From Ocean Teacher Library
Introduction to Ocean Data ExchangeContents |
Background
A number of national, regional and international programmes are collecting oceanographic data either in project funded activities or in a monitoring mode. Some of these data are contributed to the international data systems and so become readily available either in real-time or delayed mode to other researchers. But, another fraction of these observations is accumulated in home institutions; these are delayed or sometimes never reach the international community.
Those data that can be sent shortly after collection can contribute to real-time data exchange and thereby support the development of operational oceanographic services. Those that arrive in delayed mode improve the base archives used to develop climatologies, extend time series, and contribute to studies of climate change, among other activities. Because of the paucity of marine data, all observations are valuable.
Overview of Data Types Covered
Content of these documents is organized according to the delivery time frame being either real-time or delayed mode. Each is then subdivided into step-by-step instructions that address specific platform types and / or instruments. The intention is that someone who has been encouraged to submit data can simply consult the appropriate instructions for the very practical details of what needs to be done and how.
Most of the platforms or instruments referenced can operate to deliver data in real-time (usually within minutes to days of the observation being made). In some cases, such as profiling floats, that is the sole mode of operation. Real-time data transmissions use coastal radios, Inmarsat, Service Argos or other satellite communication systems to provide all or a subset of the observed data.
Real-time data have limitations that need to be recognized. Because of telecommunications bandwidth or transmission costs, the high precision measurements of which the instruments are capable may not be sent ashore for distribution. Instruments may sample at a very high frequency but report some averaged or subsampled quantity in real-time. Observations sent ashore in real-time may have errors due to instrument malfunction or drift or telecommunications problems. In making the data available quickly, it is usual to have automated data quality checking software looking for errors before the data are distributed. Such software is not capable of finding the more subtle errors and so it is common for a higher error rate to be found in real-time data streams.
In some modes of data collection, usually in research projects, instruments collect data at a higher sampling frequency than is reported in real-time, or at a higher precision. In these cases, the data are often stored on-board and returned to the operational centre at the end of the collection period and so are classed as delayed mode data. The data then pass through processing to carry out calibrations, check for possible errors and form the subject of research. These delayed mode data are of the highest quality and highest resolution available. However, the delays in these data reaching archives and becoming available to a wide user community can be months or years. In some cases, delayed mode data never reach an archive and never become available for exchange.
Data Collection Platforms
Oceanographic observations are made from ships, from moored buoys, from drifting surface buoys, and from profiling floats (including ocean gliders). There are also collections of time series made by surface instruments, such as tide gauges, or subsurface instruments, such as current meters.
Higher sampling rate data may be stored on board the instrument and available for submission later in delayed mode. This is true for research ships, for example, that record sea temperature profiles at 1 m or better resolution, but may report data in real-time only at inflection points in the profile.
Lowered Instruments
A wide variety of ships collect ocean data including merchant ships that participate in the Ship Of Opportunity Programme (SOOP), national navies, national Coast Guard vessels, research ships, fishing vessels, ferries, private vessels and vessels of other national agencies. They collect observations typically through lowered of expendable instrumentation. Variables include sea temperature, salinity, currents (speed and direction), dissolved oxygen, other chemical variables such as nutrients, information about pollutants such as oil, biological information such as types and abundance of fish or plankton, sea bottom types, etc. Though the range of variables and volume of data collected by ships is large, the number of observations reported to international data systems is significantly smaller.
Some aspects of the operation and data collection in the open ocean are overseen by the JCOMM Ship Of Opportunity Panel. Data collected by such platforms for short time scale operations, such as search and rescue, or targeted research, may have no functioning pathways for international data submission and exchange.
Moored Buoys
Moored platforms collecting oceanographic information may be operated by national weather agencies or diverse meteorological or oceanographic research programmes. The buoys operated by national agencies often are maintained for extended periods of time while those for research purposes may function for the life of the project only. Buoy instrumentation may record seawater properties as well as information on currents and waves. Typically these platforms also collect meteorological information as well (often this is the primary purpose of the mooring). The open ocean moorings often use subsurface instruments to report ocean temperature and sometimes salinity profiles. Coastal buoys may collect other information including currents, light levels at different depths, particle counters, etc. Many of these gather data at high frequency but report averaged or subsampled quantities in real-time.
The observation regime is one in which instruments are operated automatically and often for extended periods of time. Data are typically transferred ashore through telecommunications systems, often satellite systems.
The deployment and operation of the data collection in the open ocean are overseen by the JCOMM Data Buoy Co-operation Panel. Data collected by such platforms for short time scale operations, such as search and rescue, or targeted research, may have no functioning pathways for international data submission and exchange.
Drifting Buoys
Surface drifters report atmospheric variables as well as a suite of oceanographic variables including sea surface temperature and salinity. Some are deployed with subsurface instrumentation as well that measures usually temperature but sometimes salinity and even other variables sometimes.
The deployment and operation of the data collection in the open ocean are overseen by the JCOMM Data Buoy Co-operation Panel. Data collected by such platforms for short time scale operations, such as search and rescue, or targeted research, may have no functioning pathways for international data submission and exchange.
Profiling Floats and Gliders
The development of mass produced, standard models of autonomous profilers has opened a new chapter in ocean observations. The profiling instruments are able to descend down to about 2000m and ascend to the surface on a predetermined schedule while sampling temperature, salinity, and occasionally other water properties. Some are outfitted with wings (gliders) that allow them to direct their movements during ascent and descent to a degree. These instruments can operate unaided for years. Initial models report data on a preset time schedule through satellite systems. More recent models permit two-way communications so that on-board programming can be altered to change the characteristics of the sampling.
Gliders are a form of profiling float that use “wings” on a torpedo shaped body to exert some control over the location of the instrument. These instruments can sample the ocean is essentially the same way as profiling floats. As such, they will be treated together.
The Argo Programme is an internationally co-ordinated system for deployment, data acquisition and dissemination, and product development. As yet there is no co-ordinated system for managing glider data.
Towed and Underway Instruments
There are a number of instruments that operate either as on-board sensors or by towed sensors. On-board sensors include those for sea surface temperature, salinity, nutrients, oxygen, and fluorescence. Sensor development is proceeding rapidly so that the ability to automatically measure new variables is increasing. Typically, these sensors are installed on ships, most often research vessels, but increasingly on commercial or citizen operated ones as well. It is common for surface meteorological observations to be made coincident with the oceanographic measurements.
The JCOMM Global Ocean Surface Underway Data Project is organized to acquire oceanographic measurements from vessels. Not all vessels contribute as yet. A similar project, the Shipboard Automated Meteorological and Oceanographic System, was largely focused on meteorological observations from research vessels operated by the USA. These two projects have co-operated to try to fuse together a single system for all such observations.
Towed instruments are typically used to acquire hydrographic or seismological measurements. Hydrographic measurements include single and multi-beam instruments to measure both water depth but also provide information on bottom characteristics. Seismological instruments are used for measuring properties of rocks and sediments at and below the water, sediment interface. National hydrographic services are well organized in an international community through the International Hydrographic Organization.
Seismic data are less well organized, but there are organizations such as the Ocean Drilling Project, and Ocean Seismic Network that work to co-ordinate activities.
Towed instruments also include sleds that operate close to the bottom and typically have video cameras (film or digital) mounted on them. Many kilometers of the sea floor are represented in these videos. There is no international program that deals with such observations. As well, management of such videos or the information extracted from them is not well managed in nations.
Subsurface Drifters
The existence and operation of subsurface drifters, such as SOFAR or RAFOS floats, has been going on for many years. These began and have continued to operate as research funded projects. While some of these data may have reached national archives, there is no international co-ordination for these data.
Time Series Instruments
Included in this heading are instruments that are fixed to coastal structure, such as typical tide gauges, as well as those that are placed on subsurface moorings. These measure a wide variety of variables including surface elevations, water properties (temperature, salinity, etc.), and ocean currents. Those instruments attached to coastal station and making surface measurements, are increasingly being automated with data transmissions to co-ordinating facilities on a daily or more frequent basis. Surface elevation data from tide gauges has long been co-ordinated internationally by the Global Sea Level Observing System. National systems are often operated by or closely associated with hydrographic organizations because of the importance to shipping. It is common for there to be many more gauges operating in a country that are reporting data to the international programme.
Instruments on subsurface moorings are not often capable of reporting data in real-time. It is common practice to store observations internally and these only become available when the mooring is recovered. They typically sample at intervals of seconds to minutes depending on the objectives of the programme for which they were deployed. Tide gauge measurements may go to the same data centres as coastal gauge data, but this is not always assured. Current meter data are often the responsibility of individual nations. There is not international repository for such data, nor any single focal point for the data. However, a catalogue of known current meter observations is maintained, though this is incomplete.
Novel data such as those acquired by acoustic tomographic instruments lie purely within the research domain. While the number of such programmes is small, the volume of data is large and requires significant processing capabilities to extract ocean properties such as density. There is no internally co-ordinated programme for such data.
Animal Tags
In recent years capability has developed to apply what are commonly called “tags” to many different kinds of aquatic animals. One type is a tag that attached externally to animals and at a preset time release from the animal, float to the surface and report positions, and perhaps other variables. Some tags are surgically implanted, typically in fish, and their movements are tracked by acoustic receivers. Some of these may also record physiological measurements of the animal. Other kinds of tags are attached to the body and record water properties as the animal forages for food.
Data from tags that release from animals are not fully co-ordinated internationally. Rather there are a number of national programmes, some span a number of countries. The Tagginfg Of Pacific Predators is one such example.
The Ocean Tracking Network is an international programme designed to co-ordinate the collection and management of data from surgically implanted acoustic tags.
The Sea Mammal Research Unit at St. Andrews University in Scotland co-ordinates the data collection and reporting of much of the data collected on diving animals such as seals. Some of these data are reported in real-time.
Overview of Activities Seeking Real Time Data Inputs
There are two reasons to encourage real-time data inputs. The first is simply as a way to make data available as quickly as possible after collection to users who require them, as discussed below. The second is that data reported in real-time act as a notification of a data collection activity from which delayed mode data may be expected. It is a way for the international data system to be aware on a large scale about data collection activities taking place, without necessarily direct involvement in each and every program.
The clients for real-time data include the operational meteorological and oceanographic communities. These groups, epitomized by national weather centres, use in-situ observations as input to computer models. Models are used to fill in gaps in the observations to show both the current and predicted state of the ocean and atmosphere. The predictions can be from short time scales of hours to days, to seasonal or longer. More and more meteorological models are being connected to oceanographic models and in-situ ocean data keep the models aligned with reality.
Real-time data are used directly in hazard warning or mitigation situations. For example, real-time sea level observations are used to gauge the level of possible flooding during extreme events, or simply to ensure the safety of shipping in confined waters.
A number of real-time data collection activities are co-ordinated through the Joint Commossion on Oceanography and Marine Meteorology, JCOMM. JCOMM operates an information centre to assist.
Overview of Activities Seeking Delayed Mode Data Inputs
Delayed mode data are used in many different circumstances. Because of their high quality and high resolution, they form the backbone of research. They contribute to analyses of trends over time and to the formulation of climatologies. Climatologies have many uses; they provide the ability to assess recent observations, and assist in preparing data for ingestion by models.
Delayed mode data are also of importance in calibrating real-time observations. In the Argo program, for example, high quality, delayed mode temperature and salinity observations from CTDs are used to assess the real-time data collected by profiling floats and to make adjustments for instrument drift. These are crucial for finding the more subtle errors in float data.
Modellers often will carry out re-analyses of historical data to build reference data sets. These make use of the high-quality delayed mode data that have replaced real-time observations. These can be particularly valuable in assessing extreme events and developing better performing models.
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Information about this article
Short title: Introduction to in-situ data exchange
Description: This provides background information about platforms and modes of data exchange.
Expertise level: beginner
Author: bob.keeley
Approval status: approved
Approved by: bob.keeley
Last change: 2012-2-8
Subsection of: Exchanging In-situ Ocean Data
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