ENGRG Introduction to GIS

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1 ENGRG Introduction to GIS Michael Piasecki December 01, 2017 Lecture 12: GPS Systems

2 Lecture 7: Introduction To GPS November 27, 2017 ENGRG Intro to GIS 2

3 November 27, 2017 ENGRG Intro to GIS 3

4 Introduction to GPS 1. Basic of GPS GPS history and application Segments of GPS GPS Signals 2. How does GPS work? 3. GPS Errors GPS Error Sources Measurements of GPS error Error Correction November 27, 2017 ENGRG Intro to GIS 4

5 Global Positioning System (GPS) Satellite navigational system that provides accurate coordinates worldwide. Satellites and computers to locate positions Controlled by the Department of Defense, US Air Force Usable by anyone, anytime, for free systems: U.S. NAVSTAR (Navigation Satellite Timing And Ranging), the official DoD name for GPS Russia GLONASS (Global Navigation Satellite System) EU Galileo Global Navigation Satellite System (build by EU and ESA) Chinese Compass System November 27, 2017 ENGRG Intro to GIS 5

History: The UAVSTAR GPS 1973 1977: Proof of concept 1976: US Congress approved development 1978: First satellites launched Assets belongs to US Government Stewardship via US Dept of Defense First

6 History: The UAVSTAR GPS : Proof of concept 1976: US Congress approved development 1978: First satellites launched Assets belongs to US Government Stewardship via US Dept of Defense First real operational test for GPS technology was the Gulf War in 1990 June 26, 1993, the 24th satellite into orbit Full constellation achieved in 1995 Selective Availability turned off by President Clinton in May 1 st, 2000 But also authorization of GPS III modernization, starting 2017 Currently 31 satellites in orbit of various ages and type Ultimately 62 are planned for November 27, 2017 ENGRG Intro to GIS 6

7 Non US Positioning Systems GLONASS Global Navigation Satellite System Russian Federation Ministry of Defense Has deteriorated over time; not complete Being restored to full availability in partership with India GALILEO EU + 6 non EU countries: China, India, Israel, Morocco, Saudi Arabia and Ukraine First 4 satellites in orbit by 09/12/2012 from Kazakhstan 30 satellite (27 + 3) Full operation expected in 2019 Pentagon: unnecessary; potential security threat during wartime November 27, 2017 ENGRG Intro to GIS 7

8 Non US Positioning systems Baidou: China s regional system that China proposed to expand into a global system named COMPASS. QZSS: Japanese proposed regional system, adding better coverage to the Japanese islands; Indian regional Satellite System (IRNSS): India s proposed regional system. November 27, 2017 ENGRG Intro to GIS 8

9 GPS Three Segments Space Segment:the constellation of satellites Control Segment: Monitors system performance and adjusts satellites (USAF) Users Segment: users with receivers November 27, 2017 ENGRG Intro to GIS 9

10 GPS Three Segments November 27, 2017 ENGRG Intro to GIS 10

11 Space Segment November 27, 2017 ENGRG Intro to GIS 11

12 Space Segment System consists of 24 satellites in the operational mode; As of 2014, 32 actively satellites; Altitude: 20,200 Km with periods of 12 hr. Current Satellites: Block IIF $25,000,000; 2000 KG Solar powered, backup batteries, rocket boosters Hydrogen Maser Atomic Clocks November 27, 2017 ENGRG Intro to GIS 12

13 Hydrogen Master Clock These clocks lose one second every 2,739,000 million years The GPS satellites are nothing more than a set of clocks in the sky November 27, 2017 ENGRG Intro to GIS 13

14 GPS Orbits November 27, 2017 ENGRG Intro to GIS 14

15 Control Segment Schriever November 27, 2017 ENGRG Intro to GIS 15

Consolidated Space Operations Center: CSOC Master Control Station is located at the Consolidated Space Operations Center (CSOC) at Schriever Air Force Station near Colorado Springs

16 Consolidated Space Operations Center: CSOC Master Control Station is located at the Consolidated Space Operations Center (CSOC) at Schriever Air Force Station near Colorado Springs Track the satellites for orbit and clock determination Time synchronization Upload the Navigation Message Manage DOA (dead on arrival) November 27, 2017 ENGRG Intro to GIS 16

secure system Civilians need unrestricted access In

17 User Segment: Military and Civilian GPS on the Battlefield Conflicting Interests Military needs a secure system Civilians need unrestricted access In Rainforest, Brazil November 27, 2017 ENGRG Intro to GIS 17

18 Satellite Signals (2+3) 2 Microwave Carrier Codes Atomic clocks on satellites generate a pure sine wave Fundamental frequency, f o MHz L1 and L2 carrier waves f 1 = f o x 154 = MHz (19 cm) f 2 = f o x 120 = MHz (24 cm) Other Carrier Codes L3 ( MHZ) used by Nuclear Detonation Detection System L4 ( Mhz) Being studied for additional ionospheric correction. L5 ( Mhz): proposed for civilian safety of life (SoL) signal. November 27, 2017 ENGRG Intro to GIS 18

19 Satellite Signals (2+3) 3 Pseudorandom codes (Binary code) Navigation message must be modified, or modulated, to contain information C/A Code Coarse/Acquisition Code available for civilian use on L1 (3 to 300 meters) P Code Precise/Private Code on L1 and L2 used by the military (30 centimeters to 30 meters) November 27, 2017 ENGRG Intro to GIS 19

20 Satellite Signals Navigation Message Modulates on L1 and L2 50 Hz Entire message is 1500 bits; 30 sec Includes information such as: Predicted satellite ephemeris data. Predicted satellite clock correction model coefficients. GPS system status information The GPS system ionospheric model Almanac: used to identify where satellites will be and when (the bus schedule ) November 27, 2017 ENGRG Intro to GIS 20

21 Satellite Signals C/A (Course/Acquisition) Code Modulates on L1 carrier MHz Pseudo Random Noise (PRN) code Entire message 1023 bits transmitted at Mbit/s => hence it repeats every millisecond Wavelength of 300 m Hence total sequence is about 300km long Unique C/A from each satellite Highly orthogonal to each other => code division multiple access (CDMA) recognition of multiple satellites on same frequency November 27, 2017 ENGRG Intro to GIS 21

22 Satellite Signals P (Precise or Private) Code Much more complicated Modulates on L1 and L MHz PRN (pseudo random noise) code Wavelength of 30 m Anti Spoofing mode includes an encrypted W code to create the Y code Classified decryption November 27, 2017 ENGRG Intro to GIS 22

23 GPS Signals November 27, 2017 ENGRG Intro to GIS 23

24 GPS Signals: Navigation Message and also its health status orbital information November 27, 2017 ENGRG Intro to GIS 24

25 GPS: Satellite Ranging Simple: Distance = Speed * Time Measuring distance from satellite(s) by Knowing the location of the satellite(s), and Measuring travel time of radio signals between the target and the satellites). Pseudo range: range with error November 27, 2017 ENGRG Intro to GIS 25

26 GPS: How does it work? The GPS receiver and a satellite produce the same signal at a given time. Good clocks important Receiver measures the delay between generating a time signal and receiving the same time from the satellite. Simple! t Time Difference 1 t 0 Range distance = c * (t 1 -t 0 ) November 27, 2017 ENGRG Intro to GIS 26

27 GPS Receivers Standard Positioning Service Usually configured with quartz clocks (less accurate than atomic) Single frequency (L1) C/A code ranging Civilian uses, typical receivers Precise Positioning Service Dual frequency (L1 and L2) P code P code contains higher resolution info Two frequency channels enables atmospheric corrections Commonly used for national interests Signals from 4 Satellites are required November 27, 2017 ENGRG Intro to GIS 27

28 4 Satellites are required November 27, 2017 ENGRG Intro to GIS 28

29 Clock Offset The three spheres will not intersect 5 sec (wrong) 7 sec (wrong) 9 sec (wrong) November 27, 2017 ENGRG Intro to GIS 29

30 Why Four Satellites? Satellites carry highly accurate atomic (Cesium and Rubidium) clocks onboard. GPS receivers have much less accurate quartz clocks. With positional fixes from 3 satellites, a timing error of only 1/1,000,000 of a second between the satellite and the receiver equals a positional error of 300 meters or more on the ground! November 27, 2017 ENGRG Intro to GIS 30

31 GPS: How does it work? More Satellites equals Better Resolution November 27, 2017 ENGRG Intro to GIS 31

32 GPS Accuracy GPS measurements are not totally accurate Depending on your GPS receiver, you can achieve different levels of accuracy. More satellites used, more sophisticated processing = greater accuracy More accurate receivers are more expensive GPS Receiver Accuracy Price Range Recreational 5-30 m $100-$3000 Mapping 1-5 m $10000-$50000 Geodetic < 50 cm >$50000 November 27, 2017 ENGRG Intro to GIS 32

33 Basic Positioning: Today 6-10 m C/A Code on L1 Before May 2000: m November 27, 2017 ENGRG Intro to GIS 33

Basic Positioning: Tomorrow Better resistance to interference C/A Code on L1 L2C Code on L2 New Code on L5 1-5 m Eliminates need for costly DGPS in many non safety applications

34 Basic Positioning: Tomorrow Better resistance to interference C/A Code on L1 L2C Code on L2 New Code on L5 1-5 m Eliminates need for costly DGPS in many non safety applications Differential Global Positioning System (up to 10cm accuracy) US operates one via Coast Guard; ground based system correct satellite estimates. November 27, 2017 ENGRG Intro to GIS 34

35 Systematic Sources of GPS Error Satellite clock error, ephemeris error Atmospheric Refraction Ionospheric Refraction Tropospheric Refraction Multipath Signal Obstruction Selective Availability Receiver clock error Human Error observatory.org/gps/gps_accuracy.html November 27, 2017 ENGRG Intro to GIS 35

36 GPS Errors Sources of User Equivalent Range Errors (UERE) Ionospheric effects ± 5 meter Ephemeris errors ± 2.5 meter Satellite clock errors ± 2 meter Multipath distortion ± 1 meter Tropospheric effects ± 0.5 meter Numerical errors ± 1 meter November 27, 2017 ENGRG Intro to GIS 36

37 Atmospheric Effects Signal speed varies: Refraction Signal bounced by ionosphere: Reflection Time of signal propagation affected: Error November 27, 2017 ENGRG Intro to GIS 37

38 Multi Path Error Occurs when GPS signals are reflected and the receiver detects two signal instead of one at different times. This causes confusion in some low end GPS units, but is generally easy to correct. High end receivers compensate for multipath Mapping and Survey units use a hardware solution: a special semidirectional antenna November 27, 2017 ENGRG Intro to GIS 38

39 Multipath November 27, 2017 ENGRG Intro to GIS 39

40 Signal Obstruction When something blocks the GPS signal Areas of Great Elevation Differences Canyons Mountain Obstruction Urban Environments Indoors November 27, 2017 ENGRG Intro to GIS 40

41 Obstruction November 27, 2017 ENGRG Intro to GIS 41

42 Using Off Set Positioning Used to compensate for obstruction Uses compass bearing and an offset distance to calculate the position of the obstructed target. Trimble Pathfinder Pro XR unit has this capability November 27, 2017 ENGRG Intro to GIS 42

43 Selective Availability (S/A) Government introduces artificial errors to reduce GPS position accuracy Discourages hostile forces from using GPS Largest source of error How does it work? Off setting satellite clocks. Introduction of ephemeris error by the Space Command control center Only the military has the correction information. November 27, 2017 ENGRG Intro to GIS 43

44 S/A Error Will it be turned on in case of War? 100 meters 100 meters 40 meters 20 meters November 27, 2017 ENGRG Intro to GIS 44

45 S/A Status In 1996 it was announced that S/A would be phased out and turned off within 4 years On May 1st 2000, S/A was turned off, but the military can still turn it on when necessary In 2006 S/A was turned off permanently In 2007 US gov announced the production of future generation GPS satellites, GPS III, without the S/A to be ever switched on again November 27, 2017 ENGRG Intro to GIS 45

46 Measuring GPS Error: DOP DOP = Dilution of Precision DOP is a measurement of error DOP Values usually range from 1 to 6 Low values are best November 27, 2017 ENGRG Intro to GIS 46

47 Dilution of Precision (DOP) It is best to have satellites spaced evenly around the receiver with one satellite overhead and one low on the horizon. High DOP values are found when satellites are clustered together. November 27, 2017 ENGRG Intro to GIS 47

48 Measurements of DOP PDOP (Position Dilution of Precision): the most commonly used, measures DOP in 3D. HDOP (Horizontal Dilution of Precision): measures DOP in 2D (horizontal only). VDOP (Vertical Dilution of Precision): measures DOP in the vertical only. TDOP (Time Dilution of Precision): measures DOP with respect to time. November 27, 2017 ENGRG Intro to GIS 48

49 Error Correction Differential correction Uses a base station Post processing Real time Wide Area Augmentation System, WAAS Uses reference stations to calculate corrections (<3m accurate) Even better than DGPS November 27, 2017 ENGRG Intro to GIS 49

50 Differential GPS (DGPS) Obtain GPS position at a site with known position (base station) Derive difference between actual and GPS positions Post processing vs. Real Time processing November 27, 2017 ENGRG Intro to GIS 50

51 DGPS November 27, 2017 ENGRG Intro to GIS 51

52 Differential GPS DGPS Apply appropriate correction to nearby rover positions Real time beacon receiver (USCG) with rover Real time with radio receiver with rover Post processing: With correction files, let the computer apply correction in the office Base station can be Yours (2nd GPS in field, dedicated station in office ) Government (USCG, etc.) Commercial November 27, 2017 ENGRG Intro to GIS 52

DGPS: USCG Radio Beacon The Coast Guard s maritime DGPS service provides 10 meter (2 drms) navigation accuracy, integrity alarms for GPS and DGPS out-oftolerance conditions within 10 seconds of

53 DGPS: USCG Radio Beacon The Coast Guard s maritime DGPS service provides 10 meter (2 drms) navigation accuracy, integrity alarms for GPS and DGPS out-oftolerance conditions within 10 seconds of detection, availability of 99.7% per month. Typically, the positional error of a DGPS position is 1 to 3 meters. November 27, 2017 ENGRG Intro to GIS 53

54 Wide Area Augmentation System, WAAS Developed by Federal Aviation Administration (FAA) for aircraft navigation Available to everyone in North America 25 ground stations across US monitor GPS errors (2 master stations in coast) Corrections sent to geosynchronous satellites, or satellite with a fixed position over the equator WAAS equipped GPS receiver uses corrections from satellites to improve accuracy 95% accuracy typically on order of 3 meters Not expensive (do not require additional receiver) November 27, 2017 ENGRG Intro to GIS 54

55 Wide Area Augmentation System Confirmed accuracy performance of 1 2 meters horizontal and 2 3 meters vertical throughout the majority of the continental U.S. and portions of Alaska. November 27, 2017 ENGRG Intro to GIS 55

56 Wide Area Augmentation System November 27, 2017 ENGRG Intro to GIS 56

57 Project Presentation Recall: Date: December 8 th Ignite Format; that is 21 slides at 20secs each = 7minutes Presentations on Friday 12 th : Lec 10 * (7 + 3 for change and Q&A) = 100mins (1hr 40mins) Lab 5 * (7 + 3 for change and Q&A) = 50mins That means if we start at 10:00 sharp we should be out by 12:30am => presenters be there by 9:40 so we can load PPTs Lastly: presentation order => November 27, 2017 ENGRG Intro to GIS 57

58 Project Presentation Order Random lottery! Friday 12/08 Lec Friday 12/08 Lab Sossa Awolou 1 Abu Ghazaleh Camelia Taveras Fausto 2 Oei Angela Loo Erica 3 Yu Wendy Bhuiyan Nazmul 4 Cham David Frias Jay 5 Pena Adrian Rappa Valentina 6 Hincapie Cesar Fey Jeremy 7 Ramsay Vivian Singh Harjinder 8 BREAK November 27, 2017 ENGRG Intro to GIS 58

Resection. We can measure direction in the real world! Lecture 10: Position Determination. Resection Example: Isola, Slovenia. Professor Keith Clarke

Resection. We can measure direction in the real world! Lecture 10: Position Determination. Resection Example: Isola, Slovenia. Professor Keith Clarke Geography 12: Maps and Spatial Reasoning Lecture 10: Position Determination We can measure direction in the real world! Professor Keith Clarke Resection Resection Example: Isola, Slovenia Back azimuth