Estimation of Hyrcanian forests coverage using ALOS PALSAR and MODIS satellite data (2007–2017)

Abstract

This study aims to monitor the extent changes of Hyrcanian forests using ALOS-/PALSAR-1 and ALOS/PALSAR-2 (PALSAR) mosaic data with HH and HV polarimetric bands from 2007 to 2017. To date, no comprehensive studies have been conducted on the total cover area of the Hyrcanian forests. This study attempts to provide specific and local threshold values for to extract the Hyrcanian forests cover through careful examination of satellite data over ten years. In this study, the acquired 57 PALSAR images were calibrated and converted to γ0 (dB) for the years 2007, 2010, and 2017. Then, the backscattering value ranges of the Hyrcanian forests were determined using the Decision Tree classification method. The backscattering values range from −14.5 to −7.2 dB and −17.5 to −8.5 dB for the years 2007 and 2010 and −18.5 to −7.5 dB for 2017 in the HV-band and from −7.5 to −14.5 dB for 2007 and 2010 and −6.2 to −12.5 dB for 2017 in the HH band correspond to forest. Finally, the results were compared with Japanese Aerospace Exploration Organization (JAXA) forest and non-forest (F/NF) maps from PALSAR data for validation purposes; the overall accuracies and Kappa coeffitients were 92.55%, 0.82% (2007), 91.14%, 0.79% (2010), and 88.19%, 0.74 (2017), respectively. This result shows that values between −7.2 and −13.5 dB are the best range for the Hyrcanian forests’ extent extraction from PALSAR image in the HV band. The output were further validated using three independent sources: (1) High-Resolution Google Earth (GE) image; (2) F/NF maps from the JAXA; and (3) MOD13Q1 Products (250 m spatial resolution). The results show good consistency with the mentioned datasets.