Circular No. 34/2011/TT-BTNMT stipulates technical procedures for creating seabed topography maps at a scale of 1:100,000 using direct surveying methods.

CIRCULAR

Technical regulations for the creation of marine topographic maps at a scale of 1:100,000 using direct surveying methods

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BASED ON THE LAW ON ENACTMENT OF LEGAL DOCUMENTS;

Pursuant to Decree No. 25/2008/NĐ-CP dated March 4, 2008 of the Government on the functions, tasks, powers, and organizational structure of the Ministry of Natural Resources and Environment, amended and supplemented by Decree No. 19/2010/NĐ-CP dated March 8, 2010 and Decree No. 89/2010/NĐ-CP dated August 16, 2010 of the Government;

Pursuant to Decree No. 12/2002/NĐ-CP dated January 22, 2002 of the Government on surveying and mapping activities;

Considering the proposal of the General Director of the Vietnam Marine and Island Administration, the Head of the Science and Technology Department, and the Head of the Legal Department,

c) Enterprises may be granted permission for no more than one block out of the total three dual-frequency blocks (FDD) B

PART I

GENERAL PROVISIONS

Article 1. Scope of Regulation and Applicability

1. This Circular stipulates the technical requirements necessary for the creation of marine topographic maps at a scale of 1:100,000 using direct surveying methods.

2. This Circular applies to state management agencies for the sea and islands, organizations, and individuals engaged in surveying and creating marine topographic maps.

Article 2. Marine Topographic Maps at a Scale of 1:100,000

1. Marine topographic maps at a scale of 1:100,000 are original storage maps based on data files, divided into groups and layers, and with formats suitable for standardization according to the "Regulations on Applying National Geographic Base Information Standards" issued together with Decision No. 06/2007/QĐ-BTNMT dated February 27, 2007, Decision No. 08/2007/QĐ-BTNMT dated May 14, 2007, and Decision No. 05/2008/QĐ-BTNMT dated August 26, 2008 of the Minister of Natural Resources and Environment.

2. Marine topographic maps at a scale of 1:100,000 belong to the national topographic map system, created in areas of the sea under the sovereignty, sovereign rights, and jurisdiction of Vietnam, and are a continuation of the topographic maps at a scale of 1:100,000 for the mainland.

3. Marine topographic maps at a scale of 1:100,000 are established within the national coordinate system, elevation system, and unified division method with topographic maps at a scale of 1:100,000 on the mainland. The work of creating marine topographic maps at a scale of 1:100,000 is carried out according to the approved Technical Design - Budget.

4. Each piece of marine topographic map at a scale of 1:100,000 has a map history record. The map history record is recorded on paper and established in digital form according to the model specified in Appendix No. 2 issued together with this Circular. The map history file is stored on a CD-ROM along with the original map.

Article 3. Purpose of Using Marine Topographic Maps at a Scale of 1:100,000

1. To serve planning, investigation, exploration, economic management of the sea in areas under the sovereignty, sovereign rights, and jurisdiction of Vietnam; to serve security, defense, and marine research work.

2. To serve as a database for drawing smaller-scale marine topographic maps, base maps, building geographic information systems (GIS), and compiling thematic maps.

Article 4. Requirements for Pieces of Marine Topographic Maps at a Scale of 1:100,000 Including Mainland and Islands

1. In cases where there are no existing maps for the mainland and islands, when surveying marine topographic maps, both the mainland and islands must be surveyed completely.

2. In cases where there are published maps at a scale of 1:100,000 for the mainland and islands, they must be joined with newly surveyed marine topographic maps.

3. In cases where there are published maps at a larger scale for the mainland and islands, they must be redrawn at a scale of 1:100,000 and joined with newly surveyed marine topographic maps.

Article 5. Name of the marine topographic map sheet at a scale of 1:100,000

1. For marine topographic map sheets at a scale of 1:100,000 that include land areas, the name of the map sheet shall be taken from the name of the corresponding land topographic map sheet at a scale of 1:100,000.

2. For marine topographic map sheets at a scale of 1:100,000 without land but with islands, the name of the largest island within the map sheet shall be used as the name of the map sheet.

3. For marine topographic map sheets at a scale of 1:100,000 without islands or land, no name shall be assigned; only the map sheet designation shall be marked on the map sheet.

Article 6. Overlap of Map Frame

During the process of surveying and compiling marine topographic maps at a scale of 1:100,000, whether free borders or adjacent to published map sheets, an overlap of not less than 8mm must be surveyed beyond the map frame. The part surveyed beyond the frame will only be shown on the original map and not when printing the map on paper.

Chapter II

MATHEMATICAL BASIS AND ACCURACY OF THE MAP

Article 7. Mathematical Basis of the Map

1. Marine topographic maps at a scale of 1:100,000 shall be established in the National Coordinate System VN-2000 and the current national elevation system. The central meridian is 105.^° central meridian is 105^°, 111^°, 117^°.

2. On the original map sheet and published maps, a square kilometer grid every two thousand meters must be drawn. Each square on the map measures 2 x 2 cm.

Map sheets at the border of two projection zones must also show the square kilometer grid of the adjacent zone within the map sheet along the outer frame of the map according to the prescribed model.

The presentation format of the map frame shall follow the model for presenting the frame and content outside the frame of topographic maps at scales of 1:50,000 and 1:100,000 as stipulated in Decision No. 178/1998/QĐ-ĐC dated March 31, 1998, issued by the Director General of the Land Administration General Department ("Topographic Map Symbols at Scales of 1:50,000 and 1:100,000").

3. The division of map sheets and the numbering of map sheet designations shall be carried out in accordance with Circular No. 973/2001/TT-TCĐC dated June 20, 2001, issued by the Land Administration General Department regarding guidance on the application of the Reference System and the National Coordinate System VN-2000.

4. Control points for the horizontal plane and elevation ensuring the establishment of marine topographic maps at a scale of 1:100,000 include national coordinate grids of Class I, II, III, and IV, basic cadastral grids, and elevation grids of Class I, II, III, and IV.

Article 8. Accuracy of the Map

1. For digital maps, the position of the corner points of the map frame, national coordinate points, the length of the frame edges, the diagonal of the frame, and the distance from national coordinate points to the corner points of the map frame shall have no errors.

2. Fixed GPS positioning equipment calibration points set up on shore must be national coordinate points calculated based on the global coordinate system WGS-84 and have an accuracy equivalent to national coordinate points of Class IV or higher.

3. The mean error in determining the height of the zero mark of the tide gauge station relative to the nearest national benchmark shall not exceed 0.10m.

4. The mean error in horizontal position is specified as follows:

a) The mean error in horizontal position of depth points and bottom material points relative to the coordinates of the shore positioning point shall not exceed 0.30mm on the map;

b) The mean error in horizontal position of floating objects on the water surface with their center being the symbol center on the map relative to the coordinates of the shore positioning point shall not exceed 0.50mm on the map. For mobile objects on the sea surface such as buoys and lighthouses, this error can be added to the possible range of movement of the object. For submerged objects under the seabed, the allowable error is ±1.0mm on the map.

5. The mean error in depth of depth points after conversion to the national elevation system shall be determined according to the provisions of Clause 7 of this Article and shall not exceed the following limits:

a) ±0.30m for depths up to 30m;

b) 1% of the depth for depths over 30m.

6. The mean error in depth of the main contour line relative to the zero mark of the nearest tide gauge station shall not exceed:

a) Two-thirds of the uniform height difference of the main contour line for areas with a slope less than 6 degrees;^°;

b) The uniform height difference of the main contour line for areas with a slope greater than 6 degrees.^°.

7. The mean error of depth measurement points is determined by the formula:

Where ∆ is the difference in depth between the sounding line and the check line at the intersection of the two lines; the depth at this intersection is interpolated from the two closest sounding points before and after the intersection on each line; n is the number of intersections (at least 20 points).

8. The difference in depth between sounding points and check points shall not exceed 1.5 times the limit specified in Clause 5 of this Article and shall not be systematic.

9. The limit of the difference in height between sounding points and check points shall not exceed twice the limit specified in Clause 8 of this Article, and the total number of check points with differences from 1.7 to 2 times the limit shall not exceed 10% of the total number of check points.

10. The edge error of the marine seabed topography on marine topographic maps at a scale of 1:100,000 shall not exceed the limit of 0.5mm.

Chapter III

CONTENT OF THE MAP

Article 9. Content of the Map

1. The content of the seabed topographic map at a scale of 1:100,000 for the mainland and islands includes the elements specified in the "Map Symbol for Topographic Maps at Scales of 1:50,000 and 1:100,000."

2. The content of the map for the sea area includes the following elements:

a) Seabed topography;

b) Bottom material (only shown when specifically required in the Technical Design - Estimate);

c) Shorelines and water edges;

d) Emergent and submerged banks;

đ) Artificial objects protruding above the sea surface;

e) Artificial objects on the seabed;

g) Natural objects on the sea surface and on the seabed;

h) Maritime and hydrographic elements;

i) Dangerous maritime areas and prohibited zones;

k) Vegetation;

l) Place names and other necessary annotations;

m) Sea boundary lines;

n) Frame and annotations outside the frame.

3. The content elements of the sea area are represented on the map using symbols specified in Appendix No. 3 issued together with this Circular.

Article 10. Map Symbols

1. Objects that can be depicted according to the map scale and linear objects with a width of 0.5 mm or more on the map must be drawn according to the map scale; if the object has a conventional symbol, and the area of the object's depiction according to the map scale is larger than twice the area of the conventional symbol on the map, then the conventional symbol must also be added inside the object's depiction, with the center of the conventional symbol coinciding with the center of the object.

2. Objects that cannot be depicted according to the map scale or whose depiction area according to the map scale is smaller than twice the area of the conventional symbol on the map shall not be depicted but instead represented by conventional symbols, with the center of the conventional symbol coinciding with the center of the object. Linear objects with a width less than 0.5 mm are depicted on the map using half-scale symbols, with the axis of the linear symbol coinciding with the axis of the linear object.

3. Objects that can be depicted according to the map scale but have no conventional symbol shall be depicted using temporary conventional symbols and annotated with the type of object and its specific name (if applicable).

4. Elements distributed over an area such as emergent and submerged banks, vegetation zones, prohibited zones, and hazardous areas shall be depicted by boundary dots based on their actual distribution area, accompanied by conventional symbols and annotations as specified in Appendix No. 3 issued together with this Circular.

Article 11. National Geodetic Control Points Must Be Shown on the Map

1. Points within the national coordinate grid, basic cadastral grid, and points within the national elevation grid.

2. Coordinate points within the marine geodetic control network; base coordinates for territorial waters; fixed GPS station coordinates along the coast.

Article 12. Seabed Topography

1. Seabed topography is depicted by contour lines of depth, depth annotation points, and topographic symbols. The uniform contour interval for basic contour lines is defined for each seabed topography region, depending on the slope of the seabed surface and the depth of the seabed, as follows:

In special cases where a different uniform contour interval for basic contour lines is required, it must be clearly stated in the Technical Design - Estimate.

2. Within one map sheet, only one uniform contour interval for basic contour lines is depicted. If multiple types of topography require two different uniform contour intervals within the same map sheet, this must be clearly stated in the Technical Design - Estimate and approved by the competent authority.

The annotation of the basic contour line depth is carried out according to the regulations for annotating the height of basic contour lines for topographic maps at a scale of 1:100,000 on land.

3. When the basic contour line does not fully describe the characteristics of the topography or when the distance between adjacent basic contour lines exceeds 5 cm on the map, additional contour lines must be drawn at half the uniform contour interval to depict the topography.

4. Depth annotation points on the map are recorded to 0.1 meters. The average density of depth annotation points is 20 to 25 points per square decimeter of the map. For flat seabed topography regions, the density of depth annotation points must not be less than 20 points per square decimeter of the map.² on the map.

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

6. For areas with sudden changes in topography and extremely steep slopes that cannot be depicted by contour lines, symbols are used to represent them, and the contour lines may stop at the position of these symbols. For digital contour maps, the contour lines must be continuous without breaks.

Article 13. Seabed Bottom Material

1. The content of seabed bottom material on the seabed topographic map at a scale of 1:100,000 shall only be shown upon request and must be clearly stated in the Technical Design - Budget Estimate.

2. Seabed bottom material is represented on the map using letter symbols. Sampling points for seabed bottom material have accurate coordinates equivalent to depth annotation points; the density of sampling depends on the seabed bottom material structure of the survey area and must be specifically defined in the Technical Design - Budget Estimate.

Article 14. Shoreline and Water Edge Line

1. The shoreline is the limit of the highest average annual sea level formed by the action of water over a long historical period.

2. The water edge line is the boundary of the water surface recorded at the time of mapping.

3. The shoreline and water edge line may not coincide. When creating maps, if the water edge line is more than 0.3 mm away from the shoreline according to the map scale, the water edge line must be drawn separately from the shoreline. If less than 0.3 mm, it is considered that the water edge line coincides with the shoreline and only the shoreline is depicted.

4. For sections of seabed topographic maps that include land or islands where the water edge line has been shown on the land topographic map at the same scale or a larger scale, the water edge line is taken from the established land map.

5. In cases where the water edge line cannot be accurately determined at the time of mapping, the water edge line is defined as the zero-meter contour based on the results of seabed topographic surveying.

Article 15. Shallow Banks and Submerged Banks

1. Shallow banks and submerged banks include mud banks, sand banks, rock banks, gravel banks, coral banks, and are distinguished as follows:

a) Shallow banks are banks with parts above the zero-meter contour (based on the results of map surveying);

b) Submerged banks are banks without parts above the zero-meter contour (based on the results of map surveying).

2. The depiction of shallow banks and submerged banks on the map is regulated as follows:

a) Banks with areas smaller than 15 mm on the map need not be depicted; banks with areas of 15 mm or more on the map must show the boundaries of the bank and the type of bank symbol; banks with areas of 2 cm or more on the map must depict the highest point of the bank by annotating the height or depth at the corresponding location;² On the map, it does not need to be shown; for sandbanks with an area of 15 mm² or more on the map, the boundary of the sandbank and the symbol indicating the type of sandbank must be shown; for sandbanks with an area of 2 cm² or more on the map, the highest point of the sandbank must be indicated by a note of height or depth at the corresponding position;

b) Submerged banks and the submerged portions of shallow banks, if depicted by depth contours, must draw depth contours and annotate depths; the portions of shallow banks above water (above the zero-meter contour) if depicted by depth contours must draw contours according to the regulations for land topographic maps at a scale of 1:100,000 and annotate heights.

Article 16. Artificial Structures and Objects on the Sea

1. Artificial structures and objects on the sea that must be depicted on the map include:

a) Engineering structures including drilling platforms for exploration or oil extraction, ports, breakwaters, coastal retaining walls;

b) Construction projects on the sea including marine research stations, buildings;

c) Marine aquaculture zones on the sea including bays, estuaries, enclosures, fixed fish farming rafts and cages; fishing grounds and barriers for fixed marine aquaculture.

2. The depiction of artificial structures and objects on the sea is carried out according to the provisions of Article 10 of this Circular. Structures and objects with specific names must be annotated with their names.

3. Marine aquaculture zones on the sea are depicted on the map according to the principle:

a) For individual fixed enclosures, rafts, and cages, they are depicted on the map according to scale or by symbols, depending on size as stipulated in Article 10 of this Circular;

b) For concentrated enclosures, rafts, and cages forming clusters, they are depicted on the map according to the principle of drawing the entire cluster boundary and selecting to represent the characteristics of the aquaculture cluster and annotating the species of farmed marine products;

c) For bays and estuaries with aquaculture, the aquaculture zone must be circled and annotated with the name of the marine product species;

d) For fixed fishing grounds and barriers, detailed quantities and types of fishing vessels are not depicted but only symbols and the area boundary (if necessary).

Article 17. Artificial structures on the seabed

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

2. The depiction of artificial structures on the seabed on maps shall be carried out according to the following provisions:

a) Sunken shipwrecks shall be depicted using symbols placed at the location where the shipwreck is situated on the seabed; in cases where the area of the shipwreck falls within maritime danger zones, it must be delineated and depicted according to the provisions of Article 20 of this Circular.

b) Oil pipelines, gas pipelines, power cables, and telecommunications cables shall be depicted using corresponding linear symbols, ensuring accurate positioning; in cases where field survey conditions are not available, they must be depicted based on design documents and completion drawings stored at relevant agencies.

Article 18. Natural objects on the sea surface and seabed

1. Natural objects on the sea surface and seabed include rock peaks, independent rock formations, or clusters that rise above water or are submerged below water.

2. Natural objects on the sea surface and seabed must be depicted on maps using symbols. When depicting rock peaks, in addition to symbols, the height or depth and the highest point of the rock peak must be clearly noted; if the rock peaks have specific names, these names must be noted; for objects falling within maritime danger zones, the dangerous areas must be delineated and depicted according to the provisions of Article 20 of this Circular.

Article 19. Maritime and hydrographic elements

1. Maritime and hydrographic elements that must be depicted on maps include ship channels entering ports, ship channels entering river mouth areas, buoys, lighthouses, channel buoys, channel lights, anchorage buoys, port berths, storm shelters, marine observation stations, tidal gauges, or automatic tide markers.

2. The depiction of maritime and hydrographic elements on maps shall be carried out according to the following provisions:

a) Ship channels entering ports and ship channels entering river mouth areas shall be depicted with channel boundaries, noting the depth at locations within the channel boundary, and the density must be greater than 1.5 times the general standard, and the name of the channel (if applicable) and the maximum tonnage of ships that can enter the channel must be noted.

b) Port berths, storm shelters, marine observation stations, lighthouses (including lighthouses), buoys, channel buoys, channel lights, anchorage buoys shall be depicted using corresponding symbols on the map and their names must be noted if they have specific names; for storm shelters, the depth must be noted to ensure a density greater than 1.5 times the general standard.

Article 20. Maritime danger zones and prohibited areas

1. The map title must depict the boundaries of maritime danger zones and prohibited areas according to the regulations of competent authorities.

2. Maritime danger zones such as whirlpool areas, submerged reefs, underwater or surface objects capable of posing dangers to maritime traffic must be depicted by delineating the dangerous area boundaries and noting the word "dangerous" at the corresponding position. Prohibited areas must be depicted by delineating the prohibited area boundaries accompanied by the note "prohibited area".

Article 21. Plants

1. Plants depicted on the map include mangrove areas along the coast and plant regions at the seabed.

2. The depiction of plants on the map shall be carried out in accordance with the following provisions:

a) Mangrove areas along the coast shall be depicted according to the regulations for plant areas as stipulated in "Topographic Map Symbols at Scales of 1:50,000 and 1:100,000."

b) Plant regions at the seabed shall only be depicted according to specific regulations in the Technical Design - Budget Estimate.

Article 22. Recording of Place Names and Other Necessary Notes

1. Place names including sea names, bay names, estuary names, river mouth names, island names, archipelago names, cape names, sandbank names, beach names, channel names, creek names, coastal lagoon names, harbor names, lighthouse names, and other natural and man-made place names must be depicted on the map using corresponding font styles and sizes. Place names recorded on the map must be officially announced by competent state management agencies; when an object has multiple names, research must be conducted to determine the official name, and in cases of difficulty, a report must be submitted to the state management agency responsible for surveying and mapping for decision-making.

2. Other necessary notes include textual explanations of the characteristics and attributes of geographic features and technical parameters of these features, which must be depicted on the map using corresponding symbols and font styles and sizes for each type of geographic feature.

3. The font style and size for recording place names and other necessary notes shall be selected according to the regulations in "Topographic Map Symbols at Scales of 1:50,000 and 1:100,000."

Article 23. Maritime Boundaries

1. Maritime boundaries include the baseline of the territorial sea; maritime boundary (territorial sea boundary); outer limit of the exclusive economic zone; maritime boundary dividing lines between countries; continental shelf boundary.

2. Maritime boundaries that have sufficient legal basis must be fully depicted on the map; the method of depiction must be specifically stated in the Technical Design - Budget Estimate.

Article 24. Frame and Notes Outside the Frame

1. The frame and notes outside the frame of the topographic seabed map at a scale of 1:100,000 shall be implemented according to the provisions of Clause 2, Article 7 of this Circular.

2. Magnetic declination shall be determined and depicted according to the following provisions:

a) For map sheets containing land areas, magnetic declination shall be taken from the magnetic declination depicted on the topographic map of the land area.

b) In cases where magnetic declination cannot be determined on maps at scales of 1:50,000 and 1:100,000, it must be measured and determined. The method and density of measurement points for determining magnetic declination must be specifically stated in the Technical Design - Budget Estimate; in special cases where it is not possible to measure to determine magnetic declination, a report must be submitted to the state management agency responsible for surveying and mapping for decision-making.

Chapter IV

 PROVISIONS ON SURVEYING AND DRAWING MAP CONTENT

Article 25. Equipment and Machinery Used in Surveying and Establishing Topographic Seabed Maps at a Scale of 1:100,000

1. Survey vessels meeting the following conditions:

a) Capable of sailing according to the regulations for Class III limited vessels;

b) Capable of sailing safely when wind force is less than or equal to Force 7;

c) Able to accommodate the installation of survey equipment on board;

d) Equipped with adequate marine safety equipment and facilities to ensure the safety of survey machinery and equipment.

2. Synchronized survey equipment on board the vessel:

a) Multi-beam or single-beam echo sounder capable of providing two data outputs including depth profile and digital data files with machine accuracy ≤ ± 5 cm + 0.1% D (D is the depth measured);

b) Positioning equipment including DGPS receivers with positioning accuracy meeting the requirements for map establishment;

c) Water speed measuring device with accuracy of 1 m/s;

d) Wave sensor with accuracy of 5 cm;

đ) Sonar scanning device;

e) Marine survey software: Software with functions to collect, synchronize, and integrate data from positioning devices, depth sounders, compasses, wave corrections, etc. (Hydro Navigation, QINSy...);

g) Digital terrain model;

h) Marine survey computer with at least two COM ports;

i) Pilot navigation display screen;

k) Bottom sampling equipment;

l) Offshore tide measuring equipment;

m) Deep sounding equipment testing device: Speed of sound measuring device, check bar;

n) Auxiliary equipment including generator, battery, battery charger, and ammeter;

3. Equipment at the DGPS signal correction station on shore.

4. Equipment for processing data and editing maps:

a) Minimum hardware equipment includes one workstation;

b) A0 plotter;

c) Software includes: - Intergraph software suite (MGE, Microstation 95, IRAC B, C, Oracle database management system), AutoCAD, Hydro, GPSurvey 2.35a, Iplotdriver client, Iplotdriver pack, and similar software;

- Other software or versions with similar functionality;

- Construction unit's application programs;

5. The machinery and equipment used in surveying and establishing topographic seabed maps at a scale of 1:100,000 must be synchronized, meet the accuracy requirements of the map, and be tested and calibrated according to current regulations.

Article 26. Procedure for conducting surveys and creating maps

1. Collecting information, materials, and surveying the measurement area.

2. Designing technical plans and preparing technical design - budget estimates.

3. Preparing, inspecting, and testing machinery and equipment. Preparing work documents, contacting local authorities, and transferring production forces to the construction site.

4. Offshore survey work:

a) Conducting offshore surveys on vessels equipped with echo sounders and DGPS positioning systems according to the following procedures:

- Step 1. Establishing tide gauge stations and monitoring tidal levels (in cases where shore-based tide gauge stations are not used, tidal levels are monitored using offshore measuring devices).

- Step 2. Installing equipment on the survey vessel.

- Step 3. Inspecting and testing machinery and equipment on-site.

- Step 4. Designing corrections for differential measurements from the static station (Base Station).

- Step 5. Collecting depth data and positioning along the designed survey lines in marine survey software.

- Step 6. Collecting depth data and positioning along the designed check lines in marine survey software.

- Step 7. Sampling bottom sediment according to the design set in marine survey software.

- Step 8. Processing and calculating depth data files (Hydronav files).

- Step 9. Processing check data and evaluating the results of offshore surveys.

- Step 10. Identifying objects at sea and conducting hydrographic surveys (if applicable).

- Step 11. Conducting supplementary and re-surveys.

b) Conducting detailed surveys on land and in shallow waters where vessels cannot enter, according to the following procedures:

- Step 1. Establishing control grids for coordinates and elevations.

- Step 2. Surveying topography and objects using electronic total stations.

- Step 3. Measuring depths using poles and sounding rods and determining the coordinates of the depth points using DGPS receivers.

- Step 4. Surveying shoreline using DGPS receivers.

- Step 5. Monitoring tidal levels during pole and sounding rod depth measurements.

- Step 6. Processing survey data (correcting tidal levels, calculating coordinates and depths or elevations) of detailed depth measurement points.

5. Onshore processing includes:

a) Checking depth tapes (if available), survey results, and processing field data.

b) Building a database for seabed topographic surveys.

c) Editing and compiling original seabed topographic maps.

d) Writing map descriptions.

đ) Storing and preserving original data and digital maps using data management software.

e) Recording original map data and map descriptions onto CD-Rs.

g) Printing original maps using inkjet printers.

6. Product inspection and acceptance work includes:

a) Inspecting surveys and processing field data.

b) Acceptance inspection of seabed topographic map products (onshore processing).

The technological steps are carried out sequentially, with some steps in the offshore survey being conducted simultaneously.

For subsequent steps that utilize the results of previous steps, they can only be carried out after the results of the previous steps have been inspected and meet technical requirements.

7. The technological flowchart and detailed implementation are specified in Appendix 1 attached to this Circular.

Article 27. Tidal Level Monitoring

1. Tidal level monitoring must be conducted concurrently with depth measurements throughout the entire duration of offshore surveys.

2. Methods for tidal level monitoring include:

a) Using water level gauges at tide gauge stations to measure water levels.

b) Using automatic tidal level monitoring equipment (automatic tide gauges) installed at tide gauge stations to determine water levels.

c) Using offshore water level monitoring equipment to determine water levels.

3. The maximum distance between two tide gauge stations or tidal level monitoring stations shall not exceed 50km.

4. The height of the "0" mark at tide gauge stations must be measured from national elevation points of Class IV or higher, or from national coordinate points with connected elevation measurements having equivalent accuracy to geometric leveling of Class IV or higher.

Elevation measurements from national elevation points to the "0" mark at tide gauge stations must be conducted through geometric leveling. The design for elevation measurements must be clearly stated in the Technical Design - Budget Estimate and ensure the accuracy of the "0" elevation mark at tide gauge stations as stipulated in Clause 3, Article 8 of this Circular; if other methods are used for elevation measurements that still meet the required accuracy, they must be clearly stated in the Technical Design - Budget Estimate and approved by the competent authority.

5. Guidelines for reading water levels on water level gauges are as follows:

a) The time interval between two readings on the water level gauge is 30 minutes and should be taken at whole hours or half-hour marks, except as provided in point b of this clause.

b) The time interval between two readings on the water level gauge is 10 minutes and should be taken at every 10-minute mark during the 30 minutes before high tide or low tide and the 30 minutes after high tide or low tide.

c) Each reading must be taken twice on the water level gauge, the first reading at the water level at the wave base, and the second reading at the water level at the wave crest; readings should be accurate to the centimeter; the water level reading value is the average of the two readings.

d) To transfer readings between different water level gauges, simultaneous readings must be taken on both gauges; the difference in water level height between the two gauges must not exceed 1cm.

7. The instantaneous water level height is determined as follows:

a) When tidal level monitoring is done using water level gauges:

- Calculate the water level height at each reading time by adding the reading on the water level gauge to the height of the "0" mark on the gauge.

- The water level height at a specific time is the interpolated value between consecutive readings before and after that time on the water level gauge.

b) In the case of using an automatic tide gauge, the sea level height at a given time is the reading taken from the automatic tide gauge band for mechanical tide gauges or the reading taken from the data file for digital tide gauges.

Article 28. Seabed Topography Surveying

1. Methods for seabed topography surveying include:

a) For deep-sea areas where survey vessels can operate, positions are determined using satellite positioning technology GPS, and depths are measured using echo sounders along sounding lines.

b) For shallow waters where survey vessels cannot enter, positions are determined using satellite positioning technology GPS or electronic total stations, and depths are measured using sounding poles.

2. Equipment used in depth measurement includes:

a) Survey vessel;

- The sounding lines must be specifically designed in the Technical Design - Budget Estimate.

b) In the case of using multi-beam echo sounders:

- Sounding lines must be perpendicular to the slope of the seabed surface to ensure consistent width of the swath;

- The density of sounding lines depends on the depth of the seabed and the beam angle of the multi-beam echo sounder and must be designed to ensure that the area swept by the echo sounder beam covers the entire seabed surface within the survey area and that the coverage area between adjacent sounding lines does not fall below 5% of the width of the swept area along the sounding line.

- The sounding lines must be specifically designed in the Technical Design - Budget Estimate.

4. Check sounding lines:

a) In the case of using single-beam echo sounders, check sounding lines must be designed to meet the following requirements:

- Check sounding lines must intersect with sounding lines at an intersection angle of no less than 45° and no more than 135°, preferably 90°;^°, preferably 90^°;

- The total length of check sounding lines must not be less than 10% of the total length of sounding lines and must be evenly distributed throughout the survey area.

b) In the case of using multi-beam echo sounders, check sounding lines must be designed to meet the following requirements:

- Check sounding lines must intersect with sounding lines at an intersection angle of no less than 45° and no more than 135°;^° and not exceeding 135^°, preferably 90^°;

- The total length of check sounding lines must not be less than 4% of the total length of sounding lines and must intersect sounding lines at both ends and in the middle of the sounding lines;

- In addition to relying on check sounding lines, the results of depth measurements must be verified based on data from the swept area between adjacent sounding lines.

5. Survey equipment installed on the survey vessel must be set up and checked according to the following regulations:

a) The antenna of the satellite positioning device GPS must be placed in an unobstructed location, avoiding electromagnetic interference and multipath effects. The center of the GPS antenna must align with the center of the echo sounder transducer on a vertical line; if alignment is impossible, the offset factors must be determined and entered into the control software for the measurement process;

b) The gyrocompass must be securely mounted on a flat surface such that its axis is parallel to the ship's longitudinal axis; if parallel installation is not possible, the angle between the gyrocompass axis and the ship's longitudinal axis must be determined and entered into the control software for the measurement process. For satellite compasses, the two antennas must be installed like the GPS antenna and on the same horizontal plane. They must be installed longitudinally along the ship (to measure longitudinal roll) or horizontally across the ship (to measure lateral roll);

c) The wave correction sensor must be installed as close to the ship's center of gravity as possible. Proper orientation and horizontal leveling of the machine must be ensured to minimize system errors caused by installation;

d) The transmitting and receiving transducers of the multi-beam echo sounder must be securely installed in the optimal position to avoid acoustic interference on the survey vessel. The online speed measuring device must be installed directly at the transducer head of the system;

đ) Before and after production runs, the accuracy of the GPS satellite positioning device, the echo sounder, and the gyrocompass must be tested; for the echo sounder, the speed of sound transmission in seawater at the survey site must also be determined and entered into the echo sounder;

e) The draft of the echo sounder must be accurately measured to the centimeter and entered into the echo sounder; the draft must be checked daily before and after measurement;

g) After installing the entire system on the survey vessel, measurements must be conducted to determine the following factors:

- The offset readings (offsets) of the equipment on the survey vessel. Note the points: the ship's center of gravity, points describing the size, shape, and direction of the ship; the antenna mounting point for positioning; the antenna for the gyrocompass (if it is a satellite compass); the installation point for the wave correction sensor; the installation point for the transducer of the multi-beam echo sounder; the waterline mark;

- Establish a table showing changes in the ship's draft according to speed and changes in load;

- The tilt (longitudinal and lateral) of the surface where the wave correction sensor is installed relative to the ship's balanced axis; - The tilt (longitudinal and lateral) of the surface where the acoustic transducer (transducer) of the multi-beam echo sounder is installed relative to the ship's balanced axis;

- The directional offset due to installation of the gyrocompass, transducer, and wave correction sensor relative to the ship's balanced axis.

All positions of the equipment must be represented in a spatial coordinate system with the origin at the ship's center of gravity, the Y-axis aligned with the bow direction, the X-axis perpendicular to the Y-axis and pointing to the right. The Z-axis is perpendicular to the plane formed by the X and Y axes and points upwards. Positional errors of off-center points relative to this origin must not exceed ±1cm. Measurement errors of angles of installed equipment must not exceed ±0.1 degrees;

h) The design of sounding lines and transformation parameters of reference systems must be entered into the control software for the measurement process; these transformation parameters must be checked daily before measurement.

6. During the measurement period, sounding lines and check sounding lines must be carried out strictly according to the design, with deviations from the designed lines not exceeding 100 meters.

7. On each sounding line, the distance between two consecutive points, where each point is simultaneously measured for depth and position, must not exceed 200 meters.

8. The depth measurement and positioning process must be fully recorded in the depth measurement logbook.

9. The coordinates of measurement points determined using satellite positioning technology GPS in the global coordinate system WGS-84 must be converted to the national coordinate system VN-2000. The conversion of coordinates shall be carried out using the following method:

a) Input the coordinate transformation parameters into the control software before conducting measurements;

b) Marine topographic surveying is conducted in the global coordinate system WGS-84, and all positioning data shall be converted according to the provisions of Decision No. 05/2007/QĐ-BTNMT dated February 27, 2007, of the Ministry of Natural Resources and Environment on the use of coordinate transformation parameter systems between the International Geodetic Reference System WGS-84 and the National Geodetic Reference System VN-2000, and Circular No. 1123/ĐĐBĐ-CNTĐ dated October 26, 2007, of the Surveying and Mapping Department guiding the use of coordinate transformation parameters from the International Geodetic Reference System WGS-84 to the National Geodetic Reference System VN-2000 and vice versa.

10. Marine topographic surveys using sounding poles for shallow waters shall be carried out according to the following regulations:

a) The density of depth measurement points using sounding poles shall not be less than 30 points per square meter on the map;² b) The determination of the coordinates of the sounding pole using satellite positioning technology GPS is performed in manual logging mode to record the coordinate data of the depth measurement points into the measurement file.

Article 29. Sampling of Bottom Material

1. Sampling of bottom material shall be carried out when there is a requirement to measure bottom material. Bottom material is sampled using a scoop or a core sampler.

2. Requirements for sampling of bottom material:

a) The density of bottom material sampling points shall be based on specific requirements for bottom material information and specified in the Technical Design - Estimate;

b) The coordinates of the bottom material sampling points shall be determined using satellite positioning technology GPS with an accuracy equivalent to the accuracy of point depth positioning;

c) The process of sampling bottom material shall be conducted independently in deep water areas and simultaneously with depth measurement using sounding poles in shallow water areas;

d) Bottom material samples shall be analyzed on-site, numbered, and recorded in the bottom material sampling logbook;

đ) In deep water areas where it is impossible to sample bottom material, devices for analyzing bottom material attached to depth measuring equipment may be used to collect information about bottom material.

Article 30. Determination of Shoreline Position

1. Where there is a visible shoreline at the site, the coordinates of the shoreline shall be determined using a satellite positioning device GPS or an electronic total station.

2. Where there is no visible shoreline at the site, the position of the shoreline shall be determined as the highest tide line in the measured area during the field survey period; the highest tide line shall be determined using a satellite positioning device GPS.

Article 31. Natural and Artificial Structures

1. For structures and objects above sea level, their positions shall be determined using a satellite positioning device GPS, and their heights shall be determined using a tape measure or trigonometric leveling.

2. For structures and objects partially above and partially below sea level, their positions shall be determined at low tide.

3. For structures and objects submerged under water, their positions shall be determined using seabed acoustic scanning methods; if this cannot be done, specific provisions shall be made in the Technical Design - Estimate.

4. Where structures and objects can be drawn to scale on the map, the positions of their outlines and centers shall be determined; where structures and objects are too small to be drawn to scale on the map, the positions of their centers shall be determined (the determination of the center of structures and objects may be carried out through direct measurement or indirect calculation).

4. In cases where the shape of works and objects is drawn according to the scale of the map, the position of the perimeter and center of the work or object must be determined; in cases where the area of the work or object is too small to be drawn according to the scale of the map, the position of the center of the work or object must be determined (the determination of the center of the work or object can be carried out by direct measurement or indirect calculation).

Article 32. Determining Aquatic Vegetation

1. For floating aquatic vegetation on the sea surface or semi-submerged, the position shall be determined using satellite GPS positioning equipment or electronic total stations at low tide as follows:

a) In cases where the aquatic vegetation has an area larger than 15mm² on the map, the boundary line must be determined;

b) In cases where the aquatic vegetation consists of various types of plants growing separately in different areas with each area having an area larger than 15mm² on the map, the boundary line for each separate area must be determined;

c) In cases where the aquatic vegetation consists of various types of plants intermixed or growing separately but each area does not exceed 15mm² on the map, a common boundary line for the entire aquatic vegetation must be determined.

2. For submerged aquatic vegetation, the position shall be determined using seabed scanning methods; if it cannot be determined using seabed scanning methods, specific provisions must be made in the Technical Design - Estimate.

3. The name of each type of plant when identified must be recorded in the measurement logbook; if the name cannot be identified, the type of plant or a description of the plant must be recorded in the measurement logbook.

Article 33. Determining Maritime and Hydrographic Factors

1. The positions of maritime and hydrographic factors shall be determined using satellite GPS positioning equipment;

2. The position of lighthouses shall be determined at the center of the light; height shall be determined using measuring tapes or trigonometric leveling;

3. The position of mooring buoys shall be determined at the center of the buoy;

4. The position of marker buoys, channel buoys, and channel lights shall be determined at the edge of these devices;

5. The position of ship channels entering and exiting ports and ship channels entering and exiting river mouths shall be determined according to the positions of marker buoys, channel buoys, and channel lights;

6. The position of hydrographic observation stations shall be determined at the center of water level gauge number 01 or at the center of automatic tide gauges; if the hydrographic station has both a water level gauge and an automatic tide gauge, the position shall be determined at the center of the automatic tide gauge;

7. The names of maritime and hydrographic factors and the channel carrying capacity must be recorded in the measurement logbook.

Article 34. Determining Shoals

1. The position of exposed shoals and the coordinates and elevation of the highest point of the shoal shall be measured and determined at low tide using satellite GPS positioning equipment or electronic total stations.

2. The position of submerged shoals and the coordinates and elevation of the highest point of the shoal shall be measured and determined using echo-sounding methods, sonar depth sounders, or sounding poles.

Chapter V

ESTABLISHING THE BASE MAP

Article 35. Method of Representing Map Content

The method of representing map content shall be carried out in accordance with the provisions of Sections 1.6, 1.7, 1.8, and Sections from 9.4 to 9.12 of the "Technical Regulations for Digitizing Topographic Maps at Scales of 1:10,000, 1:25,000, 1:50,000, and 1:100,000" issued by Decision No. 70/2000/QĐ-ĐC dated February 25, 2000 of the Director General of the Land Administration General Department.

Article 36. Names and Annotations on the Map

The names and annotations of topographic seabed map contents recorded in the measurement logbook shall be entered onto the map according to their coordinates and represented by corresponding symbols.

Article 37. Contents of Map Layers

The contents of the layers of the seabed topographic map are adjusted compared to the contents of the layers of the topographic map on land as follows:

Number KH (according to KH 1998)

a) Layer 5 (constant depth contour);

b) Layer 6 (annotation for constant depth contour).

b) Layer 6 (depth annotation)

Article 38. Elevation of Shoreline and Water Edge Lines

The elevation of shoreline and water edge lines on seabed topographic maps shall be determined as follows:

1. In cases where the shoreline and water edge lines are determined during field surveys, the elevations of these lines shall be based on the field survey measurements.

2. In cases where the shoreline and water edge lines have been determined on topographic maps of land or islands at a scale of 1:100,000, the elevations of these lines shall be based on the elevations of the topographic maps of land or islands.

Article 39. Establishment of Original Maps

The establishment of original maps for seabed topographic maps at a scale of 1:50,000 on land shall be carried out according to the Technical Regulations for Establishing Original Maps for Topographic Maps at a Scale of 1:50,000 on Land and the "Technical Regulations for Digitizing Topographic Maps at Scales of 1:10,000, 1:25,000, 1:50,000, and 1:100,000."

The inspection and acceptance of products of seabed topographic maps at a scale of 1:100,000 shall be conducted in accordance with the regulations of the Ministry of Natural Resources and Environment.

Article 41. Publication of Maps

The publication of seabed topographic maps at a scale of 1:100,000 shall be carried out in accordance with the regulations for publishing topographic maps at a scale of 1:100,000 for land areas.

Chapter VI

IMPLEMENTATION

Article 42. Implementation Provisions

This Circular shall take effect from September 15, 2011.

The Director of the Vietnam Administration of Seas and Islands shall be responsible for guiding, monitoring, and inspecting the implementation of this Circular. Any difficulties encountered during implementation shall be promptly reported to the Ministry of Natural Resources and Environment for study, amendment, and supplementation as appropriate.

Any difficulties encountered during implementation shall be promptly reported to the Ministry of Natural Resources and Environment for study, amendment, and supplementation as appropriate./.