CONTINUOUSLY OPERATING REFERENCE STATIONS (CORS)

SURCON QUESTION: CONTINUOUSLY OPERATING REFERENCE STATIONS (CORS) USING GNSS WOULD BE THE SAVIOUR OF NIGERIAN SURVEYS.

Continuously Operating Reference Stations (CORS) is a technological breakthrough in geodetic positioning. It uses Global Navigation Satellite Systems (GNSS) to establish active geodetic reference framework for surveying, mapping and navigation. Since they are continuously operating, CORS have been referred to as “living” control framework that are fast replacing traditional passive control points. Whereas traditional control points must be placed on hilltops, CORS can be placed in valleys and built-up areas where they are needed.

A Continuously Operating Reference Station consists of a viable GNSS receiver and antenna that are set up in a stable manner and in a safe location with a reliable power supply. The receiver continuously receives satellite data files and uploads them onto a computer system at a Central Processing Centre (CPC). The dedicated personal computer makes the data available on the internet, to which users can connect to determine their position. A remote user needs only one rover receiver and a registered mobile phone internet connection to access the Central Processing Centre. A user with a single frequency rover can establish sub-meter precision while sub-centimeter precision can be established with a dual frequency rover.

CORS supports real-time three-dimensional positioning. It has nation-wide coverage, and is compatible with global reference systems. Unlike traditional control points, CORS can be established up to 250 Kilometers apart to form a network of geodetic reference framework covering an entire nation, a continent, or even the earth at large. As the network continuously downloads satellite data files, it establishes, refines and re-establishes national, regional and international geodetic reference systems. National and regional datums can thus be redefined. When these local and regional GNSS CORS are connected to International GNSS Service (IGS) analysis centres, the satellite data can be used in the progressive realization of the International Terrestrial Reference Frame (ITRF). In that regard, GNSS CORS network becomes an important national infrastructure that supports geodetic and geoscientific studies. In the following sections, some benefits of CORS in sustainable development of Nigeria shall be discussed.

Being a network of geodetic control stations, CORS will greatly enhance the proposed mapping of the entire country. Instead of spending funds to establish large number of first- and second-order geodetic control stations, CORS will become geodetic backbone needed to extend controls to project sites. Thus, CORS will facilitate location and mapping of all landed properties and resources in the country.

CORS reduces physical equipment and infrastructures needed to carry out surveying and mapping projects and thereby reducing cost. Moreover, CORS eliminates the need for densification of controls to specific project sites, reducing time spent on the project and increasing productivity. Instead of using two receivers, a base and a rover, the surveyor will need only one rover that is connected to a COR station, thereby reducing survey equipment cost. Therefore, CORS will practically reduce labour, cost and time spent in mapping projects across the nation.

The establishment and operation of CORS in Nigeria will enhance the realization of unified geocentric and vertical datums, and will support efforts to establish a precise geoid for Nigeria and the African region.

Furthermore, the use of CORS network will enhance constant monitoring of ground and structural subsidence in the coastal and minefield areas of the country. The use of CORS will also enhance land, sea and air-borne navigation, car and asset tracking, and location-based services. In summary, CORS network will provide infrastructural backbone for surveying, mapping, navigation and management of the country’s resources.

Applications of GNSS CORS are as many as the applications of surveying and mapping. Possible field applications of CORS services include mapping, navigation, engineering survey, topographic survey, boundary survey, construction staking, utility extension survey, flood study and analysis, property tax mapping, photogrammetric control survey, wetland and soil location survey, climate change variability and adaptation, and so forth.

In conclusion, since it is continuously gathering GNSS data files and making them available to remote receivers for the determination of precise position, CORS network has become a “living” backbone for surveying, mapping and navigation projects. If established and operational in Nigeria, CORS would reduce cost of carrying out surveying and mapping projects in Nigeria. It would eliminate the necessity of establishing traditional geodetic control monuments and control densification. It would also reduce the number of survey equipment used per project. CORS network in Nigeria would greatly enhance the much-expected mapping of the entire country. We might as well say that GNSS CORS would become the savior of Nigerian survey.

DISCLAIMER: This material is only an attempt to answer an examination question, though written from a background of solid knowledge and practical experience in Surveying and Geoinformatics. It has not gone through peer review. Therefore, all views and opinions expressed therein remain the responsibility of the author and do not necessarily represent that of any institution.  Feedback on corrections and constructive criticisms are welcome. Thank you.