**Preface to "ALOS-2/PALSAR-2 Calibration, Validation, Science and Applications"**

Dear Readers,

The Advanced Land Observing Satellite-2 (ALOS-2, nicknamed "DAICHI-2") was launched on May 24th, 2014, which is a follow-on mission of L-band Synthetic Aperture Radars (SARs) by the ALOS "DAICHI" from 2006 to 2011, and the Japanese Earth Resources Satellite-1 (JERS-1, "FUYO-1") from 1992 to 1998. Thus, global coverage and almost three decades of L-band SAR data are currently available. In addition, ALOS-4 is under development and will be launched in the Japanese Fiscal Year 2023 as a successor to Japanese L-band SAR missions.

The mission objectives of ALOS-2 that were defined to fulfill social needs include the following: 1) disaster monitoring of damaged areas, both in considerable detail and when these areas may be large, 2) continuous updating of data archives related to national land and infrastructure information, 3) effective monitoring of cultivated areas, and 4) global monitoring of tropical rain forests to identify carbon sinks. The Phased Array-type L-band SAR-2 (PALSAR-2) mounted on ALOS-2 has capabilities of high-resolution, wide-swath width, and both right- and left-looking observations, and is now operating globally to achieve these objectives. The Japan Aerospace Exploration Agency (JAXA) is continuously conducting research announcement (RA) programs that provide opportunities to use PALSAR-2 and other satellite data to engage and enhance science and application activities worldwide.

This Special Issue has collected original manuscripts on calibration, validation, science, and applications based on PALSAR-2 data. We hope that it will serve as one of the guidelines for future satellite-borne SAR missions, as well as the utilization of L-band SAR data.

> **Takeo Tadono and Masato Ohki** *Editors*
