From ALOS-2 to ALOS-4: Japan's pioneering L-band SARs for global vegetation monitoring: state-of-the-art and future perspectives

Abstract

Monitoring of land vegetation is one of the prime objectives for Earth Observation satellite missions. Due to the penetration capabilities of low-frequency radar signals through vegetation canopies, L-band SAR is widely considered as a valuable tool for advanced vegetation monitoring. Based on the physical backscattering properties of the above-ground vegetation strata, polarimetric SAR (PolSAR) imaging can provide detailed information on crucial plant parameters such as amounts of biomass, growth heights, water contents, crop types, etc. 9 years in orbit, ALOS-2 has pioneered as a veritable long-term L-band SAR land observation mission. ALOS-2/PALSAR-2 has acquired unprecedented L-band time-series data with seamless coverage of the entire vegetated land area. Based on the achievements of its predecessor, we discuss the potential of ALOS-4/PALSAR-3 for further breakthroughs in both agriculture and forest monitoring from meter scale to continental scale. Particularly, the cutting-edge capability to observe 200-km swaths in high-resolution Stripmap (SM) mode, achieved by Digital Beam Forming (DBF), will allow overcoming the limitations of ALOS-2’s widely used 50-m resolution ScanSAR modes. Better spatial resolution and image quality paired with higher revisit frequency is expected to improve the reliability of numerous applications ranging from land cover classifications to biomass and yield estimations.

Synthetic Aperture Radar in Vineyard Monitoring: Examples, Demonstrations, and Future Perspectives

“…The advancements from ALOS-2 to ALOS-4 [109], with Japan's pioneering L-band SARs and cutting-edge capability to observe 200 km swaths in high-resolution stripmap (SM) mode, also indicate significant improvements in global vegetation monitoring.…”