Ionospheric Effects on SAR, InSAR, and SAR Polarimetry – Theory and Experiences with ALOS/PALSAR
Franz Meyer(1) and Nicoll Jeremy(1)
(1) Geophysical Institute, University of Alaska Fairbanks, Faribanks, Alaska, 99775, United States
With the SAR sensor, PALSAR, on board the Advanced Land Observing Satellite (ALOS), the first spaceborne L-band SAR instrument has been launched into orbit. At L-band, the ionosphere is assumed to have considerable effects on SAR, InSAR, and SAR polarimetry. Range shifts, internal deformations, range and azimuth blurring, azimuth streaking in interferograms, interferometric phase errors, and Faraday rotation are the most prominent. PALSAR images can serve as an important database to both investigate ionospheric effects on SAR and demonstrate that ionospheric effects can be corrected.
The paper starts with a revision of the theory of ionospheric effects in L-band SAR, InSAR, and polarimetric data. A prediction method is presented that is used to find acquisitions with high ionospheric influence in the ALOS/PALSAR archive. These affected images are used to conduct a thorough analysis of ionospheric effects and investigate the possibility of their removal.
At first, the variability of ionospheric effects in PALSAR data, mainly caused by fluctuations of the Total Electron Content (TEC) along the ray path, will be presented by a series of examples. Besides the effects of temporal changes of TEC, spatial variations of TEC within the size of a SAR scene, causing spatially varying Faraday rotation, azimuth streaking and image blurring in along track direction, will be identified. Following the data analysis, methods for correcting ionospheric effects (Faraday rotation, azimuth streaking, phase bias) in PALSAR data will be introduced along with first results of the application of correction methods. Finally, the feasibility of L-band SARs for mapping the ionosphere will be proven by a set of results all around the globe.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,