Bill Henning

1
GREAT LAKES REGION HEIGHT MODERNIZATION
CONSORTIUM NGS AND REAL TIME POSITIONING
Bill Henning Senior Geodesist, PLS. 301-713-3196
x 111, william.henning_at_noaa.gov
ftp//ftp.ngs.noaa.gov/dist/whenning/GLRHMC/
2
REAL-TIME ACTIVITIES AT THE NGS

1. OPERATE AN NTRIP CASTER. (Fed. Owned/operated
   currently 8. RTCM 2.3 3.0, From Foundation
   CORS. NO CORRECTORS)
2. DEVELOP AND PUBLISH GUIDELINES DESCRIBING BEST
   PRACTICES IN RTK RTN .(RTK Users draft, RTN
   Operators draft, etc.)
3. PARTICIPATE IN MEETINGS, FORUMS, WORKSHOPS, ETC.,
   CONCERNING REAL-TIME NETWORKS. SEEK LEADERSHIP
   ROLES.(FIG, FGCS, ESRI, ACSM, RTCM, etc.)
4. RESEARCH PHENOMENA AFFECTING ACCURATE REAL-TIME
   POSITIONING. (Orbits, refraction, multipath,
   antenna calibration, geoid separations, gravity,
   crustal motion, etc.)

3
SINGLE-BASE USERS GUIDELINES

• WHY/HOW?
• Legacy equipment
• Closest base networks
• Areas with no cell coverage
• Empirical methods
• Source for background info.
• Dynamic technology

4
SINGLE BASE GUIDELINES MEANT AS A BEST METHODS
AND ALSO AS A BACKGROUND REFERENCE FOR RT

• EQUIPMENT
• GNSS SIGNAL BASICS
• PRINCIPLES OF RT POSITIONING
• ATMOSPHERIC ISSUES
• PLANNING
• BEST METHODS
• ACCURACY/PRECISION
• ATMOSPHERIC ISSUES
• MULTIPATH
• METADATA
• COMMUNICATION
• OFFICE CHECKS
• RT GLOSSARY

5
8400 MPH
8400 MPH
SVN 8
SVN 31
SVN 14
8400 MPH
EVERY EPOCH OF OBSERVATION MUST COMPUTE CHANGE IN
POSITION DUE TO EARTH ROTATION, SATELLITE ORBIT
CHANGE AND RELATIVITY!
SVN 23
8400 MPH
800 MPH /-
AT C, 1 NANOSECOND 30 CM!
6
SUNSPOT CYCLE

• Sunspots follow a regular 11 year cycle
• We are just past the low point of the current
  cycle
• Sunspots increase the radiation hitting the
  earth's upper atmosphere and produce an active
  and unstable ionosphere

2013
http//www.swpc.noaa.gov/
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WWW.SWPC.NOAA.GOV
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IONOSPHERIC EFFECTS ON POSITIONING
AVERAGE IONO- NO NETWORK
HIGH IONO- NO NETWORK
2D PRECISION/ACCURACY (CM)
SINGLE BASE RTK _at_ 10 KM
(2000-2002)
(1994-1995)
NETWORK SOLUTION _at_ 30 KM
WITH NETWORK
DISTANCE TO REFERENCE STATION (KM)
(SOURCE-BKG- GERMANY)
9
IONO, TROPO, ORBIT CONTRIBUTE TO PPM ERROR
REMEMBER GNSS EQUIPMENT MANUFACTURERS SPECS!
10
TROPOSPHERE DELAY

• The more air molecules, the slower the signal
  (dry delay)
• High pressure, Low temperature
• 90 of total delay
• relatively constant and EASY TO CORRECT FOR
• The more water vapor in the atmosphere the slower
  the signal (wet delay)
• High humidity
• 10 of total delay
• Highly variable and HARD TO CORRECT FOR

Ionosphere
troposphere
10 KM
GREATER THAN 10 KM
11
DRAFT GUIDELINES- 95 CONFIDENCE
12
THE NGS AND REAL-TIME NETWORKS
13
REAL TIME NETWORKS (RTN)- A NEW INFRASTRUCTURE!

• PERHAPS OVER 80 RTN EXIST IN THE USA WITH MANY IN
  THE PLANNING STAGES
• HOW ARE THEY ESTABLISHED?
• HOW ARE THEIR COORDINATES COMPUTED? ARE THEY
  CONSISTENT?
• HOW IS THE NETWORK ADJUSTED?
• HOW DOES THE RTN ALIGN TO THE NSRS?
• CAN USERS USE ANY MANUFACTURERS EQUIPMENT IN THE
  RTN?
• DO OVERLAPPING NETWORKS GIVE THE SAME
  COORDINATES?
• WHAT ARE THE FIELD ACCURACIES?

?
14
NGS RT WEB PAGES OPERATIONAL PROTOTYPE
CURRENT POLICY NGS WILL NOT RESTREAM RT DATA
FROM NON-FEDERAL SITES
15
RADIO TECHNICAL COMMISSION FOR MARITIME
SERVICESDIFFERENTIAL GNSS POSITIONING RTCM
SC-104

• INTERNATIONAL STANDARDS BY ORGANIZATIONS-
  non-profit scientific, professional and
  educational, governmental and non-governmental
• RTCM format is OPEN SOURCE, GENERIC
• RECOMMENDED STANDARDS FOR DIFFERENTIAL GNSS
  POSITIONING
• ALL MAJOR RT GNSS GEAR CAN USE THIS FORMAT
• IN USA, MEMBERS INCLUDE FCC, USCG, NGS, MAJOR
  GNSS MANUFACTURERS
• NTRIP STANDARDS (An application-level protocol
  that supports streaming (GNSS) data over the
  Internet)

16
NGS RTCM 3.X STREAMS
17
FOUNDATION CORS CONCEPT (SHOWN AT NOMINAL 500
KM SPACING)
18
DEVELOPING COOPERATIVE PARTNERS
USCG 86 TOTAL -38 INLAND (DOT)
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USCG DGPS TEST SITES
DRIVER, VA UPPER KEWANEE, MI NEW BERN,
NC MORICHES, NY ANNAPOLIS, MD ENGLISH TURN,
LA CARD SOUND, FL TAMPA, FL KODIAK,
AK PENOBSCOT, ME
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PBO STATIONS

• BINEX, RTCM 2.4, RTCM 3.0
• 0.6 to 2.0 seconds latency
• SERVER IN BOULDER, CO
• 97 RT STATIONS /-

http//pboweb.unavco.org/?pageid107
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PBO RT STREAMS
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http//www.ntrip.org/ 155 STREAMS TO
http//www.igs-ip.net/home
23
Position Time Series (long-term)
earthquake
2002
2003 2004 2005
2006 2007
2008
2002
2003 2004 2005
2006 2007
2008
seasonal variation
2002
2003 2004 2005
2006 2007
2008
24
EXAMPLE OF WHY RTN REFERENCE STATIONS SHOULD BE
MONITORED
SUBSIDENCE
6 MM / YEAR
ENGLISH TURN CORS
25
POSSIBLE REASONS FOR CYCLICAL MOVEMENT

• FLUID WITHDRAWAL/INFUSION
• OCEAN LOADING
• ATMOSPHERIC LOADING
• RECEIVERS
• PROCESSING
• IONO MODELING
• VOLCANIC BREATHING
• INTERMITTENT ELECTRICAL INTERFERENCE
• SNOW

26
DRAFT
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PURPOSE OF RTN GUIDELINES

• Promote consistency of RTN-generated coordinates
  with current realizations of both the North
  American Datum of 1983 (NAD 83) and the
  International Terrestrial Reference System
  (ITRS).
• Note that NAD 83 is the official spatial
  reference system for geometric positioning in the
  United States.

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OPERATING A RTN- CHAPTER ONE DRAFT
1 Include a subnetwork of the RTN into the
National CORS network. This would be three
stations If RTN has less than 30 stations, 10 of
RTN with greater than 30 stations.
2 Align all RTN reference stations coordinates
to the CORS network at 2-cm horizontal and 4-cm
vertical
3 For each reference station in the RTN, use the
Online Positioning User Service (OPUS) at
http//www.ngs.noaa.gov/OPUS/ to test for the
continued consistency of its adopted positional
coordinatesand velocity on a daily basis, and
revise the stations adopted coordinates and/or
velocity if the tests reveal a need to do so.
29
REFERENCE STATION COORDINATE DERIVATION
ALL CORS FIXEDALL CORS WEIGHTEDOPUSOPUS
HARNBEST FIT TO ONE MASTER STATION
30
Suggestions for Determining RTN Station
Coordinates
Option 1 Submit 24 hours of GPS data from each
station to OPUS for each of at least 10 days and
compute the arithmetic mean of the daily
OPUS-generated coordinates. Option 2 Process at
least 10 days of GPS data from all RTN stations
using a simultaneous network adjustment while
constraining several CORS coordinates with
weights of 1 cm in each horizontal dimension and
2 cm in the vertical dimension. NGS recommends
Option 2.
31
Suggestions for Determining Velocities for RTN
Stations

• Use the HTDP (Horizontal Time-Dependent
  Positioning) software to predict velocities for
  new RTN stations. (The predicted vertical
  velocity will be zero.)
• After 3 years, use GPS data from the RTN station
  to produce a time series of the stations
  coordinates, then use this time series to
  estimate a velocity for the RTN station.

32
OPUS-LIKE GENERATED GRAPHIC OF RTN STATIONS-
SIMILAR TO CORS 60-DAY PLOT
33
BEST METHODS FORPOSITIONING WITH RT
34
BEST METHODS FROM THE GUIDELINESTHE 7 Cs
http//www.ngs.noaa.gov/ SEARCH CLASSICAL REAL
TIME

• CHECK EQUIPMENT
• COMMUNICATION
• CONDITIONS
• CONSTRAINTS(OR NOT)
• COORDINATES
• COLLECTION
• CONFIDENCE

THE CONTROL IS AT THE POLE
35
FROM NGS SINGLE BASE DRAFT GUIDELINES CHAPTER 5 -
FIELD PROCEDURES, AND USERS CHAPTER OF RTN
GUIDELINES RT single base, either active or
passiveB Both Single base and RTN
ACHIEVING ACCURATE, RELIABLE POSITIONS USING GNSS
REAL TIME TECHNIQUES
36
CHECK EQUIPMENT

• B BUBBLE- ADJUSTED?
• RT BATTERY- BASE FULLY CHARGED 12V?
• B BATTERY ROVER SPARES?
• RT USE PROPER RADIO CABLE (REDUCE SIGNAL LOSS)
• RT RADIO MAST HIGH AS POSSIBLE? (5 5 MILES,
  20 11 MILES, DOUBLE HEIGHT40 RANGE
  INCREASE). LOW LOSS CABLE FOR gt25.
• RT DIPOLE (DIRECTIONAL) ANTENNA NEEDED?
• RT REPEATER?
• RT CABLE CONNECTIONS SEATED AND TIGHT?
• BFIXED HEIGHT CHECKED?
• RT BASE SECURE?

37
COMMUNICATION

• RT UHF FREQUECY CLEAR?
• B CDMA/CELL - STATIC IP FOR COMMS?
• B CONSTANT COMMS WHILE LOCATING
• RT BATTERY STRENGTH OK?
• B CELL COVERAGE?

38
CONDITIONS

• RT WEATHER CONSISTENT?
• B CHECK SPACE WEATHER?
• B CHECK PDOP/SATS FOR THE DAY?
• RT OPEN SKY AT BASE?
• RT MULTIPATH AT BASE?
• B MULTIPATH AT ROVER?
• B USE BIPOD?

39
CONSTRAINTS (OR NOT)

• B 4 H V, KNOWN TRUSTED POINTS?
• B CALIBRATION RESIDUALS-OUTLIERS?
• B DO ANY PASSIVE MARKS NEED TO BE HELD?
• RT BASE WITHIN CALIBRATION?
• B SAME OFFICE FIELD CALIBRATION USED?

40
CALIBRATIONS/VERTICAL LOCALIZATIONS
41
COORDINATES

• B TRUSTED SOURCE?
• B WHAT DATUM/EPOCH ARE NEEDED?
• RT GIGO
• B ALWAYS CHECK KNOWN POINTS.
• B PRECISION VS. ACCURACY
• B GROUND/PROJECT VS. GRID/GEODETIC
• B GEOID MODEL QUALITY
• B LOG METADATA

42
COLLECTION

• B CHECK ON KNOWN POINTS!
• B SET ELEVATION MASK
• B ANTENNA TYPES ENTERED OK?
• B SET COVARIANCE MATRICES ON (IF NECESSARY).
• B RMS SHOWN IS TYPICALLY 68 CONFIDENCE (BRAND
  DEPENDENT)
• B H V PRECISION SHOWN IS TYPICALLY 68
  CONFIDENCE
• B TIME ON POINT? QA/QC OF INTEGER FIX
• B MULTIPATH? DISCRETE/DIFFUSE
• B BUBBLE LEVELED?
• B PDOP?
• B FIXED SOLUTION?
• B USE BIPOD?
• B COMMS CONTINUOUS DURING LOCATION?
• B BLUNDER CHECK LOCATION ON IMPORTANT POINTS.

43
MULTIPATH
?
?
EXTRA DISTANCE
44
MULTIPATH NOISESPECULAR(DISCRETE) DIFFUSE
INSIDE GNSS NOVEMBER-DECEMBER 2008 MULTIPATH-MITI
GATION TECHNIQUES USING MAXIMUM-LIKELIHOOD
PRINCIPLE MOHAMED SAHMOUDI AND RENE JR.
LANDRY WWW.INSIDEGNSS.COM
45
CONFIDENCE

• B CHECK KNOWN BEFORE, DURING, AFTER SESSION.
• B NECESSARY REDUNDANCY?
• B WHAT ACCURACY IS NEEDED?
• RT REMEMBER PPM
• RT BASE PRECISION TO NEAREST CALIBRATION POINT
• B AVERAGE REDUNDANT SHOTS PRECISION DIFFERENCE
  WITHIN NEEDS OF SURVEY
• B BE AWARE OF POTENTIAL INTERFERENCE (E.G., HIGH
  TENSION TOWER LINES)

46
Two Days/Same Time
-10.254 -10.251
gt -10.253
THE IMPORTANCE OF REDUNDANCY
Difference 0.3 cm
Truth -10.276
Difference 2.3 cm
Two Days/ Different Times
-10.254
gt -10.275
-10.295
Difference 4.1 cm
Truth -10.276
Difference 0.1 cm
47
DRAFT GUIDELINES- 95 CONFIDENCE
48
METADATA !

• BESIDES ATTRIBUTE FIELDS, THE RT PRACTICIONER
  MUST KEEP RECORDS OF ITEMS NOT RECORDED IN THE
  FIELD,FOR INSTANCE
• WHAT IS THE SOURCE OF THE DATA?
• WHAT IS THE DATUM/ADJUSTMENT/EPOCH?
• WHAT ARE THE FIELD CONDITIONS?
• WHAT EQUIPMENT WAS USED, ESPECIALLY- WHAT
  ANTENNA?
• WHAT FIRMWARE WAS IN THE RECEIVER COLLECTOR?
• WHAT REDUNDANCY, IF ANY, WAS USED?

49
QUICK FIELD SUMMARY

• Set the base at a wide open site
• Set rover elevation mask between 12 15
• The more satellites the better
• The lower the PDOP the better
• The more redundancy the better
• Beware multipath
• Beware long initialization times
• Beware antenna height blunders
• Survey with fixed solutions only
• Always check known points before, during and
  after new location sessions
• Keep equipment adjusted for highest accuracy
• Communication should be continuous while locating
  a point
• Precision displayed in the data collector can be
  at the 68 percent level (or 1s), which is only
  about half the error spread to get 95 percent
  confidence
• Have back up batteries cables
• RT doesnt like tree canopy or tall buildings

50
THE QUICK SUMMARY BOILED DOWN

• COMMUNICATIONS THE KEY TO SUCCESS
• CHECK SHOT FIRST BEFORE NEW WORK
• REDUNDANCY FOR CONFIDENCE

200 RTN WORLDWIDE 80 RTN IN THE USA 35 DOT
WITH STATEWIDE NETWORKS PLANNED ?
51
FURTHER WORK IN THE OFFICE

• Antenna heights (height blunders are unacceptable
  and can even produce horizontal error - Meyer,
  et.al, 2005).
• Antenna types
• RMS values
• Redundant observations
• Horizontal vertical precision
• PDOP
• Base station coordinates
• Number of satellites
• Calibration (if any) residuals

52
USING OPUS-S OR OPUS RS WITH REAL TIME
POSITIONING FOR SMALL PROJECTS
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Estimated Vertical Standard Errors A CHECK ON
RT ORTHOMETRIC HEIGHTS
Estimated Horizontal Standard Errors divide by
3.6
56
LINKS FOR BROWSING
ftp//ftp.ngs.noaa.gov/dist/whenning/GLRHMC/
www.swpc.noaa.gov
http//www.ngs.noaa.gov/
http//csrc.ucsd.edu/maps/mapBrowser.html
http//www.ntrip.org/
http//igs.bkg.bund.de/index_ntrip.htm
http//sopac.ucsd.edu/cgi-bin/dbShowArraySitesMap.
cgi
http//sopac.ucsd.edu/cgi-bin/somi4i
http//pboweb.unavco.org/?pageid107
http//www.rtigs.net/