Analyzing the Inundation Pattern of the Poyang Lake Floodplain by Passive Microwave Data

Abstract

The soil wetness condition is a useful indicator of inundation hazard in floodplains, such as the Poyang Lake floodplain. Special Sensor Microwave Imager (SSM/I) passive microwave data were used to monitor watersaturated soil and open water areas of the Poyang Lake floodplain from 2001 to 2008, capturing the inundation patterns of this area in space and time. The polarization difference brightness temperature (PDBT) at 37 GHz is sensitive to the water extension even under dense vegetation. The zero-order radiative transfer model was simplified to retrieve the vertical-horizontal (V-H)-polarized effective emissivity difference from the PDBT at 37 GHz. Vegetation fractional area and vegetation transmission function were derived from NDVI to represent the vegetation attenuation. This effective emissivity difference has a quasi-linear relationship with the fractional area of water-saturated soil and standing water, no matter the frequency. Using the multifrequencypolarization surface emission (Q p ) model and the Dobson model of the soil-water mixture, the two segments of this relationship were combined into a quasi-linear model. Comparing the retrieved water-saturated soil and standing water area of Poyang Lake with the lake area obtained from the MODIS and synthetic aperture radar (SAR) image at higher spatial resolution, the calculations show a good fit with the MODIS and SAR data, with R 2 5 0.7664 and relative RMSE 5 17.74%. The cross-correlation analysis shows that the Poyang Lake extension fluctuates with a 5-day time lag with the upstream land area of water-saturated soil and standing water. Since the closure of the Three Gorges Dam, this relationship is more evident.

Modelling stream flow with a discrete rainfall–runoff model and 37 GHz PDBT microwave observations: the Xiangjiang River basin case study

“…As documented by Miller and Nudds (1996), the changes of wetland area in floodplain significantly influence changes of stream flow in the Mississippi River Valley. In our previous study (Shang et al, 2014), the upstream WSS and inundated area were highly 15 correlated with the area of the Poyang Lake downstream. In some conceptual hydrology models, such as Xinganjiang model (Zhao, 1977(Zhao, , 1984, PDM rainfall-runoff model (Moore, 2007(Moore, , 1985, TOPMODEL (Beven and Kirkby, 1979;Beven et al, 1984), VIC (Liang et al, 1994;Wood et al, 1992) and ARNO (Todini, 1996) , the saturated soil area is a conceptual parameter which determines the fast runoff produced after a storm, i.e.…”

“…The Water Saturated Soil (WSS) and inundated area, retrieved from Polarization Difference Brightness Temperature (PDBT) at 37GHz (Shang et al, 2014), is where open water or water-saturated top soil occurs, such as wet lands, ponds, lakes and rivers. Several studies indicate that the WSS and inundated area is a determinant of stream flow.…”

“…In the three implementations of the discrete rainfall-runoff model, the WSS and inundated area is used to estimate component flows produced from discrete precipitation events, and the field measurements of ground water table depth are used to estimate the base flow. The method applied to retrieve the WSS and inundated area from 37GHz PDBT has been described in detail by Shang et al (2014).…”

“…Due to the sensitivity to water content in the top soil layer, passive microwave observations at 37GHz have been used to observe water saturated soil and inundated area (Choudhury, 1989(Choudhury, , 1991Giddings and Choudhury, 1989;Hamilton et al, 2002Hamilton et al, , 1996Shang et al, 2014;Sippel et al, 1994;Sippel et al, 1998;Temimi et al, 2005). The inundated area within a river basin can be related to river discharge directly, thus 37GHz microwave observation have been used to estimate river 5 discharges using empirical relationships (Brakenridge et al, 2007;Vörösmarty et al, 1996).…”

“…2.1), then applied to the other two implementations. The retrievals of the WSS and inundated area from 37GHz PDBT data have been described in detail by (Shang et al, 2014).…”