Frequently asked questions bout ocean observations
FREQUENTLY ASKED QUESTIONS ABOUT OCEAN OBSERVATIONS
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- Questions related to instruments used to observe the ocean
- Questions related to the management and distribution of ocean observations
- Questions related to the transmission of ocean observations
- Questions related to the international coordination of ocean observations
- 1. Why, what, where and when of ocean observations Why do we need ocean observations
- 1.2) What do we need to measure in the ocean
- 1.4) When do we need to observe the ocean
- 1.5) How can data from ocean observations be accessed
- Questions related to oceanographic observations and data collection 2.1) What types of instruments do we use to observe the ocean
- 2.2) What is a direct (‘in situ’) observation of the ocean
- 2.4) Why do we need both direct (‘in situ’) and remote (satellite, aircraft) observations
- 2.5) What are ‘forecasting’ observations versus ‘research’ observations
- 2.6) What is a ship of opportunity (SOP)
- 3. Questions related to specific instruments used to observe the ocean 4.1) What is a Mechanical BathyThermograph (MBT)
- 3.2) What is an eXpendable BathyThermograph (XBT)
| FREQUENTLY ASKED QUESTIONS ABOUT OCEAN OBSERVATIONS
FREQUENTLY ASKED QUESTIONS BOUT OCEAN OBSERVATIONS Q & A FREQUENTLY ASKED QUESTIONS ABOUT OCEAN OBSERVATIONS Questions related to the why, what, where, when and how of ocean observations Why do we need ocean observations? What do we need to measure in the ocean? Where do we need to measure in the ocean? When do we need to observe the ocean? How can data from ocean observations be accessed? Questions related to ocean observations and data collectionWhat types of instruments do we use to observe the ocean? What is a direct (‘in situ’) observation of the ocean? What is a remote (e.g. satellite, aircraft) observation of the ocean? Why do we need both direct and remote observations of the ocean? What are ‘forecasting’ observations versus ‘research’ observations? What is a ship-of-opportunity? Questions related to instruments used to observe the ocean What is a mechanical bathythermograph (MBT)? What is an expendable bathythermograph (XBT)? What is an Argo float? What is a satellite-tracked surface drifter? What is a thermosalinograph (TSG)? What is an inverted echo sounder (IES)? What is an ATLAS mooring? What measurements are provided by satellites? Questions related to the management and distribution of ocean observations What is data management? How has the distribution of XBT and Argo floats evolved with time? How has the distribution of surface drifters evolved with time? How have satellite observations evolved with time? Questions related to the transmission of ocean observations What is the Global Transmission System (GTS)? What is the Shipboard Environmental data Acquisition System (SEAS)? What is the Automated Mutual-Assistance Vessel Rescue System (AMVER)? Questions related to the international coordination of ocean observations What is the International Oceanic Commission (IOC)? What is the World Meteorological Organization (WMO)? What is the World Weather Watch? What is the Global Ocean Observing System (GOOS)? What is the Integrated Ocean Observing System (IOOS)? 1. Why, what, where and when of ocean observations Why do we need ocean observations? 
The oceans cover over 70% of the earth’s surface and due to the incredible amount of heat and water moved in oceanic flows they have critical impacts on many aspects of our daily lives. Understanding and ultimately predicting ocean variability will significantly improve humanity’s ability to reduce harmful affects of extreme environmental changes (air-sea-land-ice) on society. Several goals have been specifically identified by national and international science advisory bodies as requiring increased knowledge of the ocean for the betterment of society: Both natural and anthropogenic climate change. Ocean prediction is like weather prediction in that observations are used to initialize forecast models. For instance, presently, seasonal to interannual timescale forecast models are presently being run by prediction agencies. These models require ocean observations such as temperature, much like weather models require sea level pressure, to initialize model prediction runs. Natural hazards. As they cross the ocean tsunamis leave a signature on the ocean floor of their location, speed of propagation, amplitude, etc. This signature can be observed using a network of bottom pressure gauges that have the ability to send their data in ‘real time’ (i.e., the present) to land stations for analyses and issue of warnings. 
Marine operations. Ocean currents are not stationary but change in time and space. Real time information on the location and strength of intense currents such as the Gulf Stream can either decrease or increase fuel costs depending on ship’s course relative to current’s direction and speed; National security. Submarine tracking requires observations of ocean pressure, temperature and salinity, the factors that impact the speed of sound in the water. The speed of sound controls the sound waves used to find and follow submarines. Public health. Coastal and offshore currents influence the dispersion of pollutants that can have deleterious effects on human health. Coastal marine ecosystems. Diverse coastal marine ecosystems provide a major opportunity for tourism (e.g., diving). The physical characteristics of coastal marine areas have a major impact on the health of and Living marine resources. Locations for successful commercial fisheries are dependent on and change with the physical characteristics of the resource’s habitat. To achieve the goals of understanding and ultimately predicting the effects of the ocean on these topics requires an extensive, well maintained ocean observing system.  
1.2) What do we need to measure in the ocean? Oceanography, like the land and atmospheric scientists, has several subspecialties. Geological oceanography is directed at characterizing the properties of the seafloor and sub-seafloor. Chemical oceanography is directed at the chemical constituents of seawater. Biological oceanography is directed at the biota living in the ocean. Physical oceanography is directed at the physical properties (e.g., temperature, currents) of the ocean. Each subspecialty can be further decomposed into more specific studies such as coastal areas versus the interior ocean (“blue water oceanography”), natural versus anthropogenic effects, effects at different time periods, etc. The Physical Oceanography Division of the Atlantic Oceanographic and Meteorological Laboratory concentrates on investigating and monitoring the physical oceanography of the oceans and thus the response to this and the following questions will concentrate on observations collected by physical oceanographers, with particular emphasis on data needed to study the ocean’s role in climate. To study the ocean’s role in climate, the international Global Ocean Observing System (GOOS) and Global Climate Observing System (GCOS) communities have determined that the following observations are needed either at the sea surface or through the entire water column: Ocean temperature Ocean salinity (i.e., the concentration of salt in a volume of ocean water) Sea level Vector currents Sea ice Surface heat flux (i.e., the amount of energy exchanged across the sea surface. Furthermore, the following surface atmospheric data are required to understand the physics of the ocean: Vector winds Air temperature Sea level pressure Precipitation Humidity For additional information on GOOS data requirements go to: http://gosic.org/IOS/GOOS-pdv.htm For additional information on GCOS data requirements go to: http://www.google.com/search?q=GCOS+requirements&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a 1.3) Where do we need to measure in the ocean? Where we measure in the ocean is a function of the problem addressed. For example, to study the effect of pollution from land sources on coastal areas requires data from the origins of the pollutants (i.e., land, atmosphere), the area under consideration and, not as obvious, coastal and offshore areas surrounding the area of interest. Observations from the surrounding areas, including blue water, are required because current transports can induce ‘remote’ effects on ‘local conditions’. Natural and anthropogenic climate change can be regional, hemispheric or global phenomena. Teleconnection processes are naturally occurring features that connect the physical atmospheric characteristics of spatially separated regions of the globe. These processes can range in influence from regional to global and are affected by ocean features. To fully understand anthropogenic climate change requires a global perspective. Thus, global ocean observations are needed to obtain a complete picture of the role of the ocean in global climate (e.g., how much atmospheric anthropogenic global heating is taken up by the ocean). 1.4) When do we need to observe the ocean? As with the previous question, the answer to this question is a function of the ocean property, process or effect we wish to characterize. For instance, if we are interested in providing data to assist in using SST to forecast hurricane intensity and trajectories more frequent data (hourly) are needed than if we wish to use ocean data to initialize seasonal-to-interannual climate forecasts (weekly). 1.5) How can data from ocean observations be accessed? Most oceanographic data that have been scientifically reviewed can be accessed from NOAA’s National Oceanographic Data Center at: www.nodc.noaa.gov If Global Telecommunication System access is available data can be obtained through GTS nodes. Several observation types also have independent access points. This information can be obtained by GOOGLING the instrument type and searching for data center information. 1) XBT data are available on: http://db.aoml.noaa.gov/cgi-bin/db/Bin/init_applet.x?xbtrt+XBTRTGUI.class http://www.aoml.noaa.gov/phod/hdenxbt/ax_home.php 2) Surface drifter data are available on: 2.1) http://www.aoml.noaa.gov/phod/dac/dacdata.html 2.2) http://www.meds-sdmm.dfo-mpo.gc.ca/isdm-gdsi/drib-bder/svp-vcs/index-eng.asp 3) Argo data can be accessed through: 3.1) http://www.usgodae.org/argo/argo.html 3.2)//www.coriolis.eu.org/cdc/DataSelection/cdcDataSelections.asp Questions related to oceanographic observations and data collection 2.1) What types of instruments do we use to observe the ocean? Oceanographic instruments come in many different varieties. Some are autonomous, meaning that they can be deployed either from a vessel or from the shore after which they operate independently while returning the data they collect to land based scientists usually via satellites. Other instruments are fixed to a ship and are used primarily for underway data collection. Still others are lowered and retrieved from a ship by wire, often called a ‘cast’. Yet another way of collecting ocean data is by attaching instruments to a frame or wire and anchoring them to the ocean bottom. And finally some sensors are placed on aircraft or on satellites and they make their measurements by bouncing radio and other electromagnetic waves off the surface of the ocean. Autonomous instruments include satellite-tracked surface drifters, gliders and Argo floats; instruments fixed to a ship include thermosalinographs (TSGs) and Acoustic Doppler Current Profilers (ADCPs); instruments lowered from ships as ‘casts’ include expendable bathythermographs (XBTs) and conductivity-temperature-depth packages (CTDs); moored instruments can include temperature, salinity and current sensors; and satellite sensors include altimeters, devices that measure sea surface temperature, and others. Researchers obtain the data from these different types of systems in a variety of ways. Data collected by casts from ships are recorded onboard and then brought back to land-based laboratories for analyses. Autonomous and mooring instruments collect and store data internally - some of these instruments can then transmit their data to satellites and from there to land stations in real or near-real time, while others provide their data only when the instrument is recovered by a ship. Data from sensors on satellites are transmitted via radio from orbit to land stations, allowing for quick analyses. 2.2) What is a direct (‘in situ’) observation of the ocean? A direct (or ‘in situ’) observation is one taken by an instrument that has been placed in the sea to measure a particular ocean characteristic. 2.3) What is a remote (satellite, aircraft) observation of the ocean? A remote observation is one collected by a sensor placed either on a satellite on an aircraft to measure a particular surface characteristic of the ocean via radio or other electromagnetic waves. Examples of measurements made by sensors on satellites are sea surface temperature and sea surface height. Remote observations such as sea surface temperature frequently must be calibrated by direct (‘in situ’) observations. 2.4) Why do we need both direct (‘in situ’) and remote (satellite, aircraft) observations? Satellite and aircraft mounted sensors can provide excellent spatial coverage of the oceans; satellite observations in particular provide near-global coverage and thus can provide data in areas that are difficult to reach by ships or autonomous vehicles. However satellite-based sensors only observe the surface of the ocean. In situ sensors can collect data in the subsurface ocean not accessible to remote instruments. The two different types of measurements can often be combined in useful ways to provide even more information about the ocean. For instance, satellite measurements of sea surface height can be combined with direct measurements of subsurface temperature when both are present and can generate methods for estimating either type of observation when only the other is available. 2.5) What are ‘forecasting’ observations versus ‘research’ observations? Operational agencies have a mandate to generate forecasts on a fixed schedule that are used by educators, decision makers and the public (e.g., coastal ocean conditions, ocean weather conditions, El Niño predictions). These agencies require data to initialize their forecast models prior to running the numerical models that will generate the predictions. For example, El Niño forecasters require upper-ocean temperature data to initialize their seasonal-to-interannual climate models. Thus these ocean data must be collected, transmitted and received by the forecast center on a timely schedule established by the variable to be forecast (e.g., El Niño forecasts require data approximately one week prior to the prediction run). Such operational data are said to be required in “real-time”, thus precluding any detailed and timely quality control of the data for accuracy after collection. The models include software that does a quick review of the observations and judges whether to use a data point in the forecast. Research scientists seeking to understand the physics of the ocean-climate system require the same data as operational agencies, but not on the same short time scale. Thus research observations can be reviewed in more detail to ensure their quality. These data are often called “delayed mode” data. Research data have typically been collected in limited regions of the ocean studying specific features, processes, etc. for a limited time. Fortunately, operational data provide a strong foundation on which to use research data. 2.6) What is a ship of opportunity (SOP)? A ship of opportunity is most often a commercial vessel (e.g. tanker, freighter, cruise ships) that has volunteered to collect surface meteorological and/or subsurface oceanographic data (e.g., surface winds or upper-ocean temperature). Ships of opportunity also deploy autonomous floats such as satellite-tracked-surface drifters. The ship’s officers and crew perform the data collection and deployments at no cost. Data are most often transmitted from the ship via satellite to land stations shortly after collection. Many of the ships of opportunity that work with the research community were selected because they transit the same section, allowing the scientists to monitor for changes in the ocean over time. For information on the international coordination of the ship of opportunity operations please go to: http://gosic.org/goos/SOOP-program-overview.htm 3. Questions related to specific instruments used to observe the ocean 4.1) What is a Mechanical BathyThermograph (MBT)? An MBT is an older instrument, infrequently used today, that was used to obtain vertical profiles of temperature from stationary or moving vessels. MBT’s measure temperature using a liquid-in-metal thermometer and pressure using a Bourbon tube sensor. MBT’s are deployed by wire from a winch mounted typically on the rear of a vessel. A technician or scientist operates the winch. MBT’s can only sample to a maximum depth of about 300 m; the exact maximum depth is determined by ship’s speed. Temperature profiles are recorded on a coated slide, which must be read by a scientist. MBT data are primarily used in retrospective studies of the temperature structure of the upper layers of the ocean. They are also used to generate reanalysis products (i.e., time series, typically global used, for example, to increase understanding of ocean variability). MBT’s are obsolete and have been replaced by the XBT (see next question). 3.2) What is an eXpendable BathyThermograph (XBT)? 
An XBT is a probe that is dropped from a ship, with the vessel either stopped or underway, and it measures the temperature as it falls through the water. Two very small wires transmit the temperature data, which is collected by a thermister located in the nose of the XBT, to the ship where it is electronically stored for later use. The XBT does not measure depth directly. The probe is designed to fall at a known rate, so that the depth of the probe is inferred from the time it enters the water using an empirically determined Fall Rate Equation. There are several different types of XBT probes that collect data to maximum depths ranging from 450 m to 1800 m. XBT data are collected widely by many countries in the Atlantic, Pacific and Indian Oceans and they are used in retrospective studies of the temperature structure of the upper layers of the ocean as well as to generate reanalysis products (i.e., time series, typically global used, for example, to increase understanding of ocean variability). XBT data are also used to initialize seasonal-to-interannual climate forecasts in predictions of phenomena such as El Niño. For more information on the XBT activities of the Physical Oceanography Division of NOAA’s Atlantic Oceanographic and Meteorological Laboratory go to: http://www.aoml.noaa.gov/phod/goos/ldenxbt/index.php http://www.aoml.noaa.gov/phod/hdenxbt/high_density_home.php 
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