTK Area No Bringing in Control 2 Static Observation 1 RTK Area 3 YES 2014 J.V.R. Paiva & GeoLearn, LLC 55

57 ! Network design GPS continued! Meaningless measurements because they are NOT independent! Most flagrant errors caused by not understanding that GPS does NOT measure rover s position it resolves VECTOR between base and rover GPS mistakes (& good technique) Project Area 0 miles J.V.R. Paiva & GeoLearn, LLC 56

58 GPS checking! Use an independently adjusted network or using carefully thought-out procedures set up your own! There should be a couple of short to medium-sized lines within easy reach to do quick checks of RTK and static obs.! Observe the network (should be a braced quadrilateral optimally) periodically Suggested GPS Test Network 1 2 C A B 2014 J.V.R. Paiva & GeoLearn, LLC 57

59 ! Receiver! Antenna! Ground plane! Cables! RTK-related issues! Tribrachs! Tripods! Other accessories Components Networked RTK! Many states, regional agencies and private companies setting these up! Fee or no fee! Quality needs to be examined (and monitored) great project for local associations! When done properly is a huge benefit to user accuracy, time saving, cost, huge productivity plusses 2014 J.V.R. Paiva & GeoLearn, LLC 58

60 Peripherals Just as important as the main instrumentation Chain is only as strong as its weakest link Don t forget anything! Be constantly evaluating Most important accessory: humans Consider 2014 J.V.R. Paiva & GeoLearn, LLC 59

61 Peripherals (or accessories) Tribrachs (with and without O.P.s) Tripods Cables Antenna poles Q & A 2014 J.V.R. Paiva & GeoLearn, LLC 60

62 About&the&seminar&presenter& Joseph V.R. Paiva, PhD, PS, PE Joseph V.R. Paiva is CEO of GeoLearn, LLC ( which is launching an online professional education business for the geospatial industry in early Joe started this business with his partner Bob Morris, whose most recent global industry position was President of Leica Mapping. Previously, Dr. Paiva was CTO of SADAR 3D and COO of Gatewing NV, a Belgian unmanned airborne systems company. Prior engagements in consulting were in the field of geomatics and general business, particularly to international developers, manufacturers and distributors of instrumentation and other geomatics tools. Dr. Paiva and Mr. Morris continue to be involved in consultancy through a separate partnership called GeoSpatial Associates, LLC will continue this consultancy. Joe s career includes: managing director of Spatial Data Research, Inc., a GIS data collection, compilation and software development company; various assignments at Trimble Navigation Ltd. including senior scientist and technical advisor for Land Survey research & development, VP of the Land Survey group, and director of business development for the Engineering and Construction Division; vice president and a founder of Sokkia Technology, Inc., guiding development of GPS- and software-based products for surveying, mapping, measurement and positioning. He has also held senior technical management positions in The Lietz Co. and Sokkia Co. Ltd. Prior to that was assistant professor of civil engineering at the University of Missouri-Columbia, and a partner in a surveying/civil engineering consulting firm. He has continued his interest in teaching by serving as an adjunct instructor for online course development and teaching at the Missouri University of Science and Technology. His key contributions in the development field are: design of software flow for the SDR2, SDR20 series and SDR33 Electronic Field Books and software interface for the Trimble TTS500 total station. He is a registered Professional Engineer and Professional Land Surveyor, has served as ACSM representative to the Accrediting Board for Engineering and Technology (ABET), serving as a program evaluator, team chair, and commissioner and has more than 30 years experience working in civil engineering, surveying and mapping. He writes for POB, GeoDataPoint and The Empire State Surveyor magazines and has been a past contributor of columns to Civil Engineering News. Joe has also been a consultant to the Geomatics Industry Association of America, later reorganized under the Association of Equipment Manufacturers (AEM) as the Geospatial Industry Group, Joe has organized and presented workshops and authored and edited articles for the technical press in this role. Joe can be contacted at joepaiva@geo-learn.com January 2014