DEFORESTATION DETECTION IN THE AMAZON USING ALOS-2: DIFFERENCES BETWEEN HV AND HH POLARIZATIONS REVEALED THROUGH GROUND SURVEYS

The Amazon rainforest is vital for global climate regulation and biodiversity, yet illegal deforestation continues to threaten the region. In Brazil, the Deter system, operated by the National Institute for Space Research (INPE), utilizes optical satellite data to monitor deforestation. However, optical satellites face limitations due to frequent cloud cover during the rainy season. Radar satellites, such as the Japan Aerospace Exploration Agency’s (JAXA) ALOS-2, provide an alternative by using microwaves that penetrate clouds, making them suitable for deforestation monitoring regardless of weather conditions. This study compares the performance of HV and HH polarizations in detecting deforestation using data from JICA and JAXA’s JJ-FAST system. Field surveys conducted between 2021 and 2023 across 65 deforestation sites within the Legal Amazon form the basis of the analysis. Version 3.2 of JJ-FAST, which utilizes HV polarization, and Version 4.2, which mainly employs HH polarization, were compared. The results showed that Version 4.2 was able to detect deforestation earlier than Version 3.2 in several cases, while Version 3.2 detected some sites that Version 4.2 missed. Overall, 80.70% of the sites were detected early when both versions were used. The findings suggest that utilizing both polarizations is necessary for comprehensive monitoring across different stages of deforestation. Further investigation is needed to understand the limitations of the algorithms, particularly for sites where detection was delayed or missed.