http://scholars.ntou.edu.tw/handle/123456789/196 2026-08-10T08:37:07Z http://scholars.ntou.edu.tw/handle/123456789/26805 標題: Robust Nonlinear GNSS Navigation Under Heavy-Tailed Measurement Noise Using a Cauchy-Kernel Correntropy Extended Kalman Filter 作者: Jwo, Dah-Jing; Abdi, Abdirisak Daud; Chang, Yi 摘要: In urban canyon environments, the performance of global navigation satellite systems (GNSS) is severely degraded by multipath propagation, signal occlusion, and non-Gaussian measurement noise. These effects reduce positioning accuracy and service reliability. Kalman filtering and its nonlinear extensions are widely used for GNSS positioning. However, these filters rely on Gaussian noise assumptions and are formulated using the minimum mean square error (MMSE) criterion. Consequently, their performance degrades in non-Gaussian environments. Recently, filtering methods based on the maximum correntropy criterion (MCC) have been investigated as robust alternatives to MMSE-based approaches. The performance of MCC filters is strongly influenced by the choice of the kernel function. In particular, Gaussian kernel-based MCC algorithms may suffer from numerical instability under large measurement noise and strong sensitivity to kernel bandwidth selection. These limitations compromise estimation robustness and convergence stability. To address these limitations, this study proposes a Cauchy kernel-based maximum correntropy extended Kalman filter (CKMCEKF). The effectiveness of the proposed filter was validated using both simulation and real GNSS datasets. The results confirm the superior accuracy, stability, and reduced sensitivity to kernel bandwidth selection of the proposed method. 2026-01-01T00:00:00Z http://scholars.ntou.edu.tw/handle/123456789/26798 標題: Using geochemical signatures to identify subsurface flow pathways in the intermittent reach of the Yusheng Creek in Taiwan 作者: Lee, Tsung-Yu; Yeh, Hsiu-Hao; Pan, Yen-Wei; Hsu, Shao-Yu; Chiu, Yung-Chia; Huang, Jr-Chuan 摘要: Study region: Yusheng Creek is a mountain stream in central Taiwan where the critically endangered Formosan landlocked salmon (Oncorhynchus masou formosanus) has been reintroduced but remains vulnerable to intermittent streamflow. Study focus: Subsurface flow pathways and groundwater-stream interactions were investigated using end-member mixing analysis (EMMA). Monthly water samples were collected from four observation wells, stream water, and tributaries during two monitoring periods (January-November 2017; October 2021-August 2022). Geochemical parameters and stable isotopes (delta 18O and delta 2H) were analyzed to trace water sources. New hydrological insights: Results reveal contrasting hydrological connectivity between dry and wet years. During dry years, the hyporheic zone persisted within the streambed but remained disconnected from groundwater, while upstream stream water infiltrated and migrated downstream through subsurface pathways. In wet years, the hyporheic zone and groundwater formed a hydraulically connected system, as indicated by similar geochemical signatures. These results highlight the critical role of the hyporheic zone in maintaining longitudinal connectivity in intermittent mountain streams, providing new insights into subsurface flow dynamics in humid subtropical regions. 2026-01-01T00:00:00Z http://scholars.ntou.edu.tw/handle/123456789/26792 標題: Thermal dynamics of an intermittent subtropical stream controlled by surface water-groundwater interactions: evidence from distributed temperature sensing and heat-budget modeling 作者: Pan, Yen-Wei; Chen, Yu-Cheng; Lee, Tsung-Yu; Chiu, Yung-Chia; Hsu, Shao-Yu; Chen, Che-Ming 摘要: Stream temperature in intermittent subtropical rivers exhibits pronounced spatial and temporal variability driven by surface water-groundwater interactions, yet such variability is often poorly resolved by point-based measurements. This study integrates fiber-optic distributed temperature sensing (FO-DTS), precisely georeferenced using a Real-Time Kinematic (RTK) positioning system, with a physics-based heat-budget model (HFLUX) to investigate thermal dynamics along a 782-m intermittent stream reach in Taiwan. Meter-scale FO-DTS measurements collected over a 3-day monitoring period revealed distinct longitudinal thermal regimes. Model simulations reproduced measured stream temperatures with high accuracy across upstream, midstream, and downstream segments, with root mean square errors (RMSE) ranging from 0.328 to 0.399 degrees C and normalized RMSE values below 4.1%. Sensitivity analysis indicated a downstream shift in dominant thermal controls. Discharge exerted the strongest influence in the upstream losing reach, whereas groundwater temperature became the primary control in the midstream and downstream segments, where increasing subsurface inflows dampened diel temperature variability. The optimal groundwater temperatures inferred by the model closely matched independent field measurements, allowing differentiation between hyporheic-dominated inflow in the midstream segment and shallow groundwater contributions downstream. These results demonstrate that coupling RTK-referenced FO-DTS with heat-budget modeling provides a robust framework for diagnosing surface water-groundwater interactions and thermal regimes in intermittent streams, particularly in subtropical and drought-prone regions. 2026-01-01T00:00:00Z http://scholars.ntou.edu.tw/handle/123456789/26637 標題: Significant Southern Hemisphere contribution to the Indonesian Throughflow over the last 800,000 years 作者: Kienast, Markus; Hollstein, Martina; Lehmann, Nadine; Rafter, Patrick A.; Li, Ziye; Chen, Min-Te; Mohtadi, Mahyar 摘要: The low-latitude flow of water masses from the Pacific to the Indian Ocean, the Indonesian Throughflow (ITF), is a choke point of the surface ocean return flow of the ocean conveyor belt. Even though the significance of the ITF for the modern global ocean circulation and climate has long been established, little is known about the hemispheric origin of the water masses contributing to its overall transport in the past. Here, we take advantage of the distinctly different isotopic composition of subsurface nitrate in the Northern and Southern Hemisphere source waters to document the admixture of these waters in the ITF through time. Our record of bulk sedimentary delta 15N from the Banda Sea, at the heart of the ITF, shows that Southern Hemisphere-sourced subsurface waters contributed significantly to the total ITF transport during the last 800,000 years. Because Southern Ocean processes ultimately set the biogeochemical source signature of the Southern Hemisphere endmember, the Banda Sea record implies an important conduit by which high southern latitude climate and ocean variability is transmitted into the global ocean. 2026-01-01T00:00:00Z