Circular No. 03/2020/TT-BTNMT stipulates technical requirements for the national satellite positioning station network

CIRCULAR

Technical Regulations on the National Satellite Positioning Station Network

Pursuant to the Law on Surveying and Mapping dated June 14, 2018;

Pursuant to Decree No. 27/2019/NĐ-CP dated March 13, 2019 of the Government detailing certain provisions of the Law on Surveying and Mapping;

On the basis of Decision No. 36/2017/NĐ-CP dated April 4, 2017, of the Government stipulating the functions, tasks, powers, and organizational structure of the Ministry of Natural Resources and Environment;

At the proposal of the Director of the Vietnam National Survey, Mapping and Geographical Information Center, the Head of the Science and Technology Department, and the Head of the Legal Affairs Department;

The Minister of Natural Resources and Environment issues this Circular to stipulate technical regulations on the national satellite positioning station network.

PART I

GENERAL PROVISIONS

Article 1. Scope of Regulation

This Circular sets forth technical requirements for the national satellite positioning station network in surveying and mapping activities.

Article 2. Applicability

This Circular applies to state agencies, organizations, and individuals involved in building the national satellite positioning station network; providing and using the service of the national satellite positioning station network in surveying and mapping activities.

Article 3. Definitions and Abbreviations

1. Explanation of Terms

a) Real-time Kinematic Surveying Service provided by the national satellite positioning station network: is a service capable of providing processed correction data from three or more national satellite positioning stations serving surveying and mapping activities with real-time accuracy of centimeters;

b) Data Sampling Interval: is the time interval (in seconds) at which measurements are recorded into the receiver's memory;

c) Antenna Mount: is an accessory for mounting a fixed antenna onto a benchmark pillar, capable of balancing and adjusting the direction of the antenna, typically manufactured according to international standards;

d) ZAM Steel: is an alloy of steel with zinc-aluminum-magnesium developed for new product lines, with superior corrosion resistance and high durability commonly used as construction material for buildings;

2. Abbreviations

a) GNSS (Global Navigation Satellite System): Global Satellite Navigation System;

b) GPS (Global Positioning System): United States' Global Positioning System;

c) GLONASS (Global Navigation Satellite System): Russian Global Satellite Navigation System;

d) GALILEO: European Union's global satellite navigation system operated by the European Space Agency;

đ) BDS (BeiDou Navigation Satellite System): China's Global Satellite Navigation System;

e) QZSS (Quasi-Zenith Satellite System): Japan's satellite navigation system primarily operating in the Asia-Pacific region;

g) IRNSS (Indian Regional Navigation Satellite System): Regional satellite navigation system developed by the Indian Space Research Organization;

h) IGS (International GNSS Service): International organization providing GNSS service;

i) ITRF (International Terrestrial Reference Frame): International terrestrial reference frame;

k) RINEX (Receiver Independent Exchange format): GNSS measurement data format in ASCII format used for convenient processing independent of receivers or software;

l) VRS (Virtual Reference Station): Virtual reference station;

m) MAC (Master-Auxiliary Concept): Master station - auxiliary station;

n) MAX: Correction service using master station - auxiliary station technology solution;

o) MAX: Correction service using master station - auxiliary station technology solution with adjustment;

p) Single Base: Correction service using single station technology solution;

q) RTCM (Radio Technical Commission for Maritime Services): Data structure standard for transmitting differential corrections developed by the Radio Technical Commission for Maritime Services;

r) DVR (Digital Video Recorder): Electronic device capable of receiving signals from digital cameras tasked with processing and recording images in real-time;

s) FTTH (Fiber To The Home): Pure optical fiber connection solution directly from the telecommunications provider to households or organizations;

t) Leased Line or also known as private line, this is a form of direct connection between network nodes using dedicated data transmission channels;

u) LAN (Local Area Network) or also known as local computer network: is a network system used to connect computers within a small area.

Article 4. General Provisions on the National Satellite Positioning Station Network

1. The national satellite positioning station network includes national satellite positioning stations and central control processing stations interconnected through the Internet to ensure continuous and stable data reception.

2. The central control processing station consists of a data center and a control room connected through a local area network system with functions of processing, computing, and providing services for surveying and mapping activities, high-precision positioning and navigation, and scientific research.

3. The national satellite positioning station network is constructed synchronously, covering the entire country within the national coordinate system VN-2000 and the national height system; it is continuously and regularly calculated to determine coordinates according to the International Terrestrial Reference Frame (ITRF) daily; gravity values and their variations over a ten-year measurement cycle are determined.

4. The Geoid model serving the determination of mean sea level height is a Geoid model built to suit Vietnam's territory, published simultaneously with the provision of services of the national satellite positioning station network. Mean sea level height h = H - N (where H is the geodetic height, N is the Geoid height interpolated from the aforementioned Geoid model).

5. Some coastal national satellite positioning stations need to be linked to the nearest tide gauge station to obtain sea level monitoring data for establishing the national height system, refining the Geoid model, and monitoring sea level rise.

6. The national satellite positioning station network must have the capability to expand and upgrade to meet usage requirements, ensuring compatibility with the technical infrastructure and technology of existing global satellite positioning and navigation systems.

Chapter II

NATIONAL SATELLITE POSITIONING STATIONS

Article 5. Preliminary Design of National Satellite Positioning Stations

1. National satellite positioning stations consist of two types designed according to their intended use as follows:

a) Continuous reference base stations: evenly distributed throughout the country, with an average distance between stations ranging from 150km to 200km, used as a national coordinate reference frame, for scientific research, and to serve surveying and mapping activities. The locations of the 24 continuous reference base stations already established are shown in Appendix 01 of this Circular, including 1 to 3 stations participating in the IGS network.

b) Continuous reference stations: densified between continuous reference base stations, with an average distance between stations ranging from 50km to 70km, exceptionally up to 100km. Continuous reference stations combined with continuous reference base stations form a national satellite positioning station network capable of providing real-time positioning and navigation services with centimeter-level accuracy, meeting most current precision requirements in surveying and mapping work.

2. During the design process, priority should be given to selecting locations where there are existing infrastructure facilities such as environmental resource monitoring bases, local natural resources and environment departments, People's Committees at all levels to minimize investment and operational costs while ensuring long-term stability and data security.

3. At the end of the preliminary design process, the overall location of all national satellite positioning stations must be displayed on a national topographic map at a scale of 1:1,000,000. The specific location of each station is shown on a national topographic map at a scale of 1:50,000 or larger as a basis for detailed site survey and selection for station construction.

Article 6. Naming and Numbering of National Satellite Positioning Stations

1. The name of the national satellite positioning station consists of a full name and an abbreviated name. The full name is derived from the geographical location where the station is placed. The abbreviated name includes four characters that are abbreviations of the full name, while satisfying the following requirements:

a) Easy to recognize compared to the full name;

b) Not duplicated within the network of national satellite positioning stations;

c) Not duplicated with the names already existing in the IGS network (for stations participating in the IGS satellite positioning station network).

2. The number of the national satellite positioning station consists of nine characters including: the first two characters are the country's region code, the next four characters are the abbreviated name of the station, and the last three characters are the serial number of the station within the national satellite positioning station network, where the continuously operating reference station is numbered from 001 to 039, and the continuously operating station is numbered from 040 onwards. The number of the national satellite positioning station must ensure uniqueness within the national satellite positioning station network.

Article 7. Surveying and Selecting the Location for Building National Satellite Positioning Stations

1. Based on the preliminary design results of the national satellite positioning station carried out according to Article 5 of this Circular, conduct a practical survey of the proposed construction area. The survey aims to collect the following information:

a) A group of criteria regarding basic information, including geographic location, natural characteristics, climate, transportation, socio-economic conditions, regional security...;

b) A group of criteria regarding landscape information, including information about the surrounding landscape of the proposed station placement area that may affect the quality of satellite signal reception;

c) A group of criteria regarding infrastructure information, including existing infrastructure information in the area as well as detailed information serving the installation work;

d) A group of criteria regarding GNSS monitoring: directly collecting data using a GNSS receiver for at least 24 hours at the proposed monument location with parameters set as when officially operational, to analyze and evaluate the specific quality of satellite signal reception on all monitored frequencies; assess interference, obstruction, and signal degradation for each specific satellite throughout the day; assess the impact of other types of radio waves in the area;

đ) A group of criteria regarding measurement and current survey: directly mapping the ground area, paying special attention to objects with significant height causing obstructions affecting the signal reception capability of the receiver;

e) A group of criteria regarding national coordinate points and national elevation, including checking the existence and usability of coordinate points, elevations, and gravity points in the area for connection purposes;

g) A group of criteria regarding geological information: conducting a general assessment of geological features, geomorphology, and soil at the location needed for building the continuously operating reference station monument;

h) Detailed content for each group of criteria specified in points a, b, c, d, đ, e, and g of this clause is provided in Appendix 02 of this Circular. At the end of the survey process, the survey unit must prepare a consolidated report of the survey results with confirmation from all participating parties.

2. Based on the preliminary design combined with the survey results for selecting the location to build the national satellite positioning station, proceed with formal design. The formal design diagram must fully display the basic information of the station such as: station name, station number, approximate coordinates of the station, distance to nearby stations; symbols used in the design must be clear and consistent. The formal design is submitted in both printed form on paper and digital form.

Article 8. Construction of the National Satellite Positioning Station Marker Poles

1. The national satellite positioning station marker poles must be constructed in places with stable ground, well-ventilated areas, ensuring that the skyward angle at the antenna placement position is greater than 170°. Within a 2-meter radius around the marker pole, metal roofing materials, wide-canopy trees, metal fences... should not be present to minimize multi-path interference.

2. The marker poles shall be made of reinforced concrete with a strength grade of M25 (as per TCVN 6025:1995 standard 39) or higher. The marker poles shall have a cylindrical shape with a diameter of 0.3 meters, and the height from the base of the pole to the antenna placement position shall be 4 meters. Special cases are regulated as follows:

a) In cases where there are architectural structures around the marker poles affecting signal reception, the height of the marker poles may be increased but shall not exceed 8 meters;

b) In cases where the marker poles are designed to be placed on architectural structures, the height of the marker poles may be reduced but shall not be lower than 2 meters above the roof of the architectural structure.

3. On top of the marker pole, an antenna mounting bracket shall be installed. The antenna mounting bracket must be securely attached to the marker pole, manufactured from stainless steel material, and must have basic functions such as locking the antenna, leveling the antenna on a horizontal plane, and adjusting the antenna direction (refer to Appendix 03 of this Circular).

4. At the base of the marker pole, two height markers must be affixed, including one marker protruding from the base surface and another buried underground. In cases where the marker poles are placed on architectural structures, only one height marker is required. The vertical difference between the height marker and the antenna reference point (ARP) must be determined with an accuracy of less than 2 mm. The specifications for the height markers are stipulated in Appendix 04 of this Circular.

5. The marker poles of continuously operating reference stations must be constructed on the ground and drilled deep into the stable layer, filled with reinforced concrete. The specifications for the marker poles of continuously operating reference stations are stipulated in Appendix 05 of this Circular.

6. The marker poles of continuously operating reference stations can be constructed on the ground or on solid architectural structures. The specifications for the marker poles of continuously operating reference stations are stipulated in Appendix 06 of this Circular.

Article 9. Signal Receiving Equipment of the National Satellite Positioning Station

1. The satellite positioning signal receiving antenna shall be installed on top of the marker pole through an antenna mounting bracket, leveled horizontally; the antenna direction must be oriented towards true north with an allowable deviation of no more than ±5°, and if exceeding 5°, the specific value must be recorded in the logbook. The antenna must meet the following basic requirements:

a) Use an antenna with a loop impedance capable of receiving all existing signals (frequencies) from satellite positioning systems at the time of installation, such as GPS, GLONASS, GALILEO, BDS, QZSS; it is encouraged to use antennas capable of receiving planned signals from these systems or new satellite positioning systems like IRNSS;

b) Listed in the IGS organization's list of antennas with calibrated phase centers;

c) Capable of withstanding humidity up to 100%; dust and water resistance standards must meet at least IP67 according to the International Electrotechnical Commission (IEC) standards;

d) Capable of operating in environments with temperatures ranging from -10°C to +70°C;

đ) Continuously operating reference stations must use antennas with loop impedance made of Dorne-Margolin material, and it is encouraged for other stations to use them as well;

e) Only hemispherical radomes may be used for the antenna, conical radomes are not allowed;

g) It is not permitted to remove the antenna after the station has commenced operation except for hardware repairs due to malfunctions.

2. The satellite positioning signal receiver must be placed in a dry, well-ventilated area to ensure continuous operation. The receiver must meet the following basic requirements:

a) Capable of receiving all existing signals from satellite positioning systems at the time of installation, such as GPS, GLONASS, GALILEO, BDS, QZSS;

b) Must have at least 555 channels, with a minimum of 12 channels per frequency from each of the aforementioned satellite positioning systems;

c) Capable of detecting and receiving signals from satellites at angles less than 10°, supporting multi-path interference reduction capabilities;

d) Capable of receiving signals at intervals of 1 second or less, supporting data transmission via current versions of RTCM 2.x/3.x, encouraging support for data transmission via CRM, CMR+, NMEA-0183; supporting Ntrip, TCP/IP, FTP;

đ) Must have at least two power sources, supporting direct connection to meteorological sensor devices and tilt sensors;

e) Must have basic connection ports such as RJ-45, USB, 3G/4G/5G, RS-232;

g) Dust and water resistance standards must meet at least IP67 according to the International Electrotechnical Commission (IEC) standards;

h) Capable of operating in environments with temperatures ranging from -10°C to +65°C;

i) Internal memory must be able to store data for at least 60 days, supporting extended memory connections;

k) The length of the signal cable from the receiver to the antenna must not exceed 70 meters. In special cases, signal quality measurement must be conducted before formal installation. For areas with high lightning density, the distance from the receiver to the antenna should be as short as possible;

l) The antenna cable connection to the receiver must be placed inside industrial-grade PVC or HDPE tubing and buried underground; in special cases, it may be designed to run overhead but must have a secure support system and not be overly taut. The end of the cable connecting to the antenna must be waterproofed, especially in coastal areas to prevent corrosion and rust;

m) The receiver must be set to continuously receive signals from all observable satellites for 24 hours with a signal interval of 1 second; the threshold angle in the receiver must be set to 0°.

3. The satellite positioning signal receiver and accompanying auxiliary equipment must be placed in an equipment cabinet with a fan ventilation system that automatically turns on and off through thermal relay sensors to reduce temperature within the cabinet (equipment cabinet design references Appendix 07 of this Circular).

4. The equipment cabinet should be prioritized to be placed indoors. In special cases where the distance from the room to the antenna tower is too far or there is no suitable location for placing the cabinet indoors, it may be placed outdoors. For areas with unfavorable climates such as high temperatures and heavy annual rainfall, or when outdoor placement poses security risks, a house must be constructed to ensure safety for the equipment cabinet (refer to Appendix 08 of this Circular for the design of the equipment cabinet house).

Article 10. Meteorological Sensors

1. In cases where meteorological sensors are integrated at national satellite positioning stations for scientific research, improving calculation quality, and studying weather models, the installed meteorological sensors must be specialized devices; these sensors must pass technical inspection requirements before installation.

2. Meteorological sensors must be installed close to the satellite signal receiving antenna but must not interfere with signal reception or cause interference; the height difference between the antenna reference point (ARP) and the pressure sensor of the meteorological sensor must be accurately determined with an accuracy of less than 1 cm.

3. The basic requirements for meteorological sensors are as follows:

a) Pressure measurement accuracy < ±0.1 hPa;

b) Relative humidity measurement accuracy < ±2%;

c) Temperature measurement accuracy < ±0.1°C;

d) Capable of operating in environments with temperatures ranging from -10°C to +60°C.

4. During operation, regular checks on the performance of the sensors, especially temperature sensors, must be conducted, and timely repair or replacement measures taken. Inspection, maintenance, repair, and replacement shall be carried out in accordance with Articles 7, 8, and 9 of Circular No. 70/2015/TT-BTNMT dated December 23, 2015, issued by the Ministry of Natural Resources and Environment, which stipulates technical requirements for automatic meteorological and hydrological stations.

Article 11. Power Supply

1. Each national satellite positioning station must have at least two power sources: primary power and backup power. Primary power is supplied by the national grid, while backup power is provided by systems such as UPS and batteries, ensuring continuous operation of all station equipment for a minimum of 48 hours. In areas with high annual sunshine hours, backup power can be a solar panel system.

2. Power supply for the equipment of national satellite positioning stations must be managed by a power distribution unit with an automatic switching mechanism between primary and backup power sources.

3. All electrical components must be equipped with surge protection devices to ensure the safety of the entire system.

Article 12. Data Transmission Solutions

1. National satellite positioning stations must be equipped with stable internet connections to serve data transmission to the central control and processing station. The internet connection should be designed specifically for data transmission from the station, without being shared for other purposes to ensure data security, confidentiality, and bandwidth.

2. In addition to the main internet connection via fiber-to-the-home (FTTH) or leased line, each national satellite positioning station must have an additional backup internet connection via FTTH from a different network provider than the one providing the main internet connection, or use a 3G/4G/5G connection solution in areas with stable 3G/4G/5G signals. Each FTTH connection must be provided with a static IP address to ensure stable data transmission.

3. The central control and processing station must be equipped with two internet connections via FTTH (or leased line) from two different network providers. Each internet connection must be assigned at least one static IP address. Both connections must have sufficient bandwidth to receive data transmitted from the satellite positioning stations and provide uninterrupted services to users.

4. To ensure the quality of real-time time measurement service provision, the average latency for data transmission from the satellite positioning station to the central control and processing station must be less than 50 ms for FTTH (or leased line) connections and less than 100 ms for 3G/4G/5G connections.

Article 13. Lightning Protection System

1. The direct lightning protection system shall be designed to ensure safety for equipment at national satellite positioning stations. At each station, a grounding area must be constructed in accordance with the provisions set forth in Circular No. 26/2016/TT-BTTTT dated December 7, 2016, issued by the Ministry of Information and Communications along with the National Technical Regulation on Grounding for Telecommunication Stations.

2. Equipment that may be affected by secondary lightning strikes must be installed with lightning cut-off devices including: power source, antenna connection wire with satellite signal receiver, sensor connection wire with satellite signal receiver (if applicable).

Chapter III

NETWORK INTERCONNECTION MEASUREMENT OF NATIONAL SATELLITE POSITIONING STATION

Article 14. Interconnection Measurement and Determination of VN-2000 Coordinates for the Network of National Satellite Positioning Stations

1. National coordinate points of level 0 within the area shall be used as initial points for the interconnection measurement network; in cases of expansion or densification of national satellite positioning stations, existing stations within the area can be used as initial points for the interconnection measurement network. Initial points must be evenly distributed throughout the interconnection measurement network; the number of initial points shall be based on the number of national satellite positioning stations requiring interconnection measurement but shall not be less than five points.

2. GNSS receivers placed at national coordinate points of level 0 must be multi-frequency receivers capable of receiving L1/L2 signals from both GPS and GLONASS systems; continuous simultaneous observation time shall not be less than 24 hours, starting from 7:00 AM (Vietnamese time); signal reception interval is 15 seconds; static measurement method with a minimum reception angle of 10 degrees shall be used. GNSS receivers placed at national satellite positioning stations shall be set up in accordance with point m of Clause 2, Article 9 of this Circular.

3. Calculation processing shall be performed using common GNSS processing software; during the calculation process, accurate satellite orbit data (Final Orbit) must be used to calculate baselines. The post-adjustment position error of the calculated point shall not exceed 2 cm. The calculation procedure shall follow the provisions set forth in Circular No. 06/2009/TT-BTNMT dated June 18, 2009, issued by the Ministry of Natural Resources and Environment along with the National Technical Regulation on Building the National Coordinate Network.

Article 15. Interconnection Measurement and Determination of Height for National Satellite Positioning Stations

1. Independent height lines shall be designed to determine the height for points within the network of national satellite positioning stations. Single-line design shall be used, with each line utilizing at least two high-level national height points within the area as initial points. Design, interconnection measurement, and height determination calculations shall follow the provisions set forth in Decision No. 11/2008/QĐ-BTNMT dated December 18, 2008, issued by the Ministry of Natural Resources and Environment along with the National Technical Regulation on Building the National Height Network.

2. For points belonging to continuously operating basic reference stations: design, interconnection measurement, and calculation shall be carried out according to the second-grade height measurement procedure. Initial national height points are first-grade and second-grade points. The closure error between go-and-return measurements and between two high-grade points shall not exceed ±4^L in plain areas and ±5^L in mountainous areas (L is the length of the measurement line in kilometers).

3. For points belonging to continuously operating reference stations: design, interconnection measurement, and calculation shall be carried out according to the third-grade height measurement procedure. Initial national height points are first-grade, second-grade, and third-grade points. The closure error between go-and-return measurements and between two high-grade points shall not exceed ±1oVZ in plain areas and ±12VL in mountainous areas (L is the length of the measurement line in kilometers).

4. Interconnection measurement and determination of the height of national satellite positioning stations must be conducted at all benchmarks as stipulated in Clause 4, Article 8 of this Circular. The vertical difference between the height benchmark and the antenna reference point (ARP) shall be determined using specialized steel tapes or equivalent measuring instruments and recorded separately, apart from the leveling book.

Article 16. Gravity Connection and Determination of Gravity Value at National Satellite Positioning Stations

1. Based on the existing basic gravity points and first-class gravity points within the measurement area, design the gravity connection lines to the national satellite positioning stations with second-class gravity accuracy using relative gravity measurement methods. Each line must use at least two high-level national gravity network points within the region as starting points.

2. The location for determining the gravity value at the national satellite positioning station is a height marker attached to the monument pillar. The root mean square error of the acceleration due to gravity after adjustment shall not exceed 0.05 mGal.

3. Use gravity measuring instruments with a minimum accuracy of 0.03 mGal to determine the gravity values for the national satellite positioning station network.

Article 17. Connecting the National Satellite Positioning Station Network to the International Terrestrial Reference Frame (ITRF)

1. The national satellite positioning station network is connected to the International Terrestrial Reference Frame (ITRF) through stations belonging to the International GNSS Service (IGS) network within the region. All points in the national satellite positioning network are processed and calculated regularly and continuously daily in ITRF with an accuracy of less than 2mm.

2. Use data from at least five IGS network stations, prioritizing those with stable data, long-established stations, and complete parameters related to the station as recommended by IGS.

3. Use high-precision software such as Bernese, GAMIT/GLOBK... for calculations. During the calculation process, in addition to GNSS measurements, all other relevant data must be used to enhance accuracy, such as: post-inspection antenna parameters from IGS, accurate satellite ephemeris, Earth rotation parameters, ocean tide correction models, troposphere model, ionosphere model...

4. Calculations are performed daily, starting from 00:00 (UTC time); using GNSS data with a signal reception interval of 30 seconds for processing. The results obtained serve as the basis for determining plate movement, vertical displacement, establishing reference frames and national coordinate systems dynamically, and determining transformation parameters between the national coordinate system VN-2000 and ITRF.

Chapter IV

CENTRAL CONTROL AND PROCESSING STATION

Article 18. Central Control and Processing Station

1. The central control and processing station is where the calculations, processing, and provision of services for the national satellite positioning station network take place. The central control and processing station must be located in a place with adequate technical infrastructure, stable national grid power supply, high-speed internet connectivity capability, ensuring security and data safety.

2. It has the ability to continuously receive data from national satellite positioning stations; ensuring timely calculation, processing, and provision of services to users 24 hours a day, 7 days a week.

3. It has the ability to calculate and process coordinates of points in the national satellite positioning station network in the international terrestrial reference frame (ITRF) with millimeter accuracy.

4. It has the ability to provide high-precision real-time dynamic measurement services to users quickly, accurately, and promptly via the internet.

5. It has the ability to process GNSS measurements in an online format.

6. It has the ability to control, configure, and monitor the operational status of national satellite positioning stations remotely and continuously via the internet.

7. It has the ability to monitor the operational status of GNSS measurement devices using real-time dynamic measurement services.

8. It has the ability to manage accounts that have used and are currently using services from the national satellite positioning station network.

9. It supports the calculation of atmospheric layer parameters based on GNSS data combined with meteorological sensor data from national satellite positioning stations.

10. It has the ability to store GNSS data received from national satellite positioning stations in RINEX V2.x, V3.x formats. Storage times are defined as follows:

a) Permanent storage for data with a signal reception interval of 30 seconds;

b) Minimum 20-year storage for data with a signal reception interval of 15 seconds (except for special requirements);

c) Minimum 10-year storage for data with a signal reception interval of 1 second;

d) Permanent storage for calculation results related to the establishment of reference frames and national coordinate systems.

11. It has a multi-layer security system to ensure the security and safety of the national satellite positioning station network data and user data.

12. It has the ability to automatically back up data periodically to ensure data safety.

Article 19. Data Center

1. Have a stable and high-quality national power grid system; establish a three-phase power source with backup generators to ensure sufficient power supply for the data center in case of power grid failure.

2. Large-scale uninterruptible power supply (UPS) systems ensuring the ability to maintain all equipment in the data center including servers, air conditioners, and other auxiliary devices for at least 30 minutes; encourage the establishment of backup generators and large-scale UPS systems according to the 1+1 standard.

3. Air conditioning system for cooling ensuring the ability to operate alternately and continuously, capable of controlling temperature with accuracy ±1°C and humidity ±5%.

4. Have technical floor or anti-electrical contamination isolation layer. The electrical system and equipment must be installed with lightning arresters and surge protection devices.

5. Fire alarm system capable of early smoke detection and automatic warning; capable of automatic fire extinguishing.

6. Surveillance camera system connected to digital video recorder (DVR) to monitor images inside and outside the data center on a regular and continuous basis.

7. Strong server system taking into account redundancy factors, switching system operating in parallel with optimal backup mechanisms. Cabling needs to be organized, flexible, and reusable. All cabinets, racks, panels, and cables must be uniformly labeled according to easy-to-remember and expandable principles.

Chapter V

PROVISION AND USE OF NATIONAL SATELLITE POSITIONING STATION NETWORK SERVICES

Article 20. Services provided by the national satellite positioning station network

1. Provide GNSS data with signal reception interval types of 30 seconds, 15 seconds, and 1 second in RINEX format for post-processing as specified in Clause 10 of Article 18 of this Circular.

2. Provide calculation and processing services for GNSS networks with accuracy up to millimeters in the International Terrestrial Reference Frame (ITRF).

3. Provide automatic processing and calculation services for GNSS measurements for users in an online format based on individual requests.

4. Provide real-time dynamic measurement services in the national coordinate system VN-2000 and national height system through the application of network technology solutions such as VRS, MAX, iMAX, or single base stations... for users.

5. Services provided by the national satellite positioning station network are used in surveying, topographic map creation; construction and updating of the national geographic database; cadastral surveying and map creation; scientific research and other surveying and mapping activities.

Article 21. Use of Real-Time Dynamic Measurement Services

1. Mobile GNSS measurement devices using real-time dynamic measurement services must meet the following basic requirements:

a) Be multi-frequency mobile GNSS measurement devices capable of receiving full signals from common satellite navigation systems such as GPS, GLONASS, Galileo, and BeiDou;

b) Capable of supporting Ntrip protocol connections and receiving RTCM v3.x correction data with message types from 1021 to 1027;

c) Able to receive signals from satellite navigation systems under clear conditions.

2. The accuracy when using real-time dynamic measurement services provided by the national satellite positioning station network is as follows:

Where:

- k is the distance between satellite positioning stations participating in the network processing to provide real-time dynamic measurement services. Specific areas as of December 31, 2019 are shown in Appendix 9 attached to this Circular.

- S is the distance from the mobile satellite signal receiving device location to the fixed satellite positioning station used for corrections.

- The coverage area of the Geoid model of the Ministry of Natural Resources and Environment is shown in Appendix 10 attached to this Circular.

Chapter VI

IMPLEMENTING PROVISIONS

Article 22. Effectiveness

This Circular takes effect from January 1, 2020.

Article 23. Implementation Organization

1. Ministries, ministerial-level agencies, government agencies, provincial People's Committees under central cities, and relevant organizations and individuals are responsible for enforcing this Circular.

2. During implementation, if there are difficulties, please promptly reflect them to the Ministry of Natural Resources and Environment for consideration and decision./.