ANALYSIS OF DAMAGED RICE FIELDS AND RICE RESTORATION AFTER THE GREAT EAST JAPAN TSUNAMI USING TIME-SERIES MODIS DATA

摘要

The 2011 Great East Japan Tsunami happened on 11 March, 2011, destroyed 23,600 hectares of cultivation areas in northeastern coastal area of Japan, especially in Fukushima Prefecture and Miyagi Prefecture. More than 60% of inundation area is the area of rice fields. Therefore, monitoring the damaged rice fields and restoration of rice area after the tsunami is critical to provide agronomic planners with valuable information for the effective crop management strategies. Satellite imagery can provide multi-temporal and wide region data, and the spectral profile of rice is different from other land use types. This study used Moderate Resolution Imaging Spectroradiometer (MODIS) data from 2010, 2011 and 2014 to investigate the damaged rice fields and restoration of rice areas after the tsunami. The procedure of data processing consists of four steps: (1) data pre-processing to produce the time-series Normalized Difference Vegetation Index (NDVI) data and data filtering of the NDVI time-series data by wavelet transform, (2) paddy rice mapping using support vector machine (SVM), (3) accuracy assessment, and (4) area estimation of damaged rice fields and their restoration. The mapping results indicated the overall accuracy is 88.0%, 91.7% and 90.8% and the Kappa coefficient is 0.76, 0.83 and 0.81 in 2010, 2011 and 2014, respectively. After the tsunami (2011), 84.9 % of rice fields damaged by the tsunami is estimated. In 2014, the restoration rate is 33.1%. The RMSE divided by the total area of the comparison between classification results with statistic data in 2010, 2011 and 2014 are all lower than 3%. It indicated this study can apply to the analysis of damaged rice fields and their restoration.