Multi-GNSS products and services at iGMAS Wuhan Innovation Application Center:strategy and evaluation

Over the past years the International Global Navigation Satellite System(GNSS)Monitoring and Assessment System(iGMAS)Wuhan Innovation Application Center(IAC)dedicated to exploring the potential of multi-GNSS signals and providing a set of products and services.This contribution summarizes the strategies,achievements,and innovations of multi-GNSS orbit/clock/bias determination in iGMAS Wuhan IAC.Both the precise products and Real-Time Services(RTS)are evaluated and discussed.The precise orbit and clock products have comparable accuracy with the precise products of the International GNSS Service(IGS)and iGMAS.The multi-frequency code and phase bias products for Global Positioning System(GPS),BeiDou Navigation Satellite System(BDS),Galileo navigation satellite system(Galileo),and GLObal NAvigation Satellite System(GLONASS)are provided to support multi-GNSS and multi-frequency Precise Point Positioning(PPP)Ambiguity Resolution(AR).Compared with dual-frequency PPP AR,the time to first fix of triple-frequency solution is improved by 30%.For RTS,the proposed orbit prediction strategy improves the three dimensional accuracy of predicted orbit by 1 cm.The multi-thread strategy and high-performance matrix library are employed to accelerate the real-time orbit and clock determination.The results with respect to the IGS precise products show the high accuracy of RTS orbits and clocks,4–9 cm and 0.1–0.2 ns,respectively.Using real-time satellite corrections,real-time PPP solutions achieve satisfactory performance with horizontal and vertical positioning errors within 2 and 4 cm,respectively,and convergence time of 16.97 min.

Epidemiological Aspects of Diabetic Retinopathy at the Center of the Application of the Diploma of Specialised Studies in Ophthalmology (Cadeso)/Donka-Conakry

Purpose: The authors analyzed the epidemiological and clinical aspects of diabetic retinopathy at the Center for the Application of the Specialized Studies Diploma in Ophthalmology, Gamal Abdel Nasser University (CHU/ Donka) Conakry. Diabetic retinopathy (eye damage: eye and retina) is a serious complication of diabetes that affects 50% of type 2 diabetic patients. The eyes are particularly sensitive to damage to a small vessel. Diabetic retinopathy (DR) is the retinal localization of diabetic micro angiopathy resulting in impaired blood flow in the affected territories, the consequences of which will determine the clinical manifestations of the disease. DR is the leading cause of vision loss in adults of working age. Patients and Methods: This is a longitudinal prospective study carried out at CADES/O concerning 198 diabetic patients. The selection criteria were that the media be transparent and the fundus accessible over a period of six months from February to July 2018. Results: A total of 73 patients (37%) presented with diabetic retinopathy with an average age of 49.5 +/−9 years. The sex ratio (M/F) was 0.6 with a female predominance of 59%. Liberal profession patients were the most numerous 47.5%. Type 2 diabetes was the most common (85.86%). Diabetes fundus assessment was the most common reason for consultation (52%). Arterial hypertension was the most incriminated risk factor (45.45%) followed by the poor balance of diabetes (40.90%), and the age of diabetes (28.28%). 9.5% had diabetic retinopathy complicated by rubella iris, neovascular glaucoma and retinal detachment. Conclusion: Diabetic retinopathy is a common condition for which early detection and regular monitoring must be the rule to prevent, slow down or avoids irreversible blindness if possible, induced by this pathology by a good balance of diabetes and good control of associated risk factors.

Orbit and clock products for quad-system satellites with undifferenced ambiguity fixing approach

Integer Ambiguity Resolution(IAR)can significantly improve the accuracy of GNSS Precise Orbit Determination(POD).Traditionally,the IAR in POD is achieved at the Double Differenced(DD)level.In this contribution,we develop an Un-Differenced(UD)IAR method for Global Positioning System(GPS)+BeiDou Navigation Satellite System(BDS)+Galileo navigation satellite system(Galileo)+Global'naya Navigatsionnaya Sputnikovaya Sistema(GLONASS)quad-system POD by calibrating UD ambiguities in the raw carrier phase and generating the so-called carrier range.Based on this method,we generate the UD ambiguity-fixed orbit and clock products for the Wuhan Innovation Application Center(IAC)of the International GNSS Monitoring and Assessment System(iGMAS).One-year observations in 2020 from 150 stations are employed to investigate performance of orbit and clock products.Notably,the UD Ambiguity Resolution(AR)yields more resolved integer ambiguities than the traditional DD AR,scaling up to 9%,attributable to its avoidance of station baseline formation.Benefiting from the removal of ambiguity parameters,the computational efficiency of parameter estimation undergoes a substantial 70%improvement.Compared with the float solution,the orbit consistencies of UD AR solution achieve the accuracy of 1.9,5.2,2.8,2.1,and 2.7 cm for GPS,BeiDou-2 Navigation Satellite System(BDS-2),BeiDou-3 Navigation Satellite System(BDS-3),Galileo,and GLONASS satellites respectively,reflecting enhancements of 40%,24%,54%,34%,and 42%.Moreover,the standard deviations of Satellite Laser Ranging(SLR)residuals are spanning 2.5–3.5 cm,underscoring a comparable accuracy to the DD AR solution,with discrepancies below 5%.A notable advantage of UD AR lies in its capability to produce the Integer Recovered Clock(IRC),facilitating Precise Point Positioning(PPP)AR without requiring additional Uncalibrated Phase Delay(UPD)products.To assess the performance of quad-system kinematic PPP based on IRC,a network comprising 120 stations is utilized.In comparison to the float solution,the IRC-based PPP AR accelerates convergence time by 31%and enhance positioning accuracy in the east component by 54%.

The Austrian node of the natural resources satellite remote sensing cloud service platform:examples of Sino-Austrian cooperation

The Austrian node of the Natural Resources Satellite Remote Sensing Cloud Service Platform was established in 2016 through a cooperation agreement between the Land Satellite Remote Sensing Application Center(LASAC),Ministry of Natural Resources of the Peoples Republic of China and the University of Vienna,Austria.Under this agreement panchromatic and multi-spectral data of the Chinese ZY-3 satellite are pushed to the server at the University of Vienna for use in education and research.So far,nearly 500 GB of data have been uploaded to the server.This technical note briefly introduces the ZY-3 system and illustrates the implementation of the agreement by the first China-Sat Workshop and several case studies.Some of them are already completed,others are still ongoing.They include a geometric accuracy validation of ZY-3 data,an animated visualization of image quick views on a spherical display to demonstrate the time series of the image coverage for Austria and Laos,and the use of ZY-3 data to study the spread of bark beetle in the province of Lower Austria.An accuracy study of DTMs from ZY-3 stereo data,as well as a land cover analysis and comparison of Austria with ZY-3 and other sensors are still ongoing.

传统数据中心网络向AD-DC平滑演进技术分析

本文阐述了传统数据中心网络如何向AD-DC平滑演进的三种场景,每种场景对应的迁移方案,以及通过一个示例描述整个迁移过程。随着云计算、大数据、移动互联网的兴起,数据中心流量与日俱增,业务上线节奏加快,要求数据中心网络做出快速响应,传统数据中心网络向AD-DC演进将是必然趋势,AD-DC解决方案满足数字化转型中不断扩张的网络需求,不断迭代创新为客户提供智能融合、安全可靠、先进成熟、开放包容的全栈数据中心网络解决方案,助力更多行业客户的数字化转型实践。