Alaska’s nautical charts need to be updated — we all know that. The diagram below shows the vintage of survey data currently used for today’s charts in Alaska. The graphic includes all surveys done by NOAA’s Office of Coast Survey (and its predecessors), and some limited data acquired by other agencies, i.e., the U.S. Coast Guard. Areas that are not colored in have never been surveyed or have data acquired by another source — from Russia or Japan, for instance — before the U.S. was responsible for charting in that area.
What are the differences between data collected in 1900, 1940, or 1960? Let’s take a look at a…
Brief Historical Sketch of Survey Technologies
Nautical charts have a lot of information, but mariners especially are concerned with two major components: water depths (known as “soundings”) and obstructions (like underwater seamounts or wrecks).
Different eras used different technologies to find, measure, and determine the position of the two components. Note that adoption of new systems does not happen abruptly; rather, new technologies are phased in as techniques and equipment improves.
Measuring Water Depth (Soundings)
3.7 million years ago to present day: sounding pole
It isn’t inconceivable that the earliest humanoid, Australopithecus afarensis, used sticks to gauge water depths before crossing streams and rivers. People still do it today.
Note the ancient Egyptian on the far right, using a sounding pole.
~ 2000 B.C. to 1930s: lead line
As good as they were for their eras, 19th and 20th century surveyors faced technological challenges. The first challenge was accounting for gaps between depth measurements. The second was the inability to be totally accurate in noting the position of the measurement. (In other words, a specific location out in the ocean may be 50 feet deep, but a surveyor must also accurately note the position of that specific location.)
This surveyor is casting a lead line.
Early Coast Survey hydrographers measured depths by lead lines — ropes with lead on one end — that were lowered into the water and read manually. Even though soundings were generally accurate, coverage between single soundings was lacking. And we need to remember that this was before the age of GPS. While sextants gave accurate positions when a hydrographer could fix on a shoreline feature, the further offshore the survey, the less accurate the position.
(Interesting fact: Hydrographers still use lead lines occasionally, in some circumstances — but not for a complete survey.)
There have been variations on lead lines through the centuries. From 1492 to the late 1870s, for instance, mariners used hemp rope for deep-sea soundings.
(Interesting fact: Christopher Columbus and Ferdinand Magellan each tried to measure mid-ocean depths with about 1,200 feet of hemp rope. Neither one of them found the sea bottom.)
In 1872, the hemp was replaced by small diameter piano wire (again, primarily for deep-sea work), and the weight of the lead was increased. Later, hydrographers added a motorized drum to wind and unwind the line, with a dial to record the length of the line.
(Interesting fact: In 1950, the British ship Challenger used piano wire in the first sounding that established Mariana Trench as the deepest place on earth.)
20th century to the present: echo sounders
Compare the bottom coverage achieved by the different survey methods.
1918 to 1990s: single beam echo sounder
Sonar came into its own in 1913. The first echo sounders (also known as “fathometers”) had single beams that measured the distance of the sea floor directly below a vessel. The echo sounders were able to take many more depth measurements than was possible with the lead line, but the technique still resulted in gaps between the lines where the beam measured the water depth.
The U.S. Coast and Geodetic Survey (a NOAA predecessor agency) adopted this acoustic sounding technique in 1923, installing it on USCGS Ship Guide. But full-fledged change didn’t happen right away. These early sounding systems were too large to install on survey launches used in harbor and inshore work, so from 1924 until the early 1940s many surveys were still conducted with a lead line, and many were totally acoustic — and some were hybrid, using soundings from both methods, depending on coverage area and seafloor configuration.
→ 1940: U.S. Coast and Geodetic Survey fully adopts single beam echo sounding technology
The development of smaller “portable” fathometers for shallow waters, about 1940, was a primary impetus in the obsolescence of lead line as survey technology and the adoption of acoustic systems. The development of World War II electronic navigation systems for bombing purposes led to the development in 1945 of the first survey-quality electronic navigation systems, which allowed for more accuracy in positioning.
1964 to current day: multibeam echo sounder
By mid-century, scientists were increasing the beams projected by the echo sounder, to get a broader swath of measurements. The multibeam echo sounder was developed for the Navy in 1964, but it remained secret until the late 1970s when commercially available systems were developed.
Coast Survey first used a MBES technique, called the “Bathymetric Swath Survey System,” in 1977 on NOAA Ship Davidson, for depths ranging from 160 to 2,000 feet. In 1980, NOAA Ship Surveyor installed a deep-water MBES system called “Sea Beam,” for depths from 1,600 to 33,000 feet.
About 1986, Coast Survey began using GPS to calibrate medium-frequency navigation systems while operating in the far reaches of the United States Exclusive Economic Zone. By the mid-1990s, GPS was the primary control for accurate positioning.
→ 2000: Coast Survey fully adopts multibeam surveying
By 2000, Coast Survey was performing full-coverage multibeam hydrographic surveys for charting purposes. NOAA survey ships now use multibeam echo sounders that measure navigable coastal depths from 45 to 1,000 feet. For shallower and more constricted waters, the ships deploy hydrographic survey launches with multibeam echo sounders that efficiently and safely survey areas from 12 to 200 feet deep. These systems make it possible to acquire 100% sea floor coverage in the survey grounds (excluding ultra-shallow, near-shore, or obstruction areas).
Finding Underwater Obstructions
1880s to early 1990s: wire drag
Surveyors used wire drag, not as a sounding system but as a way to look between the sounding lines to find obstructions to navigation and establish safe navigational channels. The first documented wire drag was conducted in the 1880s, in French Indochina, Gulf of Tonkin area, attaching the wire to buoys at each end and letting it drift with tidal currents.
Around 1900, the U. S. Lake Survey developed the technique of using a ¼-mile wire drag between two boats. In 1903, Coast Survey began using the technique, and within a few years was using it extensively in Alaskan waters as they looked for pinnacle rocks. Coast Survey’s Alaska wire drags were up to 3.5 miles long. (Initially, “least depths” over discovered obstructions were determined by lead line, then acoustic means and, ultimately, by divers with depth/pressure gauges.)
Survey vessels conduct wire drag operations.
1960 to present day: side scan sonar
Side scan sonar is essentially the sonar equivalent of an aerial photograph. It improves the ability to identify submerged wrecks and obstructions. Evolving from submarine detection sonars of World War I and World War II, side scan sonar was fairly well developed by 1960, when the United Kingdom Hydrographic Office started using it regularly with their surveys.
→ 1990: Coast Survey fully adopts side scan sonar for East Coast and Gulf Coast surveys
NOAA Ship Whiting used the technology in 1984-1985 for approaches to New York. U.S. Coast Survey fully adopted side scan sonar (in place of wire drag) in the early 1990s.
Side scan sonar operations use “towfish” like this one, lowered into the water and towed from the back of the vessel.
Side scan sonar captures images of objects, which improves the ability to identify submerged objects.
Today’s Charts Reflect Different Tech Eras
Each of NOAA’s 1000-plus nautical charts, even today, can contain information collected by any or all of these sounding and positioning techniques.
Most nautical charts are an amalgamation of geospatial information collected using different techniques at different times. For example, one area of a specific current-day nautical chart might be based on a lead line and sextant survey conducted in 1910, and another area on the same chart might be based on a multibeam and GPS survey conducted in 2010. If we dig deep enough, we will probably find a sounding or two from the 18th century British explorer, Captain James Cook.
NOAA cartographers mold this disparate information so that it fits together as a coherent representation of the geographic area.
So when was the data acquired for the chart you’re using? NOAA cartographers add a “source diagram” to large-scale charts. (See the diagram on the current chart 16240, pictured below.) Check yours. That will give you the years of the surveys… and now you have a better idea on the technology used by the surveyor.
This is the source diagram on nautical chart 16240.
In 2015, NOAA survey ships Thomas Jefferson and Ferdinand R. Hassler are scheduled to survey nearly 1,800 square nautical miles in the U.S. coastal waters of the lower 48 states, collecting data that will update nautical charts for navigation and other uses. In Alaska, NOAA ships Fairweather and Rainier will increase their Arctic operations, planning to acquire 12,000 nautical miles of “trackline” depth measurements of the U.S. Coast Guard’s proposed shipping route. (See this NOAA article.) The ships will also conduct several “full bottom” hydrographic survey projects, acquiring data from over 2,800 square nautical miles in survey areas along the Alaskan coastline.
We are also planning several projects for our contractual private sector survey partners, and those projects will be announced after work orders are finalized.
The Office of Coast Survey will manage the surveys that measure water depths and collect ocean floor data for charting, identifying navigational hazards, informing wind farm decisions, mapping fish habitats, and assisting with coastal resilience. Check the useful story map, 2015 Hydrographic Survey projects, for the survey outlines and more information. Coast Survey will update the map as weather and operational constraints dictate.
See the story map for all 2015 in-house projects.
Briefly, this year’s NOAA survey projects include:
1. Gulf of Maine, where chart soundings in heavily trafficked and fished areas are decades old and need updating for navigational safety
2. Buzzards Bay (Massachusetts and Rhode Island), where increased use of deeper-draft double-hull barges – and possible installation of marine transmission cable routes and wind energy development — requires updated soundings
3. Rhode Island Sound, where the Bureau of Ocean Energy Management has identified a wind energy lease area
4. Approaches to Chesapeake (North Carolina), where charts of critical navigational areas need updating for navigation and to assist the Bureau of Ocean Energy Management manage windfarm activity.
5. Approaches to Charleston (South Carolina), where updated soundings will provide the correct under-keel clearance information for the expected transit of larger and deeper-draft ships
6. Approaches to Savannah (Georgia), where the Savannah Harbor Expansion Project will increase the authorized depth of the harbor from 42 to 47 feet and updated soundings will provide the correct under-keel clearance information for the expected transit of larger and deeper-draft ships
7. Chatham Strait (Alaska), where charts need to be updated for cruise liners, ferries, Coast Guard cutters, Navy vessels, tugs, and barges that use this waterway on a regular basis or when avoiding storms in the Gulf of Alaska
8. Approaches to Kotzebue (Alaska), where deep-draft vessels have their cargo lightered to shore by shallow draft barges
9. Point Hope (Alaska), where shipping traffic is increasing due to receding ice but charted soundings are sparse and date back to the 1960s
10. West Prince of Wales Island (Alaska), where updated charts are needed by smaller vessels that use Televak Narrows as an alternate passage during foul weather
11. Shumagin Islands (Alaska), where Coast Survey needs data to create a new, larger scale, nautical chart
12. Port Clarence (Alaska), where Coast Survey needs data to create a new, larger scale, nautical chart
13. South Arctic Reconnaissance Route, where trackline data will assist consideration of the U.S. Coast Guard’s proposed Bering Strait Port Access Route Study
14. North Coast of Kodiak Island (Alaska), where we need to update charts for Kodiak’s large fishing fleet and increasing levels of passenger vessel traffic
Photo by Lt. Timothy Smith
This summer, the Bering Sea Alliance hosted a private-public summit in Gambell, Alaska, to discuss Arctic resource development and infrastructure. (See page 10 in this edition of the Nome Nugget for a good summary of the meeting.) Lt. Tim Smith, NOAA Coast Survey’s regional manager for Alaska, updated the participants on the status of Arctic nautical charts and described NOAA’s Arctic Nautical Charting Plan. He also outlined the preliminary 2015 survey plans to acquire hydrographic data around Point Hope, Point Barrow, Port Clarence, and Kotzebue Sound, as NOAA strives to ensure the navigational safety of the increasing ship traffic through Arctic waters.
In addition to his role as navigation manager and NOAA Corps officer, Lt. Smith is one of NOAA’s best photographers. His photos of the area around Gambell are better than words in conveying the beauty of this remote area of Alaska.
Photo by Lt. Timothy Smith
With the photo below, Tim reminds us that black and white photos can sometimes reveal more than full color.
Photo by Lt. Timothy Smith
by Ensign Sarah Chappel, NOAA Ship Rainier
NOAA Ship Rainier recently surveyed Whale Passage, which separates Whale Island from Kodiak Island, Alaska. The area has never been surveyed with modern full bottom coverage methods, and some project areas were last surveyed by lead lines around a hundred years ago. The area frequently experiences 7 knot currents, making rocky or shoal areas particularly treacherous. Whale Passage is a high traffic area for fishing vessels, U.S. Coast Guard cutters, barges, ferries, and small boats, which is why updating the area’s nautical charts is so important.
Strong currents push around Ilkognak Rock daymark at the entrance of Whale Passage. (Photo by LTJG Damian Manda)
The dynamics of the passage and surrounding area create several challenges for the hydrographic survey teams. The local tidal and current models are not well-known. To resolve this, Rainier was instructed to install four tide gauges in the greater project area, compared to a typical requirement for one gauge. Two of these gauges are a mere 4.5 nautical miles apart, in and just outside of Whale Passage itself. Some areas are so narrow and experience such high currents that it is only possible to survey in one direction in order to maintain control of the launch. The coxswain must plan each turn carefully, to avoid being pushed into dangerous areas. Ideally, these areas would be surveyed at or near slack tide. However, the slack in this survey area is incredibly brief and the predicted slack periods did not match what survey crews saw in the field.
The bathymetry is so dynamic that, even in relatively deep water, boat crews must remain alert for rocks and shoals. The survey teams found several large rocks in locations significantly different from where they were charted. Furthermore, the presence of large kelp beds increases the difficulty of surveying: they can foul the propellers on the launches, add noise to the sonar data, and can also obscure the presence of rocks.
While the work within Whale Passage, and the neighboring Afognak Strait on the north side of Whale Island, is challenging, it is also high-value. In addition to correcting the positions of known rocks and hazards, Rainier and her crew found a sunken vessel. Most importantly, though, they found areas that were charted twice as deep as they actually are. When the chart reads 8 fathoms (48 feet) and the actual depth is only 4 fathoms (24 feet), commercial traffic utilizing the passage could be in serious danger of running aground. Thus far, Rainier has submitted two DTON (danger to navigation) reports for depths significantly shoaler than charted. These new depths are already published on the latest version of chart 16594.
Rainier‘s multibeam sonar data shows a sunken fishing vessel in the vicinity of Whale Passage.
NOAA Ship Rainier will continue to survey the vicinity of Whale Passage, as well as the waters near Cold Bay out in the Alaskan Peninsula, for the remainder of the survey season before heading home to Newport, Oregon.
NOAA Ship Rainier recovers a survey launch after a morning of surveying and data collection. (Photo by LTJG Damian Manda)
–By Christy Fandel, Coast Survey physical scientist
Have you ever wondered what lies beneath the charted soundings on a nautical chart? While surveying Alaskan waters during the 2013 hydrographic field season, collecting bathymetry to update NOAA’s nautical charts, hydrographers revealed many interesting geologic features on the seafloor.
NOAA focuses a significant portion of our ocean mapping effort along the Alaskan coast. The Alaskan coastline represents over 50% of the United States coastline and dated nautical charts are inadequate for the increasing vessel traffic in this region. NOAA surveys are essential for providing reliable charts to the area’s commercial shippers, passenger vessels, and fishing fleets.
This past season, NOAA-funded hydrographic surveys in Alaska revealed many interesting geological features on the seafloor. Three surveys, in particular, took place in southeastern Alaska in the Behm Canal, along the Aleutian Chain within the coastal waters surrounding Akutan Island, and around Chirikof Island.
These three areas were among the areas surveyed by the NOAA Ship Rainier and surveying contractor Fugro-Pelagos during the 2013 field season.
In May, hydrographic surveying conducted by NOAA Ship Rainier in the Behm Canal revealed two distinct geological features. In the northern region of the canal, scientists identified a long, meandering ancient river. This ancient submarine river is nearly 40 km in length with up to 50 m in relief. Further south, Rainier surveyed a large volcanic-like feature. The surveyed volcano appears to have a distinct caldera, or collapse-feature that most likely formed after the volcanic eruption.
Multibeam bathymetry of the northeastern portion of the Behm Canal shows a large, meandering submarine river. The cross-sectional inset highlights the relief of the channel, nearly 50 m, as shown by the red box.
Multibeam data acquired by NOAA Ship Rainier shows a large volcanic feature in the southern portion of the Behm Canal.
Directly following the Behm Canal survey, Rainier transited west to survey the coastal waters surrounding Chirikof Island. The acquired bathymetric data revealed a stark northeast-trending fault in the southeastern portion of the survey area. This surveyed fault is distinguished by a clear misalignment across the fracture.
The red box outlines the northeast-trending fault along the coast of Chirikof Island, shown with bathymetry acquired by the Rainier.
Concurrently, an Office of Coast Survey hydrographic surveying contractor – Fugro-Pelagos – was surveying off the western coast of Akutan Island. Fugro’s hydrographers identified a large volcanic feature within the acquired bathymetric data. The surveyed volcanic feature is believed to be either a volcanic vent or cinder cone volcano. The multiple circular rings outlining this feature may represent the successive lava flows that formed the volcano.
Multibeam bathymetry acquired by Fugro, around Akutan Island, shows a large volcanic vent or cinder cone volcano, marked by multiple circular rings that represent the successive lava flows that formed the volcano.
With the upcoming 2014 hydrographic field season quickly approaching, the number of geologic discoveries will only increase. Extending all along the Aleutian Chain, from Kodiak Island to Bechevin Bay, the planned surveys for the 2014 field season will surely reveal many interesting and previously unknown geologic features.
Cold Bay Elementary School students visit the NOAA Ship Rainier
On September 13, NOAA Ship Rainier began surveying Cold Bay, its fourth project of the summer. Cold Bay is a small town on the Aleutian Peninsula approximately 540 miles southwest of Anchorage, Alaska. The town currently has approximately 88 full-time residents and boasts an airport with one of the longest runways in Alaska.
On September 19, after deploying her launches for the day, officers and crew welcomed aboard the entire Cold Bay Elementary School – all eight students, teaching assistant Mrs. Lyons, and their teacher, Mrs. Burkhardt. The students are currently between fourth and seventh grade and go to school in a state-of-the-art, two-room school-house.
During the tour, the students learned about driving the ship and making nautical charts. They saw how sonars work, and they even used a sediment sampler to determine the seafloor composition.
The students were full of questions and enjoyed learning about life on a ship. They also captured the admiration of Rainier‘s commanding officer. “When Cold Bay residents describe their town, they can also boast of wonderful elementary school students who have a desire to explore new things,” explained Cmdr. Rick Brennan. “One of the great things about working on a NOAA ship is the opportunity to meet students like this. Combining our love of the sea with their enthusiasm for learning — that’s where America’s future hydrography starts.”
This student is ready to work!
The group examines bottom samples collected by the Rainier.
Cmdr. Rick Brennan explains how davits work.
- Cmdr. Brennan with friends — and potential future hydrographers.