Proceedings Of The Marine

SUM 2015

Proceedings magazine is a communication tool for the Coast Guard's Marine Safety & Security Council. Each quarterly magazine focuses on a specific theme of interest to the marine industry.

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13 Summer 2015 Proceedings ActiveCaptain report of shoaling in Plymouth Harbor, Massachusetts. The navigational aid has been moved to the edge of the shoal, but the chart is not yet updated. In the image below, the same area, with estimated bathymetry that corroborates the report of the shoal, and shows the extent. maps and aerial photography. They are quick to load and zoom, and require little display logic, so they are now in widespread use in mobile apps, computer-based charting systems, chart plotters, and Web maps. While the tiles are provided for free to the end user, the overhead and complexity of re- sampling and redistributing the charts means that they are not frequently updated — most services only update charts annually. NOAA will soon maintain a tile service, in two forms: • an online tile service, hosted on NOAA servers, that is suitable for use in a Web map or a geographic information system; • stand-alone, portable tile packages that are suitable for disconnected applications such as chart plotters and mobile apps. These offine tiles can be replaced completely, or updated with only the individual tiles that have changed, saving precious bandwidth at sea. Survey Priority So now we can update charts quickly, get them to customers rapidly, and integrate them with other environmental intelligence to support better risk management. However, the obser- vational system that supports charting is still tuned to measure decadal changes, not annual changes. We cannot afford to re-observe and recompile all the charts every year, just because some areas have changed, so we need to focus our limited survey capacity on the most changeable areas. But where to survey? Fortunately, we have modern tools to help us with that as well. We have always welcomed reports of chart discrepancies, such as migrating shoals or new wrecks — charts are littered with notations like: "Shoal reported, 1994," and "Wreck, PA" (position approximate). These are clear signals of changing areas and have tradition- ally guided our survey requirements to some extent. We can now supplement these reports with newly available information: • Crowdsourced discrepancies. NOAA has signed an agreement with ActiveCaptain, an online interactive cruising guide, which gives NOAA access to all of ActiveCaptain's crowdsourced hazard reports. These are often very detailed, with corroboration from mul- tiple observers. • Satellite-derived bathymetry. In clear, shallow water, it is possible to estimate water depth from satellite images. While these estimates are not reliable enough to be the sole source for charted depths, they give us clear indica- tion of change. • Automated Identification System logs. NOAA has access to commercial and USCG-logged AIS databases that show vessel transit details. Occasionally, these show vessel behavior patterns that are not consistent with the chart, such as when vessels transit over land (indicating the land is no longer there), or depart consis- tently from the charted safe water route. More valuable, however, is the insight that the AIS traffc gives us into traffc patterns, which allows us to prioritize some chart discrepancies over others, based on the likelihood that it will affect vessel traffc. • Ubiquitous satellite imagery of coastlines. There are numerous free Web services that provide a base layer

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