ALBERT

Description: The GRACE and GRACE-FO gravity satellites have become an important tool for monitoring large-scale groundwater storage (GWS) changes. However, the limited spatial resolution of the monthly gravity field models obtained from GRACE/GRACE-FO and the need for separating GWS from other relevant storage changes leads to large uncertainties in monitoring GWS signals at small scales. To improve the spatial resolution and address the signal leakage, we propose a joint inversion downscaling method based on the independent component analysis method to separate the GWS changes in the North China Plain (NCP). This method combines the high spatial resolution information (0.5°) of different compartment storages simulated within WGHM and the large-scale spatio-temporal mass changes information from GRACE/GRACE-FO within a least square adjustment, and derives downscaled and isolated GWS signals. Significant interannual GWS changes are found in the results of GRACE/GRACE-FO with a long-term trend of -4.03±0.14 km〈sup〉3〈/sup〉/year from 2005 to 2022, which are confirmed by in-situ groundwater level observations. Our analysis reveals that the GWS in the NCP experienced four stages: depletion from 2005 to 2009, stability from 2010 to 2013, depletion again from 2014 to 2019, and then rapid recovery from 2020 to 2022. The recent GWS recovery occurs in both shallow and deep aquifers, due to more precipitation since 2020 in the NCP. Our results demonstrate that the method can effectively improve the spatial resolution of GRACE/GRACE-FO (increased to 50 km), enhance the ability to monitor the small-scale GWS changes, and provide important references for water resources management and decision making.

Description: Water resources are the key link within the unique landscape of the Jiuzhaigou World Natural Heritage Site. However, the earthquake on 8 August 2017 induced serious damage to the ecosystem of the Jiuzhaigou region. Water resource quantity was threatened by the direct destruction of the connectivity between the upstream and downstream river systems, whereas water quality and the original aquatic ecosystem were worsened indirectly by secondary disasters, such as landslides and debris flows triggered by earthquakes. It is urgent to protect water resources to maintain a healthy aquatic ecosystem for the Jiuzhaigou World Natural Heritage Site. Therefore, water resource protection strategies are developed by collaboratively considering water quantity, quality and aquatic ecology, including 1) studying the relationship between upstream and downstream in terms of water supply and connectivity, 2) developing emergency plans for extreme precipitation disasters and ecological water regulation schemes for extreme drought, 3) clarifying the impact of vegetation management measures on water conservation, nutrient cycling and water quality, 4) separating the contributions of earthquakes from related disasters, hydrodynamic changes, and lake bank vegetation succession to lake swamping, 5) identifying the potential water pollution risk caused by ecological restoration projects, analyzing the sources of pollutants such as nitrogen, phosphorus and atmospheric acid deposits and developing control measures, and 6) systematically evaluating aquatic ecological health and determining water ecological protection and restoration measures. This review may provide critical viewpoints for conserving aquatic ecosystems, not only in the Jiuzhai World Natural Heritage Site but also in other global conserved aquatic parks.

Description: Precise satellite clock product is an indispensable prerequisite for the real-time precise positioning service. To meet the requirement of numerous time-critical applications, real-time satellite clock corrections need to be broadcast to users with an update rate of 5 s or higher. With the rapid development of global navigation satellite systems (GNSS) over the past decades, abundant GNSS tracking stations and modern constellations have emerged, and the computation for multi-GNSS real-time clock estimation has become rather time-consuming. In this contribution, an efficient strategy is proposed to achieve high processing efficiency for multi-GNSS real-time clock estimation, wherein undifferenced method based on sequential least square is adopted. In the proposed strategy, parallel data processing and high-performance matrix operations are introduced to accelerate the processing of multi-GNSS clock estimation. The former is based on OpenMP (Open Multi-Processing), while the latter is achieved by the implementation of the Schur complement and the open-source library OpenBLAS. Multi- GNSS observations from 85 globally distributed tracking stations are employed for the generation of real-time precise clock products. The average elapsed time per epoch with the proposed strategy is 0.35, 0.68, and 2.30 s for GPS-only, dual-system, and quad-system solutions, respectively. Compared to the traditional serial strategy, the computation efficiency is significantly improved by 76.0%, 77.3%, and 77.7%, respectively. The accuracy of the estimated clocks is evaluated with respect to IGS final GPS clock products and GFZ final multi-GNSS clock products (GBM0MGXRAP), and multi-GNSS real-time precise point positioning (PPP) experiments are further carried out. All the results indicate that the proposed strategy is efficient, accurate, and can promise high-rate multi-GNSS real-time clock estimation.