<p> Global Navigation Satellite Systems (GNSS) have revolutionized our ability to access location information. In a nutshell, such systems works by measuring the distances from a set of satellites hovering over the earth in predefined orbits to a receiver through radio signals phases, in order to estimate the receiver position on earth. However, this system has its own share of error budget due to orbit errors, satellite clock error, receiver noise, Ionospheric and Tropospheric delays, satellite geometry over receiver, multipath, etc… This gives an error of up to 11 meters in position determination. This accuracy limitations makes it unsuitable for surveying applications which requires centimetric accuracy. To overcome this burden, various surveying techniques such as DGNSS, Static GPS/GNSS, RTK, and PPP are being used by geospatial community. Each of these methods applies its own principles of overcoming errors in GNSS measurements. In most of GNSS applications where precise positioning is required, users usually pair their GNSS instruments with other GNSS instruments, simultaneously observing at least one known position termed as reference station, and with the help of the readings at the reference station, a rover position can be resolved to a high accuracy depending mainly on the length of observations. </p> <p> To liberate users from setting their own reference station each time they wish to undertake GNSS measurements, the Directorate of Geographic Affairs (DAG) has established a network of Continuously Operating Reference Stations (LEB-CORS), which is capable of providing real-time positioning service through RTK/NRTK with an accuracy of ±3cm. LEB-CORS also hosts an array of different services targeted to cater requirements for different segments of geospatial and scientific community. At present, LEB-CORS Network covers all Lebanese territories on which there is internet.<br> </p> <p> LEB-CORS infrastructure is a network of permanently installed reference stations (i.e. GNSS antennae and receivers) continuously streaming raw satellite observations to a central server located at DAG. The Central sever archives and catalogues these reference stations’ data, analyses and processes them for delayed or instantaneous access by users. LEB-CORS network is comprised of 13 stations and is available 24 hours per day, 7 days a week and 365 days a year. LEB-CORS provides the following services:</p> <h3>Network RTK services for 3-centimeter real-time positioning.</h3> <p>Real-Time Kinematic (RTK) is a widely accepted technology for accurate positioning and navigation. This method is an extension of single base RTK survey technique in which, a GNSS rover connecting to a single GNSS base or reference station with known coordinates. This survey technique gives centimetric level positioning accuracy. However, by networking several such reference stations, range, accuracy and reliability of RTK survey technique can be improved multifold. This can be made possible through LEB-CORS where the central server collects all raw observations of the network’s reference stations in real time and runs a specialized software, which uses these observations and performs calculations to create a model of spatially correlated bias and their patterns of change over the whole area. These correction models are made available to users via internet so that GNSS instrument of the user can derive bias for its position and refines its position to get a centimetric level of accuracy in near real time. For utilizing this service, user will be required to have a RTK-enabled GNSS equipment, a controller unit with RTK field survey software and access to internet via Wi-Fi, mobile phone, modem or any other mean. </p> <h3>Data processing of static observations with respect to LEB-CORS.</h3> <p>At present, for GNSS measurements, users need to pair their GNSS instruments to other GNSS instruments, simultaneously observing one or more master station (a station which coordinates are known). Duration of observations in these cases increases with respect to distance between master and observed stations. With CORS in place, there is no need to use paired GNSS equipment. Using single GNSS equipment, control points with respect to LEB-CORS coordinates system can be established with shorter observation periods, and better reliability and consistency in surveying works. Users can put their GNSS rover, on their point of interest, collect data in static survey mode and upload their data in RINEX format into the processing platform. The Processing platform will process the data and provide the coordinates of the site along with the processing report.</p> <h3>Downloading of raw data of LEB-CORS stations for processing in user software.</h3> <p>For more precise coordinates processing or for various scientific applications, users can download LEB-CORS stations raw observations in nonproprietary open RINEX format or virtual RINEX data (i.e. RINEX files for a virtual reference station that can then be used for post processing calculations), and use them to process their own GNSS data at their own workstation. Scientific applications include tracking earth’s crustal movements and other Earth science related studies. Users can create customized queries (individual or multiple stations, time periods, various file formats such as RINEX 2.1, RINEX 2.11, RINEX 3, T02, TGD, DAT, T01 or VRS RINEX, and various epoch rate). </p>