Investigation on the performance of low-cost single ... · Investigation on the performance of...

Investigation on the performance of low-cost single frequency GPS Zhenzhong Su, Alain Geiger, Philippe Limpach

Institute of Geodesy and Photogrammetry, ETH Zurich, Switzerland

X-Sense partners: Fabian Neyer, Jan Beutel, Lothar Thiele, Hugo Raetzo, Stephan Gruber, Tazio Strozzi

Introduction of project X-Sense

Thursday, 01 March 2012 1 Zhenzhong Su

X-Sense:

• Geo-monitoring with GPS; Communication through WLAN

• Solar panel for battery charging

• Data processing in server; Data visualization online

• Integrate various sensing dimensions

X-Sensor project partnership:


Prof. Alain Geiger

Dr. Philippe Limpach

MSc Fabian Neyer

MSc Zhenzhong Su

Prof. Lothar Thiele

Dr. Jan Beutel

MSc Bernhard Buchli

MSc Tonio Gsell

MSc Matthias Keller

Dr. Stephan Gruber

MSc Vanessa Wirz

Dr. Tazio Strozzi

Dr. Hugo Raetzo

Overview

Motivation

PCV determination via an absolute calibrated reference receiver antenna

Results and validations

Conclusion

3 Thursday, 01 March 2012 Zhenzhong Su

Overview

Motivation



Conclusion


Motivation


Low-cost single frequency GPS equipment developed in X-Sense

Ublox chip, trimble bullet III antenna

Motivation

Time series of GPS daily static solutions


Repeatability Daily static

Std_E 2 mm

Std_N 2 mm

Std_H 3 mm

Repeatability Kinematic

Std_E 9 mm

Std_N 8 mm

Std_H 18 mm

Motivation

To provide sub-daily solutions instead of daily solutions in future Battery save and distribution Higher resolution of coordinate evolution

For short baseline most of the systematic GPS errors are eliminated in double difference processing, only the antenna Phase center variations (PCV) is neither available nor considered for low-cost antenna.

Thus we decide to estimate the antenna PCV and apply it to correct the phase measurements for better sub-daily solutions.


Overview

General introduction



Conclusion


Phase Center Variations:



∑∑= =

−+−=∆max max

1 000 )](sin)(cos)[(cos~),(

n

n

m

mnmnmnm mbmazPz αααααϕ

Normalized associated legendre functions of degree n and order m

Azimuth angle of the satellite line of sight

Zenith angle of the satellite line of sight

Antenna orientation



Setup:

Reference with absolute calibrated antenna PCV and offset

Rover is set up next to reference

PCV determination via an absolute calibrated reference receiver antenna PCV determination procedure:


Predetermine precise mean phase center of rover antenna 1. It is computed through baseline processing between rover and

reference station with 24 hours static observations.

2. The position obtained is considered as rover antenna mean phase center.

Estimate PCV of rover antenna 1. The mean phase center of rover antenna is introduced as known

parameter.

2. Antenna PCV is introduced as unknown parameters and estimated with standard least square estimation.

Realized by program PCVEST



PCVEST Import precise Satellite Ephemerids

& GPS Observations

Detect outliers and synchronize receiver clock to GPS time with code observations

Form double difference equations

Standard atmosphere model for troposphere / ionosphere

Cycle slips detection and repair

Solve ambiguity integers

Estimate PCVs

Coordinates of reference and rover

BPE script: PCVEST (BPE:Bernese processing engine)

pcvtropionsatrec NIIccL ϕλδδρ ∆+⋅++−⋅−⋅+=

[ ] ebbaaAL

eLT

mnmn

pcv

+⋅=∇

+∆∇=∇

,0,1,0,1 ......

ϕ

Overview




Conclusion


Results and validations:


azimuth

Zenith

Estimated antenna PCV

Estimated in day 188

Zenith : 0° 80°

[mm]

Results and validations: carrier phase residuals comparison for daily solution


RMS of adjusted minus measured observations (one-way L1 carrier phase residuals)

Day RMS RMS (with PCV)

188 3.1mm 2.9mm

189 3.6mm 3.4mm

190 3.2mm 3.1mm

191 3.9mm 3.6mm



Day 188



Day 189



Day 190



Day 191

Results and validations: Improvement of sub-daily (2 Hour) solutions with PCV

Day 188 RMS(without PCV) RMS(with PCV) Improvement dN [mm] 3.2 1.6 50%

dE [mm] 2.2 1.1 50%

dU [mm] 9.2 5.1 45%



dE [mm] 4.9 1.6 67%

dU [mm] 6.2 5.5 11%


dE [mm] 4.9 3.1 37%

dU [mm] 7.8 5.1 34%


dE [mm] 7.8 1.7 78%

dU [mm] 7.7 5.6 27%



Day 188



Day 189



Day 190



Day 191


Results and validations: Slight improvement of kinematic coordinates with PCV

Day 188 RMS(without PCV) RMS(with PCV) Improvement dN [mm] 4.5 4.3 2.2%

dE [mm] 3.6 3.5 2.7%

dU [mm] 5.8 5.5 5.2%

Day 189 RMS(without PCV) RMS(with PCV) Improvement dN[mm] 5.1 4.8 5.9%

dE [mm] 4.4 4.3 2.2%

dU [mm] 6.3 5.9 6.3%

Day 190 RMS(without PCV) RMS(with PCV) Improvement dN[mm] 5.1 4.8 5.9%

dE [mm] 4.1 4.0 2.4%

dU [mm] 5.6 5.3 5.4%

Day 191 RMS(without PCV) RMS(with PCV) Improvement dN [mm] 5.5 5.1 7.3%

dE [mm] 4.4 4.4 0%

dU [mm] 6.7 6.4 4.5%

Overview




Conclusion


The PCV value of Trimble Bullet III antenna with respect to the mean phase center ranges within 2 cm for our experiment.

The phase residuals are decreased by using PCV correction.

Using the estimated PCV to correct phase measurements does improve the sub-daily solutions as well as kinematic solutions.

To do:


Conclusion:

Select a day when Rover has no

movement On-site PCV estimation

Apply PCV correction (as long as the antenna

has the same orientation)

A procedure for low-cost single frequency GPS receiver on-site PCV estimation.

Thanks for your attention!

Acknowlegement is given to Swiss National Science Foundation (SNSF) and Naro-tera.

Welcome for questions.

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