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Unidata Program Center
UCAR
Boulder, CO 80307-3000
This paper is an example of what we call data interactive publications. With a properly configured workstation, the readers can click on "hotspots" in the document which bring up an interactive analysis tool called the Unidata Integrated Data Viewer (IDV). The IDV will enable the readers to access, analyze and display datasets on remote servers as well as documents describing them. Beyond the parameters and datasets initially configured into the paper, the analysis tool will have access to all the other dataset parameters as well as to a host of other datasets on remote servers.
These data interactive publications are built on top of several data delivery, access, discovery, and visualization tools developed by Unidata and its partner organizations. For purposes of illustrating this integrative technology, an atmospheric/hydrologic case study has been chosen: a July 16, 2004 convective rain event over Colorado, which illustrates how components of this process fit together. The Local Data Manager (LDM), Open-source Project for a Network Data Access Protocol (OPeNDAP) and Abstract Data Distribution Environment (ADDE) services, Thematic Realtime Environmental Distributed Data Service (THREDDS) cataloging services, and the IDV are highlighted in this example of a publication with embedded pointers for accessing and interacting with remote datasets.
An important objective of this paper is to illustrate how these integrated technologies foster the creation of documents that allow the reader to learn the scientific concepts by direct interaction with illustrative datasets, and help build a framework for integrated Earth System science.
The technology used in this publication enables you to interact directly with datasets, catalogs of datasets, as well as documents stored on remote servers. To utilize the technology effectively, it's necessary to have a well-configured desktop workstation (at least 512 MB of memory) with the Java Webstart application installed.
The images and animations that show up on your screen via the Unidata Integrated Data Viewer (IDV) are not just pictures; they are interactive visualizations generated from the datasets, portions of which are accessed from remote servers or from the disks on your own desktop workstation. Rather than viewing images generated by clicking on a web page, the processes involved in this publication are more akin to those one would use to access research datasets from data providers, convert those datasets into a format that is compatible with a data analysis and display tool at your local site, then using that tool to work with the data interactively.
In this sample case, the datasets you start with are the output of forecast models:
The NCEP model output is approximately is approximately 52 MB in size. The Workstation ETA covers less area and time but at a much higher resolution and results in an output file that's over 800 MB -- nearly a Gigabyte of data. These datasets are stored on a computer at the National Center for Atmospheric Research; the IDV interacts with them via established client/server protocols. A key element of the client/server technology used in these documents and visualizations is that only the needed parts of the huge files are transferred as they are requested. In spite of that, it takes a while to transfer even that subset and render the images on your workstation.
Since these are not pre-generated pictures, you have access to the complete IDV visualization system and to all the data on the server. Thus you can interact directly with the data to create your own visualizations. In fact, you can access other datasets and include them in the analysis.
If you don't already have Webstart installed, the instructions
for doing so can be found at
The
Unidata WebStart Instruction Page.
Once you have webstart running on your workstation, the IDV configured with the appropriate datasets can be started by clicking on the following line:
Temperature forecasts from NCEP national forecast and high-res. local Colorado Workstation ETA.
These forecast models were run at nearly the same time.In fact the NCEP ETA model high resolution output (12Km) was used to initialize the higher resolution Workstation model which covers only the Colorado area in a nested grid.
The forecasts were for July 16, 2004, a day in which there was considerable weather activity through Colorado. The visualization shown in this bundle compares the predicted temperatures at 2 meters above the surface. For those of you who aren't able to get the IDV running on your workstation, the screen dumps below gives you a sense of the kind of visualization you'd be looking at.
The ETA model output is shown as contour (plan view) white lines whereas the higher resolution Workstation model output is shown as color filled contours. One can readily see the detail in the Workstation model that's not there in the NCEP model which covers most of North America. Using the controls in the upper right corner of the display window, the visualization can be animated through the entire forecast time. This animation reveals the higher temporal resolution of the Workstation model since the color fill image changes for some frames where the white line contours of the national model stay constant because there is no national forecast for those intermediate times. The frames toward the end only show the NCEP model because the Workstation forecast only goes out 24 hours in time.
As you will see, HTML files (such as this one) are also viewable within the IDV which accesses it from a Web server at the UPC -- a different server from the one that provides the data. The catalogs that contain the URL pointers to the data files can be stored on still another network computer or on one's own workstation for that matter. In fact, in this example, the reader has two different views into the same HTML file. One is seen from within a Web browser and is used to invoke the IDV for interactions with the datasets; the other is actually seen from within the IDV itself. While this may be somewhat confusing at first, it does illustrate the flexibility of this approach to integrating web-based documents with tools for interactive analysis and display of environmental datasets on remote servers.
The catalogs pointing to the datasets are in the XML language. For those who understand XML or are curious about it, an example THREDDS catalog can be viewed at: http://www.unidata.ucar.edu/projects/THREDDS/DataPublications/Case2004Jul16.xml
There are two additional displays available but not active in the IDV as it comes up. These are images of a parameter called geopotential height at the surface which serves as a "proxy" for the topography underlying the model. By clicking on the control lines a the bottom of the image window, you can make either or both of them visible. One of these is for the NCEP national model; the other is for the local workstation model. Comparing these images by turning them on and off gives you some sense of the difference in resolution between the NCEP ETA and the Workstation ETA.
The image above provides a sense of the resolution of the topography in the
NCEP national ETA model whereas the one below shows the increased detail of
the Rocky Mountains in the local Workstation ETA model.
For more general background information , a concise description of the contents of various forecast models is in the NCAR Scientific Computing Division Documentation for Online Model Output Datasets: <http://dss.ucar.edu/datasets/ds335.0/docs/>
There is also a more all-encompassing description of datasets used in the atmospheric and ocean sciences in an NCAR tech note in An Introduction to Atmospheric and Oceanographic Datasets: <http://www.cgd.ucar.edu/cas/tn404/>.
A somewhat outdated overview of the ETA model is given in A Description of the Meso ETA Model: http://nimbo.wrh.noaa.gov/wrhq/96TAs/TA9606/ta96-06.html.
The Workstation ETA is documented at the Workstation Eta Homepage: http://wwwt.emc.ncep.noaa.gov/mmb/wrkstn_eta.
One of the main goals of this mini case study is to provide an entry point for learning more about the capabilities of the client/server technology that makes it possible to interact directly with the datasets and to learn a bit about the science behind the models in the process. The following activities should help in that process:
The
Unidata WebStart Instruction Page
http://www.unidata.ucar.edu/projects/metapps/webstart/IDV/index.html
Temperature
forecasts from NCEP national forecast and high-res. local Colorado Workstation
ETA
http://www.unidata.ucar.edu/projects/THREDDS/DataPublications/EtaWsEtaTemps.jnlp
Documentation
for Online Model Output Datasets
http://dss.ucar.edu/datasets/ds335.0/docs/
An Introduction to
Atmospheric and Oceanographic Datasets:
http://www.cgd.ucar.edu/cas/tn404/
A
Description of the Meso ETA Model
http://nimbo.wrh.noaa.gov/wrhq/96TAs/TA9606/ta96-06.html.
Workstation
Eta Homepage
http://wwwt.emc.ncep.noaa.gov/mmb/wrkstn_eta/
Example
THREDDS catalog
http://www.unidata.ucar.edu/projects/THREDDS/DataPublications/Case2004Jul16.xml
This material is based in large part upon work supported by the National Science Foundation.
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