This paper provides an overview and discusses the significance of Advanced Land Observing Satellites (ALOS). Japanese Earth observation programs originally consisted of two branches: the Marine Observing Satellite (MOS) for global observation and the Land Observing Satellite (LOS) for more detailed observation. The first LOS mission was conducted by the Japanese Earth Resources Satellite-1 (JERS-1) from 1992 to 1996. It was followed by the Advanced Land Observing Satellite (ALOS, “Daichi”) from 2006 to 2011. Both achieved global data acquisition with high resolution using L-band Synthetic Aperture Radar (SAR) and optical instruments. ALOS-2, a successor of the SAR mission on ALOS, has been operating very well since 2014, and ALOS-3 and ALOS-4 are now being developed for launch in Japanese fiscal years (JFYs) 2021 and 2022 to follow the optical mission and ALOS-2, respectively. In this paper, I examine the history and future of the ALOS series.
