Effects of Ionosphere and Troposphere on L-Band SAR Geometric Accuracy

This study investigated the geometric errors in L-band synthetic aperture radar (SAR) caused by the effects of the ionosphere and troposphere based on observational evidence derived from the Phased Array type L-band SAR-2 (PALSAR-2) onboard the Advanced Land Observing Satellite-2 (ALOS-2) data, which were obtained by calibration and validation works, and external numerical data. First, the ionospheric path delay (IPD) and the tropospheric path delay (TPD) on PALSAR-2 data were estimated. The results revealed that the zenith IPD ranges from approximately 1 m to 12 m, according to the observation period, due to the solar activity cycle. In contrast, the zenith TPD ranges from 2.30 m to 2.75 m depending on the seasonal variation. Next, the slant-range error of PALSAR-2 with the slant IPD and the slant TPD were compared to investigate the relationships between them. These relationships indicated a strong correlation between the slant-range error of L-band SAR and the slant IPD, whereas the correlation with the slant TPD was not confirmed. This result suggests that the effect of the ionosphere could be the significant error factor in the L-band SAR geometric accuracy. Finally, the effective geometric accuracy of PALSAR-2 was simulated by removing the IPD and TPD. As a result, the standard deviation of the slant-range error was reduced from 2.709 m to 1.206 m, and a bias of −5.288 m remained.