Further details have emerged from the US National Geospatial Intelligence Agency, of the digital chart error that contributed to the grounding of the USS Guardian on the ecologically-sensitive World Heritage Site Tubbataha reef. Although the incident involved a military vessel using a military digital chart, DNC, there are lessons for the civilian sector.
Tubbataha Reef was incorrectly positioned on the coastal scale Digital Nautical Chart — the coastal DNC showed it about 8 nautical miles from where it should have been. It was correctly positioned on the general scale DNC, and on the standard paper chart.
It all began with phantom islands, charted islands that actually did not exist. Two examples are Sandy Island in the Coral Sea which was ‘undiscovered’ formally in 2012 although questioned in 2000 by radio hams, and Dougherty Island near Australia, now believed to have been an iceberg.
Christine Phillips, public affairs officer with the NGA, says: “Prior to 2008, the charts in use included a number of “phantom islands” – the charts indicated islands that did not exist. In response to customer requests to address that problem, NGA used LANDSAT-derived imagery to update the charts. One of these images included incorrect information about the location of the section of ocean that includes the Tubbataha Reef. At the time, no other source information existed to validate that imagery data. As a result, the reef was incorrectly placed in the DNC. That was the first factor”.
Procedures are in place to capture such errors but in an example of the human element at work those procedures were not followed. Says Ms. Phillips: “In 2011, NGA obtained survey data that corrected this positioning. Due to a failure to follow established procedure, this correction was made in one portion of the DNC, but not in another.
“A single source of data is never ideal, and we use multiple sources to validate information wherever possible. As mentioned earlier, we continuously receive new and better information, from a number of sources. As more information is available from more parts of the world, we will have fewer regions where only one source of information exists. That will decrease the risk of errors like this one.”
According to Ms Phillips a ‘very tiny’ portion of the Digital Nautical Chart is derived from the same type of source data that was at the core of this issue. The remainder of the DNC holdings are drawn from multiple corroborated sources such as hydrographic surveys, information from ships at sea, and U.S. and international nautical charts, to name just a few. “As a result, we are confident in the integrity of that data”.
“That said, we are going to further review our production processes – including everything from procedures to training and qualifications to resourcing — to determine whether they could be improved. We are assembling a team of experts from across the maritime community — both inside and outside NGA — to assist.”
The error in the placement of the Tubbataha Reef in the Digital Nautical Chart was an exception, not a systemic problem, says the NGA: “And while no navigational aid is flawless, NGA is confident that the Digital Nautical Chart is safe for use in navigation
following a downloaded patch. The Chief of Naval Operations concurred with this assessment in a second message sent to the Fleet on 22 January”.
Following the grounding the NGAvery quickly determined that the primary issue in the misplacement was related to LANDSAT-based commercial imagery. Says Ms Phillips: “From January 17 through the morning of January 22, we examined and validated the accuracy of every situation in the Digital Nautical Chart where that type of data was used.
“In total, NGA reviewed DNC charts that cover more than 116 million square nautical miles of ocean. In that review, we identified only one issue of magnitude similar to the misplacement of the Tubbataha Reef. This error, which appeared on both the paper chart and the Digital Nautical Chart, rotated the placement of the southern coast of Chile toward the sea; at its widest, the discrepancy was 7,000 metres. In accordance with our standard procedures, NGA warned mariners to “navigate with caution” in this area when the error was discovered on January 20.
“A total of 25 chart areas – less than one percent of the total DNC holdings — included inaccuracies that required additional scrutiny. Only two of those – the Tubbataha Reef and the Chilean coast – were cause for concern”.