A network of differential stations is a set of constantly operating satellite differential stations installed on the ground according to a certain scheme, the relative position of which is determined in a single coordinate system, united by communication channels for collecting and processing satellite data in a single center, so as to ensure the measurement and determination of the spatial location of objects over a vast area with the same accuracy and in a single the reference frame of time and space.
The network of permanent satellite differential stations has advantages in comparison with single base stations in that it has a large coverage area and provides uniform and high accuracy due to the possibility of constructing a local error model that includes delays of GNSS signals in the ionosphere and troposphere and the formation of network differential corrections for the coverage area.
One differential station provides the determination of spatial coordinates in real time with centimeter accuracy within a radius of no more than 25-30 km. In principle, the distance of the rtk rover from the differential station can be large, for example 300 km. However, when moving away from the gps station, the positioning accuracy deteriorates in proportion to the distance. A network of differential stations can cover a large area, the more stations, the larger the coverage area. To eliminate the problem of obtaining accurate and reliable results at a distance, the stations are installed tightly with overlaps of working areas.
In order to exclude errors introduced by distortions in the atmosphere, as well as the increasing error from the distance from the nearest station, a real-time model of errors and corrective corrections is created based on data from several stations and knowledge of their exact position. Such a model implies the joint equalization of data from all stations and the calculation of the field of differential corrections for the entire network coverage area. Thanks to the network method of generating differential corrections, the user can reliably obtain coordinates at distances from the station up to 50 km, and the distance between stations can be up to 80 km. At the same time, the same accuracy is ensured over the entire coverage area.
It is more efficient to control the operation of several differential stations located on a vast territory from a single control center. Thus, this structure is a network of differential stations, uniformly managed to create a single field of corrective corrections for all users.
Centralized management and data collection from several stations in the control center allows using specialized software to simultaneously transmit differential corrections to various users to determine the location of objects and navigation in real time, organize access levels through various communication channels, archive and provide data for specialized enterprises that need high accuracy, i.e. provide a variety of services precise positioning based on satellite navigation technologies. Such a system is now called the Satellite Precision Positioning System (SSTP).
Main characteristics of the network of differential rtk base stations:
· Purpose (precise navigation, land surveying system, geodetic, surveying measurements and topography, monitoring of deformations — geodynamic polygon…);
· Number of permanent stations;
· Coverage area;
· GNSS signals used (GPS, GLONASS, Galileo, BeiDou, QZSS…);
· Services provided (post–processing data, real-time positioning – DGNSS, RTK);
· Formats of the information provided (CMR+, Leica, RTCM…);
· Openness of data (free access or paid authorization);
· The accuracy provided in various coordinate systems.
The development of networks of permanent satellite differential stations at individual sites, such as deposits, quarries, territories of cities and entire regions makes it possible to perform geodetic and surveying measurements, topographic surveys, engineering surveys and land surveying more efficiently. Efficiency is achieved by reducing the time required to determine the exact position of objects in space, reducing transportation costs and human resources. The creation of regional networks to ensure cadastral works can significantly reduce the cost of creating a reference justification (reference boundary network) and maintaining it in working order. A network of satellite differential stations can be used to consolidate a single coordinate-time basis on the territory of a region or state.
The number of constantly operating differential satellite receivers in the network may be different. The number of differential stations depends on the size of the coverage area (the area of work, the territory of the region), the availability of communication lines, the terrain and your needs. The minimum recommended number of differential stations to ensure uninterrupted network operation with guaranteed issuance of network RTK corrections is 5 (five) stations.
The network can provide a variety of services, including collecting satellite data for processing with data from users’ field receivers and providing network differential corrections to field performers using satellite equipment in RTK mode.
Advantages of a network of differential stations over single differential stations:
· Large coverage area
· Provides greater reliability
· Ability to determine ionospheric and atmospheric corrections
· Provides higher accuracy
· Unified coordinate system for all users
· Centralized management and control of all stations
· Support for various services
· Post-processing of user data
· User Management
· Fundamental infrastructure for positioning any objects
