On paper maps, the general information block of the chart shows the chart title, usually the name of the navigable water in the covered area, the type of projection and the unit of measurement (1:40,000, Soundings in Feet).
http://www.nauticalcharts.noaa.gov/mcd/learnnc_soundings.html
The numbers that appear all over the water portions of the chart are soundings.
They show how deep the water is at that point.
Large block letters at the top and bottom of the chart indicate the unit of measurement used for soundings.
So NOAA SOUNDINGS can be in FATHOMS (1 Fathom = 6 feet), FEET, or METERS (1 Meter = 3.28 feet).
Most are in feet but it depends on location and age : U.S. charts began switching from feet and fathoms to soundings in meters using the international standard for measuring depth.
Soundings in meters can be quickly converted to feet, by dividing by 3: the math isn't accurate, since a meter is slightly more than 3 ft. long, but it gives a quick, conservative estimate of the depth in feet.
SOUNDINGS IN FATHOMS indicates soundings are in fathoms or fathoms and fractions.
SOUNDINGS IN FATHOMS AND FEET indicates the soundings are in fathoms and feet.
For spot depths, the fathom will be the larger number while the fraction of fathoms or feet will be the smaller subscript number.
For example, you might see a spot depth on the chart of 42.
This indicates a depth of 4 fathoms and, if the soundings are in fathoms and feet, the small 2 indicates two feet, so in this case the depth is 4 fathoms plus 2 feet or 26 feet.
A similar convention is followed when the SOUNDINGS are in METERS or meters and tenths.
The larger number on the spot depths are in meters while the smaller number is tenths of a meter.
What about the level of water (tidal datum) ?All depths indicated on charts are reckoned from a selected level of water called the chart sounding datum.
http://www.nauticalcharts.noaa.gov/mcd/learnnc_soundingdatum.html
For NOAA charts the datum is usually Mean Lower Low Water (MLLW).
This is the average height of the lower low waters of each tidal day over a 19-year period.
Older charts use Mean Low Water and foreign charts can use other tidal datums.
The MLLW datum is lower than Mean Low Water (MLW). It is more conservative with the goal of being more safe.
You must understand the soundings and tidal datum for the chart you are using and take into consideration the height of tide and the tidal range to avoid grounding.
You also must be aware that there will be certain times of the year or weather conditions which can make the actual depth less than that depicted on the chart.
Note : If the tide table show a minus sign (like, "-1") that means that you need to subtract that number from the chart's water depth.
Similar depths are connected by dark blue Contour Lines (isolines or isobaths).
If there's no depth shown at a particular location, you can glance along the contour lines nearest the location until you see a number for the depth.
Typically, the area inside either the three fathom or one fathom contour line is tinted blue to provide quick identification of shoal water.
In the Marine GeoGarage, as we display the different charts in a seamless process, the general information for the chart may be masked by another chart.
So it could be impossible to get the info about the soundings unit.
In this case, waiting the future implementation of a user tool allowing to know the metadata associated with each chart, we advice the user to display with the 'coverage button' the reference of the map and to go to the NOAA website to read the legend and notes to confirm the unit of measurement used for the soundings :
Ex.: for chart 50 (soundings units in meters, datum MLLW) :
In some article of the last edition of Digital Ship, Andy Norris explores some common problems with ECDIS operation and chart management, specifically determining update status, loading charts and route planning.
One of the greatest obstacle to the implementation of mandatory ECDIS will be the hurdle of educating seafarers appropriately in use of the technology.
Many user shortcomings are today being blamed on the consoles and charts.
Norris cites inability to determine when an ENC was last updated as a frequent complaint. Firstly, he describes this challenge as far smaller than doing the same with paper charts.
Many ECDIS are updated simply by inserting a disk and following on-screen commands.
Despite the automation, Norris still advises users to: "keep a manual log of when a disk is loaded, together with a note on whether any problems occurred during the update process."
Finding and loading the appropriate charts from a chart catalogue is described as a necessary learned skill.
Once the correct chart is found in the library (including the largest available scale of any chart on, or immediately adjacent to, the planned route), it can be acquired very quickly, and much more easily than a paper chart.
It is often either a question of obtaining a code via email, or - in some cases - opening it (the purchase order and billing are arranged after the fact).
Finally, issues related to route planning are addressed.
Among the biggest problems here is dealing with the small screen of an ECDIS compared to a paper chart.
Here, Norris advises planning a route starting with a zoomed out image that spans full ocean crossings via great circles as waypoints, then refining the route later in larger scale charts.
He concludes by urging mariners to undertake both a manual check and an ECDIS automated check for hazards along the route.
Actually Andy Norris spoke about the need for users to develop an ECDIS “mindset.”
Significant differences in the skills need to use ECDIS compared with using paper charts required a “major adjustment” in the approach needed to ensure safe navigation, he said.
Once mastered, ECDIS provides the means to improve navigational safety but this is not achieved just by the completion of a short course.
“The skills have to be developed and honed in the context of the knowledge gained at the course and other sources of guidance. The use of ECDIS, in general, is not paper chart techniques transferred to a screen,” he said.
The use of ECDIS is a total change from using paper charts and the transition from paper charts to electronic poses a challenge for the industry, particularly for those who have no current experience of electronic charts.
Important bridge procedures are significantly affected, and these require careful analysis and consideration if ECDIS assisted groundings are to be avoided.
Link :
Listening to the ocean for more comprehensive study of the seas
Oxygen minimum zones (OMZs) are expanding in the World Ocean as a result of climate change and direct anthropogenic influence.
OMZ expansion greatly affects biogeochemical processes and marine life, especially by constraining the vertical habitat of most marine organisms.
Currently, monitoring the variability of the upper limit of the OMZs relies on time intensive sampling protocols, causing poor spatial resolution.
The French Institut de recherche pour le développement (IRD) and the Instituto del Mar del Perú (IMARPE) have developed an innovative acoustic method to observe the evolution of oxygen minimum zones (OMZs) in the world's oceans.
This new technique makes it possible to measure these oxygen-free (anoxic) zones, which are home to many marine organisms, in greater detail.
The researchers measured the vertical distribution of marine organisms, such as plankton, crustaceans and fish, in the water using routine underwater acoustic observation techniques along the Peruvian coast.
The measurements, made with the help of echo sounders, allowed them to determine the oxycline, which delimits the top of the OMZ, with high precision.
Combining the data obtained in this way with regular hydrological measurements, they managed to compile high-resolution maps that are 50,000 to 100,000 times more precise than common hydrological profiles.
As well as shedding new light on the state and spread of OMZs, the scientists were also able to calculate precisely the size of the habitat available to the Peruvian anchovy, for instance, providing information that might be of interest for fisheries management.
(IRD also uses this information to estimate the habitable volume for the world's most exploited fish, the Peruvian anchovy)
'This method ... allows performing integrated studies since acoustic data provides information on most ecosystem components [...], to which we can add ancillary information (satellite data, vessel monitoring system, top predator tagging...),"
Such integrated approaches are crucial to implement the ecosystem approach to fisheries.
"Our methodology can also be applied to other ecosystems, e.g. oceanic dead zones, and opens new perspectives for comprehensive multiscale studies on the impact of physical forcing on organisms."
OMZs are a naturally occurring phenomenon, found at depths of about 100 to 1,000 metres. They are home to numerous organisms that are specially adapted to the low-oxygen environment, including not only anaerobic bacteria but also larger organisms such as vampire squid. Oxygen-loving organisms, however, cannot survive in these zones.
OMZs currently cover about 10% of the planet's surface.
But they have been spreading for the past 50 years due to global warming and humankind's impact on the seas through rising levels of chemical nutrients (eutrophication), for example.
This opportunistic method could be implemented on any vessel geared with multi-frequency echosounders to perform comprehensive high-resolution monitoring of the upper limit of the OMZ.
IRD's approach is a novel way of studying the impact of physical processes on marine life and extracting valid information about the pelagic habitat and its spatial structure, a crucial aspect of Ecosystem-based Fisheries Management in the current context of climate change.
The findings open up new perspectives for the study of the oceans as well as the management of fisheries resources.
Links :
The End of the Line, is the world's first major feature documentary about the devastating impact overfishing has had and is having on our oceans. The film provides a dramatic expose of those in power who are taking advantage of the seas with catastrophic consequences on the world's fish supplies.
We see firsthand the effects of our global love affair with fish as food. The film examines the imminent extinction of bluefin tuna, brought on by increasing western demand for sushi; the impact on marine life resulting in huge overpopulation of jellyfish; and the profound implications of a future world with no fish, which would bring certain mass starvation and unemployment.
Filmed over two years, The End of the Line follows the investigative reporter Charles Clover as he confronts politicians and celebrity restaurateurs, who exhibit little regard for the damage they are doing to the oceans.
One of his allies is the former tuna farmer turned whistleblower Roberto Mielgo – on the trail of those destroying the world's magnificent bluefin tuna population.
Filmed across the world – from the Straits of Gibraltar to the coasts of Senegal and Alaska to the Tokyo fish market – featuring top scientists, indigenous fishermen and fisheries enforcement officials, The End of the Line is a wake-up call to the world.
With many species on the brink of extinction and mind-blowing evidence that the world may very soon face a future with very few fish, there has never been a more pressing need to bring this issue to the fore. The end of the line shows that we can all enjoy fish, but encourages viewers to think more carefully about where their fish is coming from.
Links :
- BBC News : the bitter battle over bluefin tuna
- ScienceDaily : fishing fleet working 17 times harder than in 1880s to make same catch
- Mauritania on Saturday (May 1st) launched a two-month ban on industrial fishing, FIS reported. The interruption will reportedly allow endangered fish to reproduce. The biological shutdown affects some 300 vessels operating in Mauritanian waters.
NASA will send two astronauts, a veteran undersea engineer and an experienced scientist into the ocean depths off Florida's east coast this month to test exploration concepts and learn more about working in an unforgiving, treacherous environment.
The 14th expedition of NASA Extreme Environment Mission Operations, or NEEMO 14, begins May 10.
Canadian Space Agency astronaut and veteran spacewalker Chris Hadfield will lead the NASA team on a 14-day undersea mission aboard the Aquarius Underwater Laboratory.
Take a virtual tour to learn more about the NOAA, Aquarius Underwater Laboratory: America's "Inner Space" Station.
Aquarius is the only undersea laboratory dedicated to marine science operating in the world.
Owned by the National Oceanic and Atmospheric Administration (NOAA) and managed by the University of North Carolina at Wilmington (UNCW), Aquarius operates 4.5 kilometers offshore of Key Largo, Florida 20 meters beneath the surface.
Aquarius Underwater Laboratory is marked with a yellow life support buoy that is 30' in diameter. The depth of the water where it sits is 63'. The reef wall outside the lab drops off to 160'-180'. There are yellow Sanctuary Preservation Area research only buoys that mark the site. It’s located 5 miles southeast of Tavernier at Conch Reef.
Location on the Marine GeoGarage (24°57.010' N/80°27.130' W)
During NEEMO 14, the ocean floor will simulate aspects of another planet's surface and a low-gravity environment. In October 2009, a team of aquanauts set the stage for NEEMO 14 by placing mockups near Aquarius of a lander, rover and small crane that simulates a robotic arm.
The NEEMO 14 crew will live aboard the underwater laboratory, venture out on simulated spacewalks, operate the crane and maneuver the vehicles much like explorers would in setting up a habitat on another planet. As the aquanauts interact with these developing technologies, they will provide information and feedback to NASA engineers.
The crew will simulate removing a mockup of the Lunar Electric Rover from the lander, retrieve small payloads from the lander and the ocean floor, and simulate the transfer of an incapacitated astronaut from the ocean floor to the deck of the craft. The rover and lander mockups are similar in size to vehicles NASA is considering for future planetary exploration.
While inside Aquarius, the crew will perform life science experiments focused on human behavior, performance and physiology. The mission also includes a study of autonomous crew work. There will be periods when there is limited communication between the crew and the mission control center, much like what could happen during missions to the moon or Mars.
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