Circular No. 63/2017/TT-BTNMT on technical requirements for mapping seabed topographic maps at a scale of 1:5000

 

CIRCULAR

Technical Regulations for Surveying Bathymetric Maps at a Scale of 1:5000

_________________________

Pursuant to the Law on the Sea of Vietnam dated June 21, 2012;

Pursuant to the Law on Natural Resources, Environment, and Islands dated June 25, 2015;

Pursuant to Decree No. 40/2016/NĐ-CP dated May 15, 2016 of the Government detailing certain provisions of the Law on Natural Resources, Marine Environment, and Islands;

Pursuant to Decree No. 45/2015/NĐ-CP dated May 6, 2015 of the Government on surveying and mapping activities;

Pursuant to Decree 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 General of the Vietnam Administration of Seas and Islands, the Head of the Science and Technology Department, and the Head of the Legal Department;

The Minister of Natural Resources and Environment promulgates these Circulars on Technical Regulations for Surveying Bathymetric Maps at a Scale of 1:5000.

PART I

GENERAL PROVISIONS

Article 1. Scope of Regulation

These Circulars stipulate technical requirements for direct surveying, compilation from existing sources (published by competent state authorities or authorized by competent authorities) to serve the establishment of bathymetric maps at a scale of 1:5000 in Vietnam's territorial waters. The depth area surveyed is limited to 100 meters water depth (measured according to the standard height in the VN-2000 Coordinate System).

Article 2. Applicability

These Circulars apply to organizations and individuals engaged in surveying bathymetric maps at a scale of 1:5000.

Article 3. Explanation of Terms

In this Circular, the following terms shall be understood as follows:

1. Basic control network is a coordinate and elevation control network developed from the national coordinate and elevation network to establish the surveying control network and set up static stations when necessary.

2. Surveying control network is a coordinate and elevation control network developed from the basic control network, from the nearest equipment testing points for sounding with a pole.

3. Equipment testing point is a point used to test marine surveying equipment in the surveying area. The equipment testing point is measured and connected to coordinates and elevations from points belonging to the national coordinate and elevation networks.

4. Tide gauge point is a point equipped with a water level gauge. The "0" point of the tide gauge point is measured and connected to elevations from the nearest equipment testing points, from the nearest tide gauge points, or from the nearest points of the national elevation network. The "0" point of the tide gauge point coincides with the "0" mark of the water level gauge.

5. Tide gauge elevation point is a point measured and connected to elevations from national elevation points and used as an intermediate point to connect the technical datum to the "0" point of the tide gauge point.

6. GNSS (Global Navigation Satellite System) technology, DGNSS (Differential Global Navigation Satellite System) technology are global satellite positioning and navigation technologies.

7. DGPS (Differential Global Positioning System) station: A fixed ground station within the Global Differential Positioning System.

8. SBES (Single Beam Echo-sounder): Single beam echo sounder.

9. MBES (Multi Beam Echo-sounder): Multi-beam echo sounder.

10. Area for sounding with equipment is a sea area with depths ranging from approximately 3 meters upwards and using SBES, MBES to measure seabed topography. Area for sounding with a pole is a sea area with depths less than 3 meters.

11. Sounding seabed topography with SBES is done along lines, only one row of depth points is obtained on each sounding line.

12. Sounding seabed topography with MBES is done in strips, the ship runs along lines and the depth data collected is a strip of depth data, the width of this strip of depth data depends on the capability of each type of multi-beam echo sounder and the average depth of the central beam.

13. Seabed topography scanning with MBES is a complete surface scan of the seabed topography.

14. Real Time Kinematic (RTK) technology is a GNSS real-time dynamic measurement technology: determining both the coordinates and the elevation (or depth) of the point to be measured.

15. The symbol 1:5000 is a set of symbols displayed on topographic maps at a scale of 1:5000 and bathymetric maps at a scale of 1:5000 (annexed to Decision No. 1125/ĐĐBĐ dated November 19, 1994 of the Director General of the National Land Administration).

16. Storing data and information on DVDs is the process of storing to serve product handover and related documentation between the construction unit and the storage unit as prescribed.

17. TKKT - DT: Technical Design - Budget Estimate.

Article 4. General technical regulations for surveying and creating seabed topographic maps at a scale of 1:5000

1. Seabed topographic maps at a scale of 1:5000 are large-scale topographic maps, serving as a continuation (extension) of the land topographic maps at a scale of 1:5000.

2. Seabed topographic maps at a scale of 1:5000 shall be established within a unified reference system and division method consistent with the land topographic maps at a scale of 1:5000.

3. Seabed topographic maps at a scale of 1:5000 belong to the national topographic map system, serving security, defense, and marine research work; they serve as a basis for data to compile seabed topographic maps at smaller scales, build geographic information systems, and edit thematic maps.

4. Seabed topographic maps at a scale of 1:5000 shall be directly surveyed on-site or compiled from larger-scale seabed topographic maps and established using digital mapping technology.

5. The original digital seabed topographic maps at a scale of 1:5000 shall be stored in data files, divided into groups and layers according to current technical regulations. The original digital maps shall be stored on DVDs.

6. Each piece of the seabed topographic map at a scale of 1:5000 has a map history record. The map history record is created in digital form. The map history file is stored on a DVD together with the original digital map.

7. For pieces of the seabed topographic map at a scale of 1:5000 that include land and islands, they must be represented according to the following principles:

a) In cases where there are published maps of the land and islands at a scale of 1:5000, the newly surveyed seabed topography must be joined with the existing maps of those areas;

b) In cases where there are no published maps of the land and islands at a scale of 1:5000 but there are published maps at a larger scale than 1:5000, those larger-scale maps must be compiled down to a scale of 1:5000 and joined with the newly surveyed seabed topography;

c) In cases where there are no topographic maps of the land and islands at a scale of 1:5000, the land and islands must be surveyed. The survey of the land and islands shall be carried out according to the current technical regulations for surveying land topographic maps at a scale of 1:5000;

d) In cases where it is not possible to survey the land and islands, other types of maps and charts with scales smaller than 1:5000 may be used to compile the topographic and geographic content on the land and islands. This situation must be specifically noted in the TKKT - DT.

8. The seabed topography shall be directly surveyed using the following methods:

a) The seabed topography shall be directly surveyed on-site using SBES, MBES equipment with all auxiliary machines forming the SBES, MBES system and global satellite positioning and navigation technology;

b) For coastal sea areas, the foot of islands, submerged sandbanks, and underwater reefs that cannot be directly surveyed using SBES, MBES, depth measurements must be taken using a sounding rod: electronic total stations, GNSS RTK shall be used to detail the topography and geographic features, or GNSS equipment shall be used to determine the position of the sounding point and the depth measured by the sounding rod.

9. The free margin of the seabed topographic map at a scale of 1:5000 must extend beyond the frame by at least 1 cm on the map. The part extending beyond the frame is only shown on the original digital map and not on the published map.

10. The basis for construction, inspection, and acceptance of direct surveying and compilation from existing sources to establish seabed topographic maps at a scale of 1:5000 is standards, specifications, technical regulations, and TKKT - DT approved by competent authorities. Before preparing TKKT - DT, field surveys must be conducted to collect relevant materials, documents, and information.

11. Equipment used in surveying seabed topographic maps at a scale of 1:5000 must meet the accuracy requirements of the maps and be tested, inspected, or certified according to current regulations. Inspection or certification documents for equipment must be submitted with the product.

12. When measuring depth using SBES, measurement can only proceed when wave height does not exceed 0.3 meters. If wave height exceeds 0.3 meters, a wave correction device (wave sensor) must be used.

13. When measuring depth using MBES, a wave correction device, compass, and surface speed meter must be installed compulsorily.

Chapter II

MATHEMATICAL BASIS, ACCURACY, AND CONTENT OF SEABED TOPOGRAPHIC MAPS AT A SCALE OF 1:5000

Article 5. Mathematical Basis

1. The seabed topographic map at a scale of 1:5000 shall be established within the VN-2000 coordinate system, national height system, projection zone 3 with the central meridian at 102 degrees.⁰  , with the meridian axis: 102⁰ , 105⁰ , 108⁰, 111⁰ ,114⁰, 117⁰.

2. The control network for planimetry and height ensuring the establishment of the seabed topographic map at a scale of 1:5000 includes the national coordinate grid of classes I, II, and III and the national height grid of classes I, II, III, and IV.

3. On the original map sheet and printed maps on paper, the kilometer grid in the orthogonal planar coordinate system must be displayed in the form of a cross-hatch grid according to the provisions of Symbol 1:5000.

4. The division of map sheets and numbering of map sheet serial numbers shall be carried out in accordance with the provisions of Circular No. 973/2001/TT-TCĐC dated June 20, 2001, of the General Department of Land Administration regarding guidance on the application of reference systems and national coordinate systems VN-2000.

5. The presentation format of the map frame shall be implemented according to the model of the frame display and content outside the frame according to Symbol 1:5000. In cases where mapping exceeds the frame, specific regulations must be stipulated in the TKKT - DT.

6. The digital original map must fully reflect all contents as prescribed by Symbol 1:5000; it must clearly indicate the source materials used, the method of establishment, and the name of the agency that established the digital original map.

7. The name of the map sheet is defined as follows:

a) When there is already a topographic map at a scale of 1:5000 for the mainland and islands, the name of the map sheet shall follow the name of the existing topographic map at a scale of 1:5000.

b) When there is no topographic map at a scale of 1:5000 for the mainland and islands, the name of the map sheet shall prioritize the name of populated places or geographical names on the map sheet. If an island lies across multiple map sheets, the name of the island shall be taken from the map sheet with the largest area of the island, while other map sheets with smaller areas of the island shall choose other names. For map sheets covering only sea areas, only the serial number of the map sheet needs to be recorded.

8. The original map stored on the DVD disc includes all contents as the original map printed on paper.

Article 6. Accuracy of Maps

1. The mean error of the zero point tidal height relative to the height of the nearest tide gauge check point or nearest tidal height check point shall not exceed ±0.10m. The zero point tidal height is measured using geometric leveling with technical leveling accuracy from the nearest tide gauge check points or nearest tidal height check points.

2. The mean error of the position of the depth annotation points and bottom material annotation points relative to the coordinates of the nearest coastal DGPS station or nearest marine survey equipment check point shall not exceed ±3m (equivalent to ±0.6mm on the map).

3. The mean error of the position of fixed objects on the sea surface when mapping relative to the nearest marine survey equipment check point shall not exceed ±3.5m (equivalent to ±0.7mm on the map). For mobile objects, this error is increased by the range of movement. For submerged fixed objects under the sea, the allowable error is ±7.5m (equivalent to ±1.5mm on the map).

4. The mean error of the depth of the depth annotation points after conversion to the national height system relative to the height of the nearest tidal height check point shall not exceed:

±0.30m when the depth is up to 50m;

±0.45m when the depth is from over 50m to 100m.

5. The root mean square error of the depth contour compared to the height of the nearest tide gauge point does not exceed:

5. The mean error of the contour depth relative to the height of the nearest tidal height check point shall not exceed:

±0.40m when the depth is up to 50m;

±0.50m when the depth is from over 50m to 100m.

Where:

6. The mean error of the depth is determined by the formula:- When using SBES, it is the difference in depth at the intersection between the sounding line and the sounding check line; the depth at this intersection is interpolated from the two nearest depths before and after the intersection on the sounding line and the sounding check line; n is the number of intersections;

- When using MBES, it is the difference in depth of the point located within the coverage area between two adjacent scan strips; the depth of the points within the coverage area is output according to a square grid with side lengths of 5-10m on-site; n is the number of points within the square grid.is the difference in depth of the point located within the coverage area between two adjacent swathes; the depths of points within the coverage area are output according to the grid square mesh with sides ranging from 5-10m on site; n is the number of points within the grid square.

7. The difference in depth between the sounding point and the sounding check point shall not exceed 1.5 times the provisions of Clause 4 of this Article and shall not be systematic.

8. The limit value of the height difference of the sounding points and the sounding check points shall not exceed twice the provisions of Clause 7 of this Article, and the total number of check points with differences from 1.7 to 2.0 times the provisions shall not exceed 10% of the total number of sounding check points.

9. The edge error of the seabed topography on the seabed topographic map at a scale of 1:5000 (different from the survey area) may be up to 1.3 times greater than the edge errors of the topographic map at a scale of 1:5000 for the mainland.

10. The accuracy of topographic features and objects on the mainland or islands of the seabed topographic map at a scale of 1:5000 shall be carried out according to the current technical regulations for surveying and establishing topographic maps at a scale of 1:5000 for the mainland.

11. Regulations on digitizing land and island areas from old maps and charts according to current technical regulations.

12. The accuracy of the boundary drawing of land and island areas, and sea areas from existing documents in the area to establish the seabed topographic map at a scale of 1:5000 must ensure the accuracy of the topographic map at a scale of 1:5000.

Article 7. Content of the seabed topographic map

1. The content of the seabed topographic map at a scale of 1:5000 for the land portion and island portion shall comply with the current technical regulations on surveying and creating topographic maps at a scale of 1:5000 for the mainland and the 1:5000 symbols. The basic contour interval of the contour lines, the number of height annotations for the mainland and islands shall be taken from existing topographic maps at a scale of 1:5000 in the survey area. In cases where there are no topographic maps at a scale of 1:5000, specific details on the use of smaller or larger scale topographic and nautical charts to compile the topographic and physical features of the areas on the mainland and islands in the Technical Description - Topography must be provided.

2. The content of the seabed topographic map at a scale of 1:5000 for the marine portion includes the following elements:

a) Seabed topography;

b) Bottom material;

c) Shoreline and water edge lines; high tide and low tide lines (if applicable);

d) Intertidal flats and submerged banks;

đ) Artificial objects on the sea surface;

e) Artificial objects on the seabed;

g) Natural objects on the seabed;

h) Maritime and hydrographic elements;

i) Dangerous maritime zones and prohibited areas;

k) Vegetation;

l) Place names and other necessary annotations;

m) Marine boundary lines;

n) Points for checking marine measuring equipment;

o) Frame and annotations outside the frame.

3. Other content elements (if any) in the marine portion shall be represented on the map using corresponding symbols and must be specifically described in the Technical Description - Topography according to the following principles:

a) Objects that can be depicted according to the map scale and linear objects with widths of 3 meters or more (in reality) must be drawn according to the map scale; if the object has a standardized symbol and the area of the object drawn according to the map scale is more than twice the area of the standardized symbol on the map, then the standardized symbol must be added inside the object's dimensions, with the center of the standardized symbol coinciding with the center of the object;

b) Objects that cannot be depicted according to the map scale or whose area drawn according to the map scale is less than twice the area of the standardized symbol on the map shall only be shown using the standardized symbol, with the center of the standardized symbol coinciding with the center of the object. Linear objects with widths less than 2.5 meters shall be depicted on the map using half-scale symbols, with the axis of the linear symbol coinciding with the axis of the linear object;

c) Objects that can be depicted according to the map scale but have no standardized symbol shall be shown using corresponding symbols and annotated with the type of object and its specific name (if applicable);

d) For map content elements with large areas, they shall be depicted by boundary dots based on their actual distribution area, accompanied by standardized symbols and annotations outside the map frame. If other map content elements need to be displayed on the seabed topographic map at a scale of 1:5000 and are not included in the 1:5000 symbols, supplementary symbols as prescribed in Appendix 1 accompanying this Circular shall be used.

Article 8. Level of Representation of Seabed Topography

1. Basic contour interval:

a) For areas with a slope less than 2%, the contour interval is 0.5 meters;^0, b) For areas with a slope from 2% to 6%, the contour interval is 1.0 meter;

c) For areas with a slope greater than 6%, the contour interval is 2.5 meters;⁰ d) On a single survey area, only one basic contour interval should represent the seabed topography. In special cases, two basic contour intervals may be used, but this must be specified in the Technical Description - Topography.⁰2. When basic contours do not adequately describe the characteristics of the seabed topography, or when the distance between two basic contours exceeds 5 cm on the map, half-interval contours should be used.

3. Seabed topography is represented by contour lines and depth annotations. The average density of depth annotations is 20 to 25 points per square decimeter of the map. In flat seabed areas, the density of depth annotations should not be less than 25 points per square decimeter of the map and must be evenly distributed. In complex areas, the density of depth annotations can be increased by 1.3 to 1.5 times, but it must ensure easy recognition of the topography and be consistent with the representation of contour lines on the map. 6⁰4. Depth annotations on the map should be accurate to 0.1 meters.

5. For rocky reefs, large coral reefs, and vegetation where the topography is too complex to be directly surveyed to depict the shape, contour lines may stop at the boundaries of the reef or vegetation.

6. In areas with sudden changes in topography and steep slopes that cannot be represented by contour lines, symbols should be used to indicate these changes, and contour lines may stop at the positions of these symbols.

7. On each map sheet, the deepest point measured within the marine area covered by that sheet must be indicated.

CONTROL NETWORK AND SURVEY NETWORK

5. For large coral reefs, rocky outcrops, and vegetation areas where the terrain is too complex to be directly surveyed to represent the topography, depth contours may terminate at the boundary of the reef, the boundary of the vegetation area.

6. For areas with sudden changes in terrain and steep slopes that cannot be represented by depth contours, symbols shall be used to indicate this, and depth contours may terminate at the position of those symbols.

On each map sheet, the deepest depth measured within the marine area of that map sheet must be shown.

Chapter III

CONTROL NETWORK FOR BASELINE AND SURVEYING CONTROL NETWORK

Article 9. Control Network for Baseline

1. The control network for baseline in topographic surveying of the seabed includes control points for developing the control network for surveying to serve depth measurement with a sounding rod and static stations (base stations) when using RTK technology.

2. The density of baseline control points depends on the area to be measured with a sounding rod and the degree of coverage by vegetation and the level of construction in the surrounding area. In all cases, the density of baseline control points must ensure that there is one point for every 3km² to 5km². When using RTK technology for echo sounder depth measurement, the distance from the static station to the measurement point shall not exceed 10km.

3. Baseline control points are selected at locations with stable ground, marked with stakes (with stake caps) or marked on structures on-site and must remain throughout the construction, inspection, and acceptance process. Regulations regarding point numbering and point names must be clearly presented in TKKT - DT.

4. Provisions for establishing the baseline control network, methods for arranging the baseline control network, regulations for measurement and computation of adjustment errors, and measurement book templates shall follow current technical regulations.

5. All measurement data files, measurement books, connection diagrams, results of adjustment error calculations... related to the baseline control network must be submitted along with the results.

Article 10. Survey Control Network

1. The survey control network is established to increase the density of control points serving the surveying of topography and objects in the area measured with a sounding rod. The survey control network is only constructed at one level.

2. Points within the survey control network are selected at locations with stable ground, marked with stakes (with stake caps) on-site and must remain throughout the construction, inspection, and acceptance process. Regulations regarding point numbering and point names must be clearly presented in TKKT - DT.

3. Provisions for establishing the survey control network, methods for arranging the survey control network, regulations for measurement and computation of adjustment errors, and measurement book templates shall follow current technical regulations.

4. All measurement data files, measurement books, connection diagrams, results of adjustment error calculations... related to the survey control network must be submitted along with the results.

Chapter IV

CHECKING POINTS FOR OCEAN MEASURING EQUIPMENT, TIDE GAUGING STATIONS, AND TIDE GAUGE HEIGHT CHECKING POINTS

Article 11. Checking Points for Ocean Measuring Equipment

1. Checking points for ocean measuring equipment are selected, marked, and surrounded by protective walls on-site according to National Technical Standards for Establishing Coordinate Networks. In difficult cases, markers can be attached to fixed, stable structures on-site. Checking points for ocean measuring equipment are typically designed as pairs (two) points near the location of tide gauging stations. The distance between two points must be greater than 100m on-site.

2. The position of the pair of checking points for ocean measuring equipment must ensure clear visibility between them, facilitating the testing of ocean measuring equipment. Point names and checking point numbers for ocean measuring equipment are specified in TKKT - DT.

3. Checking points for ocean measuring equipment are connected to coordinates and heights using static GNSS technology according to National Technical Standards for Establishing Coordinate Networks and National Technical Standards for Establishing Height Networks. The connection of national coordinates and heights to checking points for ocean measuring equipment and the calculation of coordinate and height adjustment errors must be clearly stated in TKKT - DT.

Article 12. Tide Observation Points

1. Tide observation points shall be located in sheltered areas with minimal influence from sea waves, flood water levels, or wind, and convenient for the entire process of water level measurement. The specifications of tide observation points must be clearly stated in the Technical Design Document - TD. Water level measuring instruments must have markings up to centimeters, with the length of the instrument not exceeding 4 meters when using topographic poles, and not exceeding 5 meters when using coated rulers.

2. The density of tide observation points depends on the area surveyed for marine topographic maps at a scale of 1:5000 in each survey area. The density of tide observation points ensures that each point can serve to correct depth measurement results within a maximum radius of 12.5 kilometers; for areas requiring surveys with small tidal range fluctuations, it allows one tide observation point to serve for correcting depth measurement results within a maximum radius of 15 kilometers; for areas requiring surveys with complex tidal fluctuations, the density of tide observation points must be increased. In the Technical Design Document - TD, the number of tide observation points, their locations, and the plan for utilizing water level measurement results to correct each map section must be clearly specified.

3. For marine areas with significant tidal fluctuations, two or more water level measuring instrument positions must be arranged, and this must be clearly stated in the Technical Design Document - TD.

4. The height of the "0" point of tide observation points shall be measured by geometric leveling with technical benchmark accuracy from the nearest marine equipment inspection point pair or from the nearest tide observation point pair according to a single-line route (suitable route).

It may be measured from one marine equipment inspection point or from one tide observation point height in special cases.

The provisions for connecting technical benchmarks to the "0" point of tide observation points comply with current technical regulations. The results of technical benchmark calculations must be compiled into a set and submitted along with the outcomes.

Article 13. Tide Observation Point Heights

1. Tide observation points located outside islands must be designed with two tide observation point heights (the distance between the two tide observation point heights should be as large as possible but must be convenient for future connection of technical benchmark heights).

2. For inland tide observation points (when there are no nearby marine equipment inspection points), only one tide observation point height needs to be arranged.

3. Tide observation point heights are marked on stable architectural features or securely pegged in place on-site (only existing on-site during the construction, inspection, and acceptance phases).

4. The height of tide observation point heights is determined using static GNSS technology from at least two points in the national height network. National height points used to connect height measurements to tide observation point heights should be selected so that the connection diagram forms an equilateral triangle. For inland tide observation point heights, if convenient, they can be designed to be connected through geometric leveling from the two nearest points in the national height network.

5. Provisions for measuring and calculating the height of tide observation point heights follow the National Technical Standards for Establishing Coordinate Networks, National Technical Standards for Establishing Height Networks, and must be clearly stated in the Technical Design Document - TD. The results of measuring and calculating tide observation point heights must be submitted along with the outcomes.

Article 14. Automatic Tide Gauge

1. For areas where automatic tide gauges are used to determine daily tidal variations, TKKT - DT must specify in detail the technical plan related to the use of automatic tide gauges.

2. The water level recording accuracy of the automatic tide gauge must be ≤ ±5cm.

Chapter V

MEASURING EQUIPMENT FOR THE SEA AND TESTING OF MEASURING EQUIPMENT FOR THE SEA

Article 15. Measuring Equipment for the Sea

1. GPS/GNSS or RTK device: horizontal accuracy ≤ ±3m, vertical accuracy (when determining height using RTK technology) ≤ ±0.10m.

2. SBES: depth measurement resolution ≤ ±3cm, depth measurement accuracy ≤ ±(10cm + 0.1% h). Where: h is the depth measured in meters.

3. MBES: depth measurement resolution ≤ ±3cm, depth measurement accuracy ≤ ±(10cm + 0.1% h). Where: h is the depth measured in meters. The beam angle ensures that the bottom scan distinguishes objects with a size ≥ 2.5m.

4. Wave sensor: wave measurement accuracy ≤ ±5cm, wave measurement range ≥ 5m, tilt angle measurement accuracy ≤ ±0.250, tilt angle measurement range ±300.

5. Sound speed meter: measurement range from 1350m/s to 1900m/s, accuracy ±0.25m/s.

6. Surface sound speed meter (when using MBES).

7. Compass: direction measurement accuracy ±0.20.

8. Dedicated computer: minimum configuration must meet software survey requirements, have sufficient ports to connect devices.

9. Dedicated software.

10. Related auxiliary equipment:

a) Static GNSS positioning satellite receiver.

b) Dynamic GNSS positioning satellite receiver.

c) RTK equipment set for real-time dynamic GNSS measurement.

d) Water level staff and sounding rod.

đ) Electronic total station.

e) Depth measuring pole.

Article 16. Testing of Measuring Equipment for the Sea

1. All machines mentioned from Clause 1 to Clause 7 and the machines and rods mentioned at Points a, b, c, d, đ Clause 10 Article 15 of this Circular must be tested or certified by the authorized agency for measuring equipment inspection before use according to the regulations of each type of machine. The testing results of each type of machine must be less than the error specified in Article 15 of this Circular to be put into use.

2. Machines mentioned from Clause 1 to Clause 7 of Article 15 of this Circular shall be tested in accordance with Circular No. 27/2011/TT-BTNMT dated July 20, 2011 of the Ministry of Natural Resources and Environment on testing and calibration of some marine mapping measuring equipment.

3. Machines and rods specified at Points a, b, c, d, đ Clause 10 Article 15 of this Circular shall be tested or certified according to the manufacturer's regulations and usage instructions of each type of machine.

4. Regulations on installation of marine measuring equipment systems:

a) The transducer head can be installed at the bow, side, or center of the ship depending on the type of SBES, MBES and dedicated or hired ships; during testing, during depth measurement, the surface of the transducer head must be regularly checked to avoid attached objects causing signal interference.

b) When using MBES: the surface sound speed meter must be installed next to the transducer head.

c) If the antenna center of the positioning device does not coincide with the transducer center (along the plumb line), the offset value must be determined and entered into the software when performing depth measurement with SBES, MBES. When determining the offset value, the time must be calm, and the ship must be securely moored.

5. After installing the machines into a marine measuring equipment system on the ship, testing of the marine measuring equipment system must be conducted. The testing of the marine measuring equipment system is carried out according to Circular No. 27/2011/TT-BTNMT dated July 20, 2011 of the Ministry of Natural Resources and Environment on testing and calibration of some marine mapping measuring equipment.

6. Other regulations on testing of marine measuring equipment:

a) SBES, MBES, sound speed meters, and dynamic GNSS positioning satellite receivers must be retested immediately after completing depth measurement. These test results must be included in the test logbook in chronological order for each machine.

c) The testing of marine measuring equipment, machines, and systems must be recorded in the field test logbook for each testing item as prescribed; calculation results must be accurately filled in the test logbook for each type of machine. The format of the test logbook for SBES, MBES, sound speed meters, and marine measuring equipment system testing is provided in Appendix 2 issued together with this Circular.

d) Testing of the MBES system must be conducted in the survey area; if the survey area does not meet the testing and calibration requirements for some marine mapping measuring equipment, the nearest testing area should be selected.

đ) For machines that use software for testing, the original data files in the software format must be submitted along with the test results.

e) All test logbooks must be signed and stamped by the head of the construction unit.

REGULATIONS ON SURVEYING CONTENTS OF MARINE BOTTOM TOPOGRAPHIC MAPS

Chapter VI

REGULATIONS ON SURVEYING CONTENTS OF THE MARINE BOTTOM TOPOGRAPHIC MAP

Article 17. Water level monitoring for adjusting sounding results

1. The water level monitoring must take place before the start of sounding, sounding checks, and after the end of sounding, sounding checks each day and each sounding session.

2. Every 10 minutes, the number on the water level gauge must be read once at even hours and even 10-minute intervals. Each time the number on the water level gauge is read, it must be read twice to the centimeter. The readings on the water level gauge must be recorded in the water level monitoring logbook. The format of the water level monitoring logbook is specified in Appendix 3 attached to this Circular.

3. In cases where the reading must be transferred from one water level gauge to another (of the same tidal observation point), both gauges must be read at least once simultaneously. The difference between the two water level gauges must not exceed 1 cm.

4. Use Microsoft Excel software to create graphs depicting daily water level changes. Daily water level change graphs must be compiled into a set, signed and stamped by the head of the construction unit, and submitted with the results.

For projects and specialized tasks requiring the representation of high tide and low tide lines on seabed topographic maps at a scale of 1:5000, continuous 24-hour water level monitoring must be conducted at tidal observation points for at least 30 consecutive days and nights. The regulations regarding the timing of water level gauge readings, frequency of readings, and accuracy are stipulated in Article 17 of this Circular.

Article 19. Determining the location of sounding points when using SBES, MBES

1. The location of the sounding points is determined by global satellite positioning (GNSS, DGNSS) with differential corrections from signals from coastal DGPS stations.

2. The location of the sounding points is determined by global satellite positioning (GNSS, DGNSS) with differential corrections from satellite subscription signals (for areas where coastal DGPS station signals cannot be received).

3. The location of the sounding points is determined by GNSS RTK.

In TKKT-DT, the specific method for determining the location of the sounding points must be presented.

Article 20. Seabed topography sounding using SBES

1. Design of sounding lines and sounding check lines:

a) Sounding lines are designed in an east-west direction or parallel to the seabed slope, with a distance of 50 meters between adjacent sounding lines on-site. The distance between consecutive depth determination points on the same sounding line is 10 meters on-site;

b) Sounding check lines are designed perpendicular to the sounding lines, with a distance of 400 meters between adjacent sounding check lines on-site. During implementation, ensure that the total length of the sounding check lines does not fall below 10% of the total length of the sounding lines. Sounding check lines should be distributed relatively evenly across the survey area. The distance between consecutive depth determination points on the same sounding check line is not more than 10 meters on-site;

c) Sounding lines and sounding check lines are designed on the VN-2000 or WGS-84 coordinate system for navigation purposes. If designed on the VN-2000 coordinate system, the seven transformation parameters according to Decision No. 05/2007/QĐ-BTNMT dated February 27, 2007, of the Minister of Natural Resources and Environment on the use of transformation parameters between the International Geodetic Reference System WGS-84 and the National Geodetic Reference System VN-2000 must be entered into the navigation software;

d) The numbering of sounding lines starts from 01 and increases sequentially from north to south in each survey area;

đ) The numbering of sounding check lines starts from 01 and increases sequentially from east to west in each survey area.

2. Sounding and sounding checks:

a) Use SBES with accuracy ≤ ±(10cm + 0.1% h); h is the depth in meters, and specialized seabed topography survey software to conduct sounding and sounding checks;

b) The transducer of the SBES is installed in an appropriate position on the vessel, ensuring technical requirements and safety throughout the seabed topography sounding process. Before daily sounding, the submergence of the transducer must be accurately determined to ±1cm and entered into the sounding device. After the end of the day's sounding, the submergence of the transducer must be rechecked. For multi-day surveys, the submergence of the transducer must be regularly checked. When there is a change in the vessel's load (increase or decrease in fuel or freshwater volume) leading to a change in the transducer submergence, the new submergence must be determined. If the difference in transducer submergence between two consecutive soundings exceeds ±3cm, this deviation must be corrected in the sounding data through interpolation over time;

c) Depending on the survey range and depth of the survey area, TKKT-DT must specify the use of sound speed input into the sounding device according to one of the following options:

- Using a machine to determine the sound speed at the deepest point of each survey area to adjust the sounding results for all map sections within that area;

- Using a machine to determine the sound speed at the deepest point of a map section to adjust the sounding results for that specific map section.

- The sound speed input into the sounding device must be rounded to m/s. Depending on the software used, the sound speed input into the software must be specified in an appropriate format.

d) The time on the marine measurement equipment system must be synchronized with the time of the clock used for water level monitoring at the tidal observation point;

đ) Prior to implementation, the construction unit must contact the management and operation units of coastal DGPS stations to ensure differential correction signals or sign contracts for satellite signal subscriptions when using dynamic GNSS devices to determine the location of sounding points;

e) During implementation, due to the influence of sea waves, wind, etc., sounding lines may deviate from the designed lines by no more than ±10 meters on-site, and sounding check lines intersect sounding lines at an angle not exceeding ±30° compared to the designed angle (90°). In cases where deviations exceed the specified limits, supplementary measurements must be taken to ensure sufficient data.

g) In cases where the sounding vessel cannot approach closely to the coastline or island shore, or the density of depth measurement points is insufficient to fully depict the coastal terrain or the foot of islands, supplementary soundings must be conducted during high tide along one or multiple lines running parallel to the foot of the coastline or encircling the foot of islands.

h) During the process of sounding and sounding verification, if submerged islands, underwater obstructions, maritime hazards, or submerged rocks are discovered, a thorough hydrographic survey must be carried out, and detailed records and descriptions must be made in the work log for subsequent processing and annotation.

i) The distance between hydrographic survey lines ranges from 05 to 10 meters on-site (in areas with underwater obstructions, submerged rocks, and maritime hazards, the distance between lines is 5 meters; in areas with submerged shoals and unusual terrain features, the distance between lines is 10 meters). The density of depth determination points on hydrographic survey lines must not exceed 5 meters on-site.

k) The results of sounding, sounding verification, and hydrographic surveys must be recorded in the sounding logbook and must be retained in the original data file format used by the software on a DVD. The template for the sounding logbook is prescribed in Appendix 3 attached to this Circular.

3. Evaluation of Sounding Accuracy:

a) Utilize linear interpolation at the intersection point of two adjacent sounding lines and verification lines to determine two corresponding depth values, then compare these values. The difference in depth between sounding and verification sounding is calculated using the formula Δ = hds - hkt.

Where:

- hds_{is the depth (obtained from the result of linear interpolation at the intersection point between the sounding line and the verification sounding line) when sounding;}- hkt

- hds_{is the depth (obtained from the result of linear interpolation at the intersection point between the sounding line and the verification sounding line) when verification sounding.}is the depth (obtained from the linear interpolation result of the intersection point between the sounding line and the check sounding line) when conducting check soundings.

b) The permissible errors shall be implemented according to the provisions of Article 6 of this Circular.

Article 21. Seabed Topography Survey Using MBES

1. Designing Seabed Topography Scanning Lines:

a) The seabed topography must be scanned to cover 100% of the surface area;

b) The direction of the scanning lines must be parallel to the contour lines (perpendicular to the slope direction of the seabed topography in the area to be surveyed); the number of scanning lines depends on the depth of the survey area and the beam width of each device (must be specified in the Technical Design - DT);

c) The overlap between two adjacent scan strips must not be less than 5% of the width of the narrower strip among the two adjacent strips. In such cases, there is no need to design verification scanning lines;

d) When two adjacent scan strips do not overlap (overlap is 0% or less than 5%), verification scanning lines must be designed. The direction of the verification scanning lines must be perpendicular to the direction of the main scanning lines. The total length of the verification scanning lines must not be less than 5% of the total length of the main scanning lines and must be evenly distributed across the area;

e) The width of the scan swath must be based on the average depth, seabed characteristics of the survey area, and technical specifications of the MBES to select the optimal beam width;

f) Design the scanning lines and verification scanning lines on the VN-2000 coordinate system or convert the entire design of the scanning lines and verification scanning lines to the WGS-84 coordinate system, input into the navigation software to form run paths (along the centerline) for guiding the scanning of the seabed topography surface without leaving gaps and ensuring the required overlap as stipulated in Clause 1 of this Article. If the design is done on the VN-2000 coordinate system, the seven transformation parameters according to Decision No. 05/2007/QĐ-BTNMT dated February 27, 2007, issued by the Minister of Natural Resources and Environment regarding the use of transformation parameters between the International Geodetic Reference System WGS-84 and the National Geodetic Reference System VN-2000 must be entered into the navigation software;

g) The identification numbers of the scanning lines and verification scanning lines of the scan strips must be numbered consecutively from 01 onwards for each type of line within the same survey area and must be detailed in the Technical Design - DT;

h) For areas near large islands, areas with many islands, and complex terrain, specific regulations regarding the direction of scanning lines, the width of scan strips, etc., must be specified in the Technical Design - DT based on the provisions of Points b, c, d, e of this Clause.

2. Seabed Topography Scanning:

a) Use MBES with accuracy ≤ ±(10 cm + 0.1% h); h is the depth measured in meters, and specialized seabed topography survey software to scan the seabed topography;

b) Use an acoustic speed measuring device installed at the transducer head (SVP-SV Profiler or equivalent) and connect it to the MBES, dedicated computer, wave correction machine, etc., to form a synchronized equipment system for scanning the seabed topography;

c) During the scanning of the seabed topography, adjust the ship's course based on the actual depth of the central ray to ensure that the entire seabed topography surface is fully covered and that the overlap between two adjacent lines meets the requirements set forth in Point c of Clause 1 of this Article;

d) During the scanning of the seabed topography, if submerged islands, underwater obstructions, maritime hazards, sunken trees, or submerged rocks are discovered, they must be recorded and described in detail in the seabed topography scanning logbook, mentioned in reports, and clearly noted in the work log for subsequent processing and annotation. The template for the seabed topography scanning logbook is prescribed in Appendix 3 attached to this Circular.

e) Regulations concerning the determination of acoustic speed, synchronization time on the marine equipment system, correction signals for range errors, the angle between scanning lines and verification scanning lines, and the gap in scanning the foot of the coastline and the foot of islands are as stipulated in Points c, d, e, g of Clause 2 of Article 20 of this Circular;

f) The digital results of the seabed topography surface scanning must be retained in the original data file format used by the software on a DVD.

3. Evaluation of Seabed Topography Scanning Accuracy:

a) The evaluation of the seabed topography scanning results is based on the data obtained from the overlapping areas between two adjacent scan strips or the overlapping areas between the scan strip and the verification scan strip;

b) The volume of points used for accuracy assessment is determined according to the provisions of Clause 6 of Article 6 of this Circular. The Technical Design - DT must specify the exact length of the side of the square grid cells when exporting points for accuracy assessment.

c) The delay periods shall be implemented in accordance with the provisions of Article 6 of this Circular.

4. Use MBES to measure depth along the profile:

a) The distance between two edge rows of two adjacent depth data profiles when measuring depth along the profile using MBES must not exceed 1 cm on the map (corresponding to 50 meters on site);

b) The direction of the profile (measured from the central ray) for measuring depth along the profile must be parallel to the contour line direction, and the direction of the profile for checking depth along the profile must be perpendicular to the direction of the profile for measuring depth. The total length of the profile for checking depth along the profile must not be less than 10% of the total length of the profile for measuring depth along the profile and must be evenly distributed across the area;

c) The implementation of depth measurement, depth check measurement, and accuracy assessment must comply with the provisions of Clause 1, 2, and 3 of this Article and must be specifically stated in the TKKT - DT.

Article 22. Measuring seabed topography depth using a sounding rod

1. Use the control network according to the provisions of Article 9 and the surveying control network according to the provisions of Article 10 of this Circular as the station for measurement. The distance from the measurement station to the detailed drawing point must not exceed 500 meters (when using electronic total stations with angular measurement error ≤±30” and edge measurement error ≤±0.10m), and must not exceed 300 meters (when using optical theodolites). The position of the point is determined by the method of total station, and the depth of the point is determined by trigonometric leveling method (measured at one level position). Every approximately 20 points measured, the standard direction must be rechecked. Measurement results must be fully recorded in the detailed measurement book. The format of the detailed measurement point book follows current technical regulations.

2. The average density of points measured by sounding rod must not be less than 40 points/0.1km² on site; in areas with simple terrain that is not fragmented, the density of points measured by sounding rod may be reduced to 30 points/0.1km² on site; in areas with complex terrain that is fragmented, the density of points measured by sounding rod must be increased to 60 points/0.1km² on site.

3. In cases where detailed seabed topography mapping is carried out by total station method using a sounding rod in areas requiring depth measurement by sounding rod, and if the surveying control network has already determined the technical elevation according to the regulations, water level observation is not necessary.

4. Under permissible conditions, GNSS dynamic equipment can be used to determine the position of the sounding rod measurement point by manually logging the positioning time and recording coordinates separately in a file according to the software format; the depth of the point is determined by the sounding rod with the smallest division marked in centimeters and recorded in the sounding rod measurement book. In this case, water level observation must be conducted according to the provisions of Article 17 of this Circular. The format of the sounding rod measurement book (when determining the position of the point by GNSS equipment) is specified in Appendix 3 issued together with this Circular.

5. The numbering of sounding rod measurement points starts from 01 up to the end within the same mapping area. When the sounding rod measurement range is large, the TKKT - DT may divide it into smaller mapping areas to specify the numbering sequence of the sounding rod measurement points.

6. Within the sounding rod measurement area, there is no need for depth verification measurement.

Article 23. Detailed Survey Using RTK Technology

1. Must use RTK equipment manufactured by specialized manufacturers and tested for construction. The measurement equipment includes GNSS/DGNSS receivers capable of receiving code and phase measurements, single frequency or multi-frequency, with edge measurement error ≤±(10mm + 1mm x D) (D is the length of the measured edge in kilometers), and equipment with real-time GNSS/DGNSS dynamic measurement function.

2. For each measurement station, use one Base station (Base station as defined in Article 9 of this Circular) with clear sky conditions allowing reception of signals from all satellites (within a 150-degree angle) available at any measurement time at the Base station and mobile units (Rover) approaching the points to be measured.

3. The distance from the Base station to the measurement point must not exceed 10km.

4. Accurately set the coordinate and height data of the Base station according to the technical guidelines of each system. Set the coordinates correctly according to the coordinate system used as stipulated in the approved TKKT-DT. The coordinate system installed in the system must be particularly noted during the installation of the coordinate system in surveying software. Parameters for converting from the WGS-84 Coordinate System to the National Coordinate System VN-2000 are provided in Decision No. 05/2007/QĐ-BTNMT dated February 27, 2007, issued by the Minister of Natural Resources and Environment regarding the use of conversion parameters between the International WGS-84 Coordinate System and the National Coordinate System VN-2000.

5. The antenna height of the Base station must be accurately measured to 02mm. The antenna height of the Rover must be accurately measured to 05mm.

6. Radio signal must be checked before and during the measurement process. Real-time positioning errors must be continuously monitored during the measurement process to ensure the quality of RTK data meets the standard. Monitor the strength of the received signal on the Rover to adjust the radio signal at the Base station.

7. Detailed surveying is carried out according to one of the following two options:

a) In cases where a boat is used for movement, the person holding the sounding rod will sit directly on the boat, the sounding rod will be aligned with the position of the Rover antenna to proceed with inserting the rod at measurement points while the boat moves. The sounding rod is inserted vertically into the seabed surface, recording the corresponding height data relative to the Rover antenna to ensure accurate depth measurement, simultaneously determining the coordinates and depth at that point. The duration for each detailed measurement point to ensure accuracy can be stopped for 2 to 5 seconds depending on the setting;

b) In cases where a boat cannot be used for movement and must move manually, the Rover antenna will be directly attached to the sounding rod, measurement data at each point will be recorded directly into the Rover, the height is determined based on the height of the sounding rod. The sounding rod is inserted vertically into the seabed surface, recording the corresponding height data relative to the positioning antenna of the Rover. The duration for each detailed measurement point to ensure accuracy can be stopped for 2 to 5 seconds depending on the setting.

When determining height (depth) using RTK equipment and the Rover is directly inserted into the seabed surface, water level observation is not required.

The template of the RTK measurement book according to the provisions set out in Appendix 3 issued together with this Circular.

Article 24. Sampling of Seabed Material

1. For sea areas with depths up to 30 meters: the sampling points for seabed material should be evenly distributed over the surveyed area, with one sample point taken for every 1 square kilometer on-site; for areas surveyed using a sounding rod, the sampling density must be doubled (16 points per square kilometer). In the Technical Report - Surveying, the specific distance between sampling lines for seabed material in areas surveyed using sonar must be detailed.

2. For sea areas with depths from 30 meters to 100 meters: the sampling of seabed material will depend on specific requirements, and the density of sampling points for seabed material in the Technical Report - Surveying will be specified accordingly.

3. Surface samples of seabed material shall be collected using specialized grabs (for sea areas with depths up to 30 meters) or gravity cores, push corers, vibracores... (for sea areas with depths from 30 meters to 100 meters). The surface layer of the seabed material sample should have a thickness of 20 to 25 centimeters. The samples of seabed material should be classified immediately on-site as sand, mud, sandy mud, gravel... and recorded in the sampling logbook without retaining the samples. The format of the sampling logbook for seabed material is prescribed in Appendix 3 issued together with this Circular.

4. For submerged reef areas and coral reefs where sampling cannot be done using specialized grabs, surveys and information collection about these areas during depth measurements must be conducted. One of the following methods should be used: backscatter processing software of the echo sounder system; underwater camera equipment; side-scan sonar equipment to represent the surface seabed material within the boundaries of these areas.

5. The regulations for determining the location of sampling points for seabed material are similar to those for determining the location of depth measurement points.

a) Coordinates of sampling points for seabed material in areas surveyed using SBES, MBES shall be recorded in data files in the format of the software used;

b) Coordinates of sampling points for seabed material in areas surveyed using sounding rods when determined by electronic total station shall be recorded in the detailed measurement logbook;

c) Coordinates of sampling points for seabed material in areas surveyed using sounding rods when determined by GNSS/DGNSS shall be recorded in data files in the format of the software used;

d) Coordinates of sampling points for seabed material when determined by RTK technology shall be recorded in data files in the format of the software used.

Article 25. Other Surveying Regulations

1. The waterline (the highest limit of water containment on the water surface) and the shoreline (determined at the time of surveying) shall be defined according to technical surveying and topographic map creation regulations at a scale of 1:5000 for land areas. The surveying range for marine areas shall extend from the shoreline downwards:

a) For areas that already have topographic maps at a scale of 1:5000 (or larger scales), the shoreline shall be taken from the published topographic map on land (or drawn from a larger scale topographic map);

b) For areas that only have topographic maps at a scale of 1:10,000 or smaller scales, it is necessary to determine the method of representing the shoreline. Depending on each specific area, based on existing maps and charts, the solution for determining and representing the shoreline in the Technical Report - Surveying must be clearly stated;

c) In exceptional cases, if the shoreline cannot be accurately determined at the time of surveying, the shoreline shall be defined as the zero-meter contour line based on the results of the seabed topographic survey.

2. Shallow banks that appear and disappear and submerged banks are regulated as follows:

a) Banks with an area less than 15 square millimeters on the map need not be represented; banks with an area of 15 square millimeters or more on the map must show the boundary of the bank and indicate the type of bank; for banks with an area of 200 square millimeters or more on the map, the highest point of the bank must be indicated by a note of height or depth at the corresponding position;

b) Submerged banks and parts of shallow banks that appear and disappear, if they can be represented by depth contours, must be drawn as depth contours and annotated with the depth; the part above water level of such banks, if they can be represented by contour lines, must be drawn according to the regulations for topographic maps at a scale of 1:5000 on land and annotated with the height.

3. Artificial objects and structures on the sea:

a) Engineering structures including drilling platforms, platform houses, ports, coastal walls, rock revetments along the coast, storm shelters;

b) Construction projects on the sea including marine research stations, channel buoys, light beacons, range beacons;

c) Marine aquaculture zones including ponds, bays, enclosures, cages, rafts for fixed marine aquaculture; fixed fishing zones on the sea. Marine aquaculture zones are depicted on maps according to the principle:

- For individual fixed enclosures, cages, and rafts for marine aquaculture, they shall be shown on the map at the appropriate scale or by symbols, depending on their size as stipulated in Article 7 of this Circular;

- For concentrated enclosures, cages, and rafts for marine aquaculture forming zones, they shall be shown on the map by outlining the outer boundary of the entire zone and selecting to annotate the name of the main type of marine product; the outer boundary shall be taken from the permit documents granting certain marine areas to organizations and individuals for use;

- For enclosures, cages, and rafts for marine aquaculture without permits, they shall be shown on the map according to the actual survey range and selecting to annotate the name of the main type of marine product;

- For ponds and bays with marine aquaculture, the aquaculture area must be outlined and annotated with the name of the main type of marine product;

- For fixed fishing zones, the number and types of fishing vessels are not detailed but only indicated by symbols and the outline of the area.

d) Artificial objects and structures on the sea shall be depicted according to the provisions of Article 7 of this Circular. Objects and structures with specific names must be annotated with their names.

4. Artificial objects and structures on the seabed must be depicted on the map, including sunken shipwrecks, oil pipelines, gas pipelines, power cables, telecommunications cables.

a) If there are detailed information, the sunken ship is marked with symbols at the location where the ship lies on the seabed. In cases where the sunken ship area falls under maritime danger objects, the dangerous area must be delineated and marked according to the regulations provided, accompanied by notes. If the sunken ship is surveyed using a side-scan sonar system, the shape of the ship should be depicted to scale, and the symbol for the sunken ship should be drawn at the center of the ship.

b) Pipelines for oil, gas pipelines, power cables, telecommunications cables shall be represented by corresponding line symbols, ensuring correct positioning. In cases where field surveying conditions are not available, they must be depicted on the map based on design documents and completion drawings stored at relevant agencies.

5. Natural features at the seabed:

a) Natural features on the sea surface and at the seabed include rock outcrops, independent rock blocks or clusters that rise above water or are submerged below water.

b) Natural features on the sea surface and at the seabed must be represented on the map using symbols. When representing rock outcrops, in addition to symbols, the height or depth and the highest point of the rock outcrop must be noted. If the rock outcrops have specific names, these names must also be noted. For natural features that fall under maritime danger objects, the dangerous area must be delineated and marked according to the provisions of Clause 7 of this Article.

6. Maritime and hydrographic elements:

a) Maritime and hydrographic elements that must be depicted on the map include ship channels entering and leaving ports, ship channels entering and leaving river mouths, buoys, lighthouses, channel buoys, channel lights, anchorage buoys, port berths, storm shelters for ships, hydrographic observation stations, tidal gauges or automatic tide markers.

b) Ship channels entering and leaving ports and ship channels entering and leaving river mouths must be shown by channel boundaries, with depth points annotated at a density greater than 1.5 times as specified in Article 8 of this Circular, and the name of the channel (if applicable) and the maximum tonnage of ships that can enter the channel must be noted.

c) Port berths, storm shelters for ships, hydrographic observation stations, lighthouses, buoys, channel buoys, channel lights, anchorage buoys must be represented on the map using corresponding symbols and their names must be noted if they have specific names. For storm shelters for ships, the density of depth points must comply with the requirements specified in Article 8 of this Circular.

7. Dangerous maritime zones and prohibited areas:

a) On the map, the boundaries of dangerous maritime zones and prohibited areas must be shown according to the provisions of maritime laws.

b) Dangerous maritime zones include areas with whirlpools, submerged reefs, sunken ships, underwater or floating objects capable of posing dangers to maritime traffic, which must be delineated and marked with the word "danger" at the corresponding locations. Prohibited areas must be delineated and marked with the word "prohibited" at the corresponding boundaries.

8. Vegetation:

a) Vegetation depicted on the map includes mangrove areas on the sea surface and vegetation cover at the seabed.

b) Mangrove areas along the coast and islands must be depicted according to the regulations for vegetation parts, as stipulated in the technical specifications for mapping topographic maps at a scale of 1:5000 and the 1:5000 land portion symbols.

c) Vegetation areas at the seabed must only be depicted on the map when complete information about the extent and type of vegetation is available through field surveys, data collection, or auxiliary equipment used during depth measurements, sample collection, and must be specifically defined in the TKKT-DT.

9. Place names and other necessary annotations:

a) Place names including sea names, bay names, river mouth names, island names, archipelago names, cape names, sandbank names, reef names, channel names, lagoon names, estuary names, port berth names, lighthouse names, and names of other natural and artificial objects must be depicted on the map using corresponding font styles and sizes. Place names annotated on the map must be those listed in the Circular issued by the Ministry of Natural Resources and Environment regarding the list of place names for residential, mountainous, hydrological, economic, and social purposes serving the creation of maps for each province and centrally-administered city. In cases where there is no circular on place names, they must be taken from the names officially announced by administrative state agencies; if an object has multiple names, research must be conducted to determine the official name, and in difficult cases, a report must be submitted to the state management agency responsible for map surveying for decision-making.

b) Other necessary annotations include textual explanations of the nature and attributes of geographic features, and technical parameters of these features must be depicted on the map using corresponding symbols and font styles and sizes for each type of feature.

c) The style and size of fonts for place names and other necessary annotations must be selected according to the provisions of the 1:5000 land portion symbols.

10. Maritime boundary lines:

a) Maritime boundary lines include baseline for territorial seas, maritime border lines, exclusive economic zone boundary lines, maritime boundary lines between countries, continental shelf boundary lines, and administrative boundary lines at various levels.

b) Maritime boundary lines that have sufficient legal basis must be fully depicted on the map. Maritime boundary lines without sufficient legal basis must be depicted using sketch lines, and the method of depiction must be clearly stated in the TKKT-DT.

11. Survey equipment check points must be accurately depicted on the map using the corresponding coordinate symbols based on the results of the survey equipment check point error adjustment calculations, and related notes must be included.

12. Use GNSS/DGNSS devices or electronic total stations to determine the boundaries of submerged shoals, submerged reefs, structures, natural and artificial objects on the sea surface and seabed with accuracy as specified in Article 6 of this Circular. The height of the objects is determined using a tape measure or trigonometric leveling. The positions of maritime and hydrographic elements such as lighthouses, buoys, channel buoys, and channel lights are determined at the center of the objects.

Chapter VII

ESTABLISHMENT OF THE BASE MAP

Article 26. Compilation of maps from old materials

1. For sea areas that already have large-scale seabed topographic maps with a scale larger than the required map scale, if assessed for accuracy, completeness, and minimal changes in terrain and objects, there is no need to remap these areas. The compilation should be carried out to convert the large-scale seabed topographic maps to a scale of 1:5000 according to general principles for compiling land topographic maps.

2. For areas on land and islands that already have large-scale topographic maps with a scale larger than the required map scale, the process of selecting and combining elements such as terrain and objects should be conducted according to general principles for compiling land topographic maps.

3. In cases where it is not possible to remap the land and islands as stipulated in Point d Clause 7 Article 4 of this Circular, the compilation of terrain and object features on the land and islands can be done using smaller-scale topographic maps or nautical charts. In the TKKT - DT, the specific technical plan (level of updating and supplementing changes in objects, positioning the area of islands, determining the shoreline) must be clearly stated.

Article 27. Representation of Terrain and Object Features on Land and Islands

The representation of terrain and object features on land and islands shall comply with current regulations for mapping and creating topographic maps at the same scale as the land.

Article 28. Representation of Terrain and Object Features on the Sea

1. The creation of original maps for seabed topographic maps shall be carried out according to general regulations for land topographic maps and Technical Regulations for Digitizing Topographic Maps at Scales of 1:10,000, 1:25,000, 1:50,000, and 1:100,000 issued together with Decision No. 70/2000/QĐ-ĐC dated February 25, 2000 by the Director General of the National Land Administration.

2. The joining of the area of seabed topographic maps at a scale of 1:5000 with land topographic maps or island topographic maps at a scale of 1:5000 shall be carried out continuously according to general regulations for land topographic maps.

3. Names and annotations of content elements of seabed topographic maps recorded in the field notebook shall be transferred to the map according to coordinates and represented by corresponding symbols.

4. The contents of groups and layers of seabed topographic maps shall be adjusted compared to the contents of groups and layers of land topographic maps as follows:

a) The terrain group layer shall be supplemented and modified as follows:

b) The transportation group layer shall be supplemented as follows:

c) The hydrographic group layer shall remove the following layers:

- Layer 5 (contour line);

- Layer 6 (annotation contour line).

5. The height of the waterline and shoreline on seabed topographic maps shall be determined as follows:

a) If the waterline and shoreline are determined during the field survey, their heights shall be taken from the field survey measurements;

b) If the waterline and shoreline have been determined on land topographic maps or island topographic maps at a scale of 1:5000, their heights shall be taken from the heights of the land topographic maps or island topographic maps.

6. During the creation of original digital maps, if encountering objects that need to be represented on the map but are not mentioned in the 1:5000 Symbol Table and this Circular, the construction unit shall proactively propose representation symbols and clearly state them in the Technical Summary Report, Quality and Quantity Inspection Report, and Acceptance Report of the competent authority.

Article 29. Map History Record

1. The construction unit operating outside must fill in all relevant information about the field survey process into the map history record file in accordance with the regulations.

2. The construction unit operating inside receives the map history record file from the external construction unit and is responsible for filling in all relevant information about the drafting and establishment of the original digital map within the internal operation process.

3. The model of the original digital map history record as prescribed in Appendix 4 issued together with this Circular.

Chapter VIII

IMPLEMENTING PROVISIONS

Article 30. Effective Date

This Circular takes effect from February 15, 2018.

The Vietnam Marine and Island Administration is responsible for guiding and supervising the implementation of this Circular.

During the implementation process, if there are any difficulties, agencies, organizations, and individuals shall promptly report to the Ministry of Natural Resources and Environment for consideration and resolution./.