What are the differences between data collected in 1900, 1940, or 1960?
Let’s take a look at a…
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
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.
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
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
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.
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
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
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.
sextants gave accurate positions when a hydrographer could fix on a
shoreline feature, the further offshore the survey, the less accurate
(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.
1492 to the late 1870s, for instance, mariners used hemp rope for
(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
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
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
→ 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.
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
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.
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
→ 1990: Coast Survey fully adopts side scan sonar for East Coast and Gulf Coast surveys
NOAA Ship Whiting
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
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.
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
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?
cartographers add a “source diagram” to large-scale charts.
the diagram on the current chart 16240
That will give you the years of the
surveys… and now you have a better idea on the technology used by
This is the source diagram on nautical chart 16240.
16240 chart in the GeoGarage platform