From Ocean Teacher Library
Towed Instruments and Underway DataContents |
Background
Along track measurements such as those made with instruments that are towed from a ship, are captured through seawater sampling systems or made by deck mounted instruments may require a multi-step process to get the data distributed in real-time. There are a variety of instruments that collect idata in this mode. While this includes towed subsurface CTDs, cameras, as well as meterorological measurements from deck mounted systems, and thermosalinograph systems., there are no co-ordinated systems in place to deal with towed, subsurface CTD or camera systems and so they are not treated here.
Deck mounted meteorological systems measure a wide variety of variables with automated systems. The Shipboard Automated Meteorological and Oceanographic System (SAMOS) started a number of years ago during the World Ocean Circulation Experiment. It was originally designed to manage data from research meteorological systems on U.S. research vessels. Over time, it has expanded to cover other U.S. vessels and now considers data from foreign vessels. A description of the program is also available as an OceanObs'09 Community White Paper as well as there being a description of the data management system.
Underway measurements of ocean temperature and salinity have been made using the thermosalinograph. This is still true, but there are now additional sensors that can be used to measure other variables such as nutrients, fluorescence, and oxygen. The data from such measurements is coordinated by the Global Ocean Surface Underway Data (GOSUD) Project. While temperature and salinity have been the focus, other variables associated with them are also handled. There is an OceanObs'09 Community White Paper dealing with surface measurements from “ferry box systems”.
There is also a well developed system for making and handling measurements from continuous plankton recorders. An OceanObs'09 Community White Paper provides a clear description of this programme. However, because this system does not analyze data within the time frames required for real-time distribution, no additional treatment is provided here.
This document deals only with oceanographic variables and so those interested in meteorological data should consult the various links provided above.
Step 1: Getting platform identifiers
In order to report data on the GTS, the ship must use an identifier called a call sign. This is assigned to a ship by each country with due notification provided to the International Telecommunication Union (ITU). Each country has a member and this information is available from the ITU web site. They can help if you need to set the ship’s identification. Alternatively, and a more straightforward route, is to consult the SOT Technical Co-ordinator at JCOMMOPS (see “Contacts” in right hand menu).
Step 2: Getting data ashore
The data gathered on board the platform need to be sent ashore. The ship can use the facilities promoted by the SOOP. To do so, contact either the SOT Chairor SOT Technical Coordinator.
Alternatively, countries may choose to get data ashore through other methods. For example, data collected by vessels will sometimes be sent ashore through email. Alternatively, for cruises of short duration (shorter than the 30 day cut off for ocean data on the GTS), the cruise operator may bring the data back to port before any preparation for dissemination occurs. Contact your national co-ordinator for ocean data management or IODE(select “contact us” in the left hand menu) for advice or assistance.
Step 3: Formating data
After the data come ashore, they must be converted to the appropriate character code form (TRACKOB) or into BUFR for distribution on the GTS.
If your country already has systems in place for reporting ocean data in real-time, it may be that ocean surface underway data are handled already. It is recommended to consult your country's national meteorological service.
If such data are not handled within your country, you are advised to consult the chair of GOSUD.
You may decide to take control of formatting the data for yourself. If so, the appropriate data formats for the GTS are generally described in the Digital Library document “Formats for Real-time Data Exchange”. This document also describes how to get the data to the GTS. At present both TRACKOB and BUFR can only handle measurements of temperature, salinity, and surface currents although newer templates for BUFR with wider reporting capability are being worked on. Talk to the chair of the Data Management Co-ordination Group of JCOMM for more information. You can also consult the GOSUD documentation. If you choose this path, it is advised to contact the GOSUD programme so that someone there who is used to handling GTS formatted data can check your formatting before it is sent to the GTS.
Step 4: Quality Control
Data providers are encouraged to examine the data they collect and to remove the most egregious errors that are present. However, it is encouraged to be cautious in doing this since outliers may be real and to miss these will skew our perception of what is happening in the ocean. Users of GTS data are aware that very detailed quality control cannot take place before the data are distributed in real-time and they accept that they will need to carry out quality control procedures on the data that are distributed. Data providers are urged to consult the GOSUD programme for references to quality control procedures employed by project participants.
Additional Resources
GTS: http://www.wmo.int/pages/prog/www/TEM/GTS/ManOnGTS_en.html
International Telecommunication Union: http://www.itu.int/
Ship Of Opportunity Programme (SOOP): http://www.jcommops.org/soopip/
World Ocean Circulation Experiment (WOCE): http://www.nodc.noaa.gov/WOCE/
Subsections of this Article
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Information about this article
Short title: Underway Instrument Data
Description: Step-by-step instructions for getting data from towed instruments on the GTS.
Expertise level: beginner
Author: bob.keeley
Approval status: approved
Approved by: bob.keeley
Last change: 2012-2-10
Subsection of: Exchanging Ocean Data in Real-time
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