Automated High-Accuracy Orthorectification and Mosaicking of PALSAR Data

The ALOS satellite was launched successfully on January 26, 2006. It has three remotesensing instruments: the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) for digital elevation mapping, the Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2) for precise land coverage observation, and the Phased Array type L-band Synthetic Aperture Radar (PALSAR) for day-and-night and all-weather land observation. In order to fully utilize the data obtained by these sensors, ALOS was designed with two advanced technologies. The first is the high speed and large capacity mission data handling technology and the second is the precision spacecraft position and attitude determination capability. These technologies will be essential to high-resolution remote sensing satellites in the next decade. This article will focus on the PALSAR sensor. PALSAR Observation Modes PALSAR provides higher performance than previous SAR sensors such as JERS-1. The high resolution mode is used most commonly in regular operation. Its maximum ground resolution of 7 meters is one of the highest among Synthetic Aperture Radar (SAR) sensors. In addition to the conventional high resolution mode, PALSAR has a ScanSAR observation mode which enables it to switch off-nadir angles from three to five times (scan by the swath of 70 kilometers) to cover wide areas: from 250 kilometers (70x3) to 350 kilometers (70x5). For comparison, the off-nadir angle for the SAR sensor on board JERS-1 was fixed at 35 degrees, and swath width was about 75 kilometers. However, the ScanSAR resolution is inferior to high-resolution mode. Another advantage of PALSAR is its polarimetry mode. The SAR sensor on JERS-1 was equipped only with a horizontal polarization transmission/receipt function, whereas PALSAR realizes both horizontal and vertical polarization. PALSAR can also simultaneously receive horizontal and vertical polarization for each polarized transmission called multipolarimetry. In addition, PALSAR can switch from horizontal to vertical polarization and vice versa at respective transmission pulse, enabling four polarizations by double simultaneous polarization a function called full polarimetry.