Introduction to NGS CORS and OPUS

Chris PearsonNational Geodetic Survey

Chris.Pearson@noaa.gov, (217) 524-2890

Key web addresses for CORS and OPUS

•CORS– http://www.ngs.noaa.gov/CORS/

•OPUS– http://www.ngs.noaa.gov/OPUS/

•OPUS DB– http: //beta.ngs.noaa.gov/OPUS/– http://www.ngs.noaa.gov/OPUS/

CONTINUOUSLY OPERATING REFERENCE STATIONS (CORS)

1300+ Installed and Operated byvarious Federal-State-local Agencies

NOAA/National Geodetic SurveyNOAA/OAR Global Systems DivisionU.S. Coast Guard - DGPS/NDGPSCorps of Engineers - DGPSFAA - WAAS/LAAS State DOTs County and CityAcademiaPrivate Companies

CORS Network Evolution1994 - 2008

1994 1997 2000

2003 2006 2008

Map

• 1,350 CORS sites (09/09)• ~ 200 organizations• 200 new sites in FY09

Illinois CORS

ILUC UIUC SCCB

Baseline Plot National

• ITRF (yyyy) International Terrestrial Reference Frame

• All coordinates change to reflect tectonic motion

• NAD83 –in stable North American coordinates are constant

• In the far west coordinates not constant so epoch dates are important

ITRF00

NAD83

HB 1

HB 2

HB 3

HB 4

HB 5

HB8HB 9

HB16HB 17

FL

GA AL MS

HB 18

NC SC

HB 19

HB 32

HB 33

HB10

HB11

HB 20

HB 21

HB 22

HB 23

HB 6

HB 7

HB 12

HB 13

HB 24

HB 25

HB 26

HB 27

HB 14

HB15

HB28

HB 29

HB 30

HB 31

HB 34

HB 35

HB 36

HB 37

HB 38

HB 39

HB 40

HB 41

HB 42

HB 43

HB 44

HB 45

HB 46

HB 47

HB 48

HB 49

HB 50

HB 51

OR WA CA AK PR VQ

VA WV MD PA DC DE NY NJ CT MA ME NH RI VT LA AR TN KY MO IL IN OH MI WI MN IA ND SD NE KS OK TX NM AZ CO UT NV ID MT WY

HELMERT BLOCKING STRATEGY

This is how each state fits into the National Readjustment

CORS

Control for the NSRS2007 adjustment

CORS were held fixed provided control at the top block

•Precise (Final)•14 days latency•1 cm accuracy•updated weekly

•Rapid•1 day latency•2 cm accuracy•updated daily

•UltraRapid•24 hrs observed / 24 hrs predicted•5 cm / 10 cm accuracy•updated 4 times/day

NGS/IGS PRECISE ORBITS

Broadcast orbits• Only 4 control stations

– All located in the tropics– Accuracy 2.5 m

Data available for each site

• Coordinates ITRF and NAD83• Datasheet ARP and phase center• Data availability (was it working

during my project)• Site Log Antenna and receiver• File downloads (Standard and UF• Time series

CORS time series

• CORS processing gives a new coordinate every day• We can estimate velocities by following the trend• The height is al ellipsoid heights rather than orthometric heights• Because of local changes CORS coordinates do not always reflect the

time series

Coordinates

• ITRF velocities are nonzero

• NAD83 velocities zero for NC Not for CA

• Current antenna listed

Datasheets• ARP• Phase

Center• Referenc

e stations• Each has

its own PID

Site log

• Receiver and antenna

• Lists every one ever installed on this site

Data availability

Standard files

• RINEX– GPS OBS

• Navigation– Broadcast

orbits• IGS

Ephemeris– High

accuracy orbits

• Rapid Ephemeris– Predicted

high accuracy orbits

User friendly CORS

http://www.ngs.noaa.gov/OPUS

You’ve got mail!

OPUS solution

Static: OPUS determines your position with a differential GPS static solution, using hours of data.

This process is repeated twice from other CORS.

XB

A

X

C

XA

XCB

How accuracies of OPUS coordinates are estimated

Rover

• Each OPUS solution uses 3 CORS

• As a result there are 3 independent baselines and 3 independent estimates of the coordinates

• The coordinates that OPUS gives are an average of the three values

• The errors are just the maximum difference between the three values

misclose

Rapid-static: OPUS first creates an atmospheric delay model from surrounding CORS data.

Your position is then quickly determined by differential GPS static solution.

Methodology – Rapid-Static Algorithm

Rover solution schemes

: 0: 0

ABX AB XB XA XB XA ABACX AC XC XA XC XA AC

ΔΔ

− + = → = +− + = → = +

B

A

X

NetworkC

A

X

RoverC

AC

AB XA

XBXC

B

AB

AC

All three CORS stations contribute to the estimation of a single set of ambiguities

One unknown baseline

OPUS-RS CoverageInterpolative Dilution of Precision (IDOP) Values

control stationphoto *

control station description *

control station monument

NGS-modeled antenna

GPS data (4+hours)

OPUS websitehttp://geodesy.noaa.gov/OPUS

for registered users

publicdatasheet

QA/QC2

reviews

OPUS Datasheet Concept

observationnotes

*optional for “existing” stations.

GPS data requirements

“OPUSable”4+ hours of dual frequency dataNGS-calibrated antennaOPUS must achieve:

≥ 90% observations used≥ 80% ambiguities fixed≤ 0.02m peak-to-peak horizontal≤ 0.04m peak-to-peak vertical

NGS-modeled antenna

GPS data (4+hours)

*optional for “existing” stations.

control station description *

control stationphoto *

metadata requirements

observationnotes

Simplified bluebooking

Submit data to OPUS-DB- Only STATIC please

OPUS statistics checked by computerPhotos reviewed by NGSDatasheet reviewed by agency

QA/QC2

reviews

quality control