Revisit the calibration errors on experimental slant total electron content (TEC) determined with GPS     

Wenfeng Nie  Tianhe Xu  Adria Rovira-Garcia  José Miguel Juan Zornoza  Jaume Sanz Subirana  Guillermo González-Casado  Wu Chen  Guochang Xu 《GPS Solutions》2018,22(3):85

The calibration errors on experimental slant total electron content (TEC) determined with global positioning system (GPS) observations is revisited. Instead of the analysis of the calibration errors on the carrier phase leveled to code ionospheric observable, we focus on the accuracy analysis of the undifferenced ambiguity-fixed carrier phase ionospheric observable determined from a global distribution of permanent receivers. The results achieved are: (1) using data from an entire month within the last solar cycle maximum, the undifferenced ambiguity-fixed carrier phase ionospheric observable is found to be over one order of magnitude more accurate than the carrier phase leveled to code ionospheric observable and the raw code ionospheric observable. The observation error of the undifferenced ambiguity-fixed carrier phase ionospheric observable ranges from 0.05 to 0.11 total electron content unit (TECU) while that of the carrier phase leveled to code and the raw code ionospheric observable is from 0.65 to 1.65 and 3.14 to 7.48 TECU, respectively. (2) The time-varying receiver differential code bias (DCB), which presents clear day boundary discontinuity and intra-day variability pattern, contributes the most part of the observation error. This contribution is assessed by the short-term stability of the between-receiver DCB, which ranges from 0.06 to 0.17 TECU in a single day. (3) The remaining part of the observation errors presents a sidereal time cycle pattern, indicating the effects of the multipath. Further, the magnitude of the remaining part implies that the code multipath effects are much reduced. (4) The intra-day variation of the between-receiver DCB of the collocated stations suggests that estimating DCBs as a daily constant can have a mis-modeling error of at least several tenths of 1 TECU.  相似文献   

Study on Sampling Rule and Simplification of LiDAR Point Cloud Based on Terrain Complexity     

Qian-ning Zhang  Ze-chun Huang  Zhu Xu  Hai-bin Shang 《Journal of the Indian Society of Remote Sensing》2018,46(11):1773-1784

It is difficult to obtain digital elevation model (DEM) in the mountainous regions. As an emerging technology, Light Detection and Ranging (LiDAR) is an enabling technology. However, the amount of points obtained by LiDAR is huge. When processing LiDAR point cloud, huge data will lead to a rapid decline in data processing speed, so it is necessary to thin LiDAR point cloud. In this paper, a new terrain sampling rule had been built based on the integrated terrain complexity, and then based on the rule a LiDAR point cloud simplification method, which was referred as to TCthin, had been proposed. The TCthin method was evaluated by experiments in which XUthin and Lasthin were selected as the TCthin’s comparative methods. The TCthin’s simplification degree was estimated by the simplification rate value, and the TCthin’s simplification quality was evaluated by Root Mean Square Deviation. The experimental results show that the TCthin method can thin LiDAR point cloud effectively and improve the simplification quality, and at 5 m, 10 m, 30 m scale levels, the TCthin method has a good applicability in the areas with different terrain complexity. This study has theoretical and practical value in sampling theory, thinning LiDAR point cloud, building high-precision DEM and so on.  相似文献   

Estimation of aerosol acidity at a suburban site of Nanjing using machine learning method     

Tao  Miaomiao  Xu  Ying  Gong  Jiaxing  Liu  Qingyang 《Journal of Atmospheric Chemistry》2022,79(2):141-151

Journal of Atmospheric Chemistry - Aerosol acidity is found to exert negative effects on ecosystem diversity and architectural appearance. Current analytical technology is unable to measure in-situ...  相似文献   

COVID-19疫情期间全球空气质量变化:臭氧响应的区域间差异          下载免费PDF全文

Rong Tang  Xin Huang  Derong Zhou  Haikun Wang  Jiawei Xu  Aijun Ding 《大气和海洋科学快报》2021,14(4):45-51

疫情期间全球各地一次排放大幅削减,而臭氧等二次污染的响应则存在着区域间差异.结合地面和卫星观测发现,同在氮氧化物大幅下降的情况下,臭氧在东亚和欧洲呈现出可达14ppb的上升信号,而北美则下降为主(约2-4ppb).我们结合气象分析和臭氧敏感性进一步讨论了臭氧响应差异性的原因,一方面受臭氧与前体物间关系的影响;另一方面来自于气象,尤其是温度.研究明晰了人为排放,化学和气象三者的内在关联,强调了在臭氧控制过程中考虑前体物削减和气象条件协同的重要性.  相似文献   

基于65-nm CMOS工艺的W波段两路电流合成型功率放大器的设计     

黄占秋  张旭  赵晨曦  康凯 《南京气象学院学报》2021,13(4):425-430

采用三级差分共源结构设计了一种基于65-nm CMOS工艺的W波段功率放大器,并利用两路电流型功率合成结构进行功率合成以提升输出功率.为了同时实现单差分转换、阻抗匹配、直流供电,匹配网络采用变压器结构.仿真结果显示,在1 V的电源电压下,该功率放大器的小信号增益为12.7~15.7 dB,3-dB带宽为84~104 GHz,饱和输出功率为14.6 dBm,峰值功率附加效率为9.7%.该功率放大器具有良好的大信号性能,且芯片的核心面积仅为0.115 mm².  相似文献   

Study on the quantitative relationship between soil in situ strength and drilling parameters     

Xiangfeng Lv  Hongyuan Zhou  Lianman Xu 《Environmental Earth Sciences》2018,77(12):469

The rational use of drilling parameters is a hot issue in the field of geotechnical engineering and geological engineering. A new method, for evaluating the bearing capacity of soils using drilling parameters was proposed. First, through the mechanical analysis of the drill bit, the preconditions and theoretical formulas for calculating the bearing capacity of soils using the bit’s torque are clearly defined. Next, drilling tests and dynamic cone penetration tests were performed on miscellaneous fill, silty clay, sandy clay, medium coarse sand and gravel sand, and the empirical formula for calculating the bearing capacity of these soils were given. Then, using the new method and the empirical formula, the bearing capacity of the soil under the roadbed was examined. The test results show that the bit’s torque is a good parameter for the evaluation of the bearing capacity of the soil. Finally, the application scope of the new method and the empirical formula is discussed, and the subsequent research directions are pointed out.  相似文献   

Characterization,modeling, and remediation of karst in a changing environment     

Zexuan Xu  Nicolas Massei  Ingrid Padilla  Andrew Hartmann  Bill Hu 《Environmental Earth Sciences》2018,77(12):476

This introductory editorial paper provides a review and prospective outlook of the achievements and challenges in karst research under a changing environment. A brief discussion of the past and future karst research has been focused on: (1) data and new technologies; (2) modeling of karst flow and reactive transport; (3) responses of karst hydrosystems to climate variability and changes across scales.  相似文献   

Study on the natural radioactivity level of stone coal-bearing strata in East China     

Naizheng Xu  Xinxiang Wei  Fuxiang Kuang  Linxi Zhang  Hongying Liu 《Environmental Earth Sciences》2018,77(21):726

Based on γ-radiation dose rate and radon concentration measurements and ²³⁸U, ²³²Th, ²²⁶Ra, and ⁴⁰K radionuclide testing, this study identifies the radioactive anomalies of stone coal-bearing strata in East China and evaluates the natural radioactivity levels in the air, solid, water and plant media in the typical area of the regional stone coal-bearing layers. The stone coal-bearing strata in East China occur in the lower Cambrian system along the margin of the Yangtze block; additionally, the radioactive anomaly area is sporadically distributed in the stone coal-bearing layers. The background values of ²³⁸U, ²³²Th, ²²⁶Ra, and ⁴⁰K are higher in the stone coal-bearing areas, and the spatial distribution of these natural radionuclides shows significant variability. ²³⁸U and ²²⁶Ra clearly accumulate in the coal, coal gangue and soil and are the main sources of the environmental radiation in coal mines. The γ-radiation shows a higher background value in the stone coal-bearing area, and this radioactive pollution cannot be ignored. Typically, the effective dose of γ-radiation exceeds the limit value of 5 mSv/a, and the total α and total β concentrations of the groundwater are 10–30 times the limit value at some points. The residents near the mining area are subjected to a higher radiation dose, and the groundwater, building materials, and plants have been contaminated by the radioactive pollution sporadically through time. It is necessary to strengthen the monitoring work of radioactive environments and to take appropriate control measures.  相似文献   

Multi-temporal scale modeling on climatic-hydrological processes in data-scarce mountain basins of Northwest China     

Jianhua Xu  Chong Wang  Weihong Li  Jingping Zuo 《Arabian Journal of Geosciences》2018,11(15):423

Previous studies showed that the climatic processes drive the streamflow of the inland river in Northwest China. However, it is difficult to quantitatively assess the climatic-hydrological processes in the ungauged mountainous basins because of the scarce data. This research developed an integrated approach for multi-temporal scale modeling the climatic-hydrological processes in data-scarce mountain basins of Northwest China by combining downscaling method (DM), backpropagation artificial neural network (BPANN), and wavelet regression (WR). To validate the approach, we also simulated the climatic-hydrological processes at different temporal scales in a typical data-scarce mountain basin, the Kaidu River Basin in Northwest China. The main results are as follows: (i) the streamflow is related with regional climatic change as well as atmosphere-ocean variability, (ii) the BPANN model well simulated the nonlinear relationship between the streamflow and temperature and precipitation at the monthly temporal scale, and (iii) although the annual runoff (AR) appears to have fluctuations, there are significant correlations among AR, annual average temperature (AAT), annual precipitation (AP), and oscillation indices, which can be simulated by equations of WR at different temporal scales of years.  相似文献   

Laboratory investigations of inert gas flow behaviors in compact sandstone     

Chaojun Jia  Weiya Xu  Huanling Wang  Wei Wang  Jun Yu  Zhinan Lin 《Environmental Earth Sciences》2018,77(6):245

The seepage evolution behavior of compact rock is significant for the stability and safety of many engineering applications. In this research, both hydrostatic and triaxial compression tests were conducted on compact sandstone using an inert gas, namely argon. A triaxial compression test with a water permeability measurement was carried out to study the difference between the gas permeability and water permeability evolutions during the complete stress–strain process. Based on the experimental data, the hydrostatic stress-dependent gas permeability was discussed firstly. A second-order function was proposed to predict and explain the gas slippage effect. The mechanical properties and crack development of the sandstone samples were discussed to better understand the permeability evolution with crack growth during the complete stress–strain process. The results show that the gas permeability evolution can be divided into five stages according to the different crack growth stages. Then, the permeability changes in the crack closure stress \( \sigma_{\text{cc}} \), crack initiation stress \( \sigma_{\text{ci}} \), crack damage stress \( \sigma_{\text{cd}} \) and peak stress \( \sigma_{\text{p}} \) with confining pressures were analyzed. Finally, we found that the difference between the corrected gas permeability and water permeability can be attributed to the interaction between the water and sandstone grains.  相似文献