PRODUCTION OF GLOBAL SURFACE WATER MAP BY MULTIPLE MICROWAVE RADIOMETERS AND ITS FUNDAMENTAL VALIDATION

Abstract

 Nomarlized Differential Frequency Index (NDFI) is calculated by multiple microwave radiometers GMI and AMSR2 to produce a daily and 0.1-degree global surface water map for five years (2013-2017). Diurnal varation and bias between sensors in NDFI are adjusted. The basic performance of the surface water map is tested with global datasets. 5-year average NDFI and inundation ratio by Global Surface Water show very high correlation around Japan. Monthly variation of NDFI and inundation ratio by Yesterday’s Earth at EORC show positive correlation along some large river channels. NDFI shows a sudden increase at daily scale in some dry areas where daily variation of NDFI and antecedent precipitation index show positive correlation. In these cases, the increase in NDFI can be caused by inland water inundation rather than flood inundation.