Browsing by Author "Cao, Ning"
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Item Advanced SAR Interferometry Methods for Ground Displacement Estimation from Spaceborne and Airborne Platforms(2016-05) Cao, Ning; Lee, Hyongki; Shrestha, Ramesh L.; Glennie, Craig L.; Lu, Zhong; Jung, Hahn ChulInterferometric synthetic aperture radar (InSAR) is a powerful technique to monitor ground deformation phenomena, such as landslides, ground subsidence, seismological activities, and volcano dynamics. In this dissertation, two major problems of the current advanced InSAR techniques are described and corresponding approaches are proposed to solve them. Among various multitemporal InSAR techniques, persistent (or permanent) scatterer InSAR (PSInSAR) has been widely used in a variety of cases due to its high accuracy and resistance to temporal and spatial decorrelations. One major drawback of the PSInSAR technique is the low spatial density of PSs, especially over non-urban areas without man-made structures. A Phase-Decomposition-based PSInSAR (PD-PSInSAR) method is developed in this dissertation to improve the coherence and spatial density of measurement points by processing the distributed scatterer (DS) dominated by two or more scattering mechanisms. PD-PSInSAR performs eigendecomposition on the coherence matrix in order to estimate the phases corresponding to the different scattering mechanisms, and then implements these estimated phases in conventional PSInSAR process. An important procedure in DS interferometry is the phase triangulation (PT). In this study, the mathematical framework for PT algorithms is proposed. This dissertation introduces two modified PT algorithms and analyzes the mathematical relations between five different PT methods. The analysis shows that these five PT methods share very similar mathematical forms with different weight values. The proposed mathematical framework supports improved understanding and advanced estimation methods for the use of PT algorithms in DS interferometry. Another major drawback of traditional InSAR is that only the deformation along the line-of-sight (LOS) direction can be detected. In order to estimate the deformation in the along-track direction, a time-domain along-track SAR interferometry (TAI) technique is proposed. Compared with existing multiple-aperture SAR interferometry (MAI) methods, the proposed technique utilizes the full aperture to generate single-look complex images, and results in higher SNR and along-track resolution. In the last part of the dissertation, a case study of Slumgullion landslide is performed to demonstrate the potentials and challenges of airborne InSAR as well as the possible solutions to improve the precision of the derived deformation measurements.Item Rapid Topographic Mapping Using Terrestrial Laser Scanning and Uav Photogrammetry: Case Study at Bryan Beach in Freeport, Texas(2018-12) Ding, Jieying 1994-; Wang, Guoquan; Khan, Shuhab D.; Cao, NingCoastal regions are generally vulnerable to impact from long-term coastal erosion and episodic coastal hazards caused by extreme weather events. Predictions of storm impact, coastal planning and resilience observations after natural events require high-accuracy and high-resolution coastal morphologic maps. Rapid topographic mapping is of critical importance for long-term coastal management and for quick response after natural disasters. Terrestrial Laser Scanning (TLS) techniques have been frequently applied to beach and dune erosion studies and post-hazard responses; however, TLS surveying is relatively slow and costly for rapid surveying. Furthermore, TLS surveying unavoidably retains gray areas that cannot be reached by laser pulses, particularly in areas where there is a lack of direct access. Aerial images taken by Unmanned Aerial Vehicles (UAVs) enable the mapping of coastal features quickly, safely, inexpensively, on short notice, and with minimal environmental impact. This study aims to develop an efficient method for acquiring highly accurate Digital Elevation Models (DEMs) applied in a beach and dune area by using the UAV Structure from Motion (SfM) photogrammetry technique. A workflow for conducting rapid and high-accuracy UAV photogrammetry survey in beach and dune environments was developed in this study. Two repeated UAV surveys were conducted within a 1-km long, 300-m wide beach-dune belt in Freeport in April and September 2018. DEMs derived from TLS and UAV datasets were used as the basic survey products for assessing the accuracy of UAV surveys. Our study showed the elevation accuracy of UAV photogrammetry varies from approximately 5 cm in the beach and front dune area to approximately 30 cm in the vegetated back dune area. Significant beach erosion was observed by comparing the DEMs derived from UAV photogrammetry datasets collected in April and September 2018. The shoreline retreated approximately 2.5 m on average during those five months. However, the vegetation line retreated over 3.5 m on average because of severe sand loss in the front dune area. The total volume of sand loss was approximately 12,000 m3 over the 1-km long beach and dune belt.Item Surface Deformation Analysis of the Houston Area: Investigating Contributions of Faults, Salt Domes, and Major Storms(2019-08) Crupa, Wanda Elena 1994-; Khan, Shuhab D.; Suppe, John; Sun, Jiajia; Cao, NingThe Houston area has undergone significant ground deformation in the last century, with the main factor being attributed to groundwater/natural gas withdrawal. However, subsidence can be due to groundwater withdrawal or excess loading brought about by heavy precipitation. Houston has recently been subjected to multiple flooding events which appear to be increasing in frequency. The Houston area is also home to faults and salt domes that contribute to surface deformation. The effect that these factors have had on ground deformation has not previously been studied; certain components of ground motion have been misinterpreted, or largely ignored in scientific studies and when making policies. In this study we investigate the contributions of surface and groundwater to subsidence using data collected over the past 30 years to model/predict groundwater fluctuations and look at the correlation with faults/salt domes and GPS data to see how surface deformation patterns have changed in recent years. The high rate of salt motion coupled with CO2 injection has resulted in uplift in southern Harris County, which acts to alleviate groundwater/gas withdrawal induced subsidence. Observed fault motion along the Long Point-Eureka Heights system is correlated with groundwater trends from 2006-20107. The northern Houston area shows strong subsidence of up to 16 mm/yr and an elongated subsidence bowl. The weakened aquifer systems in the north and southwest are more susceptible to intense subsidence and major flooding. These trends may be matched in the Woodlands and southwest Harris County in the future.