1. 1 The U.S. Continuously Operating Reference Station (CORS) System Richard Snay NOAA’s National Geodetic Survey Corbin, Virginia June 2008

2. 2 Everyone is able to know where they are and where other things are anytime, anyplace! NOAA’s National Geodetic Survey

3. 3 The Global Positioning System (GPS) Unaugmented GPS enables positioning with accuracies ranging from 1 to 10 meters.

4. 4 The CORS network enables differential GPS positioning with accuracies from 1 to 10 centimeters, or better. Continuously Operating Reference Stations (CORS)

5. 5 Sample CORS Sites

6. 6 CORS Information CORS network contains over 1,300 stations as of June 2008. Growing at rate of about 200 stations per year. Each station collects GPS signals, and NOAA makes these data freely available to the public via the Internet for post- processing applications. More than 200 organizations participate in the CORS program by sponsoring and operating one or more stations.

7. 7 CORS Partners

8. 8 Access to CORS Data In Silver Spring, Maryland (CORS-East) Anonymous File Transfer Protocol (FTP) ftp://cors.ngs.noaa.gov UFCORS - User Friendly CORS http://www.ngs.noaa.gov/UFCORS In Boulder Colorado (CORS-West) Parallel and independent data collection and on-line storage at NOAA’s National Geophysical Data Center Anonymous FTP ftp://wwwest.ngs.noaa.gov

9. 9 CORS Supports Precise Positioning After CORS: Accurate differential GPS positioning with one-person field crew. Before CORS: Accurate differential GPS positioning with multi-person field crew. AAAAAAAAAA

10. 10 Online Positioning User Service (OPUS) Submit data to www.ngs.noaa.gov/OPUS/ Data are processed automatically using NOAA computers & software Corresponding positional coordinates computed with respect to 3 suitable CORS or IGS sites Computed coordinates returned via email (usually in minutes) ● Collect at least 15 minutes of dual-frequency GPS data

11. 11 Positioning Error vs. Duration of the Observing Session

12. 12 CORS enables sub-meter differential positioning with less than a minute of GPS data

13. 13 CORS Enables Users to Determine the Travel Path of a Moving Platform

14. 14 aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa Aircraft Positioning with CORS 3D RMS error = 15 cm + 0.6 ppm

15. 15 CORS for Monitoring Horizontal Crustal Motion Horizontal velocities in the western U.S. relative to the North American Datum of 1983 as derived from geodetic observations.

16. 16 CORS for Monitoring Vertical Crustal Motion Vertical velocities associated with Glacial Isostatic Adjustment

17. 17 Tide Gauges Located Near a CORS Whose Vertical Crustal Velocity Has Been Accurately Determined CORS-calibrated tide gauge data indicate that the rate of sea level rise around North America was 1.8 +/- 0.2 mm/yr during the 1900-1999 time interval

18. 18 CORS for Monitoring Precipitable Water Vapor NOAA’s Earth Systems Research Laboratory uses CORS data to produce nowcasts of precipitable water vapor, once every 30 minutes. Transitioning to operational status starting in 2010. NOAA will seek to install “robust” CORS on Caribbean islands and on oil platforms in the Gulf of Mexico to better anticipate the effect of an active hurricane or tropical storm.

19. 19 CORS for Monitoring Space Weather NOAA’s Space Weather Prediction Center uses CORS data to map the distribution of free electrons in the ionosphere, once every 15 minutes.

20. 20 Just Around the Corner Starting later in 2008, the CORS system will: Provide GPS L2C data Provide GLONASS data Broadcast GNSS data via the Internet in real-time (on an experimental basis). (For selected sites only.) Red dots identify locations of CORS sites that collect both GPS and GLONASS data.

21. 21 CORS ADVANTAGES OVER PASSIVE REFERENCE STATIONS 3-dimensional (Lat., Long., & Ellipsoid Ht. or X, Y, & Z) Eliminates control points reconnaissance (time and money). Eliminates needing people and equipment at a control points. Direct tie to National Spatial Reference System (NSRS). CORS positions are of the highest accuracy. CORS positions and velocities are available in both NAD 83 and ITRF coordinate systems. CORS positions are continuously monitored and will be updated if the site moves.

22. 22 CORS DATA QUALITY

23. 23 Common Question CORS GPS hardware differs from our GPS hardware. Do we have to use only CORS with the same hardware?

24. 24 GPS Data: The Receiver INdependent EXchange (RINEX) Format Data file spans hourly, daily, customized (UFCORS) Data collection rates 1sec, 5sec, 10sec, 15sec, and 30sec Data file life-time hourly: 2 days + today daily: permanently Data are decimated to a 30-second rate after 30 days

25. 25 Common Question The closest CORS to our project area is 50 miles away. How can we use CORS at this distance?

26. 26 TWO TESTS FOR POSITIONING PRECISION Dual Frequency Carrier Phase Data Single Frequency Code Data

27. 27 TEST DESIGN: DUAL FREQUENCY CARRIER PHASE DATA Dual Frequency Geodetic Receivers Post-Processed with a Precise Orbits Pairs of CORS sites forming 11 Baselines Baseline lengths ranging from 26 to 300 km Various Observation Session Duration (1, 2, 4, 6, 8, 12, and 24 hours)

28. 28

29. 29 Positioning error versus distance

30. 30 Positioning Error vs. Duration of the Observing Session Dual-frequency GPS carrier-phase observations

31. 31 Time Scatter Plots (Horizontal)

32. 32 Vertical Precision Using Dual-Frequency GPS Carrier Phase Observations 95% Confidence Level

33. 33 TEST DESIGN: SINGLE-FREQUENCY CODE DATA Positioned 12 points relative to each of seven CORS sites Baseline lengths of 18, 23, 132, 165, 170, 253, and 292 kilometers Observed 1-minute sessions at a 5-second record rate (interpolated CORS data from 30 to 5 seconds) Repeated experiment 4 times over a 2-day period

34. 34 Positioning Accuracy with Code Data red = east-west blue = north-south Observation Time = 1 minute RMS error = 25 cm + 2 ppm

35. 35 COMMENTS Sub-Meter precision is possible with baseline lengths up to 300 kilometers This precision is possible using interpolated CORS data Most CORS data is available within 1-hour of the survey

36. 36 SURVEYING METHODS Static Positioning (code) Static Positioning (carrier phase) Kinematic GPS

37. 37 ACCESSING CORS DATA

38. 38 ACCESSING CORS DATA & METADATA Web address = http://www.ngs.noaa.gov/CORS/ Metadata = data about data CORSAGE = CORS Amiable Geographic Environment

39. 39 CORSAGE CORS Web Page

40. 40 CORSAGE Network Map

41. 41 CORSAGE Regional Map

42. 42

43. 43 METADATA FOR A CORS SITE Coordinates (positions & velocities) Data availability profiles (charts showing times for which data has been collected) Data sheets (descriptive information) Log files (descriptive information) Site photos Time series of positional coordinates Google Maps

44. 44 BILLINGS 1 (BIL1), MONTANA Retrieved from NGS DataBase on 01/10/01 at 09:45:16. ____________________________________________________________________________ | | NAD_83 POSITION (EPOCH 1997.0) | | Transformed from ITRF97 (epoch 1997.0) position in Sep. 2000. | | X = -1372156.022 m latitude = 45 58 16.23742 N | | Y = -4223946.947 m longitude = 107 59 47.29949 W | | Z = 4563650.156 m ellipsoid height = 874.381 m | | | NAD_83 VELOCITY | | Transformed from ITRF97 velocity in Sep. 2000. | | VX = 0.0000 m/yr northward = 0.0000 m/yr | | VY = 0.0000 m/yr eastward = 0.0000 m/yr | | VZ = 0.0000 m/yr upward = 0.0000 m/yr | |____________________________________________________________________________| CORS POSITION & VELOCITY (NAD 83)

45. 45 BILLINGS 1 (BIL1), MONTANA Retrieved from NGS DataBase on 09/25/00 at 12:27:27. ____________________________________________________________________________ | | Antenna Reference Point(ARP): BILLINGS 1 CORS ARP | | ------------------------------------------------- | | PID = AI7658 | | | ITRF97 POSITION (EPOCH 1997.0) | | Computed in Sept., 2000 using 12 days of data. | | X = -1372156.567 m latitude = 45 58 16.26213 N | | Y = -4223945.695 m longitude = 107 59 47.34150 W | | Z = 4563650.195 m ellipsoid height = 873.698 m | | | ITRF97 VELOCITY | | Predicted with HTDP_2.4 in Aug., 2000. | | VX = -0.0184 m/yr northward = -0.0106 m/yr | | VY = -0.0020 m/yr eastward = -0.0169 m/yr | | VZ = -0.0074 m/yr upward = 0.0000 m/yr | | CORS POSITION & VELOCITY (ITRF)

46. 46

47. 47 BIL1 STATION LOG FILE

48. 48 BIL1 STATION LOG FILE

49. 49 CORS SITE PHOTO

50. 50 Position Time Series (long-term)

51. 51 POSITION TIME SERIES (last 60 days)

52. 52 PRIMARY DATA FILES GPS observations at a CORS site Satellite orbits (ephemerides)

53. 53 GPS Data – RINEX Format Data file spans hourly, daily, customized (UFCORS) Data collection rates 1sec, 5sec, 10sec, 15sec, and 30sec Data file life-time hourly: 2 days + today daily: permanently Data are decimated to a 30-second rate after 30 days

54. 54 The RINEX file naming convention is as follows: {SSSS}{DDD}{H}.{YY}{T} where SSSS is the four character site identifier, DDD is the day of year, H is a letter which corresponds to an hour long UTC time block, YY is the year, T is the file type. For daily files, the format would be {SSSS}{DDD}0.{YY}{T}. Hour long UTC time block identifier (H): 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 a b c d e f g h i j k l m n o p q r s t u v w x File type Ending (T) Meteorological m Observation o Navigation n Summary s RINEX FILE NAMING CONVENTION

55. 55

56. 56  NGS is one of the eight International GNSS Service (IGS) Analysis Centers (AC) participating in the production of accurate GPS orbits:  Final Precise (~ 13 days latency)[accuracy < 4 cm]  Rapid (17 hours latency) [accuracy < 5 cm]  Ultra-Rapid (real-time) [accuracy < 10 cm]  Satellite positions in SP3 format are given (once every 15 minutes) in current ITRFxx frame IGS Satellite Ephemerides http://www.ngs.noaa.gov/orbits/

57. 57 Three ways to download CORS Information Web-based User-Friendly CORS (UFCORS) Web-based “Standard” download Anonymous FTP (File Transfer Protocol)

58. 58 UFCORS/STANDARD

59. 59 UFCORS: a Web utility enabling users to Obtain CORS data for an exact time interval Choose a sampling rate for the requested data Specify how the data files should be compressed Receive all associated data & metadata (coordinates, descriptive information, orbits) Receive information as soon as it is posted (GPS data are usually posted within an hour of the time these data are received by NOAA)

60. 60 UFCORS - page 1

61. 61 UFCORS - page 2

62. 62 Standard Download

63. 63 ACCESS TO CORS ARCHIVE VIA FTP To access the CORS public directories, follow the steps below. Type the “ftp” command followed by the Internet address as follows ftp cors.ngs.noaa.gov Respond to the following: Name(cors.ngs.noaa.gov): anonymous Password: user@company.com

64. 64 FTP is a user interface to the File Transfer Protocol. FTP copies files over a network connection between the local ``client'' (user) computer and a remote ``server'' computer. FTP runs on the client computer. The user's system must have access to the INTERNET and support the File Transfer Protocol (FTP). Some useful ftp commands are given below. asciiset ascii transfer type binary set binary transfer type bye terminate ftp session and exit cd change remote working directory dir list contents of remote directory get retrieve one file help print local help information mget retrieve multiple files mput send multiple files prompt force interactive prompting on multiple commands put send one file quit terminate ftp session and exit show display the contents of an ASCII file * Actual commands may vary among operating systems. FILE TRANSFER PROTOCOL (FTP)

65. 65 You will arrive at the ftp command level indicated by the prompt “ftp>”. If you have trouble, type “help” to print local help information or review the section FILE TRANSFER PROTOCOL for help with additional commands. The following sub-directories contain additional files and information - coordNAD83 and ITRF positional information. - graphicsCORS network maps. - itrfFiles on the IERS Terrestrial Reference Frame. - rinexRinex data files. - station_logStation information, antenna specifications, and site contacts. - utilitiesPrograms for manipulating the RINEX files. FTP DIRECTORIES

66. 66 File Transfer Protocol (FTP)

67. 67 File Transfer Protocol (FTP)

68. 68 RINEX files on the CORS file server are stored in a gzip compressed mode. These compressed files will have the extension.gz. An example is given below. ais12330.98o.gz All compressed files and executables should be transferred in binary mode. Text files should be transferred in ascii mode. Before downloading files using the FTP protocol, set the transfer mode by typing “binary” or “ascii” at the ftp prompt. Then use “get” or “mget” to retrieve the files. FILE COMPRESSION FORMAT

69. 69 Several DOS based utility programs are available to manipulate the RINEX data files. Versions also exist for other platforms such as Silicon Graphics (sgi), Sun Microsystems (sun), and Hewlett Packard (hp). decimate.exe Utility program to decimate 5 second data to a user specified rate. gzip386.exe Executable file which contains the utility "gzip.exe". inflate.exe Self-extracting utility program to uncompress files with the ".Z" extension. interpo.exe Utility program to interpolate between data epochs. Please read the documentation for this utility for more details. join24pc.exe Utility program to join two or more hourly RINEX observation or navigation files. SOFTWARE / RINEX UTILITIES

70. 70 INTERPOInterpolate RINEX observational data at faster rates using Neville’s algorithm for polynomial interpolation. interpo -i -o [ -s -e ] -n * Fields between [ ] are optional. interpo -i ais1030a.96o -o ais1030a.out -n 5

71. 71 GLOBAL NAVIGATION SATELLITE SYSTEMS (GNSS) POTENTIAL DEVELOPMENTS (2008 - 2020) US GPS – Second (L2C) and third civil codes US GPS MODERNIZATION - BLOCK III RUSSIAN GLONASS ENHANCEMENTS EUROPEAN UNION - GALILEO CHINESE – COMPASS (BEIDOU) 90+ Satellites More Robust Signal Transmissions Real-Time Unaugmented Accuracy = 1 Meter (or better!)