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  • Author or Editor: Massimo Menenti x
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Junchao Shi, Massimo Menenti, and Roderik Lindenbergh

Abstract

Glaciers in the Tibetan mountains are expected to be sensitive to turbulent sensible and latent heat fluxes. One of the most significant factors of the energy exchange between the atmospheric boundary layer and the glacier is the roughness of the glacier surface. However, methods to parameterize this roughness for glacier surfaces in remote regions are not well known. In this paper, the authors use the data acquired by Ice, Cloud, and Land Elevation Satellite (ICESat)/Geoscience Laser Altimeter System (GLAS) laser altimetry from February 2003 to November 2004 along several tracks over glaciers of the Nyainqêntanglha range in central Tibet. The authors make a study of the waveforms measured by the ICESat/GLAS laser system over mountainous and glacial areas. The surface characteristics are evaluated within laser footprints over the glacier outlines based on the glaciological inventory of the Tibetan Plateau constructed by the Cold and Arid Regions Environmental and Engineering Research Institute (CAREERI), Chinese Academy of Sciences. For this purpose, the authors extract waveform parameters: the waveform width, the number of modes, and the RMS width of the waveform. These parameters are compared with surface slope and roughness obtained from the Advanced Spaceborne Thermal Emission and Reflection Radar (ASTER) Global Digital Elevation Model (GDEM). Through this analysis, the impact of morphology on the returned laser waveform is shown for the Nyainqêntanglha range. The roughness and the slope of the surface can be quite significant and may contribute from several meters to tens of meters to the pulse extent. The waveform analysis results indicate that the received waveforms are capable representations of surface relief within the GLAS footprints.

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Haolu Shang, Li Jia, and Massimo Menenti

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 water-saturated 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 multifrequency-polarization 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 = 0.7664 and relative RMSE = 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.

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