Developing a Fully Fledged CORS Map for Africa

The modernisation of the Global Navigation Satellite Systems (GNSS) has brought about significant changes in the methods of positioning and navigation. More recently, countries are adopting the continuous observation and measurements using a network of GNSS receivers called Continuously Operating Reference Stations (CORS) as the standard. For example, Nigeria has established 11 permanent GNSS Network (NIGNET) or CORS since 2008, which has provided the incentive for the adoption of the geocentric datum in all its geodetic activities. Unfortunately, the spatial coverage of the Nigerian CORS stations on a distance of more than 300km (between the stations) seems inadequate based on the global station densification standard of the International Terrestrial Reference Frame (ITRF). This study explores the CORS network and determines the suitability of improving the density of the existing CORS stations with a view to extending their spatial coverage in Nigeria. Data obtained from various sources are processed and analysed using buffer and Digital Elevation Model (DEM) techniques. The result shows that the existing CORS stations in Nigeria only covers about 25% of the country. Therefore, the study proposes new CORS stations that improve the distribution and the spatial coverage of the existing stations (to about 96%) in line with the ITRF's standard.

The modernisation of the Global Navigation Satellite Systems (GNSS) has brought about significant changes in the methods of positioning and navigation. More recently, countries are adopting the continuous observation and measurements using a network of GNSS receivers called Continuously Operating Reference Stations (CORS) as the standard. For example, Nigeria has established 11 permanent GNSS Network (NIGNET) or CORS since 2008, which has provided the incentive for the adoption of the geocentric datum in all its geodetic activities. Unfortunately, the spatial coverage of the Nigerian CORS stations on a distance of more than 300km (between the stations) seems inadequate based on the global station densification standard of the International Terrestrial Reference Frame (ITRF). This study explores the CORS network and determines the suitability of improving the density of the existing CORS stations with a view to extending their spatial coverage in Nigeria. Data obtained from various sources are processed and analysed using buffer and Digital Elevation Model (DEM) techniques. The result shows that the existing CORS stations in Nigeria only covers about 25% of the country. Therefore, the study proposes new CORS stations that improve the distribution and the spatial coverage of the existing stations (to about 96%) in line with the ITRF’s standard. Keywords CORS, AFREF, Nigerian Geocentric Datum, GNSS, NIGNET

Nigeria, in the past five years has established about fifteen (15) Global Navigation Satellite System (GNSS) Continuously Operating Reference Stations (CORS) across the country. The CORS network is primarily meant for the implementation of African Geodetic Reference Frame (AFREF) and Zero-order Geodetic Controls for Nigeria. This GNSS CORS infrastructure provides a viable and highly scalable platform for the implementation of wide range Real Time Kinematic (RTK) services for relevant user communities in Nigeria. However, the current network architecture and post processing system of the CORS infrastructure does not meet the multi-level application needs in the country. In order to scale down the GNSS application opportunity, there is need for the implementation of this RTK Network with Central Processing Facility (CPF), where the pre-processing, detection and repair of cycle slips, and double difference ambiguities between the reference stations are determined. Thereafter, local error modeling algorithms are derived and transmitted to the users epoch by epoch or at predefined time intervals in the fields. This paper therefore aims at developing this RTK Network Service implementation model for Nigeria, leveraging on the existing Zero-order GNSS CORS Network. The developments of GNSS Infrastructure in Nigeria and existing capacity for viable Network RTK implementation were examined. The requirements and feasibility of RTK services in Nigeria were identified, and a Network RTK Service Model was developed. The benefits and potential challenges in this RTK Network Services in Nigeria were identified, and recommendations on network densification architecture and implementation strategies for service sustainability and returns on investment were made.

This paper examines quality and integrity issues that need to be managed in order to successfully operate a real-time CORS network. Important concepts in quality control such as data availability, latency, multipath, atmospheric effects, and interference are discussed. These quality indicators are examined in the context of their capacity to indicate potential problems that can degrade the quality of real-time network positioning. The issue of intelligent alerting is raised and an alternative strategy, based on the use of relative thresholds, is proposed with the aim of reducing the number of unnecessary alerts provided to operators. South Africa's CORS network TrigNet is used as a case study to test some of these concepts.

This paper examines quality and integrity issues that need to be managed in order to successfully operate a real-time CORS network. Important concepts in quality control such as data availability, latency, multipath, atmospheric effects, and interference are discussed. These quality indicators are examined in the context of their capacity to indicate potential problems that can degrade the quality of real-time network positioning. The issue of intelligent alerting is raised and an alternative strategy, based on the use of relative thresholds, is proposed with the aim of reducing the number of unnecessary alerts provided to operators. South Africa's CORS network TrigNet is used as a case study to test some of these concepts.

Advances in Meteorology, 2015

When compared to the wide range of atmospheric sensing techniques, global navigation satellite system (GNSS) offers the advantage of operating under all weather conditions, is continuous, with high temporal and spatial resolution and high accuracy, and has long-term stability. The utilisation of GNSS ground networks of continuous stations for operational weather and climate services is already in place in many nations in Europe, Asia, and America under different initiatives and organisations. In Africa, the situation appears to be different. The focus of this paper is to assess the conditions of the existing and anticipated GNSS reference network in the African region for meteorological applications. The technical issues related to the implementation of near-real-time (NRT) GNSS meteorology are also discussed, including the data and network requirements for meteorological and climate applications. We conclude from this study that the African GNSS network is sparse in the north and central regions of the continent, with a dense network in the south and fairly dense network in the west and east regions of the continent. Most stations lack collocated meteorological sensors and other geodetic observing systems as called for by the GCOS Reference Upper Air Network (GRUAN) GNSS Precipitable Water Task Team and the World Meteorological Organization (WMO). Preliminary results of calculated zenith tropospheric delay (ZTD) from the African GNSS indicate spatial variability and diurnal dependence of ZTD. To improve the density and geometry of the existing network, countries are urged to contribute more stations to the African Geodetic Reference Frame (AFREF) program and a collaborative scheme between different organisations maintaining different GNSS stations on the continent is recommended. The benefit of using spaced based GNSS radio occultation (RO) data for atmospheric sounding is highlighted and filling of geographical gaps from the station-based observation network with GNSS RO is also proposed.

Based on the results of observations from 147 permanent GNSS-stations located in Europe, between 2000 and 2010 we constructed maps of absolute and regional velocity vectors of horizontal displacement of permanent GNSS-stations for each year of the observation period. To summarize the results gathered in Europe we have identified six conventional crustal blocks (CCB) that within a block have almost stable kinematic characteristics. First CCB during the period of observation undergoes rectilinear motion in general azimuth in 118 degrees with an average linear velocity 5.4 mm per year; the second CCB over the observation period undergoes gradual rotational motion in azimuth from 54 degrees to 266 degrees with an average linear velocity 1.4 mm per year; the third CCB over the period of observation undergoes rectilinear motion in general azimuth in 298 degrees with an average linear velocity 3.2 mm per year; the fourth CCB over the period of observation undergoes rectilinear motion in general azimuth in 245 degrees with an average linear speed of 2.4 mm per year; the fifth CCB over the period of observation undergoes rectilinear motion in azimuth 51 degrees with an average linear velocity 3.0 mm per year; the sixth CCB over the period of observation undergoes curvilinear motion with an average linear rate of 2.5 mm per year. CCBs that are located in Europe coincide with tectonic structures of the crust. In particular: the border of the first and second CCB passes through the Volyn-Dvina moving zone boundary; the border of the second and third CCB is the border of the East European Platform and the Baltic Shield, the border of the second and sixth CCB is found in the Teyseyr-Tornquist Zone; the border of the fifth and sixth CCB is the Alpine-Himalayan fold belt; the fourth CCB is located on the West European plate and covers the Pyrenean peninsula the boundary of this block are Pyrenees. After analyzing the distribution maps of dilatation in Europe for the period 2000 - 2010 and the maps of migration extreme values of dilatation in Europe according to the permanent GNSS-stations in the period 2000 - 2010, we can conclude that the manifestations of extreme values of crust dilatation in Europe during 2000 - 2010 in most cases do not migrate depending on the thickness of the crust, and are linked to specific tectonic faults, their migration routes pretty well reflect the tectonic movement of plates in Europe.

In the last few years, Greece has responded to and participated in various European Spatial Data Infrastructure (ESDI) initiatives. This has made many government organizations to increasingly realize that spatial information has an important role to play in the development process of the country, mostly by providing an economic value and also contributing to several policy areas con-cerned with environmental and social needs. Most relevant initia-tives in this direction have focused so far on developing, mainly through the Hellenic Cadastre Project, the legal framework needed to underpin the creation of a national SDI (NSDI), starting from priorities aiming to utilize many applications relying on geospatial information for the development of national or regional social ben-efit programs and services, and in supporting the shared objectives of various national surveying and mapping authorities. One fundamental component of these efforts has been identified as the urgent need to estab...

International GNSS Service (IGS) is a public service that provides GNSS data at each station throughout the world. IGS can be accessed by everyone, for scientific, education, or commercial purpose. Indonesia, as part of international community, now has three GNSS stations incorporated in the IGS system. One of the three stations are managed by Geospatial Information Agency (BIG-Badan Informasi Geospasial), which is BAKO station. Recorded at the end of 2015, the GNSS station in Indonesia (Ina-CORS Station) that is operated and maintained by BIG amounted to 126 stations spread across Indonesia. Geographically, Indonesia is surrounded by active tectonic plates causing the global deformation. Supporting the mission of IGS to provides highest-quality GNSS data for earth observation and research purpose, BIG as a representation of Indonesia proposed a number of Ina-CORS station to join with the IGS system. The submitted station must comply the IGS standard. There are five main parameters of IGS station, that is the construction site of antenna monument, the availability of support equipment for measuring pressanure and temperature, type of data communication, antenna type and radome, and the capability and reliability of the satellite signal receiver. After executing a systematic study, there are 28 Ina-CORS stations that comply with IGS criteria. Those stations are in the process of proposing to become part of the IGS system. This is expected to increase the contribution of Indonesia to the world in monitoring the global deformation, earth observation research, or other application that has a benefit to the society.

Global Navigation Satellite System (GNSS) Continuously Operating Reference Station (CORS) networks are being introduced across many countries to provide improved access to positioning infrastructure for a wide range of applications and a solid platform for research and innovation involving satellite positioning technology. This paper discusses the challenges involved in establishing a CORS network, using the experiences from CORSnet-NSW as an example. The purpose of a CORS network determines the required network density and station monumentation. The logistics involved in physically building the monument and installing the electronic equipment are some of the easiest issues requiring consideration. Collaboration with other organisations hosting a CORS, long-term tenure of the land and/or building to be used, site access, system redundancy and communications all play crucial roles. In addition, several operational aspects need to be addressed in order to provide (and achieve) reliable GNSS positioning of homogeneous and high accuracy across the network. These include the consistent connection to a high-quality datum, GNSS-based height transfer considerations, the use of absolute GNSS antenna models, stability and integrity monitoring, and the possible contribution to regional or global geodesy initiatives.