Development Of Alos-4 Hardware System

ALOS-4 succeeds the concepts of ALOS-2 and hence system design of ALOS-4 satellite basically follows that of ALOS-2, except for improvements in mission performance. In order to use data sets of both ALOS-2 and ALOS-4 for monitoring long term (more than 10 years) changes, the orbit of ALOS-4 is identical to that of ALOS-2. Even though ALOS-4 and ALOS-2 share the same orbit, revisit time of ALOS-4 can be shortened by increasing the swath width. Therefore ALOS-4 utilizes digital beam forming on receive to improve observation swath width. PALSAR-3, the successor of PALSAR-2 onboard ALOS-2, is now designed as an active phased array antenna with on-board digital beam forming processor in order to increase the swath width of the 3m resolution Stripmap mode to 200 km. Transmit signal with a broad beam-width in the elevation direction is generated in order to cover the wider swath. The reflected signal from the ground is received by several independent receive channels and processed to form several antenna patterns. To achieve approximately equivalent NESZ as ALOS-2, the size of PALSAR-3 antenna is designed to be 1.2 times larger than that of PALSAR-2/ALOS-2.ALOS-4 has successfully passed its Preliminary Design Review and engineering model is currently under development. This paper describes the radar instrument design of ALOS-4.