Vol. 81, No. 5, February 1, 2000, p. 45.
Electronic Atlas of WOCE Hydrographic and Tracer Data Now Available
Reiner Schlitzer, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Copyright 2000 American Geophysical Union
To facilitate the use of the global WOCE data set, all currently available data of the WOCE Hydrographic Programme (WHP; http://whpo.ucsd.edu/whp_data.htm) have been compiled in an integrated data set. When used with the Ocean Data View visualization software for Windows, this data set constitutes an “Electronic Atlas of WOCE Data” (eWOCE) that allows graphical display and interactive analysis of the data in many different ways. eWOCE is available over the Internet at http://www.awi-bremerhaven.de/GEO/eWOCE.
The eWOCE data set (WoceBtl) contains bottle data for almost 10,000 stations from publicly available WHP sections (Figure 1). In addition to temperature and salinity observations, most stations also contain oxygen, phosphate, nitrate, and silicate data. CFC observations are provided for about 2350 stations (about 25%), and more than 650 stations contain data for carbon system parameters (for example, total inorganic carbon, alkalinity, and/or CO2 partial pressure). About 75% of the stations were occupied during the WOCE period between 1987 and 1998, while the rest of the stations are pre-WOCE and included for reference and for the analysis of temporal changes on decadal timescales.
The WoceBtl data collection will be updated when more WOCE data becomes public, and the Internet address given above will always link to an up-to-date data set. A data collection containing WOCE conductivity-temperature-depth (CTD) observations is available on request from the author. Note that users can extend the WoceBtl data collection and add data from other sources using the Ocean Data View software described below.
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To exploit the information in the WoceBtl database and to analyze and display the data, use the Ocean Data View (ODV) visualization software for Microsoft Windows 9x/NT systems, which comes with eWOCE. Before using ODV you must install it on your computer following the instructions given on the Web page. In the following, a general description of the goals and functionality of ODV is given. You can skip this section if you already know ODV and want to run eWOCE now. A review of the Ocean Data View software by Murray Brown can be found in Oceanography, 11(2), 19-21, 1998.
ODV is a Windows program for the exploration and graphical analysis of oceanographic profile data (bottle, CTD, expendable bathythermograph (XBT)). ODV lets users interactively browse large sets of station data and produce high quality station maps, general property-property plots of one or more stations, scatter plots of selected stations, property sections along arbitrary cruise tracks, and property distributions on general isosurfaces. ODV supports display of original data as colored dots or actual data values. In addition, two fast gridding algorithms allow color shading and/or contouring of gridded fields along sections and on isosurfaces (any plot with a Z-variable can be gridded, color-shaded, and/or contoured). A large number of derived quantities can be calculated quickly and can be displayed and analyzed in the same way as the basic variables stored on disk.
ODV is designed to be flexible and easy to use. Users are not required to know the details of the internal data storage format nor are they required to have programming experience. ODV always displays a map of available stations on the screen and facilitates navigation through the data by letting the user select stations, sections, and isosurfaces with the mouse. The screen layout and various other configuration features can be modified easily, and favorite settings can be stored in configuration files on disk for later use.
ODV can create and manage very large data collections. It is therefore possible to store the available global historical hydrographic data with newly arriving data on relatively inexpensive and widely available hardware and have these data ready for scientific analysis in the field or back home in the laboratory. In addition to actual research applications, ODV can be useful for data quality evaluation and for teaching and training.
The ODV data format provides dense storage and allows instant access to any station, even in large data collections. The data format is flexible: you can store data for up to 50 variables, where type and number of the variables is arbitrary and may vary from one collection to another. Typically only 1MB of disk space is required to store about 1600 bottle stations containing data for seven variables.
ODV allows easy import of new data into collections and also allows easy export of some or all data from a collection. Hydrographic data in WOCE WHP format (distributed via the Internet at http://whpo.ucsd.edu/whp_data.htm), data from the World Ocean Atlas 1994 (distributed on CD-ROM by U. S. National Oceanographic Data Center, NODC), World Ocean Database 1998 (distributed on CD-ROM by NODC), data in NODC SD2 format, and data in a TAB-separated spreadsheet format can directly be incorporated into the ODV system. ODV maintains quality flags associated with each individual data value. These quality flags can be used by ODV as a data quality filter to exclude bad or questionable values from the analysis.
In addition to the basic oceanographic variables stored in the data files, ODV can calculate and display a large number of derived variables. These derived variables (potential temperature, potential density, dynamic height, and many others) are either coded in the ODV software or defined in user-provided macro files. The macro language is easy and general enough to allow a large number of applications. Use of macro files for new derived quantities broadens the scope of ODV considerably and allows easy experimentation with new quantities not yet established in the scientific community. A separate macro editor that can be invoked from ODV facilitates creation and modification of ODV macros. Any basic or derived variable can be displayed in ODV plots, and they all can be used to define isosurfaces; for example, depth horizons, isopycnals, isothermals, or isohalines; property minimum or maximum layers like, for instance, the intermediate water salinity minimum layer can be defined as isosurfaces by use of the zero-crossing of the vertical derivative (a derived quantity) of these variables.
ODV displays color property sections and color distributions on isosurfaces in two ways, either by showing the original data at the data locations (colored dots of user-defined size or numeric values: method 1) or by projecting the original data on a variable resolution, rectangular grid and then displaying the gridded fields (method 2). While method 1 produces “honest” distributions of the data, instantly revealing regions of poor sampling and highlighting occasional bad data values, method 2 is nicer to look at and avoids the overlapping that occurs in (1) especially if large dot sizes are used. The ODV gridding algorithm is reliable and fast, and fields with thousands of data points are estimated in a matter of seconds on standard hardware. It is important to note that gridded fields are data products and that some small-scale features in the data might be lost due to the gridding procedure. In both display modes, ODV allows the export of section or surface data to ASCII files suitable for dedicated gridding, shading, and contouring software.
Color or black and white paper hardcopies of the ODV graphics screen or of individual data plots can be obtained easily via the print command or by producing PostScript files (.eps). eps files can be printed on any PostScript printer or can be included in page description documents. ODV can also write the contents of its graphics screen to GIF and EMF files suitable for inclusion in text documents or for post-processing with standard graphics software.
After successful installation, you run ODV on the WoceBtl data set by double-clicking on the WoceBtl.var file (default location: c: \ Program Files \ Ocean Data View 4.0 \ Data \ WoceBtl). ODV will load the most recent configuration and draw a station map and several data plots displaying the data of one WHP line (see Figure 2 for an example). There are configuration files for all currently available WOCE sections and you can select any one using the “Configuration>Load Configuration” option from the main menu. Note that configuration files for Atlantic, Pacific, Indian, and Southern Ocean sections are in separate subdirectories.
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Also provided are configuration files for producing plots of property distributions on depth horizons for the global WOCE data set (see Figure 3 for an example of an isosurface plot). Use these configurations as templates for producing distribution plots on isopycnals or isosurfaces defined by any other variable. Property minimum or maximum layers (for example, the intermediate water salinity minimum layer) can be selected as isosurfaces by using the zero crossing of the vertical derivative (a derived quantity) of the respective variables.
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ODV’s functionality is invoked through the main menu (just below the ODV title bar) or via pop-up menus that are activated by clicking the right mouse button. Different pop-up menus appear depending on the mouse position at the time of the click. Stations or samples are selected simply by clicking on them with the left mouse button. Information about the currently selected station and sample is listed in a text window just below the main menu. The current station and current sample are marked in the map and data plots by a red circle and red crosses, respectively. Additional information about collection variables, current cruise, selection criteria, and property values is shown in pop-up windows that appear when the mouse rests over various items in the text window or the title bar of the ODV window.
For more information on how to use ODV and to modify existing configuration templates, invoke the ODV help section by pressing F1.
