How accurate are nautical charts?   3 comments

Charts will provide more information on “zone of confidence”

It is a major challenge – some might say an impossibility – to keep all thousand U.S. nautical charts up to date. But exactly how out of date is the chart data? Chart users will get a better idea now that Coast Survey is gradually rolling out a new chart feature called the zone of confidence, or “ZOC” box. It will replace the source diagram that is currently on large-scale charts. Source diagrams, and now the improved ZOC, help mariners assess hydrographic survey data and the associated level of risk to navigate in a particular area.

The first charts to show the new ZOC box are 18622, 18682, 18754, and 11328. They were released on April 7.

Both source diagrams and ZOC diagrams consist of a graphic representation of the extents of hydrographic surveys within the chart and accompanying table of related survey quality categories. Where the old source diagrams were based on inexact and sometimes subjective parameters, however, the new ZOC classifications are derived more consistently, using a combination of survey date, position accuracy, depth accuracy, and sea floor coverage (the survey’s ability to detect objects on the seafloor).

To see the zones of confidence on charts, look for the chart markings (A1, A2, B, C, and D) on the chart itself. Check the ZOC box (located on non-water portions of the chart) for the date of the data acquisition, the position accuracy, the depth accuracy, and characterization of the seafloor for each particular zone.

ZOC categories

Why do users need a “zone of confidence?

The age and accuracy of data on nautical charts can vary. Depth information on nautical charts, paper or digital, is based on data from the latest available hydrographic survey, which in many cases may be quite old. In too many cases, the data is more than 150 years old. Sometimes, particularly in Alaska, the depth measurements are so old that they may have originated from Captain Cook in 1778.

Mariners need to know if data is old. They need to understand the capabilities and the limitations of the chart. In particular, the mariner should understand that nautical chart data, especially when it is displayed on navigation systems and mobile apps, possess inherent accuracy limitations.

Before the advent of GPS, the position accuracy of features on a paper chart was more than adequate to serve the mariner’s needs. Twenty years ago, mariners were typically obtaining position fixes using radar ranges, visual bearings, or Loran C. Generally, these positioning methods were an order of magnitude less accurate than the horizontal accuracy of the survey information portrayed on the chart. Back then, Coast Survey cartographers were satisfied when we plotted a fix with three lines of position that resulted in an equilateral triangle whose sides were two millimeters in length at a chart scale of 1:20,000. In real world coordinates, the triangle would have 40-meter sides. Close enough!

Now, with GPS, charted locations that are off by 10 or 15 meters are not nearly close enough. Mariners now expect, just as they did 30 years ago, that the horizontal accuracy of their charts will be at least as accurate as the positioning system available to them. Unfortunately, charts based on data acquired with old survey technologies will never meet that expectation.

Source data is deficient by today’s standards

The overall accuracy of data portrayed on paper charts is a combination of the accuracy of the underlying source data and the accuracy of the chart compilation process. Most nautical charts are made up of survey data collected by various sources over a long time. A given chart might encompass one area that is based on a lead line and sextant hydrographic survey conducted in 1890, while another area of the same chart might have been surveyed in the year 2000 with a full-coverage shallow-water multibeam echo sounder.

In general, federal hydrographic surveys have used the highest standards, with the most accurate hydrographic survey instrumentation available at the time. On a 1:20,000-scale chart, for example, the survey data was required to be accurate to 15 meters. Features whose positions originate in the local notice to mariners, reported by unknown source, are usually charted with qualifying notations like position approximate (PA) or position doubtful (PD). The charted positions of these features, if they do exist, may be in error by miles.

Similarly, the shoreline found on most NOAA charts is based on photogrammetric or plane table surveys that are more than 30 years old.

Another component of chart accuracy involves the chart compilation process. Before NOAA’s suite of charts was scanned into raster format in 1994, all chart compilation was performed manually. Cartographers drew projection lines by hand and plotted features relative to these lines. They graphically reduced large-scale (high-detail) surveys or engineering drawings to chart scale. Very often, they referenced these drawings to state or local coordinate systems. The data would then be converted to the horizontal datum of the chart, e.g., the North American 1927 (NAD27) or the North American Datum 1983 (NAD83). In the late 1980s and early 1990s, NOAA converted all of its charts to NAD83, using averaging techniques and re-drawing all of the projection lines manually.

When NOAA scanned its charts and moved its cartographic production into a computer environment, cartographers noted variations between manually constructed projection lines and those that were computer-generated. They adjusted all of the raster charts so that the manual projection lines conformed to the computer-generated projection.

Many electronic chart positional discrepancies that are observed today originate from the past graphical chart compilation techniques. The manual application of survey data of varying scales to the fixed chart scale was a source of error that often introduced biases. Unfortunately, on any given chart, the magnitude and the direction of these discrepancies will vary in different areas of the chart. Therefore, no systematic adjustment can automatically improve chart accuracy.

Coast Survey is addressing the accuracy problem

NOAA’s suite of over a thousand nautical charts covers 95,000 miles of U.S. coastline, and includes 3.4 million square nautical miles of U.S. jurisdiction within the Exclusive Economic Zone (which is an area that extends 200 nautical miles from shore.) About half of the depth information found on NOAA charts is based on hydrographic surveys conducted before 1940. Surveys conducted with lead lines or single-beam echo sounders sampled a small percentage of the ocean bottom. Due to technological constraints, hydrographers were unable to see between the sounding lines. Depending on the water depth, these lines may have been spaced at 50, 100, 200, or 400 meters. Today, as NOAA and its contractors re-survey areas and obtain full-bottom coverage, we routinely discover previously uncharted features (some that are dangers to navigation). These features were either: 1) not detected on prior surveys; 2) man-made objects, like wrecks and obstructions, that have appeared on the ocean bottom since the prior survey; or 3) the result of natural changes that have occurred since the prior survey.

Coast Survey is also improving our chart production system. As NOAA developed its charts over the centuries, cartographers relied on separate sets of data: one set for traditional paper charts, and another for the modern electronic navigational charts. We are currently integrating a new charting system that will use one central database to produce all NOAA chart products. The new chart system slims down the system while it beefs up performance, speeding new data and updates to all chart versions of the same charted areas and removing inconsistencies.

As always, NOAA asks chart users to let us know when you find an error on a NOAA chart. Just go to the discrepancy reporting system, give us your observation, and we will take it from there.

Posted April 8, 2016 by NOAA Office of Coast Survey in Cartography, Nautical charts

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U.S. Coast Pilot goes interactive   4 comments

Coast Survey published its earliest version of the United States Coast Pilot in 1858, as Appendix No. 44 in Coast Survey’s Annual Report. The publication, organized into nine regional volumes, provides navigational information that can’t fit on nautical charts.

The U.S. Coast Pilot has gone through many iterations over the last 158 years. In the last century, we’ve added more information and added color to the historically black and white copy. More recently, we began posting book files on the web for easy download. We have now taken the next major step, enabled by interactive digital technology, to give boaters an enhanced and more accessible product. (Please note, the improved version is not mobile-friendly. You should use a tablet or larger screen.)

Breakthroughs in digital editing and publishing have allowed us to produce the U.S. Coast Pilot in a digital format called extensible markup language (XML). People won’t notice a difference from the original format — it looks the same as the paper copy — but the online version has some neat interactive features. To find them, go to the U.S. Coast Pilot, select your volume, and then click on a chapter in the left hand HTML column.

This new version of the U.S. Coast Pilot is formatted for reading on the web. Certain place names and objects, highlighted in green, are now directly view-able on a nautical chart and linked to entries in the official U.S. Geographic Names databaseSome other features include:

  • images that embiggen when clicked;
  • an interactive table of contents for each book; and
  • raster nautical chart links (highlighted in light blue) that can be viewed with each section in the book.
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This screen grab of Coast Pilot’s HTML version shows the links to nautical charts, geotags to place names, and links to federal regulations.

Coast Survey updates the Coast Pilot weekly, and now readers can see where we made changes. The system automatically highlights changes (in gray), and retains those highlights until the next annual version is published. (The print-on-demand paper copy contains all updates made up to the time of printing.) The annual versions are published on a staggered yearly schedule.

Contact coast.pilot@noaa.gov with any questions or comments about the Coast Pilot, the format, downloads, or XML code.

Posted March 29, 2016 by NOAA Office of Coast Survey in U.S. Coast Pilot

Maria Mitchell: Coast Survey’s “indefatigable comet-seeker”   Leave a comment

Among women trailblazers, there is one who may not be sufficiently recognized: Maria Mitchell, the first female professional employed by Coast Survey. March is Women’s History Month, so it is especially appropriate to introduce this extraordinary woman to the Coast Survey audience.

According to the National Women’s History Museum, Mitchell “probably was the first woman employed in a professional capacity by the federal government. Although women had been hired as cooks, laundresses, etc., her 1849 employment appears to be the first case of a woman earning an annual salary for work based on knowledge of an academic field.”

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August 1, 1818 – June 28, 1889

Actually, Coast Survey records indicate that she began her Coast Survey career in August 1845, when the agency hired her as an astronomic observer, based in Nantucket. Coast Survey Superintendent Alexander Dallas Bache asked Marie and her father, William Mitchell, to assist in observations associated with a project to establish a cardinal point for latitude and longitude for the United States and North America. Records indicate that Bache paid her $300 a year.

Retired NOAA Captain Albert “Skip” Theberge has woven Maria Mitchell’s story into his history of the U.S. Coast Survey.

“Bache’s progressive, although somewhat tight-fisted, views on managing personnel led to the Coast Survey being the first federal agency to hire women for professional work both within its ranks as permanent personnel and on a contract basis. The astronomer, Maria Mitchell of Nantucket, was the pioneer in this radical departure from custom,” Theberge writes.

Maria distinguished herself from the outset. On January 15, 1846, William Mitchell wrote to Bache, “I may say then that about all the moon culminations, since Loomis left us, have been taken (when visible) except through a part of one lunation, when Maria and myself were absent at Worcester. Maria alternates with me in these with a zeal (shall I also say skill?) very gratifying to an old man.”

On October 1, 1847, Maria used a telescope to discover a comet. “Her discovery was a major step in establishing her fame as the foremost nineteenth century woman scientist in the United States,” Theberge observes.

People today might find it strange to discover that there was actually an internal agency debate on whether to publicize Maria Mitchell’s association with the Coast Survey. Her own father wrote to Bache in 1848, expressing fear that some of the less enlightened members of Congress might note “…why, he employs a woman what a waste of money.”

Fortunately, Bache was not swayed by such concerns. He wrote a congratulatory note to “the lady astronomer in whose fame I take personal pride as having in some degree helped to foster the talent which has here developed… We congratulate the indefatigable comet-seeker on her success; is she not the first lady who has ever discovered a comet? The Coast Survey is proud of her connection with it…”

Phebe Kendall Mitchell, Maria Mitchell’s sister, picks up Maria’s history:

“In 1849 Miss Mitchell was asked by the late Admiral Davis [Charles Henry Davis], who had just taken charge of the American Nautical Almanac, to act as computer for that work, – a proposition to which she gladly assented, and for nineteen years she held that position in addition to her other duties… In this year, too, she was employed by Professor Bache, of the United States Coast Survey, in the work of an astronomical party at Mount Independence, Maine.” (Kendall, P.M. 1896. Maria Mitchell Life, Letters, and Journals. p. 24. Lee and Shepard Publishers, Boston.)

Posted March 24, 2016 by NOAA Office of Coast Survey in Nautical charts

NOAA begins 2016 hydrographic survey season   Leave a comment

New data will update nautical charts around the country

As sure as spring arrives, NOAA vessels and independent contractors are hitting the seas for the nation’s 182nd hydrographic surveying season, collecting data for over two thousand square nautical miles in high-traffic U.S. coastal waters.

NOAA Ship Ferdinand Hassler heads out to survey.

NOAA Ship Ferdinand Hassler heads out to survey.

“Nautical charts are the foundation for the nation’s maritime economy, and NOAA hydrographers spend months at sea, surveying critical areas to ensure safe navigation for the shipping, fishing, and boating communities,” said Rear Admiral Gerd Glang, director of the Office of Coast Survey.

“Spring is the traditional beginning of the survey season,” Glang explained. “After a winter of data processing, ship maintenance, and personnel refresher training, the NOAA survey ships and Coast Survey navigation response teams are anxious to get to their survey assignments.”

U.S. waters cover 3.4 million square nautical miles, including a seafloor that is constantly changing due to storms, erosion, and development. To keep the nation’s suite of over a thousand nautical charts up to date, the Office of Coast Survey annually plans hydrographic survey projects to measure water depths and identify new navigational hazards. Survey planners consider requests by marine pilots, port authorities, the Coast Guard, the boating community and others when setting the year’s schedule.

Planned 2016 survey projects

  • Penobscot Bay, Maine, most of which hasn’t been surveyed since the 1950s, will get its first modern NOAA multibeam echo sounder survey, to acquire data for needed chart updates.
  • Buzzards Bay, Massachusetts, is the subject of a multiyear project for updating charts. 2016 is the third year, and the survey ship will validate U.S. Geological Survey interferometric survey data for charting, and will align with NOAA’s Remote Sensing Division lidar data.
  • Chesapeake Bay is also the subject of a multiyear survey project for updating charts. NOAA Ship Ferdinand R. Hassler will work offshore, while launches from NOAA Ship Thomas Jefferson will survey in the vicinity of Hampton Roads concurrent to the ship’s maintenance period in drydock.
  • Wilmington, North Carolina, survey project will support the U.S. Coast Guard Atlantic Coast Port Access Route Study.
  • Savannah, Georgia, needs hydrographic survey data for the port deepening project in preparation for post-Panamax ships.
  • Sabine, Louisiana, will have a continuation of last year’s project to survey part of the approaches to Port Arthur and Calcasieu.
  • Atchafalaya, Louisiana, will have a continuation of last year’s project to survey part of the approaches to Morgan City.
  • Approaches to SW Pass, Louisiana, will be surveyed at the request of the U.S. Coast Guard and the Bureau of Ocean Energy Management, to provide new chart data for consideration of a proposed anchorage area near Port Fourchon.
  • Chandeleur Sound, Mississippi, will have surveys to acquire critical updates since Hurricane Katrina.
  • Yukon River, Alaska, will be partially surveyed to validate a new charting approach using satellite-derived bathymetry.
  • Etolin Strait, Alaska, will also validate satellite-derived bathymetry data, as well as establish a survey corridor between Nunivak Island and mainland Alaska. This project will provide data for some of the new charts identified in the U.S. Arctic Nautical Charting Plan.
  • Dutch Harbor, Alaska, will benefit from a shore-based survey operation simultaneous with a NOAA Fishpac project, as the ship’s smaller launches will acquire more data at the site of the 2015 M/V Fennica grounding.
  • Kodiak Island, Alaska, will have another year of a multi-year surveying campaign in this critical area for increasing fishing and tourism.
  • Prince of Wales Island, Alaska, needs updated survey data to improve charts to Tlevak Strait, expanding to Sukkwan Strait and Howkan Narrows.
  • Behm Canal, Alaska, will get its third (and final) year of survey work to circumnavigate Revillagigedo Island as well as George and Carol Inlet, Alaska.

The surveys will be conducted by NOAA’s four dedicated survey ships ‒ Thomas Jefferson, Ferdinand Hassler, Rainier, and Fairweather ‒ and private companies that survey on a contract basis with NOAA. The NOAA ships are operated and maintained by the Office of Marine and Aviation Operations, with hydrographic survey projects managed by the Office of Coast Survey.

The schedule for Coast Survey’s navigation response teams (NRTs), 3-person boats that work closer in shore to acquire data for nautical chart updates, was announced earlier.

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New tips for understanding nautical chart symbols   1 comment

SymbolGlobeAs a responsible boater, you examine your nautical chart before sailing, determined to avoid problems during a nice trip along the coast. Charts are packed with symbols and abbreviations, so you might refer to the free copy of U.S. Chart No. 1, which lists all of the symbols used on NOAA nautical charts. It is an excellent quick reference for identifying unfamiliar symbols.

However, sometimes mariners need a deeper understanding…

Coast Survey is now providing additional information about complex or particularly confusing chart symbols to augment what is available in U.S. Chart No. 1. The first two tip sheets are available now. Coast Survey will add more chart symbology tip sheets to the U.S. Chart No. 1 webpage as the need arises.

Understanding NOAA chart symbology

K46.1 - FishHaven

Fish havens: The typical U.S. Chart No. 1 entry, such as this one for fish haven, lists only the name and the symbols. The tip sheet explains what fish havens are, what they look like in context with other charted features, and what restrictions may apply to them.

AnchorageSymbols

Anchorages and harbors of refuge: The anchor symbol has been used for decades to represent an anchorage on U.S. nautical charts, but the specific meaning of the symbol has evolved over the years. The tip sheet explains what the symbol means now – and, perhaps more importantly, what it doesn’t mean.

Questions or suggestions? Email USChart1@noaa.gov.

Posted March 1, 2016 by NOAA Office of Coast Survey in Cartography, Nautical charts

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Coast Survey uses unmanned technology to find submerged danger to navigation   Leave a comment

Coast Survey has been discovering and marking the locations of underwater dangers since our surveyors took the nation’s first official ocean soundings in 1834. We’ve used or developed all the technological advancements – lead lines, drag lines, single beam echo sounders, towed side scan sonars, and post-1990 multibeam echo sounders – and now we can point to a new major advancement for fast deployment and quick recovery. In February, Coast Survey’s Mobile Integrated Survey Team (MIST) used an autonomous underwater vehicle (AUV) to locate a submerged buoy that was interfering with anchorages in the Chesapeake Bay.

“You and the crew of the HASSLER put us right where we needed to be!” said a confirmation email from the U.S. Coast Guard to NOAA Lt. Ryan Wartick, one of Coast Survey’s navigation managers. “Thanks for the great work!”

The problem began in early February, when an outbound tug struck and dragged a very large buoy and its anchor to an unknown location in the vicinity of Chesapeake Bay’s Thimble Shoal Channel. The U.S. Coast Guard closed adjacent anchorages because of the potential danger to navigation posed by the submerged buoy, affecting commercial vessel operations in the area.

On February 9, Lt. Wartick sat down with the U.S. Coast Guard, and other local and federal agencies, to arrange for Coast Survey mobilization in a collaborative effort to find the missing G “11” buoy. The Coast Guard asked Coast Survey to search Anchorage “A” on Friday, February 12, and provided a 45-foot vessel for our use.

AUV preparation

Lt. Ryan Wartick and MIST responder Robert Mowery prepare the AUV for deployment.

Coast Survey’s MIST responders Robert Mowery and James Miller were able to pack up the AUV in Maryland and drive to USCG station on Naval Little Creek amphibious base, where they set up, calibrated, and hit the water on February 12 – and promptly located five potential targets, one of which looked especially promising.

buoy

AUV’s image of buoy

This side scan imagery, acquired by the Hydroid REMUS 100 AUV during the Coast Survey MIST initial search on February 12, shows the sunken buoy – although, at that time, the team was not 100% confident it was the buoy. The intensity of the sonar return and the dimensions of the target strongly supported their suspicion that this was the buoy, but the target was at nadir on the side scan profile, which introduces uncertainty in this type of system. They did, however, deem it the most likely among the five possible targets revealed by the AUV data.

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Fortunately, NOAA Ship Ferdinand Hassler was departing Norfolk on February 17, on their way to their survey project for the approaches to the Chesapeake, and so they made a slight adjustment in their route. The ship’s hydrographers used their multibeam echo sounders to check the targets, based on the MIST AUV data, and they confirmed that the top AUV target was indeed the buoy. The multibeam data also verified that none of the other search targets pose a danger to navigation or risk fouling an anchor for ships in the anchorage.

With the confirmation, the U.S. Coast Guard was able to remove the buoy and re-open the area for maritime traffic.

Buoy is recovered.

Buoy is recovered.

The Coast Survey Development Lab has been evaluating the use of autonomous underwater vehicles as tools for hydrographic surveying in support of NOAA’s nautical charting mission. The use of AUVs, in collaboration with NOAA’s manned survey fleet, could greatly increase survey efficiency. Additionally, as this response confirmed, their flexible deployment options make AUVs a valuable tool for marine incident response.

Happy 209th anniversary to the Office of Coast Survey, the oldest federal scientific organization   3 comments

The Office of Coast Survey dates from 1807, when much of the commerce between the states was by coastal shipping. And all foreign trade, especially critical to our prosperity, had to come by ship. With so many ships coming into our ports and harbors, shipwrecks were common, and it was clear the young maritime nation needed accurate nautical charts.

NINTH CONGRESS OF THE UNITED STATES
At the Second Session,
Begun and held at the city of Washington, in the territory of Columbia,
on Monday the first of December, one thousand eight
hundred and six.

AN ACT to provide for surveying the coasts of the United States.

Be it enacted by the Senate and House of Representatives of the United States of America, in Congress assembled, that the president of the United States shall be, and he is hereby authorized and requested, to cause a survey to be taken of the coasts of the United States, in which shall be designated the islands and shoals, with the roads or places of anchorage, within twenty leagues of any part of the shores of the United States; and also the respective courses and distances between the principal capes, or head lands, together with such other matters as he may deem proper for completing an accurate chart of every part of the coasts within the extent aforesaid.

Sec.2. And be it further enacted, that it shall be lawful for the president of the United States, to cause such examinations and observations to be made, with respect to St. George’s bank, and any other bank or shoal, and the soundings and currents beyond the distance aforesaid to the gulph stream, as in his opinion may be especially subservient to the commercial interests of the United States.

Sec. 3. And be it further enacted that the president of the United States shall be, and he is hereby authorized and requested, for any of the purposes aforesaid, to cause proper and intelligent persons to be employed, and also such of the public vessels in actual services, as he may judge expedient, and to give such instructions for regulating their conduct as to him may appear proper, according to the tenor of this act.

Sec. 4. And be further enacted, that for carrying this act into effect there shall be, and hereby is appropriated, a sum not exceeding fifty thousand dollars, to be paid out of any monies in the treasury not otherwise appropriated.

[signed] Nathan Macon, Speaker of the House of Representative
[signed] Geo. Clinton, Vice President of the United States, and President of the Senate

I certify that this act did originate in the House of Representatives.
[signed] John Beckley, Clerk

February 10, 1807
Approved
[signed] Thomas Jefferson

See the NOAA library for more resources on Coast Survey heritage

An Act

Posted February 10, 2016 by NOAA Office of Coast Survey in History

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