JJ-FAST (JICA-JAXA Forest Early Warning System in the Tropics)

JJ-FAST (JICA-JAXA Forest Early Warning System in the Tropics) is an L3 deforestation alert product derived from ALOS-2 PALSAR-2 ScanSAR acquisitions, distributed by JAXA EORC.^[1] The system operates independently of cloud cover by exploiting L-band SAR backscatter, generating alerts across tropical forest regions in Southeast Asia, the Congo Basin, and the Amazon.

The product resolution is cited at 100 m in some eoPortal documentation for the PALSAR-2 Wide ScanSAR mode;^[2] the JAXA Earth-graphy data page states a 50 m output grid for JJ-FAST delivery.^[3] According to JAXA site documentation reviewed in May 2026, the minimum mapping unit is 1.5 hectares as of algorithm version 4.0, and a version 4.2 release from April 2026 is referenced on the JJ-FAST portal. A terrain-induced false-detection mask based on the ALOS World 3D DEM was added to the processing chain in July 2023.^[1]

The product update cycle is approximately 42 days, driven by ALOS-2's 14-day orbital repeat combined with ScanSAR tile composition and processing latency.^[4] This is slower than optical alert systems under clear-sky conditions and slower than the RADD SAR alert system. Accuracy statistics are not confirmed from a publicly accessible primary source; the underlying algorithm paper is paywalled.^[4] Data are available open-access via the JJ-FAST portal subject to registration.