Atmospheric Correction

Contact Persons

Michael Jehle

David Small

Erich Meier

Keywords

Atmosphere, Ionosphere, Troposphere, Path Delay, TEC

Quick Reference

Satellites observing and measuring the Earth's surface with electromagnetic waves are subject to atmospheric path delays. These atmospheric effects on radar signal propagation experience modification in signal velocity and direction and can be considered by simple modeling. In order to increase the geolocation accuracy of spaceborne SAR applications we developed a software tool that accounts for atmospheric path delays.
Consequently, RSL has been collecting GPS measured total electron content (TEC) data from the astronomical institute of the university of berne (AUIB) in order to be able to correct SAR data with corresponding TEC data.

Timeframe

The atmospheric correction software tool was implemented in 2004 at our institute. Since then, maintenance and update of the algorithms and the parameter data base has been a permanent task.

Some Results

The goals of our software tool are:

• straightforward monitoring of current states of zenithal ionospheric path delays using bi-hourly generated TEC maps at AUIB;
• calculate pixel based ionospheric and tropospheric path delays for spaceborne L to X-band SAR / radar applications;
        As an example for the application of the collected TEC maps the figure below shows mean TEC levels for the years 1997 to 2004. It is clearly visible that the variations in yearly mean TEC follow the 11- year solar cycle. This is used among others for the generation of ionospheric models.
• accurate data calibration in order to provide the closest geolocation possible;
• an instrument which is designed to be easily integrated into other software environments enabling...
• improved a-priori knowledge of the geometry of a SAR acquisition.

Partnerships

All major elements of this project (software development, data base implementation and permanent update) were sponsored by, and have been carried out in cooperation with, the German Space Research Centre (DLR). Current projects on the correction of electromagnetic wave propagation through the atmosphere are carried out in cooperation with SARMAP and ESA. SARMAP, European Space Agency (ESA).

Publications

• Jehle M., Frey O., Small D., Meier E. and Nüesch D. [2004]:
  Improved Knowledge of SAR Geometry through Atmospheric Modelling,
  Proceedings of the EUSAR 2004 Conference, Ulm, Germany
• Jehle M., Rüegg M., Small D., Meier E. and Nüesch D. [2005]:
  Estimation of Ionospheric TEC and Faraday Rotation for L-band SAR,
  12th Int'l Symp. on Remote Sensing, 19.-22.9.2005, Bruges, Belgium.
• Jehle M., Small D. and Meier E. [2006]:
  Comparison of different TEC map estimation methods,
  13th Australasian Remote Sensing and Photogrammetry Conference, 20.-24.11.2006, Canberra, Australia