JSG T.24

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JSG T.24: Multiresolutional aspects of potential field theory

Chair:Dimitrios Tsoulis (Greece)
Affiliation:Comm. 2, 3 and GGOS


Many geodetic parameters can be retrieved using various techniques of space geodesy. For instance, all satellite techniques are sensitive to a geocenter motion and gravity field variations. However, some techniques are affected more by systematic observation errors than other techniques. Earth’s rotation parameters from sub-daily to daily temporal scales can be determined using all techniques of space geodesy with higher or lower accuracy, and with better or worse temporal resolutions. Precise orbits of satellites may be based on a single technique or multiple techniques that shall mitigate system-specific orbital systematic errors.

Recently, a series of satellite missions co-locating different space geodetic techniques has been launched:

  • SLR and GNSS: Galileo (all satellites), GLONASS (all satellites), QZSS (all satellites), IRNSS (all satellites), GPS (2 satellites), BeiDou/COMPASS (selected satellites), CHAMP, GRACE-A/B, GOCE, SWARM-A/B/C, ICESat-2, COSMIC-2, Terra-SAR, TanDEM-X, GRACE Follow-On A/B, etc.
  • DORIS and SLR: TOPEX/Poseidon, ENVISAT, CRYOSAT-2, SARAL and Jason-1 (after 2009),
  • VLBI and SLR: RadioAstron,
  • VLBI, SLR, and GNSS: APOD,
  • DORIS, GNSS and SLR: Jason-2/3, HY-2A and Sentinel-3A/B,
  • SLR, VLBI, GNSS and DORIS: GRASP and E-GRASP (planned missions).

SLR retroreflectors are passive and relatively cheap devices; thus, they are installed on-board many low- and high-orbiting satellites. Many low-orbiting satellites for ocean monitoring are equipped with DORIS and GNSS receivers for precise orbit determination, and with SLR retroreflectors for the orbit validation. DORIS receivers are installed on many satellites which require precise ephemeris and orbit below 2000 km. Missions dedicated to Earth’s gravity field recovery are typically equipped with GNSS receivers and SLR retroreflectors. Most of the GNSS satellites are equipped with SLR retroreflectors (except for GPS). VLBI telescopes are typically slow as they are dedicated to tracking extra-galactic quasars. Hence, many VLBI telescopes have problems with tracing fast-moving low-orbiting targets that are planned for co-location on-board satellites. However, first experiments using the APOD satellite with a VLBI transmitter and SLR retroreflector was successfully performed in Australia. Unfortunately, the APOD GPS receiver failed soon after the satellite launch which caused some issues with the accuracy of the determined orbit when the number of SLR observations was insufficient.

Despite many LEO satellites equipped with two or three techniques of space geodesy, the full potential of the co-location on-board LEO has not yet been entirely explored in terms of deriving combined geodetic parameters. SLR observations to LEO are typically used only for validation of GPS-based or DORIS-based orbits. SLR observations to LEO and GNSS do not contribute at all to realization of the International Terrestrial Reference System despite GNSS and LEO satellites contributing to GNSS and DORIS solutions, respectively.

Recently, the International Laser Ranging Service initiated a series of special tracking campaigns dedicated to tracking new LEO and GNSS spacecraft which increased the amount of collected data with a perspective of their full co-location in space. The combination of solutions based on GNSS, SLR, LLR, DORIS and VLBI requires a profound investigation of biases and systematic effects affecting all individual techniques. Neglecting systematic effects may lead to degradation of solutions and to absorption of various systematic effects by global geodetic parameters.

The main goal of this JSG is to investigate methods to combine global geodetic parameters derived from multiple techniques of space geodesy with the major focus on those missions capable of co-locating and integrating different observation techniques. We aim at improving quality and reliability of global geodetic parameters and realization of the terrestrial reference system through integration of different microwave techniques with laser techniques. We will also explore benefits emerging from co-locating geodetic techniques on-board low and high-orbiting satellites. We aim at detailed analyses related to system-specific issues and systematic effects emerging from combining different techniques of space geodesy, and at the assessment of their contributions to combined global geodetic parameters.


  • Bibliographical survey and identification of multiresolutional techniques for expressing the gravity field signal of finite distributions.
  • Case studies for different geometrical finite shapes.
  • Comparison and assessment against existing analytical, numerical and hybrid solutions.
  • Computations over finite regions in the frame of classical terrain correction computations.
  • Band limited validation against available Earth gravity models.

Program of Activities

  • Active participation at major geodetic meetings.
  • Organize a session at the forthcoming Hotine-Marussi Symposium.
  • Compile a bibliography with key publications both on theory and applied case studies.
  • Collaborate with other working groups and affiliated IAG Commissions.


Dimitrios Tsoulis (Greece), chair
Katrin Bentel (USA)
Maria Grazia D'Urso (Italy)
Christian Gerlach (Germany)
Wolfgang Keller (Germany)
Christopher Kotsakis (Greece)
Michael Kuhn (Australia)
Volker Michel (Germany)
Pavel Novák (Czech Republic)
Konstantinos Patlakis (Greece)
Clément Roussel (France)
Michael Sideris (Canada)
Jérôme Verdun (France)

Corresponding members

Christopher Jekeli (USA)
Frederik Simons (USA)
Nico Sneeuw (Germany)