RICE AREA MAPPING WITH TIME SERIES ANALYSIS OF SENTINEL-1 SAR IMAGERY IN AYUTTHAYA PROVINCE,CENTRAL THAILAND

摘要

Rice monitoring in Thailand is highly significant and indispensable, as rice is the country's most important crop, and around 60 percent of Thai farmers mainly plant rice. Synthetic Aperture Radar (SAR) is a suitable tool for monitoring rice cultivated in cloudy and rainy weather because of its ability of using microwave radiation to pass through clouds. In this study, Sentinel-1 VH-polarized SAR images were used to map the rice-growing areas in Ayutthaya province, one of the leading rice producing provinces in the country, during the wet season (May-November) in 2015. Four essential steps were required for conducting the study: (1) image pre-processing, including radiometric and geometric correction, as well as speckle noise removal, (2) Normalized Difference Sigma Naught Index (NDSI) calculation using SAR time series images, during the rice growing season, (3) rice growing area classification with applying a NDSI threshold, and (4) mapping accuracy assessment, by comparing with ground reference data. The classification results indicate the overall accuracy of 87% and Kappa coefficient of 0.74. This study demonstrates the potential of the applicability of Sentinel-1 VH-polarized SAR imagery for rice area mapping in Central Thailand.