Polarimetric Calibration of ALOS/PALSAR

This report presents the polarimetric calibration results of ALOS/PALSAR and discusses a stability of polarimetric calibration parameters during the calibration phase of ALOS and an influence of Faraday rotation on them. PALSAR is the first spaceborne polarimetric L-band synthetic aperture radar and its polarimetric data is expected to be utilized in various remote sensing applications. However, the distortions due to the radar hardware and the ionosphere are included in measurement data which consists of the scattering matrix. The influence by the radar hardware occurs as channel imbalance and crosstalk. The ionosphere causes Faraday rotation which rotates a polarization plane of radar wave. Thus, polarimetric calibration for removing the distortions from the measured scattering matrix is an important issue for PALSAR. Amazon data was used to estimate the polarimetric calibration parameters, because this area is located in the vicinity of the equator and the effect of Faraday rotation was expected to be small. Quegan method which is one of the polarimetric calibration methods was applied to the data. Although this method can not deal with Faraday rotation, the channel imbalance and the cross-talk can be derived accurately. The Amazon data showed that the channel imbalance remained stable during the calibration phase and the cross-talk was very small regardless of the descending path (daytime observation) and the ascending path (nighttime observation). Faraday rotation angle was calculated by Freeman method. This result showed that Faraday rotation angle in Amazon area was less than 1 degree. Moreover, Tomakomai data was compared with Amazon data and indicated that there was a correlation between the cross-talk and Faraday rotation. These parameters of descending path data were higher than those of ascending path data. Therefore, it was confirmed that Amazon data has little influence of Faraday rotation and is suitable for deriving the polarimetric calibration parameters.