National Geodetic Survey Andria Bilich amp Gerald Mader Geosciences Research Division National Geodetic Survey The Antcal Team Steven Breidenbach Hong Chen Kendall Fancher Charles ID: 130349
Download Presentation The PPT/PDF document "GNSS Absolute Antenna Calibration at the" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
GNSS Absolute Antenna Calibration at theNational Geodetic Survey
Andria
Bilich
& Gerald
Mader
Geosciences Research Division
National Geodetic SurveySlide2
The Antcal Team
Steven
Breidenbach
Hong ChenKendall FancherCharles GeogheganDavid GietkaHeeyul HanDennis Lokken
Frank MarionJaya NetiGiovanni SellaBruce TranJarir SalehMark Schenewerk
2Slide3
Talk OutlineWhat is antenna calibration?
Relative versus absolute
Motivation for NGS absolute facility
NGS methods and observation modelsExample resultsTools for the customer3Slide4
Where do I receive the signal?
Where is the “phase center”?
Antenna reference point (ARP)
Antenna element
Nonphysical and inconstant point floating in space?!
4Slide5
Calibration = Map of “Inconstant Point”
mm of phase advance/delay
Mean point being positioned
… phase center offset: PCOSpatial variations about the mean … phase center variations: PCV5
0 elevL1: 2.5 mmL2: -1 mm20 elevL1: -0.5 mmL2: 2.0 mm
PCO
[ENU]
PCV
(
elev
)Slide6
PCV
Azimuthal
Dependence
6Slide7
Why Do I Need Calibrations?Antenna introduces several mm-cm of phase advance/delay -> range errors
Input to most GNSS data processing software
Omitting calibrations can cause problems:
Long baselinesCombining multiple antenna modelsHeight errors7Slide8
Relative vs. Absolute
Relative
Absolute
Calibration valuesRelative to a reference antenna (AOA D/M_T)Independent of reference antennaMethodStationary antennasTest antenna movesAdvantagesStraightforward mathSample full hemisphere and low elevation anglesLimitations
Cannot sample full patternRequires robot and rigorous accounting of angles & rotations8Do not combine relative and absolute calibrations!Slide9
Why Go to Absolute?Better/fuller description of phase behavior
0-10
elevation coverageAzimuthal variationsMultipath removed/negatedThe way of the futureInternational GNSS Service (IGS) standardUsed in OPUSUsed in CORS multiyear [IGS08 epoch 2005.0 and NAD 83(2011) epoch 2010.0]9Slide10
Who Does Absolute Calibrations?
Geo++
TU Darmstadt
MethodField with GNSS signalsAnechoic chamber with pure sine wavesRobot3-axis, PCO held fixed2-axis, PCO movesInstitutionFor-profitUniversity10Up and coming
: Australia, ChinaSlide11
NGS Absolute CalibrationMotivations and Goals
Serve high precision needs of U.S. surveying and geodesy communities
Multi-frequency, multi-GNSS calibrations
2-D (elevation, azimuth) phase center patternsFree calibration service w/ quick turn-aroundCalibration values publicly distributed via InternetCompatibility with IGS ANTEX values11Slide12
Compatibility with IGS
12
IGS ANTEX as “truth”
IGS Antenna Working Group acceptable deviations< 1 mm for high elevations (>= 10)< 2 mm for low elevations (0-10)Slide13
NGS Calibration Facility and Methods
13
Hi, I’m Pete.Slide14
Modelled Factors
E
N
V
PCO [ENU]
PCV (
az,el
)
PTU:
A priori
position
Frame rotation(s) between robot and local frame
Rotation arm length
Phase windup (antenna motion)
GPS/PC clock offsets
14Slide15
Calibration Setup
Carrier phase single differences
Short baseline (5 m)
Simplified multipath environmentCommon clock (heading receiver)Remaining factors = phase centers (ref, test), differential multipath, hardware bias15Slide16
Time Difference of Single Differences
Closely spaced time pairs + robot motion =
PCO/PCV at reference antenna removed
slowly varying biases (differential MP, hardware bias) minimized
16
Fixed reference antenna
Test antennaSlide17
Why Robot?
Introduce angle changes for TDSD
Better spatial coverage
17Slide18
NGS Robot Limitations
2-axis = cannot sample full angular range
Motor box limits tilt
Tilt introduces change in antenna height above ground … multipath?18Slide19
4-stage Process
“
holes” in coverage
Each antenna run for 4 cardinal directionsCombined for full coverage19Slide20
Estimation strategy
20
North
EastSouthWestSlide21
So Many Variables!Elevation cutoffs
Local frame
Antenna frame
Order/degree of harmonicsData spacing/distributionRobot motion scenario (delta pan)21Slide22
NGS Calibration Results
22Slide23
NGS Catalog to Date
IGS comparison
AOA D/M_T
Topcon CR-G3Javad RingAnt D/MTrimble Zephyr Geodetic (GPS)Trimble Zephyr 2 (GNSS)Ashtech Whopper23Previously uncalibrated antennas
ITT chokerings (NGA)Topcon CR-G5 FullWaveSlide24
Allen Osborne chokering rev T AOAD/M_T
24
s/n 149Slide25
Allen Osborne chokering rev T
deviation
25
< 1 mm(elev > 10)< 2 mm(elev <= 10)L191%90%L297%
100%Slide26
Javad RingAnt-DM
JAVRINGANT_DM
26
s/n 00553Slide27
Javad RingAnt-DM
deviation: shifted to IGS PCO values
27
< 1 mm(elev > 10)< 2 mm(elev <= 10)L193%96%L277%
69%Slide28
Javad RingAnt-DM
deviation: keeping NGS PCO values
28
< 1 mm(elev > 10)< 2 mm(elev <= 10)L1100%100%L290%
92%Slide29
Trimble Zephyr 2TRM55971.00
29
s/n 30255823Slide30
Trimble Zephyr 2deviation, S/N 30255823
30
< 1 mm
(elev > 10)< 2 mm(elev <= 10)L199%99%L281%67%Slide31
Trimble Zephyr 2deviation, S/N 30212854
31
< 1 mm
(elev > 10)< 2 mm(elev <= 10)L198%97%L271%67%
Different serial number, different deviationsSlide32
Trimble Zephyr 2L1 Type Mean
32
test 1: 0.90 0.40 66.69
test 2: 0.58 0.16 67.57test 3: 0.48 0.40 65.99test 4: 0.73 -0.42 65.96test 5: 0.94 -0.19 66.26test 6: 0.61 -0.01 65.88std : 0.18 0.33 0.65NGS MEAN: 0.71 0.06 66.39IGS MEAN: 1.29 -0.19 66.73Diff : 0.58 -0.25 0.34Slide33
Trimble Zephyr 2L2 Type Mean
33
test 1: 0.61 1.50 58.32
test 2: 0.20 1.24 58.65test 3: 0.12 0.71 57.84test 4: -0.41 -0.16 57.93test 5: -0.16 0.18 58.63test 6: -0.25 0.80 57.63std : 0.37 0.62 0.43NGS MEAN: 0.02 0.71 58.17IGS MEAN: 0.38 0.61 57.69Diff 0.36 -0.10 -0.48Slide34
Trimble Zephyr 2L1 Type Mean: NGS vs
IGS
34Slide35
Trimble Zephyr 2L2 Type Mean: NGS vs
IGS
35Slide36
Outstanding QuestionsSource of histogram bias and skew towards negative residuals
Misfit at < 20
Type meanCommon PCO or individual PCOs?Statistics?Number of antennas required?36Slide37
Development Next StepsIGS AWG approval
Permanent piers
GLONASS
More automated data retrieval/processing37Slide38
NGS Calibration Services
Database, website, processes and policies
38Slide39
New Website
Revamped along with database
Photo & drawing
mouseovers for easy IDANTINFO and ANTEX formats39Slide40
Formal Policy DocumentApproved by ESC
Purpose/Goal
Clear expectations
Make our jobs easierDoc contentsCalibration process and stagesEligibility for calibrationRights and responsibilities (both NGS and antenna provider)40Revisions expected with manufacturer input after calibration tracking system comes onlineSlide41
Antenna Intake
Request calibration via web form
Tracking system
Customer notification emails41Slide42
Conclusions and OutlookGood agreement with IGS type means... but needs improvement
Pending approval from IGS Antenna Working Group
Soon to be “open for business”
For more informationhttp://www.ngs.noaa.gov/ANTCALEmail andria.bilich@noaa.gov or NGS.AbsAntCal@noaa.gov42