IAG Joint WorKing Group 4.3.8: GNSS tropospheric products ...iag-gnssclimate.oma.be/Documents/Work Plan/JWG_4_3_8_WorkPla… · From 2015 until 2019, the Joint Working Group 4.3.8

International Association of Geodesy IAG (2015 – 2019 term) Commission 4 Positioning and Applications Sub-Commission 4.3 Atmosphere Remote Sensing IAG JWG 4.3.8: GNSS tropospheric products for Climate

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Pacione Rosa - Pottiaux Eric

E-GEOS/ASI-CGS – ROYAL OBSERVATORY OF BELGIUM/STCE

IAG JOINT WORKING GROUP 4.3.8: GNSS TROPOSPHERIC PRODUCTS FOR

CLIMATE

International Association of Geodesy IAG (2015 – 2019 term) Commission 4 Positioning and Applications

Sub-Commission 4.3 Atmosphere Remote Sensing


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Contents 1. Introduction and Background .................................................................................................................... 3

2. Main Scientific Objectives ......................................................................................................................... 4

3. State-of-the-Art and Planned Activities..................................................................................................... 5

Objective 1: REPRO ........................................................................................................................................ 5

Objective 2: HOMO ........................................................................................................................................ 7

Objective 3: ASSIM ........................................................................................................................................ 9

Objective 4: FORMAT .................................................................................................................................. 11

Objective 5: COOP ....................................................................................................................................... 12

4. Summary of the Individual Contributions w.r.t. the Objectives .............................................................. 14

5. Links to External Bodies ........................................................................................................................... 15

6. Forthcoming activities ............................................................................................................................. 15

7. JWG Outreach Presentation .................................................................................................................... 15

8. Reference ................................................................................................................................................. 16

Appendix A. Terms of Reference (ToR) ........................................................................................................ 17

Appendix B. Member List ............................................................................................................................. 18

Appendix C. Individual Inquiry Answers ...................................................................................................... 19


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The IAG Joint Working Group 4.3.8: “GNSS tropospheric products for Climate” Work plan reference document

Revision List and Comments:

8 Aug. 2016 V 1.0 R. Pacione and E. Pottiaux 1st draft of the work plan. 27 Feb 2017 V 1.0a R. Pacione and E. Pottiaux First Revision of the draft version to be sent to members for review.

1. Introduction and Background From 2015 until 2019, the Joint Working Group 4.3.8 on ‘GNSS tropospheric products for Climate’ is part of IAG Sub-Commission 4.3 ‘Atmospheric Remote Sensing’, which is imbedded in IAG Commission 4 on ‘Positioning and Applications’.

This reference document describes the work plan, organisation and planning of the activities of this IAG JWG. The document is based on the individual inputs provided by the members (see Appendix C) along the lines reported in the Term of Reference (ToR, see Appendix A). It will be updated during the course of the JWG. The activities are grouped following the five scientific objectives listed in the ToR, and summarized in Section 2. The main targeted results and deliverables are datasets, reports and scientific papers, which will be elaborated in collaboration between the participants.

A dedicated Website has been set-up http://iag-gnssclimate.oma.be/index.php and

A dedicated mailing list (http://mailman-as.oma.be/mailman/listinfo/iag.gnssclimate) was also establish for the communication between the members.

http://iag-gnssclimate.oma.be/index.php

http://mailman-as.oma.be/mailman/listinfo/iag.gnssclimate


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2. Main Scientific Objectives

The ToR lists five main scientific objectives, which are:

Objective 1: Assess existing reprocessed troposphere solutions and provide recommendations for the forthcoming reprocessing activities (Acronym: REPRO).

Objective 2: Set-up a common GNSS climate dataset on which different homogenization methodologies can be tested. The homogenized common long-term dataset can then be reused for climate trends and variability studies within the community (Acronym: HOMO).

Objective 3: Stimulate the data assimilation of GNSS troposphere products in Climate Models (Acronym: ASSIM).

Objective 4: Review and update GNSS-based product requirements and exchange format for climate (Acronym: FORMAT).

Objective 5: Strengthen the cooperation between geodesists and climatologists (Acronym: COOP).


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3. State-of-the-Art and Planned Activities

Objective 1: REPRO Assess existing reprocessed troposphere solutions and provide recommendations for the forthcoming reprocessing activities.

State-of-the Art

Several long-term (20+ years) reprocessed tropospheric solutions currently exist and are available for climate studies. These time series have been produced using various software and various strategies, and includes GNSS stations belonging to various network scale: this includes e.g. tropospheric datasets from the International GNSS Service (IGS troposphere repro 1 and TIGA), from EUREF (EPN troposphere repro 2) and from regional (e.g. over Japan) and local re-analysis.

Planned Activities

Even if these datasets have been carefully reprocessed, and usually supported by a long-term experience as analysis centre by the producers (e.g. as an EPN or IGS AC), these time series need to be evaluated/assessed prior to any use in climate studies. Indeed, these time series (from different datasets) have been produced with various software and various strategies, and includes GNSS stations belonging to various network, and no clear statement has been established on how coherent they are together in a climate perspective. In addition, they can still suffer from artificial breaks or changes (see also hereafter the homogenisation objective). The evaluation/assessment can include for example a comparison against climate models (e.g. ERA-Interim) and against other sources of tropospheric observations/models (e.g. satellite observations). For that, the database tool system ‘GOP-TropDB’ (developed by Jan Dousa and his team) can support this activity. In addition, several members proposed to study the impact of processing strategy changes on the final troposphere products, the comparison of tropospheric parameters derived with a double-difference versus a PPP approach, the impact of the network design, the impact of station’s equipment, as well as a proper methodology for the screening of these final estimates. This should also allow studying if the trends estimated in the ZTD time series could still suffer from error sources like uplifts due to GIA and other effects. Also comparing successive reprocessing campaigns of the same historical GNSS data (as foreseen in Japan) will provide such insights. It is foreseen that the expertise gained by setting up a proper assessment framework and the various studies proposed by the members will also allow to draw recommendations for forthcoming reprocessing activities.


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Major Tasks and Deliverables

• Inventory: list major reprocessed time series and their characteristics available for climate studies along the lines of what done during the WG3 of the COST Action ES1206. This will serve to fill the common database mentioned in the objective two on homogenisation. Other datasets necessary for the evaluation/assessment framework (radiosonde, WVR, models…) should be identified as well.

• Evaluation/assessment framework: propose a complete strategy for the assessment of any reprocessed time series and apply this framework to at least one of the identified dataset.

• Recommendations: propose recommendations for further reprocessing activities and their assessments.

Contributor List (12)

• Jan Dousa • Yoshinori Shoji • Tong Ning

• Olivier Bock • Norman Teferle • June Wang

• GFZ Team • Andrzej Araskiewicz • Eric Pottiaux

• George Liu • Katazyna Stepniak • Rosa Pacione


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Objective 2: HOMO Set-up a common GNSS climate dataset on which different homogenization methodologies can be tested. The homogenized common long-term dataset can then be reused for climate trends and variability studies within the community.

State-of-the Art

In the last years, several groups studied the homogeneity of the re-processed GNSS ZTD time series. They clearly showed evidence that these time series, even if carefully reprocessed, still suffer from inhomogeneity which e.g. may impact the calculation of the long-term water vapour trend (and its associated error), hence preventing a correct and precise interpretation in terms of climate change and time variabilities. Consequently, initiatives raised in order to homogenise these time series. As such, very recently, a sub-WG of the COST Action ES1206 was created to gather research groups having different statistical methods (e.g. the penalized maximal t-test modified to account for first-order autoregressive noise in time series, ‘PMTred’, used by Tong Ning) that can be used to detect change points in time series, hence potentially to be used to homogenise them. The working group uses the 1st tropospheric reprocessing of the IGS (IGS repro 1) and aims to inter-compare these methods, identify their capability, advantages and drawbacks in identifying these change points, with the final goal to come up with a homogenised dataset for further climate trends and variability studies within the community.

Planned Activities

The work started within the COST Action ES1206 sub-WG on “Data Homogenisation” will be continued and finalised within this JWG and possibly extended to other GNSS tropospheric datasets (e.g. the new EPN troposphere repro 2, the dataset from Uni. Luxembourg for TIGA…) with as main objective to come up with a homogenized version of these datasets. All detected change points and resulted offsets will be open-accessible to all other researchers within the community for validation in order to generate a homogenized common long-term dataset. In that context a specific attention will be given to the available meta-data necessary for the homogenization, process and their exchange format (see also objective 4 on product requirements and exchange formats). The ultimate objective if this activity is to use the homogenized long-term datasets for further studies, e.g. determination of the long-term trends of the water vapour, and/or investigation the temporal and spatial variability of the water vapour.


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• Datasets: establish at least one common GNSS climate datasets, which can be homogenised and then used for climate trends and time variability studies. These datasets can then be completed with other datasets necessary for the evaluation/assessment framework (radiosonde, WVR, models…).

• Homogenisation methods: apply and assess different homogenisation methods on selected tropospheric datasets.

• Homogenised datasets: Come up with a homogenised version of the selected datasets suitable for climate studies.

• Applications: use the homogenised long-term datasets for climate trend and time variability studies. This can also be completed (and thereby validated/invalided) with similar studies based on satellite observations and climate model outputs.

• Recommendations: propose recommendations for forthcoming homogenisation activities.


• Jan Dousa • Olivier Bock • Andrzej Araszkiewicz

• Eric Pottiaux • GFZ Team • Tong Ning

• Roeland Van Malderen • Norman Teferle • June Wang


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Objective 3: ASSIM Stimulate the data assimilation of GNSS troposphere products in Climate Models.

State-of-the Art

Little has been done in the past to use GNSS reprocessed troposphere products for data assimilation in climate models. This field of research has however seen starting some recent initiatives. As such, in the framework of the European FP7 project UERRA (Uncertainties in Ensembles of Regional Re-analysis, http://www.uerra.eu/), the U.K. Met Office (Gemma Halloran) are preparing to assimilate the reprocessed ZTD dataset covering 1996-2014 into a 12 km European Reanalysis of the state of the atmosphere since 1979, using a 28-day moving average O-B (Observation minus model background) as a bias correction, in a hope this will mitigate against any bias changes which have not been eliminated during reprocessing of the ZTD data. In parallel to that, it exists in several initiatives to use re-processed GNSS tropospheric datasets for climate model validation (e.g. for high-resolution climate models running at convection-permitting scale) and derivation of trends. An example is the assessment of Euro-CORDEX (Coordinated Regional Climate Downscaling Experiment) climate model simulation for which IGS Repro1 has been used. If results are convincing, this first step towards data assimilation in European climate model will greatly stimulate the climate community to carry out similar activities, including in high-resolution models where most of the benefits can be expected.

Planned Activities

The European Reanalysis project in which the U.K. Met Office take part will be used to promote in a two-way dialogue the assimilation of reprocessed ZTD datasets in climate models. The link with projects aiming at the validation of climate models based on GNSS tropospheric datasets will also be used to promote the data assimilation. Beside the data assimilation of the “standard” ZTDs, it should be though as well if more sophisticated tropospheric products such as horizontal gradients and the so-called slant tropospheric delays can be assimilated as well in climate models.


• Establish a strong link with the European Reanalysis project and other similar existing projects. • Promote the data assimilation of ZTDs/IWVs in climate re-analysis. • Investigate if other tropospheric products, such as horizontal gradients and slant delays, can be

assimilated as well. • Recommendations: propose recommendations for producing tropospheric delays for data assimilation

in climate models.


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• Gemma Halloran • Olivier Bock • June Wang

• Eric Pottiaux • GFZ Team


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Objective 4: FORMAT Review and update GNSS-based product requirements and exchange formats for climate.

State-of-the Art

Current state-of-the-art for GNSS-based climate product requirement can be found in the E-GVAP product requirement document (v 1.0). This document is based on very generic recommendation of the WMO and needs to be updated within the scope of this JWG. Concerning the tropospheric product exchange format, there is currently an initiative within the framework of the COST Action ES1206 GNSS4SWEC/WG3 to standardize the SINEX-TRO format. This standardization needs to be continued. About the meta-data, little is done. Most people rely solely on the station log files and its associated ASCII format. A proposal of standardisation for the meta-data exchange (with additional information w.r.t. the station log files) has been initiated within the COST Action ES1206 sub-WG3 “Data Homogenisation”. This can be possibly using GeodesyML.

Planned Activities

The standardization of the SINEX-TRO format will be continued and coordinated with the activities of this JWG. If the need for it is clarified (e.g. adding additional information such as those related to Earthquakes), the standardization of the exchange format for the meta-data will also be continued. This format aims to possibly include more information than those included in the station log files to help e.g. in the homogenisation activities. Also, conversion tools from those standardized format to specific format used in the communities may be needed, developed and shared. For instance, the U.K. Met Office (Gemma Halloran) developed the tool necessary for converting the current SINEX-TRO to the BUFR format used by the meteorological community and is ready to help the community with this or help to refine any other format.


• Finalise the standardisation of the SINEX-TRO exchange format. • Finalise the standardisation of the meta-data exchange format if necessary. • Develop and share the necessary conversion tools.


• Gemma Halloran • Jan Dousa • June Wang

• Rosa Pacione • Olivier Bock

• Eric Pottiaux • GFZ Team


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Objective 5: COOP Strengthen the cooperation between geodesists and climatologists.

State-of-the Art

Currently, the collaboration between geodesists and climatologists is based more on individual interaction rather than having a proper framework for this cooperation. However, some initiatives exist to broaden the perspective, such as the COST Action ES1206 GNSS4SWEC. In addition, some existing collaborations and bodies can be used to strengthen this cooperation such as E-GVAP (egvap.dmi.dk), the GRUAN Precipitable Water Task Team (http://www.dwd.de/EN/research/international_programme/gruan/tt_gnss-pw.html) and GEWEX water vapor assessment (G-VAP) (http://gewex-vap.org).

Planned Activities

The cooperation between geodesists and climatologists will be strengthened by promoting existing and ongoing GNSS reprocessing activities delivering tropospheric products, which can be used for local, regional or global climate studies. This include the use of such GNSS-based tropospheric products for 1) climate model validation, 2) data assimilation in climate models, and 3) direct use of long-term homogenised tropospheric time series for studying the climate change and its time variabilities. The wider use of such products requires defacto a better communication channel between both communities, hence scientific outreach, and can be improved by promoting the use of GNSS in climate sciences in the PhD degrees, Doctoral-training programme and early career researchers in geodesy and geophysics to guarantee a multi-disciplinary research approach, as proposed by Uni. Luxembourg. Finally, the closer link between both communities will support the 4 other objectives by e.g. allowing to better define the recommendations for forthcoming GNSS reprocessing activities and the product requirements.


• Setup a dedicated website. • Scientific Outreach (papers, presentation…). • Technical documents (e.g. with the product requirements and the exchange formats). • Share common tools. • Establish a two-way communication channel between geodesists and climatologists. • Introduce the topic “use of GNSS for climate sciences” in Geodesy and Geophysics programmes at

university.

http://www.dwd.de/EN/research/international_programme/gruan/tt_gnss-pw.html

http://gewex-vap.org/


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• Gemma Halloran • Olivier Bock • Eric Pottiaux

• Norman Teferle • GFZ Team • Rosa Pacione

• George Liu • June Wang


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4. Summary of the Individual Contributions w.r.t. the Objectives

Objective RVM JD OB GFZ EP RP MS GL YS NT AA KS TN GH JW REPRO

HOMO

ASSIM

FORMAT

COOP

JD = Jan Dousa

OB = Olivier Bock

RVM = Roeland Van Malderen

GFZ = GFZ Team (Galina Dick, Fadwa Alshawaf, Robert Heinkelmann…)

GL = George Liu

YS = Yoshinori Shoji

NT = Norman Teferle

AA = Andrzej Araszkiewicz,

KS = Katarzyna Stepniak

TN = Tong Ning

GH = Gemma Halloran

JW = June Wang

MS = Marcelo Santos


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5. Links to External Bodies

• IGS (The International GNSS Service, http://www.igs.org), including the IGS Troposphere and the TIGA (The GPS Tide Gauge Benchmark Monitoring, http://adsc.gfz-potsdam.de/tiga/index_TIGA.html) working groups.

• EUREF (The Reference Frame Sub-Commission for Europe, http://www.euref.eu). • GRUAN (The GRUAN GNSS-PW Task Team, http://www.dwd.de/EN/research/international_

programme/gruan/tt_gnss-pw.html) • E-GVAP (The EUMETNET EIG GNSS water VApour Program, http://egvap.dmi.dk). • European FP7 project UERRA (Uncertainties in Ensembles of Regional Re-analysis, http://www.uerra.eu/) • GEWEX water vapor assessment (G-VAP, http://gewex-vap.org).

6. Forthcoming activities

An IAG workshop on ‘Satellite Geodesy for Climate’ is planned on September 19-21, 2017, in Bonn, Germany. This is a joint workshop between the IAG SC 2.6: ‘Gravity and Mass Transport in the Earth System’, the IAG JWG 2.6.1: ‘Geodetic Observations for Climate Model Evaluation’, and the IAG JWG 4.3.8: ‘GNSS Tropospheric Products for Climate’. More information can be found here: http://www.igg.uni-bonn.de/apmg/index.php?id=ws2017

7. JWG Outreach Presentation

1. IAG JWG 4.3.8: GNSS tropospheric products for Climate, R. Pacione, E. Pottiaux and JWG members, COST ES1206 Workshop, march 8-10 2016, Reykjavik, Island.

2. IAG JWG 4.3.8: GNSS tropospheric products for Climate, E. Pottiaux, R. Pacione and JWG members, IAG Commission 4 Symposium Wroclaw, Poland, September 4-7, 2016 http://www.igig.up.wroc.pl/IAG2016/

http://www.igs.org/

http://adsc.gfz-potsdam.de/tiga/index_TIGA.html

http://www.euref.eu/

http://www.dwd.de/EN/research/international_%20programme/gruan/tt_gnss-pw.html

http://www.dwd.de/EN/research/international_%20programme/gruan/tt_gnss-pw.html

http://egvap.dmi.dk/

http://www.uerra.eu/

http://gewex-vap.org/

http://www.igg.uni-bonn.de/apmg/index.php?id=ws2017

http://www.igg.uni-bonn.de/apmg/index.php?id=ws2017

http://www.igig.up.wroc.pl/IAG2016/


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8. Reference 1 Pacione, R., Araszkiewicz, A., Brockmann, E., and Dousa, J.: EPN Repro2: A reference GNSS

tropospheric dataset over Europe, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-369, in review, 2016.

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PLEASE CONTINUE….


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Appendix A. Terms of Reference (ToR) Version 1.0

Terms of Reference In many part of the world, huge efforts are ongoing for providing homogeneously reprocessed GNSS solutions that are the basis for deriving very precise coordinates, velocities and troposphere parameters (namely Zenith Total tropospheric Delays and Horizontal Gradients). These regional and global reprocessing campaigns are possible thanks to the availability of 19+ years of observations from permanently observing GNSS stations located worldwide (e.g. the IGS network), their regional densifications (e.g. the EPN network), and of reprocessed global orbit and clock products (e.g. those provided by the IGS Analysis Centers). These long-term time series of homogeneously reprocessed troposphere parameters will provide a GNSS climate data record with high potential for climate monitoring. Unfortunately, these time series still suffer from inhomogeneity (for example instrumental changes, changes in the station environment) which can affect the analysis of the long-term variability.

The main objective of the working group is to assess existing reprocessed GNSS tropospheric products, foster the development of forthcoming reprocessing activities and promote their use for climate research.

Objectives:

• Assess existing reprocessed troposphere solutions and provide recommendations for the forthcoming reprocessing activities.

• Set-up a common GNSS climate dataset on which different homogenization methodologies can be tested. The homogenized common long-term dataset can then be reused for climate trends and variability studies within the community.

• Stimulate the data assimilation of GNSS troposphere products in Climate Models. • Review and update GNSS-based product requirements and exchange format for climate. • Strengthen the cooperation between geodesists and climatologists.


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Appendix B. Member List

Name Institute Country Andrzej Araszkiewicz Military University of Technology Poland Eric Pottiaux ROB, Royal Observatory of Belgium Belgium Fadwa Alshawaf GFZ, GeoForschungsZentrumPotsdam Germany Felix Norman Teferle University of Luxembourg Luxembourg Galina Dick GFZ, GeoForschungsZentrumPotsdam Germany Gemma Halloran Met Office UK United Kingdom George Liu Zhizhao Hong Kong Polytechnic University Hong Kong Jan Dousa GOP, Geodetic Observatory Pecny, RIGTC Czech Republic June Wang Department of Atmospheric and Environmental Sciences,

University at Albany United States

Katarzyna Stepniak University of Warmia and Mazury Olsztyn, Poland Poland Marcelo Santos UNB, University of New Brunswick Canada Olivier Bock IGN LAREG, Univ Paris Diderot France Robert Heinkelmann GFZ, GeoForschungsZentrumPotsdam Germany Roeland Van Malderen Royal Meteorological Institute of Belgium Belgium Rosa Pacione E-GEOS S.p.A ASI/CGS Italy Sibylle Vey GFZ, GeoForschungsZentrum, Potsdam Germany Tong Ning Lantmateriet, Swedish Mapping, Cadastre and Land Registration

Authority Sweden

Yoshinori Shoji Meteorological Research Institute Japan


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Appendix C. Individual Inquiry Answers

Roeland Van Malderen, Belgium (Royal Meteorological Institute of Belgium, [email protected])

Future plans of our group (Eric, Hugues (?) and me) in this activity are

• Try out a neighbour-based homogenization tool (HOMER, outcome of a COST action on homogenization) on the EPN repro 2

• Time variability analysis of this homogenized dataset

In the more recent future, we would like to

• Publish finally the IWV time variability analysis of our IGS repro , GOMESCIA, ERA-interim datasets • Compare the IWV time variability of some European GNSS sites with Climate Model output (in collaboration with

my colleague Julie Berckmans) • Validate the IWV/ZTD time variability of different European Climate Models (with different horizontal scales,

including convective permitting schemes) with GNSS retrievals (e.g. within the framework of the European ERA4CS project BATMAN, if approved).

Marcelo Santos, Canada (UNB, University of New Brunswick, [email protected]

Coming

Jan Douša, Czech Republic (GOP, Geodetic Observatory Pecný, RIGTC, [email protected])

• Assess existing reprocessed troposphere solutions and provide recommendations for the forthcoming reprocessing activities.

• Set-up a common GNSS climate dataset on which different homogenization methodologies can be tested. The homogenized common long-term dataset can then be reused for climate trends and variability studies within the community.

• Product evaluation/comparison in GOP-TropDB

Olivier Bock, France (IGN LAREG, Univ Paris Diderot, [email protected])

I will certainly contribute to all 5 points, though I will have more specific activities on point 1 & 2: assess existing datasets and establish reference dataset (done in COST/WG3). I will also supervise a PhD on homogenization starting next year.

GFZ contribution to the objectives of the WG:

Fadwa Alshawaf, Germany (GFZ, German Research Centre for Geosciences, Potsdam, [email protected]) Galina Dick, Germany (GFZ, German Research Centre for Geosciences, Potsdam, [email protected]) Robert Heinkelmann, Germany (GFZ, German Research Centre for Geosciences, Potsdam [email protected]) Sibylle Vey, Germany, (GFZ, German Research Centre for Geosciences, Potsdam, [email protected])

mailto:[email protected]






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Assess existing reprocessed troposphere solutions and provide recommendations for the forthcoming reprocessing activities:

1) GFZ participates in the activities of the GRUAN (GCOS Reference Upper Air Network), a reference climate observation network. This network will eventually comprise about 30-40 reference sites worldwide, designed to detect long-term trends of key climate variables. GFZ established a centralized processing centre for IWV data as a contribution to the GRUAN

2) GFZ runs the Water Vapor Radiometer (HATPRO) and uses the measurements for validation of tropo products. The WVR measurements can be provided for validation studies

3) GFZ can contribute by checking the homogeneity of the products for each GNSS station (mainly in Germany) and by time series analysis for trend detection (GNSS, VLBI, radiosonde, etc)

Set-up a common GNSS climate dataset on which different homogenization methodologies can be tested. The homogenized common long-term dataset can then be reused for climate trends and variability studies within the community:

1) GFZ has an archive with15-minute ZTD/IWV estimates (mainly for Germany) since 2005 and with hourly ZTD/IWV estimates for 2001-2005. Also an archive of the slant delays (mainly for Germany) is available since 2007

2) GFZ has a re-processed long-term dataset of TIGA stations (about 800 globally distributed GNSS stations)

3) GFZ has an archive of RINEX raw observations for SAPOS network (Germany) since 2001

GFZ can provide all available datasets.

Stimulate the data assimilation of GNSS troposphere products in Climate Models:

1) Assimilating slant delays

2) GFZ has close cooperation with KIT for using the GNSS-based IWV to provide 3D fields IWV through a tomographic approach

3) Assimilating GNSS-based IWV to check the output grids of the weather research and forecasting model

4) Include other available data from radiosondes, atmospheric models (ECMWF, NCEP, WMO), VLBI (10 min temporal resolution)

Review and update GNSS-based product requirements and exchange format for climate:

Contribution through GFZ activities in GRUAN GNSS-PW Task Team

Strengthen the cooperation between geodesists and climatologists:

GFZ can contribute through

1) cooperation with SAPOS - German provider of GNSS rinex data

George Liu Zhizhao, Hong Kong, (Hong Kong Polytechnic University, [email protected])

The Micro-Laboratory of Atmospheric Research and Geomatics Engineering (Micro-LARGE) at the Hong Kong Polytechnic University (PolyU), Hong Kong, can contribute to the first and the fifth objectives:



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(1) Assessment of existing reprocessed troposphere solutions and provide recommendations for the forthcoming reprocessing activities.

(5) Strengthen the cooperation between geodesists and climatologists.

For the first objective, the Micro-LARGE has proposed a PPP-based (Precise Point Positioning) tropospheric delay evaluation method to evaluate the absolute accuracy of the tropospheric data/model, instead of a relative comparison of one tropospheric data/model with another one (Liu et al., 2013). We have experience in conducting evaluation for various tropospheric models, including 9 dry models and 18 wet models (Chen and Liu, 2016)

We can also contribute to the implementation and realization of the fifth objective as we are closely working in the geodetic domain. We can help the dissemination of homogeneous tropospheric datasets to a wider geodesy community and promote a wider use of improved tropospheric datasets. At the same, we can help communicate with geodesy community to discuss the improvement of tropospheric products.

Chen, Biyan, and Zhizhao Liu. 2016. “A Comprehensive Evaluation and Analysis of the Performance of Multiple Tropospheric Models in China Region.” IEEE Transactions on Geoscience and Remote Sensing 54 (2): 663–78. doi:10.1109/TGRS.2015.2456099.

Liu, Zhizhao, Min Li, Weikun Zhong, and Man Sing Wong. 2013. “An Approach to Evaluate the Absolute Accuracy of WVR Water Vapor Measurements Inferred from Multiple Water Vapor Techniques.” Journal of Geodynamics 72 (December): 86–94. doi:10.1016/j.jog.2013.09.002.

Yoshinori Shoji, Japan, (Meteorological Research Institute, [email protected])

1. In which of the objectives identified in the ToR you plan to contribute (&how) We have made long term GPS retrieved PWV dataset using Japanese dense GPS network since 1994 using IGS's reprocessed orbit ephemerides with GIPSY OASIS II software package. Comparison with nearby radiosonde observation has revealed that some discontinuity in both bias and standard deviation occurred in GPS PWV in 2003-2004. The discrepancy might be caused by antenna change from ground plane type to choke ring one. In the JWG, we will re-analyse the Japanese historical GPS data using IGS's repro2 orbits with RTKLIB software package and compare its performance with our previous reprocess results. 2. What is your state-of-the-art, and which are your short-, mid- and long-term goals/tasks w.r.t. to this JWG. (note: this is just a draft plan, and have not been authorized in my institute) (1) State-of-the-art Using newest orbit (repro2) and new analysis tool (RTKLIB). (2) short-term goal 2016: Starting reanalysis (3) mid-term goal 2017: comparison with radiosonde and previous analysis results. (4) long-term goal 2018-20: Reanalyzing both Japanese and IGS GPS data in order to contribute to re-analysis experiment of the Japan Meteorological Agency (JMA).

Felix Norman Teferle, Luxembourg (University of Luxembourg, [email protected])

Objectives:

1. Assess existing reprocessed troposphere solutions and provide recommendations for the forthcoming reprocessing activities.


mailto:[email protected])


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Through our activities as part of an analysis center for the IGS TIGA WG we regularly carry out reprocessing activities and provide long-term homogeneous parameter time series, including zenith tropospheric delay. We have also carried out evaluations of the GNSS-derived ZTD time series with those extracted from ERA-Interim.

2. Set-up a common GNSS climate dataset on which different homogenization methodologies can be tested. The homogenized common long-term dataset can then be reused for climate trends and variability studies within the community.

We can contribute with our GNSS-derived ZTD time series prior to and after homogenization. The time series stem from a reprocessing for 1995-2015 using the Bernese GNSS Software 5.2 in a double-difference network strategy of 700+ globally distributed stations.

3. Stimulate the data assimilation of GNSS troposphere products in Climate Models.

N/A

4. Review and update GNSS-based product requirements and exchange format for climate.

N/A

5. Strengthen the cooperation between geodesists and climatologists.

Through our PhD degrees and Doctoral Training Programme in Geodesy and Geophysics we introduce early career researchers in geodesy and geophysics to issues and topics in climate science. In this way our graduates are sensitized to the topic and are prepared for related multi-disciplinary research.

Andrzej Araszkiewicz, Poland (Military University of Technology, [email protected])

I see myself in the first two objectives: Assess existing reprocessed troposphere solutions and provide recommendations for the forthcoming reprocessing activities; Set-up a common GNSS climate dataset on which different homogenization methodologies can be tested. The homogenized common long-term dataset can then be reused for climate trends and variability studies within the community. In fact, I am thinking over successive benchmarks on different strategies, models etc, to test the impact of each of them to final troposphere products. Right now we are working on the dependence between estimated ZTD and estimated vertical position, from the viewpoint of long-term changes. In brief, we want to check if the uplifts (GIA and other effects) can interfere the trends in estimated ZTD. Suitable abstract was submitted to the 16th EMS/11th ECAC. If they come out interesting results, we will go in this direction.

Katarzyna Stepniak Poland (University of Warmia and Mazury Olsztyn, Poland, [email protected])

I would like to contribute in the first objective. So far, I have worked on assessment of the ZTD estimates obtained from different GNSS data processing based on the Polish permanent network ASG-EUPOS. I studied the accuracy of ZTD data post-processed in DD mode and PPP mode with Bernese v. 5.2 software and the impact/improvement of processing strategy and ZTD data screening. I also developed my own network design strategy which gives more accurate and homogenous estimates for atmospheric research. In the long-term, I plan to focus on global solutions from IGS Analysis Centers.




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Tong Ning, Sweden (Lantmäteriet, Swedish Mapping, Cadastre and Land Registration Authority, [email protected])

I will mainly contribute to two objectives: 1. Assess existing reprocessed troposphere solutions and provide recommendations for the forthcoming reprocessing activities. 2. Set-up a common GNSS climate dataset on which different homogenization methodologies can be tested. The homogenized common long-term dataset can then be reused for climate trends and variability studies within the community. State-of-the-art:

Using a statistical test, the penalized maximal t test modified to account for first-order autoregressive noise in time series (PMTred), to identify the possible mean shifts (changepoints) in the long-term dataset, i.e. water vapour time series [1]. All the detected changepoints and resulted offsets will be compared to the ones given by other methods for validation. Eventually a homogenized common long-term dataset will be provided for further climate trends and variability studies within the community.

Short-term goals:

Changepoints detection on the existing reprocessing troposphere data sets, i.e., Onsala data set which includes 123 sites in Europe covering a time period of 17 years (1997 to 2013) and/or other long-term dataset available within the community. Mid-term goals: All detected changepoints and resulted offsets will be open-accessible to all other researchers within the community for validation in order to generate a homogenized common long-term dataset. Long-term goals: Using the homogenized common long-term dataset for further studies, e.g. determination of the long-term trends of the water vapour, and/or investigation the temporal and spatial variability of the water vapour.

[1] Homogenized Time Series of the Atmospheric Water Vapor Content Obtained from the GNSS Reprocessed Data, Ning et al., Journal of Climate, DOI: 10.1175/JCLI-D-15-0158.1 .

Gemma Halloran, United Kingdom (Met Office UK, [email protected])

Our current status is that we have taken your reprocessed ZTD dataset, converted it to BUFR, and are preparing to assimilate it into a 12km European Reanalysis of the state of the atmosphere since 1979. To do this, we have chosen to implement a 28 day moving average O-B (Observation minus model background) as a bias correction, in a hope this will mitigate against any bias changes which have not been eliminated during reprocessing of the ZTD data. In the short-medium term, once this reanalysis is underway, we plan to look at the output from this to make sure this bias correction strategy is appropriate. In terms of the objectives where I can contribute, I hope it will primarily be:

• Stimulate the data assimilation of GNSS troposphere products in Climate Models – through promotion of what we are doing in the European Reanalysis project here

• Review and update GNSS-based product requirements and exchange format for climate – Since I have now gone through the process of converting Sinex to BUFR, I can help others with this, or help to refine any other formats

mailto:@metoffice.gov.uk


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• Strengthen the cooperation between geodesists and climatologists – again, through promotion of what we are doing in the European Reanalysis

But I may be able to contribute in some small ways to the other objectives if I can be of assistance.

June Wang, USA (Department of Atmospheric and Environmental Sciences, University at Albany, [email protected])

June Wang’s potential contributions (in red):

Objectives:

6. Assess existing reprocessed troposphere solutions and provide recommendations for the forthcoming reprocessing activities. Will contribute to this objective through GRUAN GNSS-PW Task Team on assessing GNSS PW products.

7. Set-up a common GNSS climate dataset on which different homogenization methodologies can be tested. The homogenized common long-term dataset can then be reused for climate trends and variability studies within the community. Could provide our 2-hrly, long-term GNSS PW dataset for evaluation and use the resulted common climate dataset to study PW trends, extreme events and diurnal variations and for other applications.

8. Stimulate the data assimilation of GNSS troposphere products in Climate Models. More interested in climate model evaluations.

9. Review and update GNSS-based product requirements and exchange format for climate. Contribute through GRUAN GNSS-PW Task Team activities.

10. Strengthen the cooperation between geodesists and climatologists. Will continue to do this through both my own research and GRUAN communities.