ABSTRACT BOOK - IPQ Boo… · ABSTRACT BOOK PORTUGUESE INSTITUTE ... Traceable electronic distance meters in air – towards novel standards for baseline calibration ... EDM, GNSS-based

Metrology for long distance surveying

ABSTRACT BOOK

PORTUGUESE INSTITUTE FOR QUALITY

21st November 2014

Auditório, IPQ, Caparica

PORTUGAL

www.ipq.pt

Metrology for Long Distance Surveying

IPQ, Caparica | Portugal | 21st November 2014

INTRODUCTION

The accurate measurement of distances of up to kilometres is the basis of modern surveying

and geodesy. A number of most critical tasks, however, like

• sensitive surveillance networks at critical sites

• local ties at geodetic fundamental stations

• high-precision sub-surface surveying work

require measurement uncertainties of typically 1 mm or better for distances of more than

several hundred meters in uncontrolled environments – unachievable with current state of the

art instrumentation, neither with optical nor with GNSS-based distance metrology.

To respond to this need for improvement in measurement technology, EURAMET and the EU

funded the joint research project (JRP) SIB60 “Metrology for long distance surveying” within

the European Metrology Research Programme (EMRP). This project started in July 2013 and

unites metrologists, surveyors and geodesists from 15 European research institutions.

The JRP-Consortium would like to invite interested parties from surveying, geodesy, science

and application to discuss the first results of this project and to share conclusions.



IPQ Local Organization

Fernanda Saraiva, ULNM

Fátima Marques, ULNM

Isabel Silva, DAESPQ

Amélia Dias, DAESPQ

Carlos Pires, ULNM

Sara Neves, DAESPQ

Olivier Pellegrino, ULNM

Isabel Godinho, ULNM

Armando Ferreira, DAG

Liliana Eusébio, ULNM

Scientific Committee

StenBergstrand, SP

Steven van den Berg, VSL

Olivier Pellegrino, IPQ

Florian Pollinger, PTB

Markku Poutanen, FGI

Fernanda Saraiva, IPQ

Jean-Pierre Wallerand, LNE-CNAM



PROGRAMME

9:00 Reception

9:30 OPENING SESSION

Jorge Marques dos Santos, President of IPQ

9:40 Introduction to EMRP JRP SIB60 “Metrology for long distance surveying”

Florian Pollinger, PTB, Coordinator of JRP SIB60

9:55 SESSION I: Challenges of distance metrology in surveying

Chairman: Wolfgang Niemeier, Technical University of Braunschweig

10:00 Geodetic and Alignment activities at CERN

Dominique Missiaen, CERN

10:30 Measuring the earth surface deformation using SAR interferometry and GPS

João Catalão Fernandes, FCUL

10:50 Short GNSS baseline with short-length session, what precision level can we expect?

Nuno Lima, LNEC

11:10 BREAK AND POSTER SESSION

11:40 SESSION IIa: GNSS-based distance metrology – understanding uncertainty contributions

Chairman: Sten Bergstrand, SP

11:45 Submillimetric GNSS distance determination: an account of the research at the Universitat Politècnica de València (UPV)

Sergio Baselga, Luis García-Asenjo and Pascual Garrigues, Universitat Politècnica de València

12:05 Investigations on the influence of near-field effects and obstruction on the uncertainty of GNSS-based distance measurements

Florian Zimmermann, University of Bonn

12:25 On the influence of the troposphere on GNSS-based distance metrology: modeling and experiments

Steffen Schön , T. Krawinkel, T. Kersten, University of Hanover

12:45 LUNCH

13:45

SESSION IIb: GNSS-based distance metrology – towards standardized field characterization

Chairman: Florian Pollinger, PTB

13:50 Metrological Control of Global Navigation Satellite System (GNSS) Equipment

Teresa F. Pareja, Miguel C. Cortés Calvo, Universidad Politécnica de Madrid

14:10 A field test procedure to check GNSS antenna calibration parameters

Markku Poutanen, FGI

14:35 SESSION III: Traceable electronic distance meters in air – towards novel standards for baseline calibration

Chairman: Jean-Pierre Wallerand, LNE-CNAM

14:55 Electronic Distance Meter Technology inside Trimble’s Geospatial Instruments

Christian Grässer, Trimble

PROGR AM M E ►►►

Metrology for long distance surveying | IPQ, Caparica | 9:00 | 21

st November 2014

15:15 Spectroscopic inline thermometry

Tuomas Hieta, MIKES

15:35 A 1550 nm telemeter for outdoor application based on off-the-shelf components

Joffray Guillory et al., LNE-CNAM

15:55 A refractivity-compensated absolute distance interferometer as prospective novel primary standard for baseline calibrations

Karl-Meiners-Hagen, PTB

16:15 BREAK AND POSTER SESSION

16:45 SESSION IV: Frequency-comb based distance metrology – fundamental technology for future application

Chairman: Florian Pollinger, PTB

16:50 Heterodyne many-wavelength interferometry

Jutta Mildner, PTB

17:10 Spectrally resolved frequency comb interferometry for long distance measurement

Steven van den Berg, VSL

17:30 CLOSING SESSION

POSTER SESSION

Common-clock experiments with GNSS-based distance meters

Julia Leute, Thomas Krawinkel, Andreas Bauchand Steffen Schön, PTB, University of Hanover

Uncertainties of GNSS baselines related to ITRF

D. Tengen, C. Homann, W. Niemeier, Technical University of Braunschweig

The INRIM experimental set-up to characterize the effect of the turbulence

M. Zucco, M. Astrua, INRIM

A GPS-based local tie vector at the Onsala Space Observatory

Tong Ning, Rüdiger Haas, Gunnar Elgered, Chalmers University of Technology

Elevation dependent deformation of the Onsala 20 m telescope

S. Bergstrand, SP

High accuracy laser ranging and amplitude-to-phase coupling

Michel Lintz, Observatoire de la Côte d'Azur

Design of the external optical cavity for multiplication of repetition rate of Er:dopped fs comb

Radek Smid, Adam Lesundak, Lenka Pravdova, and Ondrej Cip; Institute of Scientific Instruments of AS CR; CZ

Femtosecond frequency comb mode selection by external optical cavity

Adam Lesundak, Steven van den Berg; Institute of Scientific Instruments of AS CR; CZ

Dispersion compensation for absolute distance measurement based on the femtosecond optical frequency comb

Tengfei Wu, Li Zhang, Shuai Xing and Zhiguo Liang; P.R.China

Investigation of uncertainty of GNSS-based distance metrology using EPN Double Stations data

Aleksei Liubzhyn, Pavel I. Neyezhmakov, Yevgen M. Zanimonskiy, Volodymyr S. Kupko and others; UKRAINE

Rua António Gião, 2, 2829-513 Caparica | Portugal | Tel +351 212 948 136 Fax +351 212 948 223

www.ipq.pt

http://www.ipq.pt/



ABSTRACTS



OPENING SESSION

Introduction to EMRP JRP SIB60

“Metrology for long distance surveying”

1st

Workshop on Metrology for Long Distance Surveying Caparica, Portugal, 21

st November 2014

Introduction to EMRP JRP SIB60 “Metrology for long distance surveying”

F. Pollinger1,*

, M. Astrua2, A. Bauch

1, S. Bergstrand

3, N. Bhattacharya

4, A. Bosnjakovic

5, L. Eusebio

6,

E. Filipe6, C. Francese

2, B. Görres

7, J. Guillory

8, T. Hieta

9, C. Homann

10, J. Jokela

11, U. Kallio

11,

T. Kersten12

, H. Koivula11

, T. Krawinkel12

, H. Kuhlmann7, V. Kupko

13, A. Lesundak

14, J. Leute

1,

F. Marques6, K. Meiners-Hagen

1, M. Merimaa

9, J. Mildner

1, W. Niemeier

10, P. Neyezhmakov

13,

O. Pellegrino6, C. Pires

6, M. Poutanen

11, F. Saraiva

6, S. Schön

12, D. Tengen

10, S. A. van den Berg

15,

J.-P. Wallerand8, F. Zimmermann

7, M. Zucco

2

1 Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany

2 Instituto Nazionale di Ricercia Metrologica (INRIM), Strada delle Cacce 91, 10135 Torino, Italy

3 SP Technical Research Institute of Sweden, P. O. Box 857, 50115 Borås, Sweden

4 Optics Research Group, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft,

Netherlands

5 Institut za mjeriteljstvo Bosne i Hercegovine (IMBiH), Augusta Brauna 2, BA-71000 Sarajevo, Bosnia and Herzegovina

6 Instituto Português da Qualidade (IPQ), Rua António Gião 2, 2829-513 Caparica, Portugal

7 University of Bonn, Institute of Geodesy and Geoinformation, Nußallee 17, 53115 Bonn, Germany

8 Conservatoire National des Arts et Métiers (CNAM), 292 rue Saint-Martin, 75141 Paris Cédex 03,, France

9 Centre for Metrology and Accreditation (MIKES), Tekniikantie 1, 02151 Espoo, Finland

10 Technische Universität Braunschweig, Institut für Geodäsie und Photogrammetrie, Pockelstraße 3, 38106 Braunschweig,

Germany

11 Finnish Geodetic Institute, PL 15, Geodeetinrinne 2, 02431 Masala, Finland

12 Leibniz Universität Hannover, Institute für Erdmessung, Schneiderberg 50, 30167 Hannover, Germany

13 National Scientific Centre “Institute of Metrology” (NSC-IM), 42 Mironositskaya Street, 61002 Kharkov, Ukraine

14 Institute of Scientific Instruments, Academy of Sciences of the Czech Republic, Krávopolská, 612 64 Brno, Czech Republic

15 National Metrology Institute VSL, Thijsseweg 11, 2629 JA Delft, The Netherlands

* Corresponding author: [email protected]

Keywords: traceability, EDM, GNSS-based distance meters, local tie metrology, EMRP

Abstract

In December 2012, the European Metrology Research Programme (EMRP) [1] decided to

fund the three-year international joint research project (JRP) SIB60 “Metrology for long

distance surveying” [2] in the framework of its “SI Broader Scope II” targeted program. The

project unites metrologists, surveyors and geodesists in a major effort to develop novel

technologies and methods to improve traceability and to reduce uncertainties of length

metrological tools used in surveying, both of optics-based (electro-optic distance meters

(EDM)), and of GNSS-based technologies.

The major scientific and technical objectives of the project are :

(1) To focus on the optical measurement in air, in particular on the inline compensation

of the refractive index along the whole beam path, but also on the impact of

turbulences on the measurement, targeting a relative uncertainty of 10-7

over a

distance of 1 km.

„

mailto:[email protected]

1st


st November 2014

(2) To gain a better understanding of the uncertainty of GNSS-based distance metrology.

The studies will allow the development of a sound uncertainty model and an

optimized field calibration procedure, targeting absolute uncertainties of 1 mm and

better.

(3) To explore different concepts for the application of femtosecond laser-based

many-wavelength interferometry to long-distance metrology with a targeted relative

measurement uncertainty significantly better than 4x10-7

under controlled

environment indoor and well-monitored conditions outdoor.

(4) To develop solutions to improve state-of-the-art surveying practice immediately,

ranging from field-capable optical standards with relative uncertainties of 10-7

for

long-distance baseline calibrations, over refined guidelines for the calibration of both

EDM and GNSS-based distance meters, up to an extensive inter-comparison of major

primary geodetic baselines in Europe.

(5) To investigate different approaches to real-time monitoring of local ties at geodetic

fundamental stations, both experimentally and theoretically. Thus, fundamental

metrology for the Global Geodetic Observing System (GGOS) is developed adhering

the overall target to reduce uncertainty of reference frames to 0.1 mm.” [2]

In the first 14 months of the project duration, major challenges have been tackled. Concepts

of novel primary optical refractivity-compensated standards have been realized. Field-

capable prototypes are currently being characterized, improved and verified. Complex

uncertainty contributions to GNSS-based distance measurements, like influence of

troposphere and near-field are being experimentally studied, and a field-procedure for the

verification of electromagnetic antenna calibration parameters was developed and is being

tested. In addition, larger space-geodetic campaigns are prepared to investigate different 3D

real time concepts for local tie metrology at geodetic fundamental stations.

This presentation is intended to introduce the project as a whole to the participants of this

first public Workshop and give a broader survey of first achievements. It should set a

common basis for fruitful discussions on technical details, but also on the broader picture

during the day, and beyond.

The presented joint research project SIB60 “Surveying” receives funding by the European

Metrology Research Programme (EMRP). The EMRP is jointly funded by the EMRP

participating countries within EURAMET and the European Union

[1] www.emrponline.eu

[2] JRP SIB60 Surveying, Publishable JRP Summary Report for JRP SIB60 Surveying, www.

emrp-surveying.eu, (2014)



SESSION I

Challenges of distance metrology

in surveying

1st


st November 2014

Survey activities at CERN

Dominique Missiaen1,*

1 CERN, 1211 Geneva 23, Switzerland

* [email protected]

Keywords : CERN, survey, alignment, metrology

Abstract

CERN, the European Laboratory for Particle Physics, is the first laboratory in the world for

fundamental research and especially at High Energy. Its flagship, the Large Hadron Collider

(LHC), a circular proton-proton collider of 27 km of circumference, has permitted the

discovery of the Higgs’s particle in 2012 inside its two large experimental detectors ATLAS

and CMS.

All along the 27 km vacuum chamber, many accelerator components are interacting with the

particle beam: quadrupole magnets are either focusing or defocusing the beam, dipole

magnets are bending it to give its circular shape, accelerator cavities produce a higher speed

and many other secondary equipment provide with information on the beam characteristics.

All these components have to be aligned with an accuracy never reached before, typically a

couple of mm as an absolute accuracy and 0.1-0.2 mm as a relative one.

The talk will present the specific techniques which are used at CERN to achieve the

requested accuracy and the geodetic needs for the future big projects in the domain of

particle physics.

1st


st November 2014

Measuring the earth’s surface deformation using InSAR and GPS

João Catalão

Instituto D. Luiz, Faculdade de Ciencias da Universidade de Lisboa

Campo Grande, 1749-016 Lisboa, Portugal


Keywords : Deformation, GPS, SAR interferometry

Abstract

Space-borne global positioning systems brought new insights to the geodetic science

providing means to measure the position, and their time variation, of points on the earth’s

surface, with unprecedented accuracy. Among others, the Global Position System (GPS)

offers an accuracy and spatial coverage that was not available using classical methodologies.

Despite its high accuracy, GPS-based systems are point-like measurements with a scarce

distribution on the earth’s surface that can be complemented with synthetic aperture radar

interferometric (InSAR) measurements. In fact, these imaging system provides measurements

of deformation in the satellite line of sight of vast areas of the earth surface with a time

resolution of about 6 days (at the equator). The repeat-pass space-borne SAR interferometric

approach is based on the phase comparison of two synthetic aperture radar (SAR) images

acquired at different times with slightly different looking angles. The acquisition of SAR

images was initiated regularly by ESA in 1992 with the launch of the ERS1 satellite and was

followed by ERS2, ENVISAT and the Setinel-1A (2014) missions. In this communication we

will present a method to derive accurate spatially dense maps of 3-D terrain displacement

velocity based on the merging of terrain displacement velocities estimated by time series of

interferometric synthetic aperture radar data acquired along ascending and descending orbits

and repeated GPS measurements. The method uses selected persistent scatterers (PSs) and

GPS measurements of the horizontal velocity. It is shown that accurate vertical velocities at

PS locations can be retrieved if smooth horizontal velocity variations can be assumed. The

proposed methodology is applied to the case study of Azores islands and Singapore

characterized by important tectonic and subsidence phenomena, respectively.

Acknowledgments

This is a contribution to Project MEGAHazards (PTDC/CTE-GIX/108149/2008) funded by

FCT, Portugal.

1st


st November 2014

Short GNSS baseline with short-length session, what precision level can we

expect?

José Nuno Lima1,*

1 Laboratório Nacional de Engenharia Civil, Avenida do Brasil, 101 -1700-066 Lisboa, Portugal


Keywords : GNSS, short-length session, short baseline, precision

Abstract

To test the viability of the GNSS with short-length sessions in the measuring of

displacements at large dams, the Division of the Applied Geodesy of the Concrete Dams

Department, of the National Civil Engineering Laboratory (LNEC), has carried out several

studies on a 325 m baseline, with different length observation sessions.

Precise GNSS relative positioning requires the using of carrier-phase observations, at the least

of two receivers, and fixing the integer ambiguities. With increasing distance between

receivers, ambiguity fixing becomes more difficult because ionospheric and tropospheric

effects do not cancel sufficiently in double difference. A most common procedure in static

relative positioning is to increase the length of the observation session and/or to apply

atmospheric models and corrections. In general, increasing the length of the observation

session promotes the decrease of the uncertainty of the displacements measured by the GNSS.

In fact, we have carried out several tests in LNEC campus, on a 325 meters length GNSS

baseline, with different length sessions, from 1 minute to 24 hours, which are proving this

statement. Figure 1 present the results obtained: the standard deviations for the relative

position, in North component (purple balls), East component (blue balls) and height

component (orange balls) decrease with the increasing of the session length.

As shown in Figure 1, the standard deviation for relative positioning in N component is

similar for the E component, but for the height component it is 3 times higher. For example,

we obtained for length sessions of 5 minutes the value 1.8 mm for standard deviation in

horizontal component and the value 5.7 mm for standard deviation in vertical component.

mailto:jnplima@lnec.

1st


st November 2014

Figure 1: Standard deviations for relative position, in N component (purple balls), in E component

(blue balls) and in height component (orange balls), on a 325 m GNSS baseline, obtained from

1minute, 5 minute, 10 minute, 15 minute, 30 minute, 1 hour, 8 hour and 24 hour session length. T is

the length session expressed in hours.



SESSION IIa

GNSS-based distance metrology –

understanding uncertainty

contributions

1st


st November 2014

Submillimetric GNSS distance determination: an account of the research at

the Universitat Politècnica de València (UPV)

Sergio Baselga1,*

, Luis García-Asenjo1 and Pascual Garrigues

1

1 Cartographic Engineering, Geodesy and Photogrammetry Department, Universitat Politècnica de València, Valencia,

Camino de Vera s/n, Spain


Keywords : Distance measurement, GNSS, calibration baseline.

Abstract

In this contribution we present our approach to investigate the capabilities of GNSS for

determining distances up to 1 km with submillimetric accuracy. Among the initial

assumptions that may lead to consider GNSS as a potential submillimetric measuring tool we

find its high stability at the global scale (1 ppb) and the low noise (at the submillimeter level)

that may attain some modern receivers in their phase observations.

Our approach is specifically tailored to the problem of determining only the slant distance that

substantially differs from the traditional geodetic approach where ambiguities are usually

determined and the baseline spatial orientation is also required. We only use L1 phase

observations along with an ambiguity free model that only requires the knowledge of the

approximate coordinates of the baseline ends within a few centimeters, which is easily

achievable e.g. by means of an initial PPP processing.

Some preliminary results were obtained after an automated processing of different baselines

in 1h timespans along entire years, which resulted in nearly 9000 values for each baseline and

year. We identified the multipath effect of one sidereal day period as the major source of

GNSS length variation. We also experienced that antenna calibration accuracies play a non-

negligible role in this question, fact that was already concluded in previous studies. We found

variations to be considerably mitigated after a 24 h observation time and corresponding results

to be consistent in the long term below the millimeter level although some unmodelled effects

of the order of a few tenths of a millimeter still remained. In addition, we also found that

robust estimation computed as a global optimization problem permits further reduction of

those variations.

Once the inner consistency of GNSS lengths has been found to be stable at the few

submillimeter level in the mid and long term (days to months) there remains the question of

comparison with the absolute SI meter. This comparison should be conducted in outdoor

facilities that have been proved stable to the submillimeter level and whose distances have

been traced to the SI meter. Few test fields meet such demanding requirements, e.g. Nummela

Standard Baseline. Therefore we decided to transfer absolute scale from Nummela to our test

field in the UPV in 2012 and carry out periodical deformation monitoring in cooperation with

the Universidad Complutense de Madrid (UCM) using a Mekometer ME5000. Ongoing

GNSS campaigns in our facility are now being conducted in order to assure that GNSS

lengths are not only self-consistent and stable in the long term below the millimeter level but

also accurately related to the absolute meter.


1st


st November 2014

Investigations on the influence of near-field effects and obstruction on the

uncertainty of GNSS-based distance measurements

Florian Zimmermann1,*

, Heiner Kuhlmann1

1 University of Bonn, Institute of Geodesy and Geoinformation, Nussallee 17, 53115 Bonn, GERMANY

* [email protected]

Keywords: antenna near-field effects, antenna spacer, satellite shadowing scenarios

Abstract

These investigations are performed within the joint research project SIB60 “Surveying” of

the European Metrology Research Programme (EMRP). The EMRP is jointly funded by the

EMRP participating countries within EURAMET and the European Union.

Antenna near-field effects are one of the accuracy limiting factors on GNSS-based distance

measurements. In order to analyse these influences, a measurement campaign at an EDM

calibration baseline site near Munich was performed. During the campaign, 6 pillars of the

baseline site with distances between 19 and 1100 meters were equipped with different kinds

of antenna mounts. In particular, spacer types of different length and material were used to

increase the distance between the pillar and the antenna and thus, to analyse the possibility to

separate or minimize the impact of antenna near-field effects from the coordinate

determination process. Prior to the measurement campaign, the PCOs and PCVs of the

GNSS-antennas were calibrated in an anechoic chamber at the University of Bonn. The

intention of these investigations is to identify an optimum configuration for the antenna set-

up by comparison of the GNSS-based distance measurements from 90 baselines with diverse

combinations of antenna mounts to known reference values of height and distance.

The analysis of the computed differences reveals that the most critical step during the

measurement process is the precise levelling and centering of the antenna set-up on the

reference point of each pillar. Uncertainties ascribed to the centering of the antennas can lead

to maximal deviations of up to 3 millimetres in the distance component and thus, lead to a

high variance of the differences and a deterioration of the uncertainty level. It becomes

obvious that the precise centering and levelling of the antennas is a non trivial process,

independent from the spacer length.

First results show that using different spacer type materials, i.e., aluminium and carbon fibre

does not significantly improve the distance measurements and thus, can be excluded as an

option to optimize the antenna set-up. Furthermore, also no differences between the different

spacer lengths can be identified yet.

In addition to antenna near-field effects, satellite obstructions are a further problem in high

precision GNSS-based length measurements, since it is usually not possible to work in an

optimum surrounding, i.e., nearly free of multipath and free horizon. Several shadowing

scenarios will be presented, which will be used to analyse and quantify the influence of

satellite shadowing by numerical simulations on observations by otherwise perfectly

calibrated antenna set-ups.


1st Workshop on Metrology for Long Distance Surveying

Caparica, Portugal, 21st November 2014

On the influence of the troposphere on GNSS based distance metrology:

modeling and experiments

Thomas Krawinkel, Tobias Kersten* and Steffen Schön Leibniz Universität Hannover, Institut für Erdmessung, Schneiderberg 50, 30167 Hannover, Germany


Keywords: GNSS, troposphere, local ties

Abstract

Apparent coordinate changes in GNSS time series represent a significant issue in GNSS reference station networks. Especially co-located stations and other GNSS reference stations are influenced by the type of GNSS processing. By varying observables or hardware equipment (antenna changes) apparent coordinate changes mainly in the up-component can be expected although an individually and absolute calibrated GNSS antenna remains in the same geometrical place. In this contribution the authors propose a classification to understand and to model these variations. Therefore the systematic effects on the GNSS observables are categorised into (1) a mathematical and (2) a physical effect. This classification allows analysing the individual contributions of the different impacts on the apparent coordinate changes. A comprehensive data analysis with 9 different reference station antennas is presented. It will be shown that L1 and L2 time series show high consistent repeatability of less than 1mm variations for identical antenna types. In the case of additionally estimated troposphere parameters it will be shown that a direct link between troposphere parameters and station height with a relation of 1:-3 can be expected. It is verified that 1mm tropospheric correction leads to -3mm in the up-component regardless of the used antenna equipment. Gained insights will be discussed in the context of coordinate discrepancies in the local ties of ITRF (International Terrestrial Reference Frame) and recommendations will be given to significantly reduce this issue in GNSS processing. They can be summarized as follows: In small scaled networks with similar tropospheric conditions it is advisable to reduce the apparent offsets by using double differences. If this should not be possible and additionally troposphere parameters have to be estimated, this presentation shows how to significantly reduce the mathematical effect on the station height by applying an additional correction. This contribution is embedded in the joint research project SIB60 “Surveying”, funded by the European Metrology Research Programme (EMRP) participating countries within EURAMET and the European Union.

mailto:[email protected]�



SESSION IIb

GNSS-based distance metrology –

towards standardized field

characterization

1st


st November 2014

Metrological Control of Global Navigation Satellite System (GNSS)

Equipment

Teresa F. Pareja1,*

, Miguel C. Cortés Calvo2

1 Laboratorio de control metrológico de instrumental geodésico y topográfico. Universidad Politécnica de Madrid. Campus

Sur. Carretera de Valencia km 7; 28031 Madrid, Spain

2 Laboratorio de control metrológico de instrumental geodésico y topográfico. Universidad Politécnica de Madrid.

* [email protected]

Keywords : GNSS, networks control, traceability, uncertainty

Abstract

The studies carried out so far for the determination of the quality of measurement of geodetic

instruments have been aimed, primarily, to measure angles and distances. However, in recent

years it has been accepted to use GNSS (Global Navigation Satellite System) equipment in

the field of Geomatic applications, for data capture, without establishing a methodology that

allows obtaining the calibration correction and its uncertainty.

The purpose of this contribution is to establish the requirements that a network must meet to

be considered a Standard Network with metrological traceability, as well as the methodology

for the verification and calibration of GNSS instrumental in those standard networks. To do

this, a technical calibration procedure, based on ISO17123-8:2007, has been designed,

developed and defined for GNSS equipment determining the contributions to the uncertainty

of measurement. The procedure, which has been applied in different networks for different

equipment, has allowed determining the expanded uncertainty of such equipment following

the recommendations of the Guide to the Expression of Uncertainty in Measurement of the

Joint Committee for Guides in Metrology (JCGM).

Based on high technical quality studies and observations carried out in these networks

previously, it has been possible the estimation of local calibration corrections for high

accuracy GNSS equipment in standard networks. In addition, the uncertainty of calibration

correction has been calculated using two different methodologies: the first one by applying

the law of propagation of uncertainty, while the second has applied the propagation of

distributions using the Monte Carlo method. The analysis of the obtained results confirms the

validity of both methodologies for estimating the calibration uncertainty of GNSS equipment.

1st


st November 2014

A field test procedure to check GNSS antenna calibration parameters

Ulla Kallio*, Hannu Koivula, Sonja Nyberg, Markku Poutanen and Jorma Jokela

Finnish Geodetic Institute, Geodeetinrinne 2, 02430 Masala, Finland


Keywords : GNSS antenna, calibration, test field

Abstract

The Global Positioning System (GPS) and other satellite navigation systems, altogether

called Global Navigation Satellite Systems (GNSS), offer tools to measure distances with

millimetre accuracy and with no need of visibility between the receivers. In the viewpoint of

metrology the traceability of measurements is uncontrollable because the distance obtained

with the GNSS measurement cannot be unambiguously conducted from the definition of

metre. Within the SIB60 project the Finnish Geodetic Institute has built a GNSS test field at

the Metsähovi Observatory. The test field having a traceable scale transferred from the

Nummela Standard baseline will be used for testing optimum processing strategies of GNSS

observations and to validate calibrations of individual GNSS-antennas.

We describe the structure and use of the GNSS test network at Metsähovi. A part of the

network will be used for validation of antenna calibrations. Due to its structure, it is called

“Revolver” and its design is based on the simulations and test measurements during the

SIB60 project. It consists of concrete pillars with a special centring system to attach the

GNSS antennas. The tolerances for holes and bolts follow ISO 286-2 H7 and h7. Tests and

measurements were done at the test field during the summer 2014. In this presentation we

describe the procedure, measurements, and first results obtained. We also discuss future

plans for the network.

This project is performed within the joint research project SIB60 “Surveying” of the European Metrology Research Programme (EMRP). The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.

A part of the FGI GNSS test field with the “Revolver” shown inside the circle.




SESSION III

Traceable electronic distance meters

in air – towards novel standards

for baseline calibration

1st


st November 2014

Electronic Distance Meter Technology inside

Trimble’s Geospatial Instruments

Christian Graesser*, Martin Koehler

Trimble AB, 18211 Danderyd, Rinkebyvägen 11, Sweden


Keywords : Pulsed, phase-shift, distance meter, Laser, Trimble

Abstract

The presentation will give an insight into Trimble’s electronic distance meter (EDM)

technology used in the total stations and scanners. That includes the three different methods

phase shift EDM, pulsed averaging and direct sampling EDMs applied in the instruments.

The generation, sampling and evaluation of the signals will be presented as well as the

optical setup. The calibration and traceability of the measurement systems will complete the

talk.


1st


st November 2014

Spectroscopic inline thermometry

T Hieta1,*

, T Fordell1, M Vainio

1,2, M Merimaa

1

1 Centre for Metrology and Accreditation (MIKES),Tekniikantie 1, Espoo 02151, Finland

2 Laboratory of Physical Chemistry, Department of Chemistry, A. I. Virtasen aukio 1, University of Helsinki, Helsinki 00014,

Finland


Keywords : laser spectroscopy, refractive index of air, air temperature, interferometry

Abstract

In optical distance measurements it is essential to know the refractive index of air with high

accuracy. Commonly, the refractive index of air is calculated from the properties of the

ambient air using either Ciddor or Edlén equations, where the dominant uncertainty

component is in most cases air temperature. The method developed in MIKES utilises direct

absorption laser spectroscopy of oxygen to measure the average temperature of air. The

method allows measurement of temperature over the same beam path than in optical distance

measurement, providing spatially well matching data. Indoor and outdoor measurements

demonstrate the effectiveness of the developed method.

The MIKES work in SURVEYING EMRP project aims to extend the measurement distance

of oxygen thermometer up to 1 km using simplified single laser set-up for extra robustness

and simplicity. The new set-up designed for field applications include large diameter optics

and separate transmitting and receiving end.

The EMRP project SIB60 “Surveying” is jointly funded by the EMRP participating countries

within EURAMET and the European Union.


1st


st November 2014

A 1550 nm telemeter for outdoor application based on off-the-shelf

components

J. Guillory1, J. G. Marquez

1, A.-F. Obaton

1, D. Truong

1, C. Alexandre

2 and J.-P. Wallerand

1*

1 Laboratoire Commun de Métrologie (LNE – Cnam), 1 rue Gaston Boissier, 75015 Paris, France

2 Conservatoire National des Arts et Métiers (Cnam), Laboratoire CEDRIC/LAETITIA, 292 rue St-Martin, 75003 Paris, France


Keywords: optical telemetry, phase measurement, intensity modulation, absolute distance meter.

Abstract

We will present at the workshop the development of a telemeter based on an intensity-

modulated laser diode. It has the advantage to be more robust than classical fringe counting

interferometers, especially for long-distance outdoor propagation, and less expensive than

superheterodyne synthetic-wavelength interferometers [1]. For such a system, we aim a

relative resolution of 10-7

, i.e. some micrometers at short range or 100 µm over 1 km.

In this telemeter, depicted in Figure 1, the distance D is determined by measuring the phase

shift Φ accumulated by a Radio Frequency (RF) carrier that has been transposed in the

optical domain and propagated in free space until a reflective target. The calculation of this

distance is detailed in Figure 1.

In practice, we use affordable optoelectronic components coming from the

telecommunication world. Thus, an optical beam at 1550 nm is emitted by a Distributed

FeedBack laser diode (DFB), RF modulated by an Electro-Absorption Modulator (EAM) and

boosted by an Erbium-Doped Fiber Amplifier (EDFA). The signal is then propagated in free

space: an off-axis parabolic mirror collimates the beam at the fiber output, and after

reflection on a corner cube, reinjects it in the same fiber. Lastly, the optical signal is

converted by a free-space photodiode into an electrical one and down-converted at 10 MHz

since our phasemeter cannot directly measure high frequencies. An optical switch has also

been implemented in the setup to compare successively the measured distance to a reference

distance that does not vary during the measurement process. Thus, every variation observed

on the reference path is interpreted as a drift from the system (temperature evolution) and is

removed.

Tests have been performed outdoor, during a sunny day with temperatures ranging from 32

to 34 °C over a 100 m length asphalt road. In these harsh conditions that induce strong air

turbulences, the optical beam was affected by a large intensity noise. The latter was

converted by the reception chain in phase noise, but by selecting the phase values of same

amplitudes, a standard deviation less than 25 µm has been reached for a 1310 MHz

modulation frequency.

The next step will consist in determining the temperature along the optical path with a

precision of ± 0.1 °C, which is the required accuracy for the air index calculation. To this end,

a second wavelength at 780 nm will be added to the system. Thus, the measured distance will

be corrected taking advantage of the dependence of the chromatic dispersion of the refractive

index with air temperature [2] [3].

[1] S. Azouigui et al., Rev. Sci. Instrum., 81, 053112, 2010.

[2] K.B. Earnshaw et al., Appl. Opt., Vol. 11, Issue 4, 1972.

[3] K. Meiners-Hagen et al., Meas. Sci. Technol., 19, 2008.

1st


st November 2014

Figure 1: Experimental setup.

This project is performed within the joint research project SIB60 “Surveying” of the European Metrology Research Programme (EMRP). The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.

lens

RF

LOS

S

mixer

Ph

ase

mete

r

10MHz.

amplifier

Reference path

single

chipEAMDFB

PDbias

tee

Bias

voltage

Att.

RF = radio frequency synthesizerLO = local oscillator

S = RF splitter

DFB = distributed feedback laser diode

EAM = electro-absorption modulator

EDFA = erbium doped fiber amplifier

SMF = single mode fiber

Att. = variable optical attenuator

PD = free-space photodiode

optical splitter

(used as a circulator)

off-axis

parabolic

mirror

distance D

Target

fiber connector(FC/APC)

corner

cube

Measure path

optical switch

Φ

sine wave that has

been propagated

in free-space

electrical

sine wave

10MHz

1310MHz

1300MHz

mirror

EDFA

SMFisolator

RFfn

ckD

22

ΦCnfRFk

the measured phase shiftthe speed of light in vacuumthe group refractive indexthe frequency modulation (1310MHz)an integer number of 2π modulowithin the distance to be measured.

RFf

1st


st November 2014

A refractivity-compensated absolute distance interferometer as prospective

novel primary standard for baseline calibrations

Karl Meiners-Hagen1,*

, Florian Pollinger1 and Alen Bošnjakovic

2

1 Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116 Braunschweig

2 Institut za mjeriteljstvo Bosne i Hercegovine (IMBiH), Augusta Brauna 2, BA-71000 Sarajevo, Bosnia and Herzegovina


Keywords: EDM calibration, refractivity compensation, multi-wavelength interferometry, surveying

Abstract

Traceable calibrations of geodetic baselines based on optical distance metrology are limited

by the influence of the refractive index of air. Especially the knowledge of the air

temperature in the measuring path limits the accuracy since the temperature distribution

depends heavily on the weather conditions.

Within the EURAMET joint research project SIB60 ‘Metrology for long distance surveying’

an absolutely measuring heterodyne interferometer is developed for a measuring range of

1 km with a targeted accuracy of 0.1 mm. The refractive index of air as the dominating

uncertainty source for interferometric length measurement is compensated by the two-color

method which based on the knowledge of dispersion. This device is intended as a future

primary standard for baseline calibrations.

Two frequency doubled Nd:YAG lasers emitting both wavelengths at 532 nm and 1064 nm

are the light sources for the interferometer. The frequency of one laser is stabilised onto the

other with a frequency difference of 20 GHz at 1064 nm, corresponding to 40 GHz at 532 nm

wavelength. The resulting synthetic wavelengths of 15 mm and 7.5 mm are used for the

length measurement. Therefore, the unambiguous measuring range is limited to only 7.5 mm

for this approach. To increase the unambiguous measuring range, longer synthetic

wavelengths are generated by acousto-optic frequency shifters which are also used for the

generation of the heterodyne frequencies. The results of the long synthetic wavelengths are

used to get the fringe order of the short ones resulting in a large measuring range with the

uncertainty determined solely by the short synthetic wavelengths.

The results for 532 nm and 1064 nm deliver optical path lengths corresponding to the

mechanical length multiplied by the refractive index of air for each wavelength. Due to the

dispersion in air the optical path lengths differ by an amount of approximately 4 µm/m. The

effective refractive index of air can be calculated from this difference which resolves the

typical problems of the outdoor measurement of the environmental parameters.

The interferometer head which is typically mounted on a pillar of a baseline is designed to

ensure outdoor capability and compatibility with standard geodetic equipment.

First results with this interferometer at the 50 m interference comparator of the PTB will be

presented.

This project is performed within the joint research project SIB60 “Surveying” of the

European Metrology Research Programme (EMRP). The EMRP is jointly funded by the

EMRP participating countries within EURAMET and the European Union




SESSION IV

Frequency-comb based distance

metrology – fundamental technology

for future application

1st


st November 2014

Heterodyne many-wavelength interferometry

Jutta Mildner1,*

, Karl Meiners-Hagen1 and Florian Pollinger

1



Keywords: length metrology, femtosecond frequency comb, many-wavelength interferometry,

MSTAR

Abstract

Up-to-date long distance metrology in engineering, geodesy and surveying ask for relative

measurement uncertainties of better than 10-7

, which are not available yet. A promising tool

to push optical-based measurement techniques into this regime are broadband optical

frequency combs. These sources offer the opportunity to generate synthetic wavelengths

from the optical to the microwave range and are capable of directly tracing the measured

distance to the SI definition of the metre.

In this contribution we present a novel concept of a heterodyne many-wavelength

interferometer based on only one frequency comb in contrast to different approaches1.

Inspired by the MSTAR demodulation method2 a direct heterodyne phase detection of

individual comb lines is aimed at. To this end a single high-repetition rate fiber-based optical

frequency comb with stabilized carrier envelope offset (CEO) is used as a seed laser. By

cavity-filtering two coherent combs of different mode spacing in the GHz band are generated

and subsequently used as local oscillator and measurement beam for heterodyne

interferometry. Based on this scheme, a complete chain of synthetic wavelengths from the

macroscopic (millimetre regime) to the interferometric range (nanometre resolution) can be

realized in theory, making full phase unwrapping possible without additional high-accuracy

information. This large dynamic range together with the opportunity of more robust optical

set-ups would pave the way for future applications in surveying and engineering.

Development and demonstration of a prototype filtering unit with tuneable spacing in the

super high frequency (SHF) band will be presented, including simulations and experiments

on positioning sensitivity. Furthermore, we want to discuss the deployed stabilization

schemes as well as current progress on optimization measures.




1I. Coddington, W. C. Swann, L. Nenadovic and N. R. Newbury, Nature Photonics 3, 351 (2009)

2O. P. Lay, S. Dubovitsky, R. D. Peters, J. P. Burger, S.-W. Ahn, W. H. Steier, H. R. Fetterman and Y. Chang,

Opt. Lett. 28, 890 (2003)


1st


st November 2014

Spectrally resolved frequency comb interferometry for long distance

measurement

Steven A. van den Berg1,*

, Sjoerd van Eldik2 and Nandini Bhattacharya

2

1 VSL, Thijsseweg 11, 2629 JA, Delft, The Netherlands

2 Technische Universiteit Delft, Lorentzweg 1, 2628 CJ Delft, The Netherlands


Keywords : frequency comb, interferometry, distance metrology, high-resolution spectroscopy

Abstract

The invention of the femtosecond frequency comb has been a step change in the field of

optical-frequency metrology, with a wide outreach to other fields, like high-resolution

spectroscopy, femtosecond-pulse shaping and absolute distance measurement. A fs comb

frequency comb laser emits a spectrum consisting of equally spaced optical frequencies, with

a mutual spacing equal to the repetition frequency of the laser. We have investigated the

femtosecond frequency comb as a potential new source for accurate absolute long-distance

measurements, exploiting the unique properties of the comb and utilizing the direct

traceability to the SI second. The latter is realized by phase locking the frequency comb to an

atomic clock. In this contribution we focus on distance measurement with a mode-resolved

frequency comb laser. The frequency comb light is sent into a Michelson interferometer,

consisting of a measurement and a reference arm. Subsequently, the interferometer output is

analyzed with a high resolution spectrometer based on a virtually imaged phase array (VIPA)

and a grating. The VIPA spectrometer unravels the 1~GHz spaced comb frequencies to

distinct modes. As a result, interferometry on the level of individual modes (wavelengths)

can be observed. The distance is determined from both spectral interferometry and massively

parallel homodyne interferometry of about 9000 frequency comb modes. We have delivered

an experimental proof of principle of homodyne frequency comb interferometry by

measuring a short displacement with an unraveled comb and a counting helium-neon laser

simultaneously, showing an agreement of tens of nanometers[1]. Recently, we have extended

the measurement range to tens of meters, which – according to preliminary results – shows

an agreement within 10-7

, relative to the counting helium-neon laser that probes the same

interferometer displacement for comparison. This application of a fs frequency comb for

distance measurement can be considered as a combination of multiwavelength

interferometry with thousands of continuous wave (cw) lasers and spectral (dispersive)

interferometry. It overcomes the limitations of the individual techniques, combining an

interferometric scheme with a large range of non-ambiguity. This allows for non-incremental

absolute measurement of an arbitrary distance with a single frequency comb laser.

Reference

[1] S.A. van den Berg, G.J.P. Kok, S.T. Persijn, M.G. Zeitouny and N. Bhattacharya, Many-

wavelength interferometry with thousands of lasers for absolute distance measurement,

Phys. Rev. Lett. 108 183901 (2012)



POSTER SESSION

1st


st November 2014

Common-clock experiments with GNSS-based distance meters

Julia Leute1,*

, Thomas Krawinkel2, Andreas Bauch

1 and Steffen Schön

2


2 Leibniz Universität Hannover, Institut für Erdmessung, Schneiderberg 50, 30167 Hannover, Germany


Keywords : GNSS-based distance meters, common-clock, troposphere

Abstract

Connecting two GNSS receivers to the same external frequency (“common-clock”) enables

an analysis based on single-difference carrier phase observations without determining the

receiver clock error at every epoch. At baselines of different length this setup is used to study

tropospheric effects on GNSS-based distance measurements.

Common-clock GNSS experiments on a short (ca. 250 m) and a very short baseline (ca. 5 m)

were carried out from October 16th to 30th 2013 at PTB. Absolutely calibrated antennas

were used to suppress antenna effects. The setup included geodetic receivers from different

manufacturers to study the effects of receiver choice.

In March 2014 zero baseline experiments were performed to investigate the effect of

different external frequency standards.

Results of the single-difference analysis of various baselines will be presented.





1st


st November 2014

Uncertainties of GNSS baselines related to ITRF

W. Niemeier10

, D. Tengen10

, C. Homann10

,

10 Technische Universität Braunschweig, Institut für Geodäsie und Photogrammetrie, Pockelsstraße 3, 38106 Braunschweig,

Germany

Keywords: local tie, uncertainties, Monte Carlo simulation

Abstract

Local tie measurements determine the coordinate differences between reference points of

different space geodetic sensors.

Coordinate differences are required in ITRF or the IGS realization of the ITRF.

Using IGS precise ephemerides GNSS baselines (coordinate differences) can be determined

in ITRF (IGS) system directly.

The coordinate differences determine the orientation of the net. This is important because

coordinate differences between reference points are needed no absolute coordinates.

Additional information of a combined network with GNSS and totalstation is desirable

because the accuracy of totalstation measurements is better than the accuracy or baselines

from GNSS.

Local tie networks of different extension (50m, 300m, 1000m) will be analyzed using Monte-

Carlo simulation.

Uncertainties according to GUM will be considered in the mentioned simulation for:

GNSS:

(antenna height, antenna calibration)

totalstation station:

(setup error, instrument- and target heights, angles, distances)

Additionally, instrumental errors and atmospheric effects will be modelled.




1st


st November 2014

The INRIM experimental set-up to characterize the effect of the turbulence

on the propagation of a laser beam in air

M. Zucco1,*

, M. Astrua1

1 Istituto Nazionale di Ricerca Metrologica (INRIM), Strada delle Cacce 91, 10135 Torino, Italy


Keywords: Turbulence, distance measurement

Abstract

The accuracy and stability of the measurement of distance in air with optical techniques is

limited by turbulence effects and by gradients of temperature. The turbulence vortices are

moved by wind or by convective motion across the laser beam causing the overall fluctuation

of the index of refraction and the wavefront distortion. At the same time, the presence of

gradients of temperature causes beam deflections and beam wandering.

These effects have an important influence on the laser beam used for distance measurement

or for optical communication. Phase fluctuations would add a phase jitter to the demodulated

signal and cause fluctuations in the measured distance. The beam wandering causes the

transversal displacement of the laser beam across the entrance aperture of the receiving set up

to cause an amplitude modulation that is translated into fluctuations of the measured distance.

Finally, beam bending is in addition induced by thermal gradients leading to longer optical

paths.

In particular, in case of beam bending, there are many theoretical and experimental studies in

literature of this effect based on turbulence theory. An early study relates the angle of arrival

with its variance [1]. From the structure parameter of the index of refraction it is possible to

obtain the correction to the geodetic measurement [2].

At INRIM a device is under development to characterize these effects. A first set-up is based

on a modulated laser at 1550 m that is split in two parallel beams having a variable distance.

By changing the beam distance and measuring the relative phase fluctuation between the two

transmitted beams it is possible to estimate the dimension of the vortices of the turbulence

and the kind of noise associated to the fluctuation. At the same time, the beam wandering and

deflection due to the gradient of the index of refraction in air is measured by measuring the

displacement of the spot on a position sensitive detector (PSD) and on a CCD camera. From

the PSD output it is possible to obtain a fast analysis of the wandering of the laser center of

mass. From the image taken from the camera it is possible to analyze the distortion of the

wavefront, at a lower rate. To measure in real time the temperature gradient in air an array of

fast thermometers has been developed. The device will be described and the first preliminary

measurements will be presented.

[1] F. K. Brunner, “Vertical Refraction Angle Derived from the Variance of the Angle-of-

Arrival Fluctuations”, In: E. Tengström und G. Teleki (Ed.), Refractional Influences in

Astrometry and Geodesy, Reidel Publ. pp. 227-238 (1979)


JRP SIB60 Surveying, 1. Workshop "Metrology for Long Distance Surveying", 21 November 2014, Caprice/Lissabon, Portugal

Poster contribution

Title: A GPS-‐based local-‐tie vector at the Onsala Space Observatory

Authors: Tong Ning, Rüdiger Haas, Gunnar Elgered

Affiliation: Chalmers University of Technology, Department of Earth and Space Sciences, Onsala Space Observatory, SE-‐439 92 Onsala (Sweden)

Abstract: So-‐called local-‐tie vectors at geodetic co-‐location stations are important pieces of information for the international terrestrial reference frame (ITRF). The Onsala Space Observatory is a co-‐location station contributing to the ITRF and operates equipment for geodetic Very Long Baseline Interferometry (VLBI) and Global Navigation Satellite System (GNSS) observations since several decades. The local-‐tie vector between the reference points of the instruments used at Onsala for VLBI and GNSS was previously observed several times by classical geodetic measurement techniques. In the summer of 2013 two gimbal-‐mounted GNSS-‐antennas were installed on the radio telescope, one on each side of the telescope dish, and several 24 hour long measurement campaigns were performed. Five semi-‐kinematic and four kinematic campaigns were conducted during July to September 2013. For the semi-‐kinematic campaigns, the telescope was pointed to different azimuth and elevation directions, spending up to 30 minutes at one position. The kinematic campaigns were conducted during normal geodetic VLBI-‐sessions where the telescope is continuously in motion and either tracking radio sources (slow motion) or slewing to new targets (fast motion). The GPS-‐data recorded with 1 Hz sampling during these campaigns were analyzed together with data from the ONSA site with a in-‐house developed software applying the double-‐difference analysis strategy with ambiguity-‐resolution. Phase-‐centre variation corrections were calculated for the rotated GNSS-‐antennas and applied in the data analysis. The resulting positions of the two GNSS-‐antennas on the telescope were used to determine its reference point and axis offset. Doing so, the so-‐called local-‐tie vector between the reference point of the telescope used for geodetic VLBI and the ONSA GNSS-‐monument was determined directly in the geocentric GPS-‐based reference frame. The results from the nine campaigns show standard deviations of 2.1 mm, 0.8 mm and 2.6 mm for the X, Y-‐ , and Z-‐axis respectively. The disagreement with respect to the coordinate differences calculated from the ITRF2008 coordinates of the reference points at epoch 2013 are 0.8 mm, 0.2 mm and 8.5 mm for the X-‐, Y-‐ and Z-‐components. The result for the axis offset has a standard deviation of 2.9 mm and differs by 0.5 mm from the results derived from classical geodetic measurements in 2002 and 2008.

1st


st November 2014

Elevation dependent deformation of the Onsala 20 m telescope

Sten Bergstrand1,*

, Magnus Herbertsson1, Jörgen Spetz

1 and Claes-Göran Svantesson

1

1 Department of Measurement Technology, SP Technical Research Institute of Sweden, Borås, Brinellgatan 4, Sweden


Keywords : VLBI, Antenna deformation, Terrestrial reference frames, delay correction

Abstract

We measured the deformation of the 20 m telescope at the Onsala Space Observatory with a

terrestrial laser scanner at eight different elevations in order to quantify the elevation

dependent deformation of the telescope. Preliminary analysis indicate paraboloid

deformations of order 5 mm, which will affect the signal path in the telescope and result in a

reference frame scale error unless accounted for.



EMRP participating countries within EURAMET and the European Union. The EMRP is

jointly funded by the EMRP participating countries within EURAMET and the European

Union.

1st

Workshop - Metrology for Long Distance Surveying IPQ, Caparica, Portugal, 21

st November 2014

High accuracy laser ranging and amplitude to phase coupling

Michel Lintz 1*

, Duy-Ha Phung 1, Mourad Merzougui 1, and Christophe Alexandre 2

1 ARTEMIS, Observatoire de la Cote d'Azur, Bd de l'Observatoire, 06300 Nice, France

2 CNAM, 292 rue Saint Martin, 75003 Paris, France


Keywords : Laser ranging, phase measurement, amplitude-to-phase coupling, optical demodulation.

Abstract

High accuracy laser ranging often uses high frequency modulation of a laser beam. In our

laser ranging setup we use a 20GHz modulation, where both the optical wavelength and

synthetic wavelength information are encoded, to achieve nanometric precision. But the

principle of our measurement method implies large amplitude variations that give rise to

severe systematic effects through the amplitude-to-phase (AM-to-PM) coupling in the

photodiode. In long distance measurements in air, even if the measurement method implies

no variation of the beam power, significant variations, sometimes called "scintillation", can

result from atmospheric turbulence, due to the modification of the beam wavefront during

propagation.

The strategy that consists, prior to the ranging measurements, in recording the phase-vs-

intensity dependence with the aim of numerically correcting of the phase data does not fully

solve the problem: we observe that, in addition to the dependence with intensity, the phase

data exhibit a dependence as a function of the time after the optical power has changed. This

corresponds to the evolution of the temperature of the photodiode junction and substrate after

the dissipated Joule power (photocurrent X bias voltage) has changed.

We characterize this behavior, and study different ways to reduce amplitude to phase

coupling. Finally, we show that optical demodulation, rather than electrical demodulation, of

the high frequency optical modulation, allows to reject, by orders of magnitude, the

photodiode AM-to-PM coupling and associated systematic errors.

1st


st November 2014

Design of the external optical cavity for multiplication of repetition rate of

Er:dopped fs comb

Radek Šmíd, Adam Lešundák, Lenka Pravdová, and Ondřej Číp

Institute of Scientific Instruments of AS CR, v.v.i, Královopolská 147, 61264 Brno, Czech Republic


Keywords : Fabry-Perot cavity, laser frequency comb, repetition rate multiplication

Abstract

Optical frequency combs (OFCs) have spectrum composed of many equally spaced spectral

lines. They have already been employed in wide range of applications reaching from

astronomical spectrograph calibration, spectroscopy of gases, optical and microwave

waveform generation, synthesis of optical frequencies to RF domain in time and frequency

branch of metrology. Ability of controlling of frequencies of spectral components to extreme

precision and stability is the main advantage of this tool. The repetition rate of femtosecond

pulses defines frequency spacing between neighboring modes in the comb spectrum.

One of important application of combs is a long distance interferometry. Resolution of the

long distance measurement depends on the repetition rate of the optical frequency comb.

Commercially available solid state OFCs can reach the repetition rate up to 1 GHz (like

Ti:Sapphires) and they have enough optical power per each comb teeth. On the other hand

they are quite sensitive to the external mechanical vibrations and to cleanliness.

Commercially available Er-doped fibre OFCs can reach the repetition rate of 250 MHz. The

advantage of them is their robustness, they can be more easily transportable and they don’t

need high degree clean rooms. The laser repetition rate is limited physically by the length of

the laser cavity.

In outdoor application for long distance measurement is the fiber system more quite handy.

Therefore it is interesting to increase the repetition rate of the Er-doped OFC. In this work we

present the design of the external optical cavity based on Fabry-Pérot etalon (FPC) applied to

250 MHz Er-doped fiber OFC to increase its repetition rate. We constructed a Fabry-Perot

cavity (FPC) based on transportable cage system with two mirrors in plan-concave symmetry

including the mode-matching lenses, fiber coupled collimation package and detection unit.

The system enables full 3D angle mirror tilting and x-y off axis movement as well as distance

between the mirrors. The free spectral range of the FPC was 1 GHz therefore the distance

between the mirrors was set to 150 mm.

We compared the designed based on a plan-concave pair of silver mirrors with the pair of

dielectric mirrors. The silver mirrors deposited in our institute are made by (40.2+/-0.9) nm

silver layer. The transmission of 3.5 – 4.0 % and the reflectivity of 98.64% correspond to the

finesse of 195. Curved mirror radius was 800 mm. The commercially available pair of plan-

concave dielectric mirrors with group delay dispersion from 0 fs2 to -400 fs

2 at 1400-1800 nm

was compared with the pair of silver mirrors. The dielectric mirrors reflectivity is 99.8 % and

corresponds to finesse of 1569. The curved mirrors radiuses were 1000 mm.

The authors would like to thank for support to the projects GPP102/12/P962 and

GP102/10/1813 funded by Grant Agency of the Czech Republic.


1st


st November 2014

Femtosecond frequency comb mode selection by external optical cavity

A. Lesundak1, S. A. van den Berg

2

1 Institute of Scientific Instruments, Academy of Sciences of the Czech Republic, Krávopolská, 612 64 Brno, Czech Republic

2 National Metrology Institute VSL, Thijsseweg 11, 2629 JA Delft, The Netherlands


Keywords: traceability, Frequency comb, Fabry-Perot cavity, many-wavelength interferometry

Abstract

The topic of the research presented in this work is related to the Work Package 3, Task 3.1 of

JRP-SIB60 Surveying, which explores different application concepts of femtosecond laser-

based many-wavelength interferometry for long-distance metrology. This work presents a

research in selection of laser frequency comb modes – laser wavelengths – by an external

optical resonator. Ti:Sapphire pulsed laser frequency combs currently used for a massively

parallel homodyne interferometry for absolute distance measurements have large spacing

between adjacent comb modes. Those modes can be optically resolved, but this type of

frequency combs is very delicate, bulky and expensive. On the other hand, fiber laser based

frequency combs are much more suitable for field-applications, but they have narrower

spacing between individual comb modes, i.e. they have denser optical spectrum which is

impossible to resolve even with a high resolution VIPA spectrometer. Hence, reducing of the

comb modes number is necessary for field applications.

A Fabry-Perot cavity was used for this purpose and its performance was tested on Ti:Sa

frequency comb with the pulse repetition rate (spacing between modes) frep=1GHz, and the

central wavelength λc=815nm. The core of the cavity consists of two symmetrically arranged

high reflective dielectric concave mirrors with nearly zero chromatic dispersion. The cavity

acts as an optical filter transmitting only a fraction of the original spectrum. The design of the

overall setup, consisting of the cavity, mode-matching optics and cavity locking electronics,

allows a filtering ratio adjustment, selection of a transmission peak and a long-time stable

operation. We achieved the spacing between transmitted comb modes of 20GHz. In the case

when a cavity free spectral range is not an integer multiple of frequency comb repetition rate,

we achieved the spacing up to 101GHz.

The presented joint research project SIB60 “Surveying” receives funding by the European

Metrology Research Programme (EMRP). The EMRP is jointly funded by the EMRP

participating countries within EURAMET and the European Union.

mailto:lesundak@isibrno.

1st


st November 2014

Dispersion compensation for absolute distance measurement

based on the femtosecond optical frequency comb

Tengfei Wu*, Li Zhang, Shuai Xing and Zhiguo Liang

Beijing Changcheng Institute of Metrology & Measurement, AVIC, Beijing 100095, China


Keywords : femtosecond, air dispersion, transmissive grating, compensation

Abstract

The effect of air dispersion on the femtosecond pulsed width is studied in this paper. We

present the pulsed width variation with central wavelength, grating period and distance,

respectively. Then the air dispersion compensation scheme based on the high-density

transmissive grating is put forward to compress the pulsed width of femtosecond laser. The

diffracted efficiencies variation with the groove depth and the grating period under the

condition of TE and TM polarization state are also given through simulation. The scheme has

advantages of compact volume and convenient operation.


1st


st November 2014

INVESTIGATION OF UNCERTAINTY OF GNSS-BASED DISTANCE

METROLOGY USING EPN DOUBLE STATIONS DATA

Aleksei Liubzhyn1, Pavel I. Neyezhmakov

1, Yevgen M. Zanimonskiy

1,2, Volodymyr S. Kupko

1,

Alla Y. Olijnyk1, Katarzyna Stepniak

3, Pawel Wielgosz

3, Jan Cisak

4, Lukasz Zak

4

1NSC "Institute of Metrology", Kharkiv, Ukraine

2Institute of Radio Astronomy of NAS, Kharkiv, Ukraine

3University of Warmia and Mazury in Olsztyn

4Institute of Geodesy and Cartography, Warsaw, Poland


Keywords : GNSS, EPN, distance metrology

Abstract

Nowadays surveyors and researchers in geosciences are facing the challenge of measuring

distances over several hundreds of meters up to 1 kilometer with uncertainties at a single

millimeter level and below. Electronic distance meters and GNSS are available for this task

and long length metrology complies with GNSS-based short distance measurements. Both

approaches, however, are currently not capable of achieving traceability to the SI definition

of the meter with one or even sub-millimeter uncertainty over the respective distances.

The presented results were obtained in the framework of a research project aimed at fostering

the measurements up to 1 kilometer traceability to SI units. This work is dedicated to a better

understanding of the uncertainty of GNSS-based distance metrology. The influence of the

troposphere, near-field effects and multipath on the distance measurements uncertainty will

be studied in optimized configurations.

The EUREF Permanent Network (EPN) is a network of continuously operating GNSS

reference stations maintained on a voluntary basis by EUREF (EUropean REference Frame)

members. The primary purpose of the EPN is to provide access to the European Terrestrial

Reference System (ETRS89) by making publicly available the GNSS tracking data as well as

the precise coordinates of all the EPN stations.

Long time series of vector components, derived from processing GNSS data from double

EPN stations, were generated. They provide extremely rich information on variability of

GNSS solutions that together with the external data enables qualitative and quantitative

analysis of those variations as well as their reliable statistical estimate.

The experiments performed concerned the investigation of the response of the measuring

system to tropospheric perturbations as well as to site specific effects vs. measured distance.

Numerical experiments conducted indicate that the potentiality of GNSS positioning is not

fully exploited in high-end applications. Also, analysis of time series of GNSS solutions may

result in improvement of modeling of GNSS observations and GNSS-based distance

metrology.


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