检索结果-内蒙古大学图书馆

Calculation of key parameters of tropospheric mapping function based on random forest method

ADVANCES IN SPACE RESEARCH 2025年第2期75卷 1825-1839页

作者： Fan, Haopeng Li, Xinxing Xu, Zhenbang Liu, Xiaogang Wang, Min Li, Linyang Shi, Chunlin Li, Siran Hubei Luojia Lab 129 Luoyu Rd Wuhan Peoples R China Strateg Support Force Informat Engn Univ 62 Kexue Ave Zhengzhou Peoples R China Xian Surveying & Mapping Inst 5 Yanta Rd Xian Peoples R China Smart Earth Key Lab 9 Dengzhuang South Rd Beijing City Peoples R China Henan Inst Econ & Trade 58 Longzihu North Rd Zhengzhou Peoples R China

The tropospheric mapping functions (MFs) play a crucial role in estimating the delay of electromagnetic waves as they traverse the troposphere, particularly in space geodetic techniques like GNSS and VLBI, where these waves are the primary measurement tool. Currently, empirical models that rely on non-meteorological parameters are commonly used to calculate MFs, offering convenience but often yielding less accurate results in regions with volatile climates. Such inaccuracies can lead to errors in slant total delays reaching the meter- level, subsequently affecting other data products. Although authoritative bodies periodically release essential meteorological parameters for MF calculation or provide ready-made MF products, these often come with a delay of several days or require specific authorization. To address this, we introduced a method leveraging the random forest (RF) model to rapidly derive key MFs from surface observations. Experimental results indicate that the RF model significantly enhances the accuracy of MFs, with improvements exceeding 60% for the hydrostatic component and over 20% for the wet component, effectively eliminating seasonal systematic deviations;although it is somewhat inferior to the MFs from VMF3-FC, RF does not require an internet connection and can independently train and construct models, making it very suitable for independently operated systems. We further trained a series of RF models using varied sample spaces and analyzed their performance under different combinations of feature dimensions and time spans. This analysis suggests that an optimal balance exists when considering the challenges in acquiring sample data, training time, model size, computational efficiency, and accuracy. (c) 2024 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

关键词： Space geodesy Tropospheric delay mapping function Random forest Sample space

来源：评论

学校读者我要写书评

暂无评论

A new grey mapping function and its adaptive algorithm for low-light image enhancement

引用

MULTIMEDIA TOOLS AND APPLICATIONS 2023年第4期82卷 6071-6096页

作者： He, Lei Long, Wei Liu, Shouxin Li, Yanyan Ding, Wei Sichuan Univ Sch Mech Engn Chengdu Peoples R China

When taking images in low light conditions, images often suffer from low visibility. In addition to affecting the sensory quality of images, this poor quality may also significantly limit the performance of various computer vision systems. Many grey-level mapping enhancement algorithms based on classic mapping functions, such as the gamma mapping function, have been proposed in recent years to improve the visual quality of low-light images. However, the classic mapping function cannot coordinate the greyscale distribution of the bright and dark areas of the image well and may easily lead to excessive enhancement. This makes it difficult for the performance of these improved algorithms to be fully utilized. Therefore, this paper proposes a new multiparameter grey mapping method. Unlike the classic mapping function, the new mapping method is based on the enhancement strategy of compressing the bright area and then adjusting the dark area. Thus, the inherent shortcomings of the classic mapping function are fundamentally overcome. The new mapping method can not only directly control the compression of the grey space in the bright area of the image through parameters, but it can also adjust the greyscale distribution of dark areas without changing the greyscale value of the pixels in the bright area. Finally, this paper also designs an adaptive enhancement algorithm with the new mapping method as the core to verify its effectiveness and flexibility. Experimental results showed that the adaptive algorithm had excellent performance in colour rendering, brightness enhancement and noise suppression. It was also obviously better than the current similar algorithms in visual quality and quantitative tests.

关键词： Brightness enhancement Contrast enhancement Adaptive algorithm Low-light image mapping function Noise suppression

来源：评论

学校读者我要写书评

暂无评论

Improving the wet mapping function by numerical weather models

引用

ADVANCES IN SPACE RESEARCH 2024年第1期73卷 404-413页

作者： Dogan, Ali Hasan Zus, Florian Dick, Galina Wickert, Jens Schuh, Harald Durdag, Utkan Mustafa Erdogan, Bahattin GFZ German Res Ctr Geosci D-14473 Potsdam Germany Yildiz Tech Univ Fac Civil Engn Dept Geomat Engn TR-34220 Istanbul Turkiye Tech Univ Berlin D-10623 Berlin Germany Artvin Coruh Univ Fac Engn Dept Geomat Engn Artvin Turkiye

In space geodetic techniques, the mapping functions (MFs) provide the relationship between zenith and slant tropospheric delays. The MFs are determined under the assumption of spherically layered atmosphere. However, the atmosphere is not spherically layered, and the asymmetry should be considered. Therefore, tropospheric gradients are taken into account. Nevertheless, tropospheric gradients alone can not fully represent the deviation from a spherically layered atmosphere, and hence cm level errors arise especially for low elevation angles. In this study, we present new approaches to modify the wet MF to reduce mismodelling of tropospheric delays. The delays in the study were calculated using ray-tracing algorithm based on ECMWF's ERA5 dataset. We first analyzed the performances of the new approaches. Then, two Precise Point Positioning (PPP) simulation studies and a real case study were carried out for two different regions namely Germany and Turkiye. According to the results, the proposed approaches reduce the modelling errors up to by a factor 6 for both regions. Besides, simulation studies show that the approaches improve the accuracies of the ZTDs and heights. In the practical application however, we could not find a clear improvement in the PPP analyze and this might be related to the ERA5 which can not be regarded error-free.(c) 2023 COSPAR. Published by Elsevier B.V. All rights reserved.

关键词： Tropospheric delay mapping function Numerical Weather Model ERA5 PPP

来源：评论

学校读者我要写书评

暂无评论

Modeling and analysis of an ionospheric mapping function considering azimuth angle: A preliminary result

引用

ADVANCES IN SPACE RESEARCH 2022年第10期70卷 2867-2877页

作者： Chen, Jun Ren, Xiaodong Xiong, Si Zhang, Xiaohong Minjiang Univ Dept Surveying & Mapping Engn Fuzhou 350118 Fujian Peoples R China Wuhan Univ Sch Geodesy & Geomat Wuhan 430079 Hubei Peoples R China Wuhan Univ Chinese Antarct Ctr Surveying & Mapping Wuhan 430079 Hubei Peoples R China Hubei Univ Sci & Technol Sch Resources & Environm Sci & Engn Xianning 437100 Peoples R China

Generally, dual- and multi-frequency global navigation satellite system (GNSS) users can use dual- or multi-frequency combinations to eliminate the ionospheric delay. However, different vertical ionospheric models are applied for single-frequency GNSS users, which need an ionospheric mapping function for conversion. Although many mapping functions can be employed, the influence of latitude, azimuth, solar flux, and other factors are not taken into account. Thus, we proposed a mapping function, named SGG-MF, considering the influence of azimuth. The conversional results of single-layer model mapping function (SLM-MF), Klobuchar mapping function (Klobuchar-MF), modified single layer model mapping function (MSLM-MF) and SGG-MF are evaluated by using coinciding pierce point (CPP) technique as well as single-frequency precise point positioning (SF-PPP) in static mode. For the CPP technique, it is found that the mean absolute errors (MAE) of SLM-MF, Klobuchar-MF, and, MSLM-MF range from 1.5 to 2.1 TECU (total electron content unit), while SGG-MF ranges from 1.5 to 1.7 TECU. The standard deviation (STD) of SGG-MF improved by about 13.6%, 14.9%, and 13.6% compared with that of SLM-MF, Klobuchar-MF, and MSLM-MF, respectively. For the SF-PPP test, the positioning error of SGG-MF was reduced by about 6.0%, 22.9%, and 11.9% compared with that of SLM-MF, Klobuchar-MF, and MSLM-MF, respectively. (c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.

关键词： Ionosphere mapping function Azimuth TEC GNSS

来源：评论

学校读者我要写书评

暂无评论

Analysis of a mixed boundary value problem for an orthotropic elasticity using a mapping function

引用

INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES 2021年 208卷 154-166页

作者： Hasebe, Norio Nagoya Inst Technol Dept Civil Engn & Syst Management Showa Ku Gokisocho Nagoya Aichi 4668555 Japan

A solution is derived for a mixed boundary orthotropic elastic plane problem using a mapping function to solve arbitrary configurations. No stress function using a mapping function seems to have been derived. The problem is solved as a Riemann-Hilbert problem. The final exact stress functions are represented by an irrational mapping function as a closed form. Stress components are represented by one complex variable. Arbitrarily shaped hole problems can be solved by changing the mapping function. Once the analytical solution has been derived, calculating the stress components is simpler than for an isotropic problem. It is easier to use an irrational mapping function than to form a rational mapping function for an isotropic problem. As an example, an infinite plane with a square hole subjected to uniform tension is analyzed. The stress distributions are shown for Cases I and III problems corresponding to two characteristic roots of the fundamental equation. In a Case III problem, the symmetry of stress distributions is lost. A solution of an external force boundary value problem can be derived from that of the mixed boundary value problem. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Orthotropic plane Mixed boundary value problem Riemann-Hilbert problem mapping function Mittag-Leffler Theorem: square hole

来源：评论

学校读者我要写书评

暂无评论

Regional Egypt tropospheric mapping function model

引用

ALEXANDRIA ENGINEERING JOURNAL 2018年第4期57卷 4157-4165页

作者： Mohammed, Ahmed Nabil Abdelfatah, Mohamed Amin Mousa, Ashraf El-Kutb El-Fiky, Gamal Saber Zagazig Univ Construct Dept & Util Fac Engn Zagazig Egypt Natl Res Inst Astron & Geophys Helwan Egypt

It's essential to find out the delay caused by the troposphere layer to be able to get more accurate results. The precise positioning is very essential for accurate geodetic applications e.g., Crustal deformation and military purposes. The delay is usually modeled as a zenith value and a mapping function to map it to the observed angle. The current research develops a new mapping function model for Egypt through a least square analysis using ten radiosonde stations. The proposed model is a development of Herring continued fraction equation for dry case and wet case separately. The developed model coefficients depend on latitude and day of year. The produced model as well as Niell, Vienna and Chao models are all evaluated using Precise Tropospheric Delay database (PTD). The test data are 36 days over the year 2015 representing winter, spring, summer and fall. The obtained results clearly showed the proposed model is more accurate for Egypt than other models for both dry and wet cases. (C) 2018 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V.

关键词： mapping function Troposphere Database PTD

来源：评论

学校读者我要写书评

暂无评论

Evaluation of anisotropic mapping function using JMA 10-km spectral model

引用

TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES 2008年第171期51卷 16-21页

作者： Ichikawa, Ryuichi Bevis, Michael Foster, James Mannoji, Nobutaka Natl Inst Informat & Commun Technol Kashima Space Res Ctr Kashima Japan Ohio State Univ Columbus OH 43210 USA Univ Hawaii Honolulu HI 96822 USA Japan Meteorol Agcy Tokyo Japan

We obtain a set of pointed wet delay observations at a total of 81 stations at 9 separate time epochs by ray tracing through the output fields of a Japanese numerical weather model with a grid spacing of 10 km. For each station-epoch, we invert the simulated data set, consisting of 4000 pointed delays, using an isotropic and an anisotropic delay model. The isotropic model has only one parameter-the zenith wet delay (ZWD). The anisotropic delay model of Chen and Herring has two additional lateral gradient parameters. We find that the anisotropic model leads to a much better fit between the delay model and the delay observations. On the other hand, the ZWD parameters estimated using the differing delay models are almost identical. This implies the ZWD estimates are not greatly perturbed by lateral heterogeneity of the atmosphere.

关键词： water vapor atmospheric path delay mapping function numerical weather model space geodesy GPS VLBI ray tracing

来源：评论

学校读者我要写书评

暂无评论

A New Mapped Weighted Essentially Non-oscillatory Method Using Rational mapping function

引用

JOURNAL OF SCIENTIFIC COMPUTING 2016年第2期67卷 540-580页

作者： Wang, Rong Feng, Hui Huang, Cong South Univ Sci & Technol China Dept Math Shenzhen Guangdong Peoples R China Wuhan Univ Sch Math & Stat Wuhan 430072 Hubei Peoples R China Guilin Univ Technol Coll Sci Guilin Guangxi Peoples R China

In this paper, we develop a new mapped weighted essentially non-oscillatory method for hyperbolic conservation laws by proposing a new family of mapping functions, which includes the mapping function in Henrick et al. (J Comput Phys 207:542-567, 2005) as one of its members. The new family of mapping functions has three parameters, namely m, n and k. When it is applied to the -th-order WENO-JS methods, , 4, 5 and 6, it is well defined and monotonically increasing with proper choice of m, n and k. Furthermore, it can achieve the optimal order of accuracy at or near critical points in smooth regions with proper choices of n. The new family of mapping functions uses rational functions, thus it is a family of smooth functions (Note that, the mapping function in Feng et al. (J Sci Comput 51:449-473, 2012) is only piecewise continuous). Among the new family of mapping functions, the new mapping function with has the best performance (i.e., no matter for short time or for long time simulations, it provides the more accurate numerical solutions).

关键词： WENO methods Hyperbolic conservation laws mapping function

来源：评论

学校读者我要写书评

暂无评论

Improvement of astronomical refraction by mapping function

引用

CHINESE ASTRONOMY AND ASTROPHYSICS 1998年第4期22卷 487-496页

作者： Yan, HJ Chinese Acad Sci Shanghai Observ Shanghai 200030 Peoples R China

In this paper we used the method of generator function to gave an improved mapping function of astronomical refraction, separately for optical and radio frequencies. We included a complete consideration of the corrections introduced by the physical and geophysical factors required in astronomy and space techniques. We used sounding balloon data to assess the actual accuracy of our corrected refraction formula. The result is 5 " at elevation 2 degrees and 1 " at elevation 5 degrees. We believe that the main factor that limits the accuracy is departure of the model atmosphere from the real atmosphere.

关键词： generating function mapping function astronomical refraction

来源：评论

学校读者我要写书评

暂无评论

Improved dry tropospheric propagation delay mapping function for GPS measurements in Egypt

引用

JOURNAL OF SPATIAL SCIENCE 2014年第2期59卷 181-190页

作者： Younes, S. A. M. Fac Engn Tanta Egypt

A large number of models and mapping functions have been developed for use in the analysis of space geodetic data. The performance of tropospheric delay prediction models used for GPS degrades at very low elevation angles. On the other hand, most standard tropospheric models were experimentally derived using available radiosonde data, which were mostly observed on the European and North American continents. In this paper an investigation is presented of several models, including those developed by Hopfield, Saastamoinen, Niell (NMF), Chao, Black & Eisner (B&E), Yan & Ping, Vienna (VMF) and Isobaric (IMF), to determine the errors of these models in predicting dry tropospheric delay and to present a new mapping function which has better low elevation angle performance up to 5 degrees and is suitable for the atmospheric conditions of Egypt. A very significant improvement in the GPS height component can be achieved by using the new mapping function especially for the atmospheric conditions of Egypt.

关键词： Egypt EMA mapping function new mapping function

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：