What are Limited Content ENCs?
In 2021 the Danish Geodata Agency (DGA) began an initiative to increase the speed of release of Electronic Navigational Charts (ENCs) coverg southwest Greenland. The goal is to release ENCs referred to internally as ‘Limited content ENCs’. These ENCs contain a newly georeferenced coastline and depth information derived only from modern multibeam survey information. Areas with depth information derived from multibeam surveys are hereafter referred to as "multibeam areas". Other information essential for safe navigation such as Aids to Navigation are also included. However, other information outside of the multibeam areas or not deemed essential is not captured. These ENCs are normal, standard ENCs that conform to the same international standards, pass the same internal validation as our existing ENCs and are distributed through the normal channels. Once released, these ENCs follow the same updating regime as existing ENCs.
Background:
DGA has a planned work program to replace the . This work has been underway for many years. The main benefit of these new charts is to publish products suitable for satellite navigation, with an accurate georeferenced coastline and depth information derived from modern multibeam surveys.
When the new paper charts and ENCs are produced they are often a mixture of new survey data and older bathymetric data from a range of sources such as single beam survey data, reported tracks of soundings, lead line measurements etc. It can take a long time to safely deconflict positional issues between modern surveys and older bathymetric information, which can slow the production process.
A decision was made to release depth information only derived from the modern multibeam data in an ENC format, where it is available, to provide safer navigation for the mariner. Often these modern surveys cover areas that have very limited published information. These ENCs are termed as ‘Limited content ENCs’. The older bathymetric information is not included at this stage but will be included when both the paper and ENC products are brought up to full content in the future.
Benefits:
The benefit to the mariner is that this releases modern, reliable depth information in areas that are often currently poorly covered, increasing safety to the mariner. These ENCs will also allow for satellite navigation to be used as they are positionally accurate.
Another benefit is that the modern data will be available for use by mariners, potentially years ahead of schedule.
What the mariner needs to be aware of:
Not all information is included in Limited Content ENCs, therefore it is important that the mariner is aware when they will need to refer to the existing paper chart and navigational publications for full information. It is important that mariners refer to existing paper charts if they navigate outside of the charted multibeam areas.
| Feature |
Limited Content ENC |
Older paper chart |
Full content ENC & modern paper chart |
| Depth information |
Modern multibeam only. Sea areas outside of multibeam are captured as Unsurveyed Areas (UNSARE) |
Existing published depth information from a variety of sources. May not include modern multibeam. |
Modern multibeam and older depth data |
| Coastline |
Modern georeferenced coastline |
Old coastline, potentially not positionally accurate |
Modern georeferenced coastline |
| Aids to Navigation |
Full cell content |
Full content |
Full cell content |
| Submarine and overhead cables |
Full cell content |
Full content |
Full cell content |
| Wrecks |
Within multibeam survey area only |
Full content |
Full cell content |
| Obstructions |
Within multibeam survey area only |
Full content |
Full cell content |
| Rocks (underwater a awash) |
Within multibeam survey area only |
Full content |
Full cell content |
| Topographical data (land elevations, land featyres) |
Not captured unless a landmark feature is part of an Aid to Navigation |
Full content |
Full cell content |
| Place names |
Not captured |
Full content |
Full cell content |
Table 1., Summary of featyre content between Limited Content ENCs ands older paper charts
The 1960s paper charts are not being updated for the modern surveys, as they will be replaced in the near future by a modern correctly georeferenced paper chart, which will include the modern surveys. This means there may be discrepancies between the ENCs and the 1960s paper charts. It is possible to identify a paper chart produced from older data as this is highlighted on the paper charts in the Notes section ‘Accuracy of the Chart’, under the chart title. The positional accuracy of depth information is reflected in the ENC in the Quality of Data (M_QUAL) meta feature and the Category Zone of Confidence (CATZOC) attribution. However, all modern surveys have been assessed against the existing published data, including the 1960s (and older) paper charts and if any safety critical information was found this has been released through the Notice to Mariners or Chart Corrections service.
It should also be noted there has been a shift in naming policy. Newly produced ENCs and paper charts use modern Greenlandic spelling and place names. Older products will still contain older Greenlandic spelling. These will be modernised as new products are produced.
When the Limited Content ENCs are brought up to full content and the new paper chart is released, there will no longer be significant discrepancies between the products.
How do I know which cell is Limited Content and which are Full content?
The difference between Limited Content ENCs and Full content ENCs is not immediately obvious.
DGA draws the mariner’s attention to the Limited content ENCs in two ways:
- There is a Nautical Publication Information (M_NPUB) feature captured over the whole area of the Limited Depiction ENC coverage area.
- There is a Caution Area (CTNARE) feature captured over the depth areas, from the coastline seaward. This CTNARE will trigger an alarm on the ECDIS to draw attention to the mariner.
LIMITED ENC DEPICTION:
Features in this area are limited to include only multibeam surveys, coastline derived from modern imagery and aids to navigation. Most other features, including bathymetry from older sources, are omitted in areas outside of multibeam surveys. Electronic Navigational Charts (ENCs) with areas of limited ENC depiction provide ENC users with multibeam bathymetry at a best scale where previously there was only smaller scale or no ENC coverage. Mariners are advised to refer to published Standard Nautical Charts for additional content outside multibeam areas.
Where can I get Limited Content ENCs from?
Limited Content ENCs are distributed and updated in the same manner as existing ENCs. Ships with their own IMO number can buy ENCs via a Value Added Reseller (and their distributor network) under IC-ENCs distribution network as they are released.
Further information can be found at the following link:
Progress to date and expected deadline
So far 37 Limited Content ENCs have been released in SW Greenland, with a goal for the final Limited Content ENCs to be published by the end of 2023. The process will then continue by bringing the ENCs up to full capture
Summary
In summary, DGA has been distributing Limited Content ENCs since 2021. They provide a method to speed up the delivery of modern multibeam depth information which can be used for satellite navigation, to the mariner. However, not all features are captured on these ENCs and the mariner must use other existing paper charts to supplement these ENCs. Guidance is given in this document on what the difference in content is and how to identify Limited content ENCs.