National Geodetic Survey Andria Bilich amp Gerald Mader Geosciences Research Division National Geodetic Survey With contributions from Steven Breidenbach Hong Chen Kendall Fancher ID: 180876
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Slide1
GNSS Absolute Antenna Calibration at theNational Geodetic Survey
Andria
Bilich
& Gerald
Mader
Geosciences Research Division
National Geodetic Survey
With contributions from
:
Steven
Breidenbach
, Hong Chen,
Kendall
Fancher
, Charles
Geoghegan
,
David
Gietka
,
Heeyul
Han, Dennis
Lokken
,
Frank Marion, Jaya
Neti
,
Jarir
SalehSlide2
OutlineMotivation
NGS methods and observation models
Example results
NGS Calibration Services
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Where do I receive the signal?
Antenna reference point (ARP)
Antenna element
Nonphysical and inconstant point floating in space?
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What is GNSS Antenna Calibration?
Create a “map” of antenna characteristics
Mean point being positioned (
PC0
)
Spatial variations (PCV)
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PC0
[ENU]
PCV
(el)
PCV
(
az,el
)Slide5
What Is The Effect of PC0/PCV?
Antenna element introduces elevation- (and azimuth-) dependent advance/delay to the carrier phase observation = PC0 + PCV
Effect on heights (with respect to elevation cutoff)
Alias into troposphere estimate
<= 10cm height errors on mixed-antenna baselines
Mixed-antenna and longer baselines demand good antenna calibrations
Published values are idealized (environment-free)
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NGS Motivations and Goals
Serve high precision needs of U.S. surveying and geodesy communities
Simultaneous multi-freq, multi-GNSS calibrations
2-D (elevation, azimuth) phase center patterns
Free calibration service w/ quick turn-aroundCalibration values publicly distributed via InternetCompatibility with IGS ANTEX values
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NGS Calibration Facility and Methods
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Calibration Setup
Single differences
Short baseline (5 m)
Simplified multipath environment
Common clock (heading receiver)Remaining factors = phase centers (ref, test), differential multipath, hardware bias
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Time Difference of Single Differences
Closely spaced time pairs + robot motion =
PC0/PCV at reference antenna removed
slowly varying biases (differential MP, hardware bias) minimized
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Fixed reference antenna
Test antennaSlide10
Why Robot?
Introduce angle changes for TDSD
Better spatial coverage
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Modelled Factors
E
N
V
PC0 [ENU]
PCV (
az,el
)
A priori
position
Frame rotation(s) between robot and local frame
Rotation arm length
Phase windup (antenna motion)
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NGS Calibration Results
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mmSlide13
Trimble Zephyr Geodetic 2(TRM55971.00)
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(mm)
North
East
Up
IGS
1.07
-0.19
67.17
30212661
1.38
-0.45
69.84
30212716
0.92-0.47
69.84Slide14
TRM55971.00phase center pattern
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mm
mmSlide15
Deviation from IGS type mean
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mmSlide16
Ashtech
Geodetic III ‘Whopper’
(ASH700718B)
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(mm)
North
East
Up
IGS
-1.67
-0.47
69.48
11885
-1.22
0.22
69.1311869-1.40
0.2369.17Slide17
ASH700718Bphase center pattern
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mm
mmSlide18
Deviation from IGS type mean
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mm
mm
mmSlide19
NGS Calibration Services
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PC0/PCV Distribution
Freely available
Distribution via website:
http://www.ngs.noaa.gov/ANTCAL
Data formats for different software:
NGS format (relative and absolute)ANTEX (absolute)
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NGS Calibration ServicesFormal policy document
Calibration process and stages
Eligibility for calibration
Rights and responsibilities
Request calibration via web formTracking system with automated customer notification emails
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Conclusions and OutlookGood agreement with IGS type means
Pending approval from International GNSS Service (IGS)
Soon to be “open for business”
For more information
http://www.ngs.noaa.gov/ANTCALEmail
andria.bilich@noaa.gov or NGS.AbsAntCal@noaa.gov
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