Continuously Operating Reference Stations

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Continuously Operating Reference Stations
Presented by Miranda Chin NOAAs National
Geodetic Survey In cooperation
with CGSIC Montpelier, Vermont August 12, 2003
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Continuously Operating Reference Stations (CORS)

• What?
• Why?
• OPUS-Online Positioning User Service

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Continuously Operating Reference Stations
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(No Transcript)
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Regional CORS Coverage
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Local CORS
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CORS OVERVIEW

• National CORS Network
• Cooperative CORS Network
• Combo CORS

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National CORS Network

• Network contained over 400 stations as of July
  2003
• Growing at rate of 6 sites per month
• Provides code range (C/A, P1, P2) and carrier
  phase observations (L1, L2)
• Provides meteorological data at some sites
• Designed to meet requirements for
• High Accuracy Static Kinematic Positioning
• Geophysics / Crustal Motion
• Meteorology / Water Vapor in Atmosphere
• Space Weather / Free Electrons in Ionosphere

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National CORS Network (continued)

• National CORS data transferred to NOAAs National
  Geodetic Survey in Silver Spring, MD
• GPS and met data converted to RINEX format
• Data made available to public via
• World Wide Web
• File transfer protocol
• Currently 9 years of CORS data are online for
  immediate access
• Parallel CORS Data Site being established at
  NOAAs National Geophysical Data Center in
  Boulder, CO

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Cooperative CORS Network

• GPS base stations whose data are freely
  disseminated by cooperating organizations
• NGS provides link from its web site to that of
  each cooperating organization
• Site coordinates must be consistent with the
  National Spatial Reference System

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National CORS Cooperative CORS
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COMBO CORS
The term Combo CORS designates a station whose
GPS data is distributed both by NOAAs National
Geodetic Survey and by a cooperating
organization. Such accessibility to CORS data is
highly desirable.
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a a a a a a a a
CORS Partners Federal
Federal Highway Administration Federal Railway
Administration Federal Aviation
Administration Forecast Systems
Laboratory National Geophysical Data
Center NASA US Geological Survey US Army Corps of
Engineers US Air Force US Naval Observatory
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CORS Partners States
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CORS Partners Scientific
International GPS Service (IGS) University
Navstar Consortium (UNAVCO) Scripps Orbit
Permanent Array Center
PANGA
EBRY
BARD
BAYONET
BARGN
SCIGN
Plate Boundary Observatory SuomiNet
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CORS Partners International
Canada
International Earth Rotation Service
(IERS) International GPS Service (IGS)
Mexico
Guatemala El Salvador Honduras Nicaragua
Jamaica
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CORS Partners Private Industry
If you want to see where GPS is going, then
keep your eye on the GPS manufacturers. Bill
Strange Former Manager National CORS
Program
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(No Transcript)
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Stations with Meteorological Sensors
Forecast Systems Laboratory
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CORS (cont.)

• Why CORS?

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NATIONAL SPATIAL REFERENCE SYSTEMS

• The National Spatial Reference System (NSRS) is a
  consistent national coordinate system that
  specifies latitude, longitude, height, scale,
  gravity, and orientation throughout the Nation,
  as well as how these values change with time.

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NSRS(GEODETIC REFERENCE FRAME)

• A geodetic reference framework forms the spatial
  foundation for the creation of any
  Land-Information System (LIS).
• National Research Counsel Procedures and
  Standards for a Multipurpose Cadastre (1983, p.
  20).

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NATIONAL SPATIAL REFERENCE SYSTEM
ACCURATE -- cm accuracy on a global scale
MULTIPURPOSE -- Supports Geodesy, Geophysics,
Land Surveying, Navigation, Mapping, Charting and
GIS activities
ACTIVE -- Accessible through Continuously
Operating Reference Stations (CORS) and derived
products
INTEGRATED -- Related to International services
and standards (e.g. International Earth Rotation
Service, International GPS Service etc.)
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IMPROVING POSITIONAL ACCURACY
REFERENCE TIME NETWORK
LOCAL FRAME SPAN ACCURACY
ACCURACY
NAD 27 1927-1986 10 Meters
First-Order (1 part in 0.1 million)
NAD 83 1986-1990 1 Meter
First-Order (1 part in 0.1 million)
HARN 1987-1997 0.1 Meter
B-Order (1 part in 1 million)

A-Order (1 part in 10 million)
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VCAP Published Coordinates-ARP

• ITRF00 POSITION (EPOCH 1997.0)
  
• Published by the IERS in Mar. 2001.
  
• X 1369550.378 m latitude 44 15
  43.13960 N
• Y -4365534.838 m longitude 072 34
  56.56028 W
• Z 4429096.685 m ellipsoid height
  159.387 m
• 
  
• ITRF00 VELOCITY
  
• Published by the IERS in Mar. 2001.
  
• VX -0.0153 m/yr northward 0.0039 m/yr
  
• VY -0.0050 m/yr eastward -0.0161 m/yr
  
• VZ 0.0056 m/yr upward 0.0040 m/yr
  

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VCAP Published Coordinates-ARP (cont.)

• NAD_83 POSITION (EPOCH 2002.0)
  Transformed from ITRF00 (epoch 1997.0)
  position in Mar. 2002.
• X 1369550.939 m latitude 44 15
  43.10706 N Y -4365536.278 m
  longitude 072 34 56.55559 W
• Z 4429096.786 m ellipsoid height
  160.561 m
• 
  
• NAD_83 VELOCITY
  
• Transformed from ITRF00 velocity in Mar. 2002.
  VX 0.0025 m/yr
  northward -0.0014 m/yr
  
• VY -0.0031 m/yr eastward 0.0015
  m/yr
• VZ 0.0016 m/yr upward 0.0038
  m/yr

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VCAP Published Coordinates-L1

• ITRF00 POSITION (EPOCH 1997.0)
  
• Published by the IERS in Mar. 2001.
• X 1369550.393 m latitude 44 15
  43.13960 N
• Y -4365534.889 m longitude 072 34
  56.56031 W Z 4429096.737 m
  ellipsoid height 159.461 m
• The ITRF00 VELOCITY of the L1 PC is the same as
  that for the ARP.

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VCAP Published Coordinates-L1 (cont.)

• NAD_83 POSITION (EPOCH 2002.0)
• Transformed from ITRF00 (epoch 1997.0) position
  in Mar. 2002.
• X 1369550.954 m latitude 44 15
  43.10706 N
• Y -4365536.329 m longitude 072 34
  56.55562 W Z 4429096.837 m
  ellipsoid height 160.636 m

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Data Quality Check-60 days Time Series
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CORS ADVANTAGES

• 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 and velocities are available in
  both NAD 83 and ITRF coordinate systems.

• CORS positions are of the highest accuracy.

• CORS positions are continuously monitored and
  will be updated if the site moves (2cm
  horizontal 4cm vertical.)

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Common Question

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

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OPUS Online Positioning User Service
http//www.ngs.noaa.gov/OPUS/ opus_at_ngs.noaa.gov
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WHAT IS OPUS?

• On-line Positioning
  User Service

• Provide GPS users faster easier access to the
  National Spatial Reference System (NSRS)

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HOW DOES OPUS WORK?

• Submit RINEX file through NGS web page

• Processed automatically with NGS computers
  software

• With respect to 3 suitable National CORS

• Solution via email (usually in minutes)

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OPUS USES 3 CORS SITES
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HOW DO I USE OPUS?
Go to OPUS web page www.ngs.noaa.gov/OPUS

• - Enter your email address

• - Enter/Select RINEX file

• - Select antenna type from menu

• - Enter antenna height in meters (defaults to
  ARP)

• - OptionalState Plane Coordinates

• - Select up to 3 base stations (optional)

• - Upload File

Check your email (usually only takes a few
minutes)
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WHAT ARE SOME OPUS GUIDELINES?

• Must submit dual-frequency (L1/L2) data

• Must submit at least 1-hr of data

• No kinematic/Rapid Static

• No Glonass

• Correct vertical requires
• antenna type
• antenna height

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(No Transcript)
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GETTING TO OPUS
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OPUS Web Page
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OPUS - Select Reference Site(s)
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HOW IS THE ANTENNA HEIGHT MEASURED?
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WHY DO I NEED THE ANTENNA TYPE?
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Antenna Calibration Facility in Corbin, Virginia
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Antenna Phase Center Variation
. . . . . . . . . . . .
SV 20
SV 20
SV 14
SV 14
Note that SV elevation and varying phase patterns
affect signal interpretation differently
Antenna Type B
Antenna Type A
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Antenna Phase Center Variation
. . . . . . . . . . . .
SV 20
SV 20
SV 14
SV 14
Different Phase Patterns
Note that SV elevation and varying phase patterns
affect signal interpretation differently
Antenna Type B
Antenna Type A
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ELECTRONIC PHASE CENTER

• Phase Center Variation (mm)

• Elevation Angle (deg.)

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HOW ARE OPUS POSITIONS COMPUTED?

• NGS PAGES software

• Ionosphere free

• Tropospheric scale height adjusted

• Fixed ambiguities

• Average solution to 3 suitable CORS

• ITRF and NAD83 positions returned

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WHAT DOES OPUS OUTPUT LOOK LIKE?
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READING OPUS OUTPUT (input)

• The version of the PAGES software used for
  processing

• The ephemeris used (OPUS will use the best
  available)
• igs final post-fit orbit-better than 5 cm (14
  days wait)
• igr rapid post-fit orbit-better than 10 cm (2
  days wait)
• igu ultra-rapid predicted orbit-better than
  25 cm (available immediately)

• The antenna name and antenna reference point
  height you entered

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READING OPUS OUTPUT (process results)

• Start/end dates/times of your file

• Ratio and of observations used in solution

• Ratio and of fixed/total ambiguities

• Overall RMS of the solution

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READING OPUS OUTPUT (coordinates)

• Reference Frames Epoch Date

• Independent NAD83 ITRF solutions

• Orthometric ht. is based on current geoid model

• Peak to peak error is the difference between
  max and min error for individual solutions

• Peak to peak error may differ between NAD and
  ITRF solutions and are usually the worst in the
  up component

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READING OPUS OUTPUT (coordinates)

• Universal Transverse Mercator (UTM) coordinates

• US National Grid

• State Plane coordinates are given (if
  requested)

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READING OPUS OUTPUT (control)

• Base Stations used in positioning

• The closest published station listed in the NGS
  IDB

• Disclaimer

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WHAT IS A GOOD SOLUTION?

• No hard rules - only guidelines

• Make sure antenna type and antenna height
• are correct

• Review statistics
• should use 90 or more of your observations
• at least 50 of the ambiguities should be fixed
• overall RMS should seldom exceed 3.0 cm
• peak to peak should seldom exceed 5.0 cm

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HOW CAN I IMPROVE MY RESULTS?

• The best way to get more accurate results is to
  observe longer sessions

• Data sets of at least four hours have been shown
  to produce more reliable results

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HOW DO I GET HELP?

• First use the Links on the OPUS page

• detailed discussions of guidelines

• description of processing techniques

• description of output

• guidelines for successful use

• Submit specific questions at OPUS web page
• http//www.ngs.noaa.gov/OPUS/

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WHAT CHANGES ARE PLANNED IN THE FUTURE?

• Inclusion of Cooperative CORS in the base
  station selection process

• Better treatment of RINEX-2 header errors is
  being implemented. Some translators are not
  compliant with the RINEX-2 standard

• Single frequency data processing is being
  considered

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QUESTIONS?
http//www.ngs.noaa.gov/OPUS/ opus_at_ngs.noaa.gov