Worldwide PPP-evaluation of kinematic GPS tracks for evaluation of TanDEM-X

Project progress:

  • Study: June 2007 – October 2007
  • Test measurements and test analysis: December 2007 – February 2008
  • Project duration: September 2008 – December 2010

Project goal:

Several Methods have been proposed to evaluate the TanDEM-X topography model, e.g. PDGPS, PPP, etc. For efficiency reasons PPP (Precise Point Positioning) has been used as kinematic evaluation method to analyze the GPS tracks gathered around the globe:

Cooperation partners:

  • German Remote Sensing Data Center (Deutsches Fernerkundungsdatenzentrum)
  • German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt)


  • Two frequency receivers have been used for data acquisition. 








Figure 1: Measurement interrupted by a bridge  (iigs; © Google)

  • 15 kinematic GPS-tracks have been acquired on different continents.










Figure 2: Overview over evaluated GPS-Tracks
 (© iigs)

  • The raw data were recorded in RINEX format (Receiver Independent Exchange Format). To increase precision and reliability of the results, two strategies were used. On the one hand, the kinematic results are analyzed twice before they are combined. The analysis is done with the „GPS-Inferred Positioning SYstem and Orbit Analysis SImulation Software (GIPSY-OASIS (GOA II))“ from the American „Jet Propulsion Laboratory (JPL)“ and with „Canadian Spatial Reference System (CSRS) PPP Online Service“ (CSRS, 2009) of the „Natural Resources Canada“ (NRCan). On the other hand, an evaluation of the final results using PDGPS has been realized. For this reference stations close to the measurement tracks have been chosen. Only the trajectory points within a radius of 20km of the respective reference stations are evaluated using this method.






Figure 3: Analysis process (Quelle: iigs)


  • The summed up length of all tracks is approx. 52,778km.
  • RMS of the height difference is below 0.7m.
  • Availability of all measurements is below 65%.
  • The correlation between height differences (external accuracy) and internal accuracy (software output) usually exists, but cannot be used as an indicator.
  • The gaps in the results are usually caused by shadowing during data acquisition. Other possible reasons are e.g. the different receivers and equipment used.


  • Zheng,B., Schwieger, V., Kosmann, D.: Evaluierung des TanDEM-X Geländemodells mittels kinematischem GPS. 100. DVW-Seminar INTERGEO-AKADEMIE, Köln, 4. und 5. Oktober 2010.
  • Schweitzer, J., Zheng, B., Schwieger, V., Kosmann, D.: Evaluation of the TanDEM-X Digital Elevation Model by PPP GPS –Analysis and Intermediate Results–. XXIV FIG International Congress 2010, Sydney, Australia, 11-16 April 2010.
  • Huber, M., Wessel, B., Kosmann, D., Felbier, A., Schwieger, V., Habermayer, M., Wendleder, A., Roth, A.: Ensuring globally the TanDEM-X height accuracy: Analysis of the refernce data sets ICESat, SRTM and KGPS-Tracks. International Geo Science and Remote Sensing Symposium, Kapstadt, Südafrika, 12.-17.07.2009.
  • Schwieger, V., Schweitzer, J., Kosmann, D.: GPS Precise Point Positioning as a Method to Evaluate Global TanDEM-X Digital Elevation Model. 7th FIG Regional Conference, Hanoi, Vietnam, 19.-22.10.2009.
  • Kosmann, D., Wessel, B., Schwieger, V.: Global Digital Elevation Model from the TanDEM-X and the Calibration/Validation with Worldwide Kinematic GPS-Tracks. XXIV FIG International Congress, Sydney, Australia, 11.-16.04.2010.


Dipl.-Ing. Bimin Zheng
Prof. Dr.-Ing. habil. Volker Schwieger