remiconnesson/oceanservice-noaa-facts huggingface dataset:
# How long does it take to produce a nautical chart?

## The time needed to make a new nautical chart depends on how many pieces of the puzzle are in the box.

![NOAA's Office of Coast Survey produces nautical charts for the Great Lakes and U.S. territories.](AnthonyKlemm.jpg "Nautical charts for the Great Lakes and U.S. territories.")

NOAA's Office of Coast Survey produces nautical charts for U.S. coastal waters, including the Great Lakes and U.S. territories.

Cartographers create new nautical charts by piecing together a puzzle. Sometimes all the pieces are in the box, other times surveyors and others have to go out into the field to gather the pieces of missing information. To a large degree, the more pieces are on hand, the quicker the chart assembly time.

Nautical charts are uniquely designed to provide information needed for ships to safely navigate. Natural features, such as the depth of the water, the shape of the shoreline, and the locations of rocks and other dangers, are critical pieces of the chart. The position and characteristics of man-made objects, such as bridges and cables that may pass over navigable rivers, and the delineation and depth of dredged channels, are also key bits of information. A distinct set of features (rarely shown on other maps) include the positions and descriptions of buoys, beacons and lights, called aids to navigation.

For a new chart, some of this information will already be available. If the required data is not available or the information is too old, then NOAA must acquire new data from a range of providers: NOAA's own hydrographic survey ships and planes (water depth and shoreline), the U.S. Army Corps of Engineers (ship channel limits and depths), and the U.S. Coast Guard (aids to navigation information) and many others.

Compiling the data may take as little as six months; but scheduling, collecting, and processing new hydrographic or topographic surveys can extend chart creation to several years, depending on the location and extent of the surveys required and competing requirements from other charts.

Once a new chart is created, the work has only begun. Keeping a chart up-to-date is never ending. Changing shoreline, shifting seafloors, silt deposits, discovery of submerged dangers, and repositioned buoys are only a few reasons why nautical charts must be constantly updated.
# What is a meteotsunami?

## Meteotsunamis are large waves caused by storms.

![a stormy ocean, iStock image](/facts/meteo960.jpg)

Stormy weather over the ocean can sometimes fuel the development of meteotsunamis, a series of waves typically much smaller and less destructive than those associated with seismically generated tsunamis.

## Seiches and meteotsunamis. What's the difference?

[Seiches](/facts/seiche.html) and meteotsunamis are often grouped together, but they are two different events. Winds and atmospheric pressure can contribute to the formation of both seiches and meteotsunamis; however, winds are typically more important to a seiche motion, while pressure often plays a substantial role in meteotsunami formation. Sometimes a seiche and a meteotsunami can even occur at the same time. Seiches are standing waves with longer periods of water-level oscillations (typically exceeding periods of three or more hours), whereas meteotsunamis are progressive waves limited to the tsunami frequency band of wave periods (two minutes to two hours). Seiches are usually limited to partially or fully enclosed basins, such as Lake Erie. Meteotsunamis can occur in such basins but are also prevalent on the open coast. A single meteotsunami can travel long distances and influence a very large range of the coastline.

![](/bootstrap/img/shadow1.png)

You’ve heard of tsunamis—those giant oceanic waves triggered primarily by earthquakes that can roll ashore, causing loss of life and disaster. But have you heard of meteotsunamis?

Meteotsunamis are large waves that scientists are just beginning to better understand. Unlike [tsunamis](/facts/tsunami.html) triggered by seismic activity, meteotsunamis are driven by air-pressure disturbances often associated with fast-moving weather events, such as severe thunderstorms, squalls, and other storm fronts. The storm generates a wave that moves towards the shore, and is amplified by a shallow continental shelf and inlet, bay, or other coastal feature.

Meteotsunamis have been observed to reach heights of 6 feet or more. They occur in many places around the world, including the Great Lakes, Gulf of America, Atlantic Coast, and the Mediterranean and Adriatic Seas.

Identifying a meteotsunami is a challenge because its characteristics are almost indistinguishable from a seismic tsunami. It can also be confused with wind-driven [storm surge](/facts/stormsurge-stormtide.html) or a [seiche](/facts/seiche.html). These uncertainties make it difficult to predict a meteotsunami and warn the public of a potential event. However, NOAA scientists have identified atmospheric conditions that are likely to generate a meteotsunami and continue to work on ways to forecast them.
# Are tides higher when the moon is directly overhead?

## High tides **do not coincide** with the **location of the moon**.

![Earth viewed from the surface of the moon](/facts/moon-tide.jpg)

This [NASA image](https://images.nasa.gov/details-as08-14-2383.html) from the Apollo 8 mission shows the Earth viewed over the horizon of the moon. While the moon and sun cause tides on our planet, the gravitational pull of these celestial bodies does not dictate when high or low tides occur.

Tides originate in the ocean and progress toward the coastlines, where they appear as the regular rise and fall of the sea surface. Thanks to Sir Isaac Newton’s 1687 discovery, we know that tides are very long-period waves that move through the ocean in response to [forces exerted by the moon and sun](/facts/tides.html). _However, these gravitational forces do not control when high or low tide events occur._ Other forces, more regional than the moon or sun, control the tides. Many of them have to do with the geography and shape of the Earth.

The [shape of our planet](/facts/geodesy.html) has a lot to do with differences in gravitational pull at various locations. If Earth was a true sphere covered by an ocean of constant depth, then it would be true that a high tide event would occur at the location with the moon overhead. The tidal "bulge" would move around the Earth with the moon, but this is not the case with our planet. The Earth is not a true sphere, but bulges slightly at the Equator. It is also dotted with large land masses (continents). Areas where the Earth’s surface is higher, such as mountains, have a stronger gravitational force than do places where the surface is lower, such as a valley or cavern. At the same time, the depth of the world ocean varies greatly. All of these factors play into the height of the tides.

Another thing to consider when thinking about tides is the dimension of time. There are lags in time when an observer experiences high or low tide, and the lag varies from one location to another. For example, the rising slope of the ocean floor approaching the U.S. East (known as the continental rise, continental slope, and continental shelf) slows down the tidal "bulge" or "wave" of water. The lag can be hours or even close to an entire day in some parts of the world. Think of the wave or bulge that you see when you throw a rock into a pond. The wave travels outward in a ring. If there is a tree or other obstruction in the pond, the ring of waves would travel and wrap around it. The same holds true for the tides.

NOAA's [Center for Operational Oceanographic Products and Services](https://tidesandcurrents.noaa.gov/) uses advanced acoustic and electronic equipment to measure and monitor the tides along our coasts. NOAA has water observation stations in more than 3,000 locations around the U.S. to observe water levels and generate tidal predictions.
# What is a NOAA tide table?

![daily tide predictions for Eastport, Maine, for January 1-6, 2022](/facts/daily-tide-eastport.png "What is a NOAA tide table?")

_This image shows the daily tide predictions for Eastport, Maine, for January 1-6, 2022 generated through the modern electronic tide predictions service._

![screenshot from first NOAA tide table publication](/facts/tide-tables.jpg)

_This image shows daily tide predictions for Eastport, Maine, for January-February 1867. This page is from the first edition of a national annual tide table publication created in 1866 by the U.S. Coast Survey, a predecessor of NOAA._

Tide tables provide the times and heights of high tide and low tide at more than 3000 locations along the U.S. coastline. NOAA’s [Center for Operational Oceanographic Products and Services](https://tidesandcurrents.noaa.gov/) and predecessor agencies have produced annual tide tables for more than 150 years. These annual publications were produced in print form from 1865 to 2020 and were superseded by electronic predictions beginning in 2021. NOAA tide tables offer predictions on a daily, monthly, or annual basis.

Tide tables are different from tide charts. A tide chart is a printed map showing water levels on an hourly basis throughout a bay or an estuary at a particular point in time. Such charts were only available for only a few locations around the nation. However, these printed tide charts have been superseded by modern, digital hourly forecast models and graphical products.

To obtain tide predictions, tidal current predictions, or forecast model data, visit NOAA's [Tides and Currents](https://tidesandcurrents.noaa.gov/faq.html#03) website:

-   [NOAA Tide Predictions](https://tidesandcurrents.noaa.gov/tide_predictions.html)
-   [NOAA Current Predictions](https://tidesandcurrents.noaa.gov/noaacurrents/Regions)
-   [Operational Forecast System Models](https://tidesandcurrents.noaa.gov/models.html)
# Where do I get real-time coastal conditions?

##### **Did you know?**

_There are two versions of nowCOAST: one version is for use by the general public and one version is enhanced for mariners. The map for mariners adds many additional features, such as raster and electronic nautical chart (RNC/ENC) underlays, National Weather Service coastal marine zone forecasts, and offshore weather observations from ships and buoys. Look for the button in the upper right corner of the application to choose which version you would like to view._

NOAA's [nowCOAST](https://nowcoast.noaa.gov/) is a GIS-based webmap service that provides frequently updated weather and ocean observations along with coastal and marine weather forecasts 24 hours a day. The free online map viewer offers point-and-click access to 60 NOAA data products and services all in one place. With nowCOAST, you can get a one-stop-shop look at coastal conditions — real-time and forecast — before you do or plan anything on the water.

The nowCOAST map viewer displays animated observations for the past four hours and forecasts for the next seven days. The map incorporates data from NOAA's [National Ocean Service](https://oceanservice.noaa.gov/); [National Weather Service](http://www.weather.gov/); and [National Environmental Satellite, Data, and Information Service](https://www.nesdis.noaa.gov/). Data includes watches, warnings, and advisories for hazardous weather and marine weather conditions such as special marine warnings and gale warnings — even far offshore. It also provides near-real-time weather radar data, weather satellite imagery, and lightning strike density data for both land and overwater areas, sea surface temperature analyses, and predictions from NOAA’s ocean forecast models. Advanced users may also ingest maps of NOAA data and predictions directly into third-party applications using [nowCOAST web map services](https://nowcoast.noaa.gov/help/#!section=mapservices).

Did you know? - *There are two versions of nowCOAST: one version is for use by the general public and one version is enhanced for mariners. The map for mariners adds many additional features, such as raster and electronic nautical chart (RNC/ENC) underlays, National Weather Service coastal marine zone forecasts, and offshore weather observations from ships and buoys. Look for the button in the upper right corner of the application to choose which version you would like to view.*
# What is a Hydrophone?

## A hydrophone is an underwater device that detects and records ocean sounds from all directions.

![A hyrdophone is mounted to the sea floor as small fish swim all around the scene kicking up sediment](/facts/hydrophone.jpg)

People often think that the underwater world is silent. In fact, numerous marine organisms use sound for communication, reproduction, and to seek prey. The hydrophone pictured here is located within [Gray's Reef National Marine Sanctuary](https://sanctuaries.noaa.gov/vr/grays-reef/hydrophone-and-spade.html) in Georgia. This is one of four locations where hydrophones are used to collect soundscape data within the National Marine Sanctuary system.

Just as a microphone collects sound in the air, a hydrophone detects acoustic signals under the water. Most hydrophones are based on a special property of certain ceramics that produces a small electrical current when subjected to changes in underwater pressure. When submerged in the ocean, a ceramic hydrophone produces small-voltage signals over a wide range of frequencies as it is exposed to underwater sounds emanating from any direction.

By amplifying and recording these electrical signals, hydrophones measure ocean sounds with great precision. While a single hydrophone can record sounds from any direction, several hydrophones simultaneously positioned in an array, often thousands of miles apart, result in signals that can be manipulated to “listen” with greater sensitivity than a single device. Omni-directional and hemi-directional hydrophones pick up sound from a particular direction and can be used to track fish movements.

In addition to NOAA's National Marine Sanctuaries, NOAA’s [Pacific Marine Environmental Laboratory](https://www.pmel.noaa.gov/) (PMEL) also frequently uses hydrophones. PMEL acquires long-term data sets of the global ocean acoustics environment to identify and assess acoustic impacts from both human activities and natural processes, such as underwater volcanoes, earthquakes, and icequakes on the marine environment.

###### **Search** Our Facts

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“You would think that the deepest part of the ocean would be one of the quietest places on Earth. Yet there is almost constant noise,” says Robert Dziak, NOAA PMEL research oceanographer and scientist. “The ambient sound field is dominated by the sounds of earthquakes, both near and far, as well as by the distinct moans of baleen whales, and perhaps the clamor of a Category 4 typhoon that just happened to pass overhead.”

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Did you know? - “You would think that the deepest part of the ocean would be one of the quietest places on Earth. Yet there is almost constant noise,” says Robert Dziak, NOAA PMEL research oceanographer and scientist. “The ambient sound field is dominated by the sounds of earthquakes, both near and far, as well as by the distinct moans of baleen whales, and perhaps the clamor of a Category 4 typhoon that just happened to pass overhead.”
# What is the difference between an AUV and a ROV?

VIDEO: What's the difference between an AUV and an ROV? Here's what you need to know in one minute. [Transcript](#transcript)

![NOAA Ship Nancy Foster's Chief Boatswain Greg Walker and Bosun Group Leader James Best work with scientist Tim Battista to prepare the ocean glider for launch.](/facts/preparing-for-launch.jpg)

_From left, NOAA Ship Nancy Foster's Chief Boatswain Greg Walker and Bosun Group Leader James Best work with scientist Tim Battista to prepare the ocean glider for launch._

AUV stands for autonomous underwater vehicle and is commonly known as uncrewed underwater vehicle. AUVs can be used for underwater survey missions such as detecting and mapping submerged wrecks, rocks, and obstructions that can be a hazard to navigation for commercial and recreational vessels.

An AUV conducts its survey mission without operator intervention. When a mission is complete, the AUV will return to a pre-programmed location where the data can be downloaded and processed.

A remotely operated vehicle (ROV) is an unoccupied underwater robot that is connected to a ship by a series of cables. These cables transmit command and control signals between the operator and the ROV, allowing remote navigation of the vehicle. An ROV may include a video camera, lights, sonar systems, and an articulating arm. The articulating arm is used for retrieving small objects, cutting lines, or attaching lifting hooks to larger objects.

While there are many uses for ROVs, some of the most common hydrographic applications include object identification (for submerged navigation hazards) and vessel hull inspections. An ROV is not intended to be a replacement for hydrographic diver investigations, but could serve as a substitute if divers are not available or diver safety is in question.

### Video Transcript

Here are two uncrewed ocean explorers. Can you spot the difference between the two? One, an AUV or Autonomous Underwater Vehicle, explores ocean depths without any attached cables. Researchers drop an AUV in the ocean pick it up at a pre-selected position. Like an AUV, a Remotely Operated Vehicle is unmanned. The difference is that an ROV is connected to a ship by cables. A person on the ship “drives” it around. ROVs are often used when diving by humans is either impractical or dangerous, such as working in deep water or investigating submerged hazards. ROVs and AUVs carry equipment like video cameras, lights, robotic arms to grab things. By going where humans can’t go, these underwater robots help us safely study the ocean.
# How does NOAA monitor water levels around the nation

## NOAA monitors water levels in the U.S. with the National Water Level Observation Network.

![A National Water Level Observation Network station in San Francisco, California](/facts/nwlon.jpg "How does NOAA monitor water levels around the nation?")

An NWLON station in San Francisco, California.

The National Water Level Observation Network (NWLON) is a permanent observing system that includes 210 continuously operating water level stations throughout the U.S. and its territories. NWLON is the “go-to” source for government and commercial-sector navigation, recreation, and coastal ecosystem management.

Accurate water level data is critical for many coastal activities, from navigation and engineering to restoration and preservation. In addition to water levels, the stations measure other oceanographic and meteorological parameters such as water temperature and wind speed. NOAA uses this information to ensure safe navigation through access to real-time data 24 hours a day, seven days a week. NOAA nowcast and forecast models use the data to provide a look into present and future oceanographic conditions, which can enhance tsunami and storm surge warnings. NOAA also uses this data to publish annual tide predictions.

NWLON provides historical as well as present-day water level information. Historical data is used to compute relative local mean sea level trends and to understand the patterns of high tide events. The first water level observing stations were established in the 1850s, and some have been collecting data ever since!

NWLON is managed by NOAA’s Center for Operational Oceanographic Products and Services.

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Approximately one-quarter of NWLON stations are located in the Great Lakes to provide water level data for the international management of those water resources.

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**Last updated:** 06/16/24  
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Did you know? - 

- Approximately one-quarter of NWLON stations are located in the Great Lakes to provide water level data for the international management of those water resources.
# What is a ghost forest?

![a maritime forest](/facts/ghost-forest.jpg "What is a ghost forest?")

_A ghost forest on Capers Island, South Carolina._

As [sea level](/facts/sealevel.html) rises, more and more saltwater encroaches on the land. Along the world’s coasts and estuaries, invading seawater advances and overtakes the fresh water that deciduous trees rely upon for sustenance. The salty water slowly poisons living trees, leaving a haunted ghost forest of dead and dying timber. Still standing in or near brackish water, the decaying trees of a ghost forest resemble giant graying pillars that protrude into the air.

Researchers report that the rapid increase in ghost forests represents a dramatic visual picture of environmental changes along coastal plains located at or near sea level. In many areas, rising sea levels combine with [land sinking from the last ice age](/facts/glacial-adjustment.html), as is currently happening in the Chesapeake Bay watershed.

The Mississippi Delta region of Louisiana is undergoing changes due to rising waters, the sinking of [Earth's crust](https://pubs.usgs.gov/gip/dynamic/inside.html), and sediments compacting along the Mississippi River. With land and water constantly shifting, woodlands die and are buried in open water. This is apparent along North Carolina’s [maritime forests](/facts/maritime-forest.html), where only a glimpse of once peaceful and verdant groves, now ghost forests, remain.
# What is Digital Coast?

## NOAA's Digital Coast provides the data, tools, and training that communities use to manage their coastal resources.

[![Digital Coast banner image](/facts/digital-coast.jpg "More than just data. Dive into the digital coast to get the data, tools, and training communities need to address coastal issues. data. tools. training. stories.")](https://coast.noaa.gov/digitalcoast/)

Data sets alone are not enough. For data to be truly useful, people often need assistance by way of relevant training and associated tools and information. The [Digital Coast](https://coast.noaa.gov/digitalcoast/) provides this complete package for the coastal management community.

People new to the Digital Coast often start with the [_topics_](https://coast.noaa.gov/digitalcoast/topics/) section. Here users find topics of interest from climate adaptation to ocean planning, plus quick access to the Digital Coast data, tools, and training most relevant to a particular topic. The [_stories_](https://coast.noaa.gov/digitalcoast/stories/) section represents another helpful starting point. These short write-ups showcase how communities use Digital Coast resources to address coastal management issues.

More experienced users usually go straight to the [_data_](https://coast.noaa.gov/dataregistry/) or [_tools_](https://coast.noaa.gov/digitalcoast/tools/) they need. The search functions of these pages help users quickly see what is available, and the landing pages provide information that is good to know before the download button is selected. New and experienced users tend to browse through the [_training_](https://coast.noaa.gov/digitalcoast/training/home.html) section, because a wide array of learning products is housed here. These include quick reference guides, detailed reports, how-to products, online training, and training brought to the location of your choosing.

The Digital Coast's success is driven, in large part, by content contributions from many trusted sources and a laser-like focus on the coastal management community.