Browsing by Author "Liu, Yi"
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Item Groundwater Level Change Management on Control of Land Subsidence Supported by Borehole Extensometer Compaction Measurements in the Houston-Galveston Region, Texas(MDPI, 2019-05-15) Liu, Yi; Li, Jiang; Fang, Zheng; Civil Engineering; NSF program: Identification of Urban Flood Impacts Caused by Land Subsidence and Sea Level Rise for the Houston-Galveston RegionAs much as 3.05 m of land subsidence was observed in 1979 in the Houston-Galveston region as a result primarily of inelastic compaction of aquitards in the Chicot and Evangeline aquifers between 1937 and 1979. The preconsolidation pressure heads for aquitards within these two aquifers were continuously updated in response to lowering groundwater levels, which in turn was caused by continuously increasing groundwater withdrawal rates from 0.57 to 4.28 million m3/day. This land subsidence occurred without any management of changes in groundwater levels. However, the management of recovering groundwater levels from 1979 to 2000 successfully decreased inelastic compaction from ~ about 40 mm/yr in early 1980s to zero in around 2000 through decreasing groundwater withdrawal rates from 4.3 to 3.0 million m3/day. The inelastic consolidation that had existed for about 63 years roughly from 1937 to 2000 caused a land subsidence hazard in this region. Some rebounding of the land surface was achieved from groundwater level recovering management. It is found in this paper that a pseudo-constant secondary consolidation rate of subsidence of 0.08 to 8.49 mm/yr emerged or tended to emerge at the 13 borehole extensometer station locations while the groundwater levels in the two aquifers were being managed. It is considered to remain stable in trend since 2000. This secondary consolidation subsidence is beyond the control of any groundwater level change management schemes because it is caused by geo-historical overburden pressure on the two aquifers. The 13 Borehole extensometers’ compaction measurements since 1971 not only successfully corroborate the need for groundwater level change management in controlling land subsidence but also yield the first empirical findings of the occurrence of secondary consolidation subsidence in the Quaternary and Tertiary aquifer systems in the Houston-Galveston region.Item Impact of aerosol non-sphericity on the satellite remote sensing of CO₂Chen, Xi; Wang, Jun; Yang, Dongxu; Xu, Xiaoguang; Yang, Ping; Dubovik, Oleg; Liu, Yi; Mishchenko, Michael; Spurr, RobertExisting algorithms for satellite remote sensing of CO₂ assume that all atmospheric aerosol particles are spherical. This assumption, however, is only valid for the atmosphere in the absence of dust particles that are non-spherical by their nature. Here, a theoretical analysis is conducted for the dusty atmosphere to analyze the impact of aerosol non-sphericity on the accuracy of CO₂ retrievals from space. The analysis begins by adding new capabilities to the UNL-VRTM, a UNified and Linearized Vector Radiative Transfer Model [1] (http://unl-vrtm.org) which can calculate both the four Stokes parameters and their respective sensitivities to aerosol properties. The new capability builds upon the existing non-spherical scattering property database [2,3] and develops an analytical method to calculate the Jacobians of these scattering properties to aerosol size distribution parameters, index of refraction, and particle shape factors. With this new capability, the UNLVRTM is upgraded to compute radiative transfer for the spectrum of Tan-Sat [4], and the subsequent retrieval of CO₂ [5] is conducted by using the UNL-VRTM synthetic data. In the presentation, we will describe the development and validation of UNL-VRTM’s new capabilities and provide an analysis of CO₂ retrieval errors due to the lack of consideration of aerosol non-spherical shape in dusty conditions.Item Inverse problem for finding parameters that control land subsidence caused by subsurface fluid withdrawal.(2011-05-18) Liu, Yi; Helm, Donald C.; Doctor of Engineering