remiconnesson/oceanservice-noaa-facts huggingface dataset:
# How do we monitor tides?

## Tide stations use advanced acoustics and electronics to monitor tides.

![Chesapeake City tide station](/facts/tide-monitor.jpg "Chesapeake City tide station")

This image shows the Chesapeake City tide station, an active water level gauge that is part of NOAA's National Water Level Observation Network, located in Chesapeake City, Md.

The Center for Operational Oceanographic Products and Services maintains a total of 210 permanent, continuously operating water level stations throughout the U.S., including the Great Lakes.

Part of each station is a recorder which sends an audio signal down a half-inch-wide sounding tube and measures the time it takes for the reflected signal to travel back from the water's surface.

In addition to measuring tidal heights, these stations also record up to 11 different oceanographic and meteorological parameters including wind speed and direction, water current speed and direction, air and water temperature, and barometric pressure.

The stations collect data every six minutes with timing controlled by a Geostationary Operational Environmental Satellite (GOES). The stations also use these satellites to transmit their data every six minutes to NOAA headquarters. Field teams can quickly check and maintain the systems using laptop computers. In addition, all of the raw and processed data are available over the Internet.
# How do we monitor currents?

## To measure currents, you need three basic tools — an observer, a floating object or a drifter, and a timing device.

![description of image](currentmeter.jpg "short caption")

Crew from the NOAA Ship _Rainier_\> use an Acoustic Doppler Current Profiler to assist in a current survey of waters near Sitka, Alaska. Results from current surveys are used to improve tidal current predictions and to support new operational forecast models.

An observer stands on a ship, throws the drifter into the water, and then measures the time that it takes that object to move along the side of a ship. As technology improved over time, oceanographers began using mechanical current meters. A ship would deploy a meter and usually some sort of rotor would turn and measure the currents. This is still the basic process today; however there are more accurate and sophisticated instruments.

Today in the open ocean, a drifter is similar to a buoy in the water that may be equipped with global positioning system technology or satellite communications that would relay data and information. Drifters can also submerge for long periods of time to measure ocean currents at a particular depth. The drifter would then resurface occasionally to send a signal with its data and position to observers on the land.

In addition to buoys, there are other tools that are used to monitor currents. The Acoustic Doppler Current Profiler is commonly used to measure currents. It is normally deployed on the seafloor or attached to the bottom of a boat. It sends an acoustic signal into the water column and that sound bounces off particles in the water. The instrument can calculate the speed and direction of the current by knowing the frequency of the return signal, the distance it traveled, and the time it took for the signal to travel.

Many oceanographers also use radio antennas and high frequency Radio Detecting and Ranging systems (radar) to measure surface ocean currents. Similar to the Acoustic Doppler Current Profiler, these shore-based instruments use the Doppler effect to determine when currents are moving toward or away from the shore or to measure the velocity of a current.

At NOAA, oceanographers use knots to measure current speed. The term knot is defined as one nautical mile per hour. One nautical mile is equal to 1.85 kilometers. One knot is also 51.44 centimeters per second.
# Who first charted the Gulf Stream?

## **Benjamin Franklin** was the first person to chart the Gulf Stream.

![Ben Franklin's map of the Gulf Stream](franklinmap.jpg  "Ben Franklin's map of the Gulf Stream")

Alexander Agassiz, a preeminent oceanographer of the 19th century, attributed the first scientific basis for exploring the Gulf Stream to American statesman Benjamin Franklin.  Franklin published this map of the Gulf Stream in 1769, 200 years before a submersible named after him drifted below the surface to study this river in the ocean.

Although first observed in 1513 by Ponce de Leon, the Gulf Stream was not charted until the early 1770s by Benjamin Franklin.

In 1843, the United States Coast Survey, NOAA’s earliest “ancestor,” set out to study the Gulf Stream in more detail. They wanted to determine the depth of the water, the temperature of the water at different depths, the characteristics of the ocean bottom, the direction and velocity of the currents at different depths, and the extent of plant and animal life. Their early observations led them to discover features such as cool and warm water banding, as well as the “[Charleston Bump](http://celebrating200years.noaa.gov/magazine/charleston_bump/welcome.html).”
# What is the Loop Current?

## The Loop Current is a **flow of warm water** that travels through the Gulf of America, past the Florida Keys, and up the Atlantic Seaboard.

![description of image](loopcurrent.jpg "short caption")

In this image from the [NOAA Environmental Visualization Lab](https://www.nesdis.noaa.gov/), the loop current in the center of the Gulf of America is large and warm, while winter-chilled water draining the Mississippi River watershed envelop the bayous and bays of Louisiana.

The Loop Current is an area of warm water that travels up from the Caribbean, past the Yucatan Peninsula, and into the Gulf of America. The current is also known as the Florida current as it flows through the Florida Strait, into the Gulf Stream, and heads north up the eastern coast of the U.S.

From the south, the Gulf of America is fed by a current of warm water from the Caribbean, which enters the Gulf between Mexico's Yucatan Peninsula and Cuba. This forms the Gulf Loop Current, which curves east and south along Florida's coast and exits through the Straits of Florida.

The Gulf Loop is variable. Sometimes, the current barely enters the Gulf of America before heading towards the Atlantic. At other times, it may travel nearly to the coast of Louisiana before swinging back towards the Florida Strait.
# Did I find the lost underwater civilization of Atlantis?

## Unusual grid patterns seen on maps of the ocean floor are created by **ships taking higher-resolution sonar readings** — to create better maps!

![Image of grid lines on map of ocean bottom](atlantis1.jpg "The grid lines that sometimes appear on maps of the ocean bottom are created by ships as they gather sea floor terrain data using sonar")

The lines seen here show the paths taken by ships using sonar to map small sections of the ocean floor in greater detail. The gridded-section shown above may look like streets in a small town, but is over 100 miles wide. The area above is one of the more frequently cited 'underwater city' locations in online lore. It's a spot northwest of the Canary Islands in the Atlantic Ocean located at the following coordinates: _31º15'15" N, 24º 15' 30"_.

With the advent of online mapping tools such as Google Earth, exploring our planet is easier than ever before. Recently, many of these tools have been updated to provide detailed seafloor mapping data, or _bathymetry_.

With legions of people around the world now exploring the seafloor, many are noticing locations along the ocean bottom marked by mysterious formations of grid-like artifacts. These formations look like they were made by humans, leading many to ask if these areas could be lost cities or underwater streets.

While these formations _are_ human-made, they are only made of data. In other words, there are no physical lines on the ocean floor. These lines are artifacts of the ocean floor mapping process.

Oceanographers use sonar—sound waves—to map the ocean bottom. These sonar readings are typically taken by ships towing submersible devices that send out sound waves. The sound travels through the ocean, bounces off the seafloor, then travels back to the ships. This process creates a sound 'image' of the peaks and valleys on the ocean bottom.

NOAA is just one of many agencies around the world that uses sonar to 'see' what the seafloor looks like. Some of these surveys of the ocean bottom cover small areas in great detail. Other surveys are broad-brushed, showing vast areas at low resolutions.

Online mapping tools take these many different sonar surveys created by a variety of agencies and organizations, stitch them together, and pile them up on top of each other in layers. Taken together, these sonar maps provide a seamless picture of what the ocean bottom looks like around the globe. However, some areas appear in more detail than others.

When you see strange grid-like formations on the seafloor while using an online mapping tool, what you are really seeing is two (or more) different maps layered on top of each other. One map may show a large, low-resolution picture of the ocean floor. This map will show little detail and will look smooth. The other map, or 'data set,' often looks like a bunch of grid-like lines overlaying the smooth, low-detail map. The path of the lines show the paths traveled by the ships that gathered these higher-resolution sonar readings of smaller patches of the ocean.
# What is Old Sow?

![the turbulent water of Old Sow ](/facts/oldsow.jpg "What is Old Sow?")

_While the turbulent water of Old Sow can be dangerous to small-craft mariners, its swirling motion has a positive environmental effect. It causes nutrients and tiny sea creatures normally found in the bay’s colder, deeper waters to rise to the surface. This process, called upwelling, ensures good eating for the resident fish and seabirds._

When the tide comes in from the Bay of Fundy, located off the Atlantic Coast between the State of Maine and the Province of New Brunswick, a tremendous amount of ocean water, called a [current](https://oceanservice.noaa.gov/facts/current.html), flows swiftly into a confined area called the Western Passage before emptying upriver into Passamaquoddy Bay. After making a sharp right turn to the north and traversing a deep trench, flowing past an underwater mountain, and encountering several countercurrents, a portion of the current "pinches off" to form the huge circular current called Old Sow, and, often, several smaller ones, nicknamed “piglets.” Circular currents of all sizes are commonly known as whirlpools, vortexes, [eddies](eddy.html), and gyres.

Old Sow varies in size but has been measured at more than 250 feet in diameter, about the length of a soccer field. While the turbulent water can be dangerous to small-craft mariners — some of whom have barely escaped a 12-foot drop into the Sow’s gaping maw — its swirling motion has a positive environmental effect. It causes nutrients and tiny sea creatures normally found in the bay’s colder, deeper waters to rise to the surface. This process, called upwelling, ensures good eating for the resident fish and seabirds.

So why is the whirlpool called "Old Sow?" According to folklore, the name refers to the "grunting" noise — which sounds like hungry pigs slurping up their slop — made by the giant churning gyre. "Sow" may also be a mispronunciation of the word "sough" (pronounced _suff_), which means "sucking noise" or "drain."
# What is a turbidity current?

## A turbidity current is a rapid, downhill flow of water caused by increased density due to high amounts of sediment.

![illustration of turbidity current](/facts/turbiditycurrent.jpg "Turbidity currents can be caused by earthquakes, collapsing slopes, and other geological disturbances.")

Turbidity currents can be caused by earthquakes, collapsing slopes, and other geological disturbances. Once set in motion, the turbid water rushes downward and can change the physical shape of the seafloor.

Turbidity is a measure of the level of particles such as sediment, plankton, or organic by-products, in a body of water. As the turbidity of water increases, it becomes denser and less clear due to a higher concentration of these light-blocking particles.

Turbidity currents can be set into motion when mud and sand on the continental shelf are loosened by earthquakes, collapsing slopes, and other geological disturbances. The turbid water then rushes downward like an avalanche, picking up sediment and increasing in speed as it flows.

Turbidity currents can change the physical shape of the seafloor by eroding large areas and creating underwater canyons. These currents also deposit huge amounts of sediment wherever they flow, usually in a gradient or fan pattern, with the largest particles at the bottom and the smallest ones on top.

NOAA scientists use current meters attached with turbidity sensors to gather data near underwater volcanoes and other highly active geological sites. Also, satellite imagery is used to observe turbidity by measuring the amount of light that is reflected by a section of water.
# What is remote sensing?

## Remote sensing is the science of obtaining information about objects or areas from a distance, typically from aircraft or satellites.

![Light Detection and Ranging image](/facts/remote-sensing.jpg "Light Detection and Ranging image")

A [Lidar](/facts/lidar.html) (Light Detection and Ranging) image created with data collected by NOAA's National Geodetic Survey.

Remote sensors collect data by detecting the energy that is reflected from Earth. These sensors can be on satellites or mounted on aircraft.

Remote sensors can be either passive or active. Passive sensors respond to external stimuli. They record natural energy that is reflected or emitted from the Earth's surface. The most common source of radiation detected by passive sensors is reflected sunlight.

In contrast, active sensors use internal stimuli to collect data about Earth. For example, a laser-beam remote sensing system projects a laser onto the surface of Earth and measures the time that it takes for the laser to reflect back to its sensor.

Remote sensing has a wide range of applications in many different fields:

-   Coastal applications: Monitor shoreline changes, track sediment transport, and map coastal features. Data can be used for coastal mapping and erosion prevention.
-   Ocean applications: Monitor ocean circulation and current systems, measure ocean temperature and wave heights, and track sea ice. Data can be used to better understand the oceans and how to best manage ocean resources.
-   Hazard assessment: Track hurricanes, earthquakes, erosion, and flooding. Data can be used to assess the impacts of a natural disaster and create preparedness strategies to be used before and after a hazardous event.
-   Natural resource management: Monitor land use, map wetlands, and chart wildlife habitats. Data can be used to minimize the damage that urban growth has on the environment and help decide how to best protect natural resources.
# What is the difference between storm surge and storm tide?

## What is a tidal wave?

## A tidal wave is a **shallow water wave** caused by the **gravitational interactions** between the Sun, Moon, and Earth.

![The  NOAA San Francisco Tide Station, in operation for more than 150 years.](tides.jpg "The NOAA San Francisco Tide Station, in operation for more than 150 years.")

The rise and fall of the tides play an important role in the natural world and can have a marked effect on maritime-related activities. The image aboves shows the NOAA San Francisco Tide Station, in operation for more than 150 years.

A tidal wave is a regularly reoccurring shallow water wave caused by effects of the gravitational interactions between the Sun, Moon, and Earth on the ocean. The term "tidal wave" is often used to refer to [tsunamis](/facts/tsunami.html); however, this reference is incorrect as tsunamis have nothing to do with tides.
# What is IOOS?

## The U.S. Integrated Ocean Observing System, or IOOS®, is a coordinated network of people and technology that work together to compile and distribute **data on our coastal waters, Great Lakes, and oceans**.

![Three 10-meter Hurricane Buoys prior to deployment.](ioos1.jpg "An image of Pisces V")

Buoys are just one of the many tools needed to collect ocean observation data. This image shows three ten-meter hurricane buoys prior to deployment.

IOOS coastal and marine data (e.g., water temperature, water level, currents, winds, and waves) are collected by many different tools including satellites, buoys, tide gauges, radar stations, and underwater vehicles. A variety of tools is needed to collect data on global, national, regional, and local levels. Some of these tools are in the water collecting data while others may be on land or in space. Most of the data collected are streamed to a database, making them easier to access.

While many of these data collection tools already exist, the benefit of IOOS is the one common system to connect all of these data so that scientists can quickly find information to track, predict, manage, and adapt to changes in our marine environment.

IOOS data supports environmental efforts such as tracking harmful algal blooms and emergency response needs by assisting with search and rescue operations. IOOS delivers the data and information needed to increase the understanding of our oceans, coasts, and Great Lakes so decision makers can improve safety, enhance our economy, and protect our environment.
# What is a benthic habitat map?

## Benthic habitat maps help protect fragile underwater areas.

![map for Pacific Island Territories](/facts/benthicmap.jpg "map for Pacific Island Territories")

Benthic habitat map for Pacific Island Territories

The term benthic refers to anything associated with or occurring on the bottom of a body of water. The animals and plants that live on or in the bottom are known as the benthos.

In ocean waters, nearshore and estuary areas are most frequently mapped. This is partly because the areas are shallow enough to map, but also because these areas are very important to preserve and manage.

Benthic habitat maps are derived from aerial imagery, underwater photos, acoustic surveys, and data gathered from sediment samples. The resulting digital map is viewed using geographic information system tools.

Policy makers, scientists, and researchers use benthic maps to make informed decisions that help protect the nation’s fragile shallow-water coastal areas.
# What's the difference between a nautical chart and a map?

## A chart is more than a map

![ a NOAA Nautical Chart](chart.jpg " A NOAA Nautical Chart")

Section of a NOAA Nautical Chart.

A nautical chart represents hydrographic data, providing very detailed information on water depths, shoreline, tide predictions, obstructions to navigation such as rocks and shipwrecks, and navigational aids.

The term “map,” on the other hand, emphasizes landforms and encompasses various geographic and cartographic products. Some examples of maps might be road maps or atlases, or city plans. A map usually represents topographical information.

A chart is used by mariners to plot courses through open bodies of water as well as in highly trafficked areas. Because of its critical importance in promoting safe navigation, the nautical chart has a certain level of legal standing and authority. A map, on the other hand, is a  reference guide showing predetermined routes like roads and highways.

Nautical charts provide detailed information on hidden dangers to navigation. Maps provide no information of the condition of a road.
# What is the bloop?

## The source of a **mysterious rumble** recorded in the ocean in 1997 is now known to have originated from an **icequake**.

![NASA Landsat image mosaic of Antarctica](/facts/bloop.jpg)

"The Bloop" is the given name of a mysterious underwater sound recorded in the 90s. Years later, NOAA scientists discovered that this sound emanated from an iceberg cracking and breaking away from an Antarctic glacier. Shown here: a [NASA Landsat mosaic image of Antarctica](https://svs.gsfc.nasa.gov/3588).

## Listen to the Bloop

 [Download this audio file.](/facts/bloop.mp3)

In 1997, researchers listening for underwater volcanic activity in the southern Pacific recorded a strange, powerful, and extremely loud sound. Using [hydrophones](/facts/hydrophone.html), or underwater microphones, that were placed more than 3,219 kilometers apart across the Pacific, they recorded numerous instances of the noise, which was unlike anything they had heard before. Not only was it loud, the sound had a unique characteristic that came to be known as “the Bloop.”

Scientists from NOAA’s [Pacific Marine Environmental Laboratory (PMEL)](https://www.pmel.noaa.gov/acoustics/sounds/bloop.html) were eager to discover the sound's origin, but with [about 95 percent of the ocean unexplored,](https://oceanservice.noaa.gov/facts/exploration.html) theories abounded. Was the Bloop from secret underwater military exercises, ship engines, fishing boat winches, giant squids, whales, or a some sea creature unknown to science?

As the years passed, PMEL researchers continued to deploy hydrophones ever closer to Antarctica in an ongoing effort to study the sounds of sea floor volcanoes and earthquakes. It was there, on Earth’s lonely southernmost land mass, that they finally discovered the source of those thunderous rumbles from the deep in 2005. The Bloop was the sound of an icequake—an iceberg cracking and breaking away from an Antarctic glacier! With global warming, more and more icequakes occur annually, breaking off glaciers, cracking and eventually melting into the ocean.

PMEL’s Acoustics Program develops unique acoustics tools and technologies to acquire long-term data sets of the global ocean acoustics environment, and to identify and assess acoustic impacts from human activities and natural processes on the marine environment.

Did you know? - NOAA and the National Park Service maintain a [network of ocean noise reference stations](https://www.pmel.noaa.gov/acoustics/ocean-noise-reference.html) covering all major regions of the United States.
# What is upwelling?

![illustration of upwelling](/facts/upwelling_960.jpg)

_This graphic shows how displaced surface waters are replaced by cold, nutrient-rich water that “wells up” from below. Conditions are optimal for upwelling along the coast when winds blow along the shore._

Winds blowing across the ocean surface push water away. Water then rises up from beneath the surface to replace the water that was pushed away. This process is known as “upwelling.”

Upwelling occurs in the open ocean and along coastlines. The reverse process, called “downwelling,” also occurs when wind causes surface water to build up along a coastline and the surface water eventually sinks toward the bottom.

Water that rises to the surface as a result of upwelling is typically colder and is rich in nutrients. These nutrients “fertilize” surface waters, meaning that these surface waters often have high biological productivity.  Therefore, good fishing grounds typically are found where upwelling is common.
# What is a tsunami?

![damage from tsunami in American Samoa](/facts/tsunami-amsam.jpg "A tsunami is a series of waves caused by earthquakes or undersea volcanic eruptions")

_On September 29, 2009, a tsunami caused substantial damage and loss of life in American Samoa, Samoa, and Tonga. The tsunami was generated by a large earthquake in the Southern Pacific Ocean._

Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. But as the waves travel inland, they build up to higher and higher heights as the depth of the ocean decreases. The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters. While tsunamis are often referred to as tidal waves, this name is discouraged by oceanographers because tides have little to do with these giant waves.