Initial Polarimetric Calibration of PALSAR

This paper discusses an initial polarimetric calibration of ALOS PALSAR. ALOS was launched on January 24, 2006. PALSAR, which is one of ALOS three sensors, is the first spaceborne L−band polarimetric synthetic aperture radar. It is expected that PALSAR polarimetric data is used for many applications such as agriculture, forestry, ocean, natural disasters etc. Thus, polarimetric calibration is an important issue, because any inversion and classification algorithms using polarimetric data depend on the calibration accuracy of the measured data. Moreover, polarimetric calibration of spaceborne SAR needs to consider Faraday rotation as opposed to airborne SAR. Since a radar wave of spaceborne SAR travels through the ionized atmosphere, its polarimetric plane is rotated. Thus, it is possible that the four complex data with respect to HH, HV, VH and VV are affected by Faraday rotation. Freeman proposed a calibration method of polarimetric SAR data subject to Faraday rotation. In this paper, we examine the polarimetric calibration of PLASAR polarimetric data using the Freeman method, and evaluate the channel imbalance and the Faraday rotation angle. The data of Tomakomai is used for the analysis of the polarimetric calibration. In the case where Faraday rotation angle is close to zero, we estimate the cross−talk of PALSAR by the Quegan method. We present the results of our calibration analysis. Moreover, we carried out a experiment to observe the Tomakomai calibration site by PALSAR and Pi−SAR (airborne polarimetric and interferometric SAR) simultaneously on August 19, 2006. Since Pi−SAR data is not affected by the Faraday rotation effect, the difference between these two data is compared.