JWG C.2: Quality control methods for climate applications of geodetic tropospheric parameters

Chair: Rosa Pacione (Italy)
Vice-Chair: Marcelo Santos (Canada)
Affiliation: Commission 4, IGS, IVS


Zenith Total Delay (ZTD) estimates are determined on a regular basis by several processing centers. For example, the IGS Analysis Centers have all their own independent ZTD solutions but, unlike other estimated parameters (e.g., orbits and satellite clocks) they are not combined. The official IGS ZTD product is the result of an independent and dedicated solution based on a precise point positioning solution. On the other hand, EUREF performs combination of ZTD estimates on a regular basis as well as the IVS, which combines ZTD estimates coming from VLBI sessions. Nonetheless, not all IGS and IVS analysis centers make available their ZTD estimates. GNSS is reaching the “maturity age” of 30 years when climate normals of ZTD and gradients can be derived. But what would be the best series to serve the climate community? What series would offer the most realistic trends? As the IGS moves towards its third reprocessing campaign (REPRO3) where all ACs are to be make available their own ZTD and gradient estimates, as the IVS is moving towards its ACs also providing ZTD and gradient estimates and as the PPP-derived IGS product continues  to be produced, there is a huge opportunity to perform quality control, using the tools of combination of parameters, to assess what would be the ZTD and gradient product best suited to be made available to climate studies.


Potential scientific questions include:

  • Are there advantages of combining ZTD estimates over not combining them? Is there any ‘loss of information’ in performing combinations?
  • Would there be difference in trends derived from them? If so, how much implication for feeding information to climate?
  • Can we trust in a combined ZTD as we trust any combined products (e.g., orbits, clock, site coordinates)?
  • What the best combination strategy can be done (not necessarily to combine exactly the same way as other products)?
  • Under what criteria can we use spectral analysis to demonstrate that a ‘good’ combined product have the same properties of the contributing solutions?
  • What metrics should be used to ascertain that the optimal set of ZTD estimates, gradients and their trends, are provided to the climate community?


  • Collaborate with IGS and IVS in the forthcoming reprocessing campaign.
  • Participate actively in IAG, AGU and EGU conferences and organize sessions
  • Organize working group meetings, splinter group meetings at the said symposia


  • Kyriakos Balidakis (Germany)
  • Sharyl Byram (USA)
  • Galina Dick (Germany)
  • Gunnar Elgered (Sweden)
  • Olalekan Isioye (South Africa)
  • Jonathan Jones (UK)
  • Michal Kačmařík (Czech Republic)
  • Anna Klos (Poland)
  • Haroldo Marques (Brazil)
  • Thalia Nikolaidou (Canada)
  • Tong Ning (Sweden)
  • Mayra Oyola (USA)
  • Eric Pottiaux (Belgium)
  • Paul Rebischung (France)
  • Katarzyna Stępniak (Poland)
  • Roeland Van Malderen (Belgium)
  • Yibin Yao (China)
  • Florian Zus (Germany)

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